Jean-Pascal Borra
email: jean-pascal.borra@u-psud.fr

Keywords: Water, Electrospray, EHD, electrical discharges, corona, wet scrubbing

Highlights:

 electrosprays is a continuous production process of self-dispersed unipolar droplets with monodisperse/unimodal size distributions (0.2 < d modal < 150 µm)  Applications of ES of aqueous solutions are reviewed with special attention for material production and bio-applications  Means to achieve steady water ES are presented with respect to electrical discharges in ambient air around the liquid cone and jet  Streamer discharges with transient and asymmetric space charges disrupt the EHD equilibrium for steady cone-jet mode, while the axisymmetric and quasi-stationary space charge is required to achieve steady water ES in the pulseless corona-assisted cone-jet mode  Empirical scaling laws of droplet properties are reminded for both steady water ES in cone-jet with a pulseless corona and without discharge  High filtration efficiencies of a lab-scale wet bipolar-scrubbers (>99%) supports that Water ES in corona-assisted cone-jet could be applied to low cost Air cleaning

Review on Water Electro-Sprays and applications of charged droplets with focus on the corona-assisted cone-jet mode for High Efficiency Particle Air Filtration by wet electro-scrubbing of aerosol

Introduction

The fragmentation of bulk liquid into droplets is used in various fields of science and technology under different key-words; 'spraying' and sometimes 'nebulization', 'pulverization' or even 'atomization'. In all cases, the liquid is divided into droplets by fragmentation of films or jets. In pressure nebulizer, the jet is formed by applying a pressure on the liquid flowing in a capillary nozzle. Otherwise, jets can arise from liquid menisci fragmentation in turbulent gas in pneumatic atomizers or from a flat surface by mechanical deformation under external forces in piezo-electric vibrating crystals [START_REF] Ashgriz | Handbook of atomization and sprays: theory and applications[END_REF]. Bursting bubbles also produce droplets from liquid jet and film fragmentation, as over ocean whitecap, source of droplets and subsequent salt nuclei involved in clouds formation. [START_REF] Blanchard | The ejection of drops from the sea and their enrichment with bacteria and other materials-A review[END_REF][START_REF] Rai | An Experimental Approach of Generation of Micro/Nano Scale Liquid Droplets by EHDA Process[END_REF].

This review addresses another spraying method with critical advantages among others; the Electro-Spray (ES) in the cone-jet mode, with focus on water ES with or without discharges in ambient air.

The interest for water drops and crystals probably arose from their unexpected shapes in permanent visible evolution. Under electrical field, the deformation is even more striking, when the more or less regular rounded drop turns into conical shapes. Since Da Vinci's description of dripping in terms of drop mass and diameter to balance the opposed inward capillary and gravity forces [START_REF] Da | The codex Leicester[END_REF], Savart and Plateau's have characterized the formation and fragmentation of neutral liquid jets into droplets by purely hydrodynamic propagation of the Plateau-Rayleigh capillary instabilities [START_REF] Savart | Mémoire sur la constitution des veines liquides lancées par des orifices circulaires en mince paroi Annales de chimie et de physique[END_REF]. Then, Rayleigh derived a relation between droplet and jet diameters (d drop = 1.89 d jet ) for the axisymmetric varicose jet break-up (Rayleigh, 1879). He also demonstrated that electrical repulsions in charged droplets accounts for Coulombian explosion with a size-dependent maximum charge limit [START_REF] Rayleigh | On the equilibrium of liquid conducting masses charged with electricity[END_REF]. Kelvin used the ES as a Voltage generator and for printing by field driven deposition of charged droplets [START_REF] Kelvin | On a Self-Acting Apparatus for Multiplying and Maintaining Electric Charges, with Applications to Illustrate the Voltaic Theory Proceedings of the Royal Society[END_REF]). Zeliny's description of ES modes [START_REF] Zeleny | Instability of Electrified Liquid Surfaces[END_REF], was detailed by Vonnegut who noticed the monodispersity of droplets that can be produced in the steady cone-jet mode of ES [START_REF] Vonnegut | Production of monodisperse liquid particles by electrical atomization[END_REF] from the equilibrium cone shape of conducting liquid submitted to electric field [START_REF] Taylor | Disintegration of water drops in an electric field[END_REF].

As a source of charged species, ES was then also considered for its potential environmental impact on cloud, fog and haze electrification [START_REF] Chalmers | Atmospheric Electricity[END_REF]. In such disturbed weather, the natural electric fields up to few kV/m leads to drop deformation with subsequent local increase of the electric field in the gas around the charged liquid cones and jets. When the threshold field of gas ionization is reached, corona discharges create ions around pending, suspended or falling drops and crystals, with subsequent space charge fields [START_REF] Zeleny | The Electrical Discharge from Liquid Points, and a Hydrostatic Method of Measuring the Electric Intensity at Their Surfaces[END_REF][START_REF] English | Corona from a Water Drop[END_REF][START_REF] Chalmers | Atmospheric Electricity[END_REF][START_REF] Janischewskyj | Corona characteristicss of simulated rain[END_REF][START_REF] Borra | Electrical and chemical consequences of point discharges in a forest during a mist and a thunderstorm[END_REF][START_REF] Sugimoto | Negative corona discharge at a tip of water cone deformed under dc field[END_REF][START_REF] Higashiyama | Negative corona discharge from a water droplet under the pulsating DC field[END_REF][START_REF] Xu | Dynamic corona characteristics of water droplets on charged conductor surface[END_REF]. In corona chargers and electrostatic precipitator (ESP) for filtration, particles are charged by collection of corona gaseous ions [START_REF] Cross | Electrostatics : principles, problems and applications[END_REF][START_REF] Parker | Applied Electrostatic Precipitation[END_REF]. When used with liquid aerosols, ES of liquid previously collected on electrodes accounts for the production of charged aerosol from the polarized electrodes in ESP (Marijnissen J.C.M. et al., 1993a;Marijnissen J. C. M. et al., 1993b) as in corona charger (Unger et al., 1999). Under AC polarization of pending drops on HV power lines, ES is also considered to account for power losses by ES and corona leakage currents [START_REF] Hara | Electrical corona and specific charge on water drops from a cylindrical conductor with high DC Voltage[END_REF][START_REF] Farzaneh | On the role of the space-charge produced by hanging water drops in the mechanism of the corona-induced vibration of HV conductors[END_REF]Borra et al., 1999d;[START_REF] Xu | Dynamic corona characteristics of water droplets on charged conductor surface[END_REF][START_REF] Yin | Corona Investigation of an Energized Conductor under Various Weather Conditions[END_REF]. Various modes of hydrodynamic and Electro-Hydro Dynamic (EHD) jet formation and fragmentation are reviewed in [START_REF] Rosell-Llompardt | Electrosprays in the cone-jet mode: from Taylor cone formation to spray development[END_REF] focusing on Electro-Spray modes, as defined by [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids: Main functioning modes[END_REF][START_REF] Cloupeau | Recipes for use of EHD spraying in cone-jet mode and notes on corona discharge effects[END_REF][START_REF] Cloupeau | Electrohydrodynamic spraying functioning modes: a critical review[END_REF] with a special attention paid to the cone-jet mode, detailed in [START_REF] Ganan-Calvo | Review on the physcis of electrospray: from electrokinetics to the operating conditions of Taylor cone-jets, and beyond[END_REF]. In that case, the drop turns into a conical shape because of the surface polarization and related outward normal electrical pressure that can only be balanced by the inward capillary pressure. This equilibrium is frequently expressed as a threshold field condition for the cone-jet formation (E cone-jet ≈ (/  0 R jet ) 1/2 ), versus the liquid properties (density = 998 kg.m -3 , viscosity = 1.002 Pa.s, surface tension 65-73 mN.m -1 , relative permittivity  r = 80, for water). Since the surface charge density increases from the cone base at the tip of the capillary, the normal electric pressure increases which leads to smaller liquid radius up to the cone-jet transition zone, where the normal electric field is maximal, as expected from models of the cone and jet shapes (Hayati et al., 1987a;[START_REF] Hartmann | Electro hydrodynamic atomization in the cone-jet mode. A physical model of the liquid cone and jet[END_REF][START_REF] Yan | Numerical modeling of an electrostatically driven liquid meniscus in the conejet mode[END_REF], and confirmed from electrical discharge localization in the gas around the liquid [START_REF] Borra | Destabilisation of sprays in the cone-jet mode by electrical dicharges on the jet[END_REF]. The surface charges are accelerated by the tangential component of the electric field along the cone surface, to the apex. Once, this EHD flow delivered from the cone to the jet is adjusted with the applied voltage to the liquid flowrate delivered to the cone, the EHD equilibrium is reached and the emerging jet breaks-up into droplets by the propagation of growing capillary instabilities. This EHD equilibrium can be maintained by increasing the voltage for lower flow rate and reversely (Hayati et al., 1987b) for all tested liquids and solutions. Even if out of scope of water ES, ES of viscous liquids has been achieved in cone-jet mode [START_REF] Ku | Electrospray characteristics of highly viscous liquids[END_REF]Rosell-Llompardt et al., 2018a), as well as for low conductivities by charge injection [START_REF] Bailey | Electrostatic spraying of liquids[END_REF]. In this steady cone-jet mode of ES, unique monodisperse/unimodal droplet size distributions can be achieved. The modal diameter can be finely tuned with liquid flowrate and conductivity and to a lower extend with the voltage, following confirmed characteristic scaling laws between the spray current of charged droplets evolving with Q Liq. n> 0 , as well as droplet size. Operating conditions and subsequent droplet properties (size and charge) produced by steady ES in cone-jet mode can be defined by different approaches, detailed in [START_REF] Ganan-Calvo | Review on the physcis of electrospray: from electrokinetics to the operating conditions of Taylor cone-jets, and beyond[END_REF][START_REF] Rosell-Llompardt | Electrosprays in the cone-jet mode: from Taylor cone formation to spray development[END_REF], versus liquid properties and geometry of spraying capillary nozzles. Moreover, these unipolar charged droplets are selfdispersed, with a quasi-maximal charge per drop, close to half of the Rayleigh limit. With such critical advantages among other spraying means, ES in cone-jet mode is a low cost environment friendly production process of monodisperse droplets from any bulk liquid. With low liquid consumption and enhanced surface of such fine self-dispersed droplets, easy to scale up, the water ES has been studied for different applications presented in the first section, with emphasis on recent developments for material production and processing as well as for bio-applications. The second section addresses the coupled physical constraints to be taken into account to achieve steady water ES in the cone-jet mode in ambient air. Indeed, with the highest surface tension around 70 mN.m -1 in STP, higher threshold field and voltages are required to reach EHD equilibrium for water in cone-jet mode than for other solvent and solutions [START_REF] Burayev | Physical processes during electrostatic atomization of liquids[END_REF][START_REF] Smith | The EHD atomization of liquids[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF]Borra et al., 1999d;Hartmann et al., 1999a;[START_REF] Hartmann | EHD atomization in the cone-jet mode physical modeling of the liquid cone and jet[END_REF]. Here, the effect of transient or quasistationary space charges of gaseous ions created by streamers and pulseless corona discharges in the gas around the liquid on the total electric field at liquid surface are depicted and related to steady/unsteady ES modes. Common ways to avoid electrical discharges or to induce a pulseless discharge are given to achieve steady water ES in the cone-jet mode, for the production of charged water spray in ambient air. Finally, the interest of water ES in the pulseless corona-assisted cone-jet mode is highlighted for the steady production of monodisperse/unimodal self-dispersed unipolar water droplets, close to Rayleigh charge limit to enhance wet electro-scrubbing efficiencies, as an alternative to fabric filters and ESP used for filtration.

Interest and applications of water electro-spray

The high surface-to-volume ratio of sprays with a particular interest for low cost, environment friendly and biocompatible water ES, has been applied to various domains, for: -propulsion by "colloidal" thruster in space, where contamination is not allowed except by water [START_REF] Huberman | Present status of colloid microthruster technology[END_REF][START_REF] Velásquez-García | A planar array of micro-fabricated ES emitters for thruster applications[END_REF][START_REF] Alexander | Voltage-modulated flow rate for precise thrust control in colloid electrospray propulsion[END_REF][START_REF] Tran | Experimental and theoretical study of cone-jet for ES microthruster considering the interference effect in an array of nozzles[END_REF][START_REF] Gamero-Castaño | Characterization of the electrosprays of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide in vacuum[END_REF]Tang HB et al., 2011;[START_REF] Borner | Prediction of fundamental properties of ionic liquid electrospray thrusters using molecular dynamics[END_REF][START_REF] Morris | Characterization of electrospray beams for microspacecraft electric propulsion applications[END_REF], -agricultural application for crop spraying of water-based solutions of pesticides on fields [START_REF] Coffee | ElectroDynamic crop spraying[END_REF][START_REF] Law | Electrostatic deposition of pesticide sprays onto ionising targets: charge and mass transfert analysis[END_REF], as well as in greenhouses [START_REF] Geerse | A multiple EHDA system for selective deposition of pesticide in greenhouse[END_REF], -Gas conditioning in terms of temperature and humidity [START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Cui | Modeling the particle scavenging and thermal efficiencies of a heat absorbing scrubber[END_REF], up to odor masking for domestic gas [START_REF] Ganesan | Investigation of EHDA for natural gas odorization[END_REF], -gas treatment for pollution abatement of harmful gases and suspended particles in exhaust fumes and smokes, detailed in the section 4, -water treatment as metal extraction [START_REF] Parmentier | EHDA for enhance mass transfer of metal salts from aqueous phase towards ionic liquids[END_REF], desalination by evaporation (Agostinho et al., 2018) or bio-decontamination [START_REF] Pyrgiotakis | Optimization of a nanotechnology based antimicrobial platform for food safety applications using Engineered Water Nanostructures (EWNS)[END_REF][START_REF] Machala | Formation of ROS and RNS in water ES through spark in air and bactericidal effect[END_REF][START_REF] Kanev | Are reactive Oxygen species generated in ES at low current ?[END_REF]. -monodisperse nano-particles production by ES of sucrose solutions (Chen DR et al., 1995;[START_REF] Kaufman | Electrospray diagnostics performed by using sucrose and proteins in the gas-phase electrophoretic mobility molecular analyzer (GEMMA)[END_REF] now developed and sold by TSI™ and Ramem™ as size-calibrated aerosol generators. Here, the neutralization of droplets can be achieved either with bipolar gaseous ions from radioactive, X-ray and DBD neutralizers or with unipolar ions from corona discharges or from evaporation of charged droplets (Liu BYH et al., 1974;Adachi M. et al., 1983;Adachi Motoaki et al., 1993;Chen DR et al., 1995;Morozov VN et al., 2007;[START_REF] Tsai | Gas-phase ion-mobility characterization of SAM-functionalized Au nanoparticles[END_REF][START_REF] Fu | A New ES Aerosol Generator with High Particle Transmission Efficiency[END_REF][START_REF] Morozov | Generation of biologically active nano-aerosol by an electrospray-neutralization method[END_REF][START_REF] Fu | Performance study of a twin-head electrospray system[END_REF][START_REF] Tsai | T-programmed ES-DMA for characterization of ligated nanoparticles in complex media[END_REF][START_REF] Liu | An electrospray aerosol generator with X-ray photoionizer for particle charge reduction[END_REF][START_REF] Tai | Protein Silver Nanoparticle Interactions to Colloidal Stability in Acidic Environments[END_REF][START_REF] You | Bionanoparticles as Candidate Reference Materials for Mobility Analysis of Nanoparticles[END_REF][START_REF] Mathon | Ozone-free post-DBD aerosol bipolar diffusion charger: Evaluation as neutralizer for SMPS size distribution measurements[END_REF]. [START_REF] Jaworek | Micro-and nanoparticle production by electrospraying[END_REF][START_REF] Jaworek | Electrospray application to powder production and surface coating[END_REF], Wu andClark (2008a, 2008b) have reviewed ES devices developed for production and processing of materials implying droplet neutralisation. Coatings have been performed by ES deposition on grounded surfaces and particle production is achieved either by injection of charged droplets in grounded liquids for composite coated particles or by neutralization of suspended droplets for the production of the dried powders. Neutralization of droplets produced by ES in cone jet mode can be achieved either in suspension by bipolar or unipolar gaseous ions, detailed just above for monodisperse particles production, as well as by coalescence of droplets with opposite polarity from two unipolar ES for powder production (see §2.1).

For Materials processing

Electro-spray in the steady cone-jet mode is, to date, mainly used for materials production, with a particular interest for composite materials such as coated powders and porous membranes deposited on surfaces. Indeed, powder production starting from ES of water based solutions and suspensions of nanoparticles is already used in numerous domains of applications from food flavoring and conservation [START_REF] Pyrgiotakis | Optimization of a nanotechnology based antimicrobial platform for food safety applications using Engineered Water Nanostructures (EWNS)[END_REF], to new materials and bio-applications (Sweet ML et al., 2014). With highly charged droplets, ES is well adapted for electric field driven applications, either for deposition on grounded electrodes, in grounded liquids or for coagulation with opposite polarity species in suspension. Of course, the control of electrical properties of droplets is an additional advantage of ES in cone-jet for deposition processes like coatings and printing (Sweet RG, 1965;[START_REF] Kamphoefner | Ink jet printing[END_REF]Jaworek, 2007a;[START_REF] Stachewicz | Single event electrospraying of water[END_REF]Jaworek, 2011). Furthermore, efficient interfacial processes, such as bipolar mixing for controlled kinetics of reactions in droplets formed by coalescence of two opposite polarity droplets from two unipolar ES. Taking advantage of the tunable size distributions of the droplets produced by ES in steady cone-jet modes, tailored dried particles can be achieved with controlled size, shape and density (Borra et al., 1997a;Borra et al., 1999a;Jaworek, 2007a, b). Dense to hollow dried particles are achieved with subsequent tunable porosity of final powders. This is especially critical to produce membranes with defined apparent exchange surface and composition required in most industrial domains from energy production, conversion, and storage and more generally to catalysis or polymers membranes [START_REF] Castillo | Nanostructured porous coatings via electrospray atomization and deposition of nanoparticle suspensions[END_REF][START_REF] Kelder | EDHA for Energy Production, Storage and Conversion Devices[END_REF]Rosell-Llompardt et al., 2018a). The properties of the dried particles, including composition, size and morphology can be tuned by controlling the initial droplet size and the drying conditions with related droplet evaporation rates and subsequent production rates of nanoparticle suspended in the droplet on the one hand and on the other, the diffusion rate of so-formed nano-crystal. Production and transport of so-formed nuclei in the droplet controls the size and concentration profile of nanoparticles in the droplet and the related agglomeration rate, which is critical to achieve different morphologies of the final dried particles [START_REF] Vehring | Pharmaceutical Particle Engineering via Spray Drying[END_REF]. Kodas and Hampden-Smith described aerosol-based processes for the production of materials, including reactive and non-reactive spray drying [START_REF] Kodas | Aerosol processing of materials[END_REF][START_REF] Messing | Ceramic Powder Synthesis by Spray Pyrolysis[END_REF][START_REF] Wilhelm | Electrospray evaporation and deposition[END_REF][START_REF] Vehring | Pharmaceutical Particle Engineering via Spray Drying[END_REF]. Some examples of reactive spray pyrolysis used for the production of oxide particles are detailed in [START_REF] Rulison | Synthesis of yttria powders by electrospray pyrolysis[END_REF]Borra et al., 1997a;[START_REF] Okuyama | The formation of ultrafine particles of metal sulfide by the ES pyrolysis method[END_REF]Chen CH et al., 1999;[START_REF] Lenggoro | Preparation of ZnS nanoparticles by electrospray pyrolysis[END_REF][START_REF] Bastide | WS2 closed nanoboxes synthesized by spray pyrolysis[END_REF][START_REF] Jaworek | Electrospraying route to nanotechnology: An overview[END_REF][START_REF] Shi | Investigation of ES and application for the synthesis of fine ceramic powder[END_REF][START_REF] Xie | EHD atomization: A two-decade effort to produce and process micro-/nanoparticulate materials[END_REF][START_REF] Tang | High Performance Metal Oxide-Graphene Hybrid Nanomaterials Synthesized via Opposite-Polarity Electrosprays[END_REF]Tang J et al., 2017a;Tang J et al., 2017b) and non-reactive drying of droplets leading to nano-particles from water based solutions in (Tang K et al., 1994b;[START_REF] Vehring | Pharmaceutical Particle Engineering via Spray Drying[END_REF][START_REF] Maißer | EHD generation of monodisperse nanoparticles in sub-10 nm size range from electrolytic salt solution[END_REF]. Such nuclei are formed by nucleation or crystallization when the maximum solute concentration (solubility constant) is reached, either at the surface or in the volume of the droplet. Surface nucleation occurs from evaporation or from interfacial reaction of liquid with gaseous reactants. In that case, the kinetics of product formation in the droplet depends on the surface temperature and on reactants concentrations in the liquid interface, limited by slow diffusion from gas phase. Since the same chemical reactions can be induced in volume when two droplets with opposite polarities are mixed by electrocoalescence, positive and negative ES have been used to increase the apparent reaction rate between the same reactants dissolved in controlled relative concentrations in droplets produced by ES with opposite polarities, (Borra et al., 1997a;[START_REF] Camelot | Bipolar coagulation: Charge distribution of coagulated droplets[END_REF]Borra et al., 1999a;[START_REF] Verdoold | Scaling-up the bipolar coagulation process[END_REF][START_REF] Jaworek | Electrospraying route to nanotechnology: An overview[END_REF][START_REF] Verdoold | Modeling a bipolar-coagulation reactor using coupled population balances[END_REF][START_REF] Fu | Performance study of a twin-head electrospray system[END_REF]Liu Q et al., 2014a;[START_REF] Xie | EHD atomization: A two-decade effort to produce and process micro-/nanoparticulate materials[END_REF][START_REF] Tang | High Performance Metal Oxide-Graphene Hybrid Nanomaterials Synthesized via Opposite-Polarity Electrosprays[END_REF]Tang J et al., 2017a). Recent production of "smart" composite materials are also based on the production of nanoparticles in liquid droplets, as described above, from drying and eventual reaction in the liquid drop but as well by the direct ES of nano-suspensions, i.e. of droplets with suspended solid nanoparticles. In that case, composite coatings including nanoparticles are deposited by ES of water-based suspension. ES deposition of living bacteria and bio-molecules and self-patterning of Carbon nanotube and graphene in watersuspension have been achieved. It is also used for the production of nano-composite materials doped with nano-oxides, polymer fibers loaded with Metal catalysts for fabrics, porous membranes for energy production with fuel-cells, conversion in solar cells and storage in capacitors, sensors for gas detection [START_REF] De Juan | On-line Sizing of Colloidal Nanoparticles via Electrospray and Aerosol Techniques[END_REF]Chen CH et al., 1999;[START_REF] Jayasinghe | A novel ceramic printing technique based on electrostatic atomization of a suspension[END_REF]Jayasinghe et al., 2005a, b;Wang DZ et al., 2005;[START_REF] Jayasinghe | Electrospraying a nanoparticulate suspension[END_REF]Wang DZ et al., 2007a;[START_REF] Yu | Effect of viscosity of silver nanoparticle suspension on conductive line patterned by EHD jet printing[END_REF][START_REF] Kim | Use of an electrospray for the generation of bacterial bioaerosols[END_REF][START_REF] Prajapati | A technology update: Electro spray technology[END_REF][START_REF] Wang | EHDA deposition and patterning of a carbon nanosuspension[END_REF][START_REF] Wang | Formation of a catalyst membrane by EHDA Layer-by-Layer deposition for methanol fuel cells[END_REF][START_REF] Krella | Protective properties of Al2O3+TiO2 coating produced by ES deposition method[END_REF][START_REF] Castillo | Nanostructured porous coatings via electrospray atomization and deposition of nanoparticle suspensions[END_REF][START_REF] Kelder | EDHA for Energy Production, Storage and Conversion Devices[END_REF].

For bio-applications

Bio-applications of water-based solutions ES are expected to become soon a fruitful investment for technological companies. As an example of these tremendous markets to be developed for allergies detection and treatment, DBV Technology ™ recently achieved the fabrication of skin-compatiblepatches for lactose and peanuts allergy detection by ES deposition. To do so, ES of an aqueous protein solution is used for deposition on a patch of required amount of dried proteins per patch, with 100% efficiency i.e. without any mass loss of dissolved proteins. Moreover, the dried protein are homogeneously distributed on the patch due to electrostatic repulsions, to avoid postdeposition electro-coagulation, with their initial allergenic properties. Production capacity in the order of millions of patches per year (DBVtechno.), already enables large scale commercialization in malls rather than as performed today with long and expensive tests in specialized services of hospitals (Fig. 1). Other medical powders are produced in the industry for pills and cream processing. Eventual coating may be used for stabilization of light sensitive materials, for accurate localization within the micrometer range resolution from electromagnetic properties, as well as for storage and transport without agglomeration from mechanical and chemical properties [START_REF] Ho | Redispersible drug nanoparticles prepared without dispersant by electro-spray drying[END_REF], Another important application of coated reactants or medical principles is the time-controlled delivery by diffusion across a porous coating or dissolution of the coating [START_REF] Vehring | Pharmaceutical Particle Engineering via Spray Drying[END_REF]. ES is also tested in drug delivery inhalers of dried powders (Tang K et al., 1994b;[START_REF] Ijsebaert | Electrohydrodynamic spraying of inhalation medicine[END_REF]Chen DR et al., 2010;[START_REF] Carvalho | The function and performance of aqueous aerosol devices for inhalation therapy[END_REF], as well as for deposition of biomolecules such as genes, allergens (DBVtechno.), anticorps IgH or living bio-organisms like bacteria and viruses for chemical and bio-sensors [START_REF] Boda | Electrospraying an enabling technology for pharmaceutical and biomedical applications: A review[END_REF][START_REF] Kavadiya | Electrospray deposition of biomolecules: applications, challenges, and recommendations[END_REF]. ES of charged droplets collected in liquid is also applied to emulsion and suspension preparation. For instance, cytocompatible capsules suspended in water are achieved by "water in water" emulsions formed when two immiscible solutes are mixed by spraying 15% dextran aqueous solution in 8% PEG aqueous solution [START_REF] Song | All-Aqueous Electrosprayed Emulsion for Fabrication of Cytocompatible Microcapsules[END_REF]. This is also used for the production of composite particles suspended in liquids, e.g. with a chitosan core electrosprayed in a calcium phosphate solution for encapsulation of liquids up to living yeast cells in hydroxyapatite shell [START_REF] Yunoki | Preparation of Inorganic/Organic Polymer Hybrid Microcapsules with High Encapsulation Efficiency by an Electrospray Technique[END_REF] and with polystyrene beads electrosprayed in a aqueous solution for surface functionalization and immunoassay bio-diagnostic [START_REF] Foti | Electrospray induced surface activation of polystyrene microbeads for diagnostic applications[END_REF]. Otherwise, water ES is also investigated for bio-decontamination of surfaces and of water. ES of aqueous suspension of bacteriophages has been achieved for for surface decontamination after collection on grounded surfaces [START_REF] Jung | Generation of Nonagglomerated Airborne Bacteriophage Particles Using an Electrospray Technique[END_REF]. Besides, coupling the UV photo-catalysis of TiO 2 nanoparticles suspended in water for Reactive Oxygen Species production, decontamination of bacteria in water has been achieved using water ES without electrical discharges i.e. without plasmas [START_REF] Hong | Electrical sterilization of E. coli by electrostatic atomization with a photo-chemical catalyst[END_REF], while water ES with electrical discharges is also used for water treatment (see below §-2.3 Other application of water electrospray with electrical discharges). Finally, the most spread application of water-based solution ES has been developed for bio-molecules analysis. Here ES is used as an ion source to produce ionized species from liquid droplets, then analyzed either (i) by mass spectrometry, referred as ES Ionization-MS [START_REF] Thompson | The dynamics of liquid metal ion sources[END_REF][START_REF] Yamashita | NEGATIVE-ION PRODUCTION WITH THE ELECTROSPRAY ION-SOURCE[END_REF][START_REF] Whitehouse | Electrospray interface for liquid chromatographs and mass spectrometers[END_REF][START_REF] Fenn | Electrospray ionization-principles and practice[END_REF][START_REF] Wilm | Electrospray and Taylor-Cone theory, Dole's beam of macromolecules at last?[END_REF][START_REF] Xu | On-Line Probe for Fast Electrochemistry/Electrospray Mass Spectrometry. Investigation of Polycyclic Aromatic Hydrocarbons[END_REF][START_REF] Juraschek | Pulsation phenomena during electrospray ionization[END_REF][START_REF] Pozniak | Negative ion mode evolution of potential buildup and mapping of potential gradients within the ES emitter[END_REF][START_REF] Loo | ESI-MS and ion mobility analysis of proteasome complex[END_REF][START_REF] Marginean | ES characteristic curves: In pursuit of improved performance in the nanoflow regime[END_REF][START_REF] Pozniak | Current Measurements within the Electrospray Emitter[END_REF] used for macromolecules analysis and quantification near atmospheric pressure by online HPLC MS/MS, in both polarities or (ii) by mobility analysis of so-produced droplets/dried residues by ES-DMA for Differential Mobility Analyzers or as GEMMA for Gas-phase Electrophoretic Mobility Molecular Analyzer [START_REF] Lewis | ES-CPC: A molecule counting LG detector for macromolecules[END_REF][START_REF] Kaufman | Macromolecule analysis based on electrophoretic mobility in air: Globular proteins[END_REF][START_REF] Mouradian | DNA analysis using an ES scanning mobility particle sizer[END_REF][START_REF] Kaufman | Analysis of biomolecules using electrospray and nanoparticle methods: The gas-phase electrophoretic mobility molecular analyzer (GEMMA)[END_REF][START_REF] Kaufman | Analysis of a 3.6-MDa hexagonal bilayer hemoglobin from Lumbricus terrestris using a gas-phase electrophoretic mobility molecular analyzer[END_REF][START_REF] Kaufman | Electrospray diagnostics performed by using sucrose and proteins in the gas-phase electrophoretic mobility molecular analyzer (GEMMA)[END_REF][START_REF] Bacher | Charge-reduced nano ES ionization combined with DMA of peptides, proteins, glycoproteins, noncovalent protein complexes and viruses[END_REF][START_REF] Tsai | Gas-phase ion-mobility characterization of SAM-functionalized Au nanoparticles[END_REF][START_REF] Tsai | T-programmed ES-DMA for characterization of ligated nanoparticles in complex media[END_REF][START_REF] Tai | Protein Silver Nanoparticle Interactions to Colloidal Stability in Acidic Environments[END_REF][START_REF] You | Bionanoparticles as Candidate Reference Materials for Mobility Analysis of Nanoparticles[END_REF][START_REF] Almaier | Nano ES coupled to DMA (GEMMA) for the characterization of proteinaceous nanoparticlesfrom small peptides to functional protein complexes: A review[END_REF]. These analytical methods are still under development with new microfluidic facilities for "nanoemitter" to reach unequaled sensitivity for biomolecules like DNA, lipoprotein at sub-nL.min -1 [START_REF] Bacher | Charge-reduced nano ES ionization combined with DMA of peptides, proteins, glycoproteins, noncovalent protein complexes and viruses[END_REF][START_REF] Marginean | ES characteristic curves: In pursuit of improved performance in the nanoflow regime[END_REF][START_REF] Wang | High-aspect-ratio silica nozzle fabrication for nano-emitter ES applications[END_REF][START_REF] Gibson | Nanoelectrospray emitters: Trends and perspective[END_REF][START_REF] Marginean | Picoelectrospray Ionization-MS using narrow-Bore chemically etched emitters[END_REF].

Other application of water electrospray with electrical discharges

Despite unstable negative water ES discussed in the next section, a new application of water ES with negative corona discharge targets analytical emission spectroscopy of dissolved species in water, that can be analyzed through light emitted from the discharge after evaporation and plasma excitation of initially dissolved species [START_REF] Pohl | Crtical evaluation of Low power APGD between a flowing liquid cathode and a metal anode for element analysis by optical emission spectroscopy[END_REF], as performed by ICP-AES in low pressure RF plasmas. Surface and Water bio-decontamination has been achieved using water ES with electrical discharges. Indeed, aqueous mixtures of hydrogen peroxide with formic and acetic acids and esters as well as nitrogen oxides and acids are used for surface decontamination (Alasri et al., 1992). Similar species are produced by plasma in humid air or in water droplet and films exposed to air plasma, as reported in labscale corona discharges [START_REF] Lecuiller | Analysis of regimes and zones of corona discharge from the point of view of ozone production[END_REF][START_REF] Sisterson | An evaluation of lightning and corona discharge on thunderstorm air and precipitation chemistry[END_REF][START_REF] Borra | Electrical discharge regimes and aerosol production in point-to-plane dc high-pressure cold plasmas[END_REF] as well as in the troposphere to account for fog acidification by corona point discharges from trees [START_REF] Borra | Electrical and chemical consequences of point discharges in a forest during a mist and a thunderstorm[END_REF]. Post-discharge surface decontamination has thus been achieved by plasma [START_REF] Hoenig | Destruction of bacteria and toxic organicchemicals by a corona discharge[END_REF][START_REF] Odic | Plasma sterilization technologies and processes[END_REF] as well as by water ES with discharges for suspensions of Escherichia Coli (Lee HK, 2001;[START_REF] Lee | Effect of electrostatic atomization on electrical sterilization[END_REF]. Indeed, Reactive Oxygen and Nitrogenous Species produced by corona [START_REF] Kanev | Are reactive Oxygen species generated in ES at low current ?[END_REF] and by spark [START_REF] Machala | Formation of ROS and RNS in water ES through spark in air and bactericidal effect[END_REF] have been proposed by [START_REF] Pyrgiotakis | A chemical free, nanotechnology-based method for airborne bacterial inactivation using engineered water nanostructures[END_REF] to account for bacterial inactivation. More generally, ES of other organic solvents than water with dissolved reactants can also be performed simultaneously with electrical discharges, as well as by post-discharge ES injection of droplets downstream a discharge to develop new plasma-based aerosol processes (see 5-Conclusion). At last, steady water ES in a particular corona-assisted cone-jet mode can also be used as addressed in section 4.3, for particle removal from gas stream by bipolar Coulombian coagulation on scrubbing droplets, detailled in section 4.

Water ES modes with and without discharges

This section focuses on steady water ES in cone-jet mode for the unique tunable unimodal size and charge distributions, required for physical studies and applications of monodisperse non-agglomerated unipolar droplets that can be achieved in ambient air at STP conditions. Here are depicted, the effect of electrical discharges in the gas on the electric field along the liquid surface and the consequences on the ES stability as well as means to suppress the discharges. Finally, working conditions for steady Water ES with and without discharges are discussed with respect to capillary geometry versus conductivity and flowrate.

ES modes characterization

The steady cone-jet is one of the ES modes detailed in [START_REF] Zeleny | Instability of Electrified Liquid Surfaces[END_REF][START_REF] Vonnegut | Production of monodisperse liquid particles by electrical atomization[END_REF][START_REF] Smith | The EHD atomization of liquids[END_REF]Hayati et al., 1987b;[START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids: Main functioning modes[END_REF][START_REF] Cloupeau | Electrohydrodynamic spraying functioning modes: a critical review[END_REF][START_REF] Jaworek | Classification of the modes of EHD spraying[END_REF]. These modes have been investigated versus functioning conditions in the flowrate-voltage space for different conductivities and capillaries, based on:

-Observation of cone and jet shapes [START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids: Main functioning modes[END_REF][START_REF] Cloupeau | Electrohydrodynamic spraying functioning modes: a critical review[END_REF][START_REF] Jaworek | Classification of the modes of EHD spraying[END_REF], among others, with shape evolution confirmed for precession and multi-jet modes [START_REF] Jaworek | Forms of the multijet mode of electrohydrodynamic spraying[END_REF][START_REF] Noymer | Stability and atomization characteristics of electrohydrodynamic jets in the cone-jet and multi-jet modes[END_REF], the spindle and intermittent cone-jet modes with fast and CCD imaging (Kim HH et al., 2011;[START_REF] Pongrác | Fast imaging of intermittent electrospraying of water with positive corona discharge[END_REF] and for the first droplet emission in cone-jet [START_REF] Ganan-Calvo | The onset of electrospray: the universal scaling laws of the first ejection[END_REF]. In cone-jet, the cone is steady with either a steady jet for axisymmetric varicose fragmentation or a whipping jet for asymmetric kink fragmentation at larger flowrate (see 3.3.1.4). -Measurements of the mean current versus flowrate and conductivities for comparison to scaling laws established for the cone-jet (see 3.2 and 3.3.1.4). For unsteady ES modes, oscilloscope measurements of currents are useful to define the droplet emission frequency of dripping or spindle modes, and even critical to deal with ES destabilization by transient discharges such as pre-onset streamers, streamers and sparks [START_REF] Borra | Destabilisation of sprays in the cone-jet mode by electrical dicharges on the jet[END_REF]Borra et al., 1999d;[START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF][START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF][START_REF] Pongrác | Fast imaging of intermittent electrospraying of water with positive corona discharge[END_REF][START_REF] Verdoold | A generic electrospray classification[END_REF][START_REF] Pongrác | Effects of corona space charge polarity and liquid phase ion mobility on the shape and velocities of water jets in the spindle jet and precession modes of water electro-spray[END_REF], as first reported on pending drops (see introduction) and confirmed by emission spectroscopy [START_REF] Meesters | Generation of micron-sized droplets from the Taylor cone[END_REF][START_REF] Jaworek | Corona discharge in electrospraying[END_REF]. -Droplets properties (size distributions, charge per drop) and spray expansion (2D velocities, fluxes and concentration profiles) evaluated from Laser Phase Doppler measurements at different radial positions from the symmetry axis of nozzle, cone, jet and spray, versus voltage, flow rate and conductivity [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF][START_REF] Snarski | Experiments characterizing the interaction between 2 sprays of electrically charged liquid droplets[END_REF][START_REF] Dunn | Droplet diameter, flux and total current measurements in an EHD Spray[END_REF]Tang K et al., 1994b[START_REF] Tang | Generation of Monodisperse Water Droplets from Electrosprays in a Corona-Assisted Cone-Jet Mode[END_REF][START_REF] Grace | Droplet motion in an electrohydrodynamic fine spray[END_REF][START_REF] Hartmann | Development of electrohydrodynamic sprays related to space charge effects[END_REF][START_REF] Naqwi | Basic studies of EHD atomization process using phase Doppler measurement Particle and Particle Systems Characterization[END_REF][START_REF] Tang | Monodisperse electrosprays of low electric conductivity liquids in the cone-jet mode[END_REF][START_REF] De Juan | Charge and size distributions of electrospray drops[END_REF][START_REF] Gañán-Calvo | Current and droplet size in the electrospraying of liquids. Scaling laws[END_REF][START_REF] Olumee | Droplet dynamics changes in electrostatic sprays of methanolwater mixtures[END_REF]Hartmann et al., 1999a;[START_REF] Ku | Electrospray characteristics of highly viscous liquids[END_REF][START_REF] Wilhelm | Cone-jet and multijet electrosprays: Transport and evaporation[END_REF]. Ideally, the cone-jet mode of ES is confirmed with all arguments. However, simple current or droplet size measurements alone is enough thanks to scaling laws specific to the cone-jet mode established and confirmed for all liquids, at least without discharges as depicted just below.

Scaling laws and characteristic times for operating conditions of cone-jet mode

The striking stability of ES in cone-jet mode for the continuous production of monodisperse or unimodal droplets size and charge distributions has triggered the interest of physicist and engineers. Operating conditions for ES in cone-jet mode (voltage-flowrate) have been addressed versus liquid properties. Scaling laws or empirical relations link the mean droplet charge and size, to both the liquid properties (density = 998 kg.m -3 , viscosity = 1.002 Pa.s, surface tension 65-73 mN.m -1 , relative permittivity  r = 80) and flowrate (de la [START_REF] De La Mora | The current emitted by highly conducting Taylor cones[END_REF]Chen DR et al., 1997;[START_REF] Gañán-Calvo | Cone-jet analytical extension of taylor's electrostatic solution and the asymptotic universal scaling laws in electrospraying[END_REF][START_REF] Hartmann | Scaling laws for droplet size and current produced in the cone-jet mode[END_REF][START_REF] Ganán-Calvo | On the general scaling theory for ES[END_REF]) amongst others. All approaches are based on the EHD equilibrium required for the cone-jet formation, with scaling law of the spray current of charged droplets and droplet size evolving with a power law of the flowrate in Q Liq. n> 0 , with n depending on the liquid properties, discussed in [START_REF] Ganan-Calvo | Review on the physcis of electrospray: from electrokinetics to the operating conditions of Taylor cone-jets, and beyond[END_REF][START_REF] Rosell-Llompardt | Electrosprays in the cone-jet mode: from Taylor cone formation to spray development[END_REF]. The minimal flowrate for steady ES in cone-jet mode depends on the liquid conductivity. It is usually defined as follow, for shorter electrical relaxation than viscous or transit times in the cone and jet to let charges drift to the cone surface [START_REF] Ganan-Calvo | Review on the physcis of electrospray: from electrokinetics to the operating conditions of Taylor cone-jets, and beyond[END_REF]. Then the cone-jet can be established if surface charges induce the required normal electric field for balanced capillary and electrical pressures, as well as the tangential electric field induced by the voltage drop in the resistive liquid to accelerate the interfacial converging liquid into a jet (Hayati et al., 1987b;[START_REF] Hartmann | Electro hydrodynamic atomization in the cone-jet mode. A physical model of the liquid cone and jet[END_REF][START_REF] Hartmann | EHD atomization in the cone-jet mode physical modeling of the liquid cone and jet[END_REF].

The electrical relaxation time ( elec =  0 / from 7µs for 0.1 mS.m -1 de-ionized water to ≈70 ns for 10 mS.m -1 rain or tap water), is compared with different hydrodynamic characteristic times, depending on the considered mode. The hydrodynamic characteristic time corresponds either (i) to the time required for the formation of different volumes ( transit/ formation ≈ V drop / Q Liq. ) as the pending drop related to the outer diameter of the capillary [START_REF] Shiryaeva | The semiphenomenological classification of the modes of electrostatic dispersion of liquids[END_REF], the cone [START_REF] Hartmann | EHD atomization in the cone-jet mode physical modeling of the liquid cone and jet[END_REF], the jet [START_REF] Gañán-Calvo | Current and droplet size in the electrospraying of liquids. Scaling laws[END_REF], the droplet emitted from the jet [START_REF] Harpur | A design method for the electrostatic atomization of liquid aerosols[END_REF], or (ii) to the characteristic times for jet formation ( ≈ .d in / ) and deformation ( ≈(.d 3 in / ) 0.5 related to inner diameter in [START_REF] Jaworek | Classification of the modes of EHD spraying[END_REF], or (iii) to the characteristic viscous time ( visc. ≈ r Liq. ². [START_REF] Pfeifer | Parametric studies of EHD spraying[END_REF][START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Shiryaeva | The semiphenomenological classification of the modes of electrostatic dispersion of liquids[END_REF][START_REF] Harpur | A design method for the electrostatic atomization of liquid aerosols[END_REF]). The minimum flowrate for cone-jet is defined as Q min = 10 -

2

. Liq. , from 10 -16 m 3 .s -1 for 4 S.m -1 sea water to 10 -12 m 3 .s -1 for 0.1 mS.m -1 deionized water [START_REF] Gañán-Calvo | The minimum or natural rate of flow and droplet size ejected by Taylor cone-jets: Physical symmetries and scaling laws[END_REF]. Whatever the approach to define the minimum flowrate is, the maximum one for the cone-jet mode is ten times higher than this minimum one for a given capillary [START_REF] Harpur | A design method for the electrostatic atomization of liquid aerosols[END_REF]. This range of water flowrate and related droplet properties can be enlarged, using micron-sized capillary nozzles. Indeed, the minimum flowrate of 60 nL.min -1 (for 10 -12 m 3 .s -1 ) calculated for 0.1 mS.m -1 water ES in cone-jet without discharge, is larger than reported for micron-sized capillaries (0.3 nL.min -1 ), but smaller than for 50/20 µm capillary (1.7 µL.min -1 ) and far below the 3 mL.min -1 reported in section 3.3.3 on larger capillaries (400/150 µm) for corona-assisted cone-jet, discussed below.

Water ES in cone-jet mode

Since Zeleny's observations of electrical discharges from water drop, ES in cone-jet was reported as destabilized or prevented by discharges [START_REF] Zeleny | Instability of Electrified Liquid Surfaces[END_REF][START_REF] English | Corona from a Water Drop[END_REF]Hayati et al., 1987b;[START_REF] Bailey | Electrostatic spraying of liquids[END_REF]. Then, "a stabilized ES mode by the pulseless corona" has been described [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF][START_REF] Cloupeau | Electrostatic spraying of liquids: Main functioning modes[END_REF], confirmed in CO 2 (Tang K et al., 1994b[START_REF] Tang | Generation of Monodisperse Water Droplets from Electrosprays in a Corona-Assisted Cone-Jet Mode[END_REF] and air [START_REF] Borra | Destabilisation of sprays in the cone-jet mode by electrical dicharges on the jet[END_REF][START_REF] Jaworek | Studies of the corona discharge in ehd spraying[END_REF]Borra et al., 1999d;[START_REF] Ehouarn | EHD atomization -Stability domains and scaling laws of the cone-jetglow mode[END_REF][START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF][START_REF] Lopez-Herrera | An experimental study of the electrospraying of water in air at atmospheric pressure[END_REF][START_REF] Jaworek | Corona discharge in electrospraying[END_REF]. Without discharges, ES works in both + and -DC as well as in AC polarities, as mentioned in the introduction to account for water ES from HV power lines. However, if corona discharges develop in the gas, ES are unstable in negative polarity due to positive ion flux to the liquid surface with high kinetic energy, while positive ES can be stabilized in the corona-assisted cone-jet mode with less energetic electron flux [START_REF] Cloupeau | Recipes for use of EHD spraying in cone-jet mode and notes on corona discharge effects[END_REF]Borra et al., 1999d;[START_REF] Sugimoto | Negative corona discharge at a tip of water cone deformed under dc field[END_REF][START_REF] Higashiyama | Negative corona discharge from a water droplet under the pulsating DC field[END_REF]. Hence, only the positive water ES is addressed below, all the more that discharge onset voltage are lower for negative than for positive electrical discharge in air at STP [START_REF] Loeb | Electrical Coronas, Their Basic Physical Mechanisms[END_REF].

Unsteady/steady water ES induced by streamer/pulseless corona space charge fields

Unsteady/steady water ES modes induced by impulse/pulseless corona are described and detailed in terms of discharge physics. The operating conditions of steady water ES in corona-assisted cone-jet mode and empirical relations between the properties of droplets are presented with spray characteristics. For positive ES in liquid cone-to-plate configuration, the same succession of discharge regimes is reported as for the reference point-to-plane configuration. In such heterogeneous electric field profiles, the development of the discharge is controlled by the space charge field, well described for air corona discharges at atmospheric pressure [START_REF] Goldman | Corona discharges In[END_REF] as well as for ES to account for the development of the spray as a cloud of unipolar charged droplets (Hartmann et al., 1999a) and for different jet evolutions with less mobile positive and negative corona space charges [START_REF] Pongrác | Effects of corona space charge polarity and liquid phase ion mobility on the shape and velocities of water jets in the spindle jet and precession modes of water electro-spray[END_REF]. Then, the total electric field is the sum of the related gaseous corona ions and charged droplets space charge fields with Laplacian electric field related to the applied potential, the electrode shape and to the gap length.

Description of unsteady/steady water ES induced by impulse/pulseless corona

ES modes are presented in Figure 2 at increasing voltages for conductivities from 0.1 to 10 mS.m -1 , metal nozzle with outer diameters from 0.4 to 1.8 mm and flowrate from 30 to 200 mL.h -1 . The related currentvoltage characteristic, with spray and corona currents are briefly reminded in Appendix A1 and detailed with material and methods for corona and spraying modes characterization in (Borra et al., 1999d;[START_REF] Ehouarn | EHD atomization -Stability domains and scaling laws of the cone-jetglow mode[END_REF][START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF].

The volume where the electric field overcomes the gas ionization onset can be localized from light emitted by the plasma. Electron avalanches occur for electric field higher than 2.5•10 6 V.m -1 in ambient air [START_REF] Lowke | Onset corona fields and electrical breakdown criteria[END_REF]. Discharge develops as transient plasma filaments, measured as current pulses, or as a steady corona confined around the liquid cone-jet transition (Figure 2b), with pulseless current (see 3.3.1.2).

-V Nozzle < V Onset discharge : dripping and jetting without discharge (field profile 1 in section 3.3.1.2): Droplets are produced from the capillary or from the jet depending on the flowrate. No discharge pulse is detected.

-V Onset discharge < V Nozzle < V pulseless corona : unsteady dripping/jetting and intermittent cone-jet (Fig 2a with profile 2 in 3.3.1.2): above the discharge threshold, non-self-sustained discharge first develops as transient plasma filaments, called "burst pulse or pre-onset streamer" up to self-sustained discharge onset, when no more external electron is required since the discharge feeds itself with electrons from previous avalanches leading to an additional continuous current [START_REF] Goldman | Corona discharges In[END_REF]. Then, up to the threshold of pulseless corona, the transient space charge produced by each plasma filament induces an asymmetric, brief and local electric field variation in the gap. as well as on electrode surface [START_REF] Marode | Mechanism of spark breakdown in air at atmospheric-pressure between a positive point and plane .2. theoretical -computer-simulation of streamer track[END_REF]. This variation of the electric field along the liquid surfacemay disrupt the EHD equilibrium required for the cone-jet, depending on the relative space charge fields from transient streamer and steady corona and droplets [START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF]. In that case, the steady cone-jet mode cannot be induced, as reported over huge ranges of conductivities (from a fraction of mS.m -1 for de-ionized water to S.m -1 for biological aqueous samples up to a few S.m -1 for sea water) and flowrates (from nL.min -1 to tens mL.min -1 ) in air, [START_REF] Juraschek | Pulsation phenomena during electrospray ionization[END_REF][START_REF] Sugimoto | Negative corona discharge at a tip of water cone deformed under dc field[END_REF][START_REF] Kawamoto | Fundamental investigation on electrostatic ink jet phenomena in pin-to-plate discharge system[END_REF][START_REF] Bruggeman | Water surface deformation in strong electrical fields and its influence on electrical breakdown in a metal pin-water electrode system[END_REF][START_REF] Shirai | Atmospheric negative corona discharge observed at tip of taylor cone using PVA solution[END_REF][START_REF] Sun | Two-phase flow regimes and discharge characteristics of a plasma electrohydrodynamic atomization[END_REF][START_REF] Shirai | Atmospheric negative corona discharge using Taylor cone as a liquid cathode[END_REF][START_REF] Higashiyama | Influence of conductivity on corona discharge current from a water droplet and on ejection of nano-sized droplets[END_REF][START_REF] Xu | Dynamic corona characteristics of water droplets on charged conductor surface[END_REF]. All these modes, other than the steady cone-jet, lead to droplets emission from the capillary or/and from the jet in dripping, micro-dripping, spindle, intermittent cone-jet, precession and (multi)-jetting modes reported, at increasing flowrate, [START_REF] Smith | The EHD atomization of liquids[END_REF]Hayati et al., 1987b;[START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Cloupeau | Electrohydrodynamic spraying functioning modes: a critical review[END_REF][START_REF] Tang | Generation of Monodisperse Water Droplets from Electrosprays in a Corona-Assisted Cone-Jet Mode[END_REF][START_REF] Borra | Destabilisation of sprays in the cone-jet mode by electrical dicharges on the jet[END_REF][START_REF] Jaworek | Studies of the corona discharge in ehd spraying[END_REF][START_REF] Ehouarn | EHD atomization -Stability domains and scaling laws of the cone-jetglow mode[END_REF]Jaworek et al., 2005; [START_REF] Pongrac | Electrospraying of water with streamer corona discharge[END_REF][START_REF] Jaworek | Corona discharge in electrospraying[END_REF]Kim HH et al., 2014;[START_REF] Pongrác | Fast imaging of intermittent electrospraying of water with positive corona discharge[END_REF][START_REF] Pongrác | Effects of corona space charge polarity and liquid phase ion mobility on the shape and velocities of water jets in the spindle jet and precession modes of water electro-spray[END_REF]. These modes, other than the steady corona-assisted cone-jet are here gathered under the generic expression "unsteady ES modes" even if by essence, droplet emission occurs with repetitive cycles of a necessarily unsteady liquid fragmentation zone. This terminology aims to highlight the interest of "steady cone-jet modes (with or without discharge)" with respect to the stable shape of the liquid cone and jet (up to the fragmentation zone) and subsequent constant monodisperse droplet properties, compared to broader or poly-modal size distributions from fluctuating electrical conditions induced by unsteady space charge fields related to transient plasma filament, as detailed below (see 3.3.1.2 Meek's criterion).

Except for the dripping mode (below the onset voltage and related threshold field of gas ionization), for all these unsteady modes of water ES in ambient air, droplets emission systematically starts or ends with a transient plasma filament. Recurrent cycles of liquid deformation and correlated discharges are reported in micro-dripping and spindle modes for lower voltages than the onset one for cone-jet: starting with a pulseless corona from the water jet elongating in the gap up to the break-up, followed after the collection of the emitted sub-millimeter sized droplet, by transient plasma filaments from the residual conical meniscus up to the next drop emission at 100-300 Hz, reported from current measurements of corona discharge around pending, falling or suspended liquid drop and electrosprays [START_REF] Zeleny | Instability of Electrified Liquid Surfaces[END_REF][START_REF] English | Corona from a Water Drop[END_REF][START_REF] Joffre | Characteristic forms of electrified menisci emitting charges[END_REF]Hayati et al., 1987b;[START_REF] Cloupeau | Electrostatic spraying of liquids: Main functioning modes[END_REF][START_REF] Cloupeau | Recipes for use of EHD spraying in cone-jet mode and notes on corona discharge effects[END_REF][START_REF] Cloupeau | Electrohydrodynamic spraying functioning modes: a critical review[END_REF]Borra et al., 1999d;[START_REF] Ehouarn | EHD atomization -Stability domains and scaling laws of the cone-jetglow mode[END_REF][START_REF] Lopez-Herrera | An experimental study of the electrospraying of water in air at atmospheric pressure[END_REF]) -V pulseless steady corona <V Nozzle < V impulse streamer : pulseless corona-assisted cone-jet mode (Fig 2b with field profile 3,in 3.3.1.2). The steady pulseless corona discharge regime also referred to as Hermstein or glow [START_REF] Goldman | Corona discharges In[END_REF] corresponds to a confined faint violet plasma around the liquid in ambient air. The pulseless corona-assisted cone-jet mode is stabilized by the stationary and axisymmetric corona space charge with related continuous current including both continuous currents of charged droplets and corona ions, as reported for water ES in air [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF][START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF] or with at least 0.5 % CO 2 (Tang K et al., 1994b[START_REF] Tang | Generation of Monodisperse Water Droplets from Electrosprays in a Corona-Assisted Cone-Jet Mode[END_REF], as well as for glycerol in air (Borra et al., 1999d;[START_REF] Ku | Electrospray characteristics of highly viscous liquids[END_REF][START_REF] Korkut | Enhanced Stability of Electrohydrodynamic Jets through Gas Ionization[END_REF], The gaseous positive-corona-ion space charge lowers the normal component of the surface electric field.

A slower polarization results from the lower field in the liquid, directly linked to the normal component of the field along the liquid cone and jet surface. This steady and axisymmetric corona space charge lowers the surface charge density next to the confined corona, as mentioned for water by [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF] and ethylene glycol by [START_REF] Ku | Electrospray characteristics of highly viscous liquids[END_REF][START_REF] Korkut | Enhanced Stability of Electrohydrodynamic Jets through Gas Ionization[END_REF] to account for steady ES in coronaassisted cone-jet. Korkut attributed the stability to partial neutralization of the jet by electrons from corona, while Gibson listed electro-chemical processes eventually affecting liquid ion composition and mobility.

In these steady EHD conditions, the pulseless-corona assisted cone-jet mode leads to unimodal size and charge distributions of droplets. Such well-controlled properties are critical for physical studies and applications of charged drop, with charge level from 30 to 70 % of the maximum Rayleigh charge limit.

-V Nozzle > V impulse streamer : unsteady intermittent cone-jet mode (Fig 2c with field profile 4 in 3.3.1.2). In this case, the pulseless corona still exists but the higher voltage also leads to plasma filaments like streamers and sparks, as seen from the larger lightning volume extending in the gap, further than the confined corona. Then, as for pre-onset streamers, the subsequent transient and asymmetric modification of the field along the liquid surface disrupts the EHD equilibrium and the steady corona-assisted cone-jet turns into intermittent cone-jet. Size distribution are then multimodal with respect to unsteady production conditions.

Electrical discharge physics for streamer development and pulseless corona  Meek's criterion for streamer development inducing unsteady ES: these transient plasma filaments

("pre-onset streamer" for voltages lower than required for the continuous self-sustained corona, as well as streamer developing further in the gap than the confined corona, for higher voltages) can only occur if the so-called Meek's criterion is reached [START_REF] Meek | A Theory of Spark Discharge[END_REF]Marode, 1975a;Meek J.M. et al., 1978). Meek stated that streamer propagation in the gap implies that the space charge field of residual positive ions left by previous avalanches after the faster collection of electrons than ions, has to be at least equal to the threshold field of air ionization (≈ 2.5•10 6 V.m -1 in STP). Avalanches can then start further in the gap between the positive space charge appearing in the high field region close to the electrode with the smaller radius of curvature and the earthed electrode, where the space charge field reinforces the total electric field. In other words, "this enables the streamer to propagate into the gap as if the high field electrode advances in the gap from the point into the low field region". Taking into account the space charge repulsion and diffusion, Raether has demonstrated that this only happens in ambient pressure when avalanches produces more than 10 +8 charges. Since this number of electrons is given by e (.d) , with d the ionization length (over which the total electric field overcomes the threshold field of discharge [START_REF] Townsend | Electricity in Gases[END_REF]), and  the ionization coefficient, this corresponds to a critical length of ionization around 10 µm (for .d=18) considering a mean free path of electron in nitrogen of 0.5 µm at STP [START_REF] Raether | Electron Avalanches and Breakdown in Gases[END_REF][START_REF] Nasser | Fundamentals of Gaseous Ionization and Plasma Electronics[END_REF]. The corresponding space charge density in the front of the streamer reaches 10 16 cm -3 but decreases within nanoseconds under diffusion, repulsion and neutralization, all charges being collected within a fraction of µs (Marode, 1975a). The effect of this transient positive space charge in propagating front of streamer on the total electric field is short but intense; higher electric field develops in the gap between the space charge and the counter electrode, and reversely on the liquid surface. Hence, during streamer development in the gap, the electric field profile along the liquid surface evolves for a few tens of ns, but the EHD equilibrium is disrupted due to the asymmetric surface field evolution around the axisymmetric cone-jet, for a duration in the order of the viscous relaxation time (~ ms) required to form again the cone-jet, until next streamer. The corresponding critical amount of charges per pulse to disrupt the EHD equilibrium lies in the order of pC at the threshold voltage but increases for higher corona current, with respect to the relative space charge fields from transient streamer and both steady corona and droplets ones, as detailed in [START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF].

To fulfill the Meek's criterion for streamer development, avalanche has to start at least at a critical "length of ionization" from the anode surface. This accounts for the higher threshold field of positive discharges in STP air from wires with smaller diameters, as detailed from theoretical analysis of Peek's law combined with Meek's criterion [START_REF] Hartman | Theoretical Evaluation of Peek's Law[END_REF] and discussed for different electrode geometries [START_REF] Lowke | Onset corona fields and electrical breakdown criteria[END_REF]. Hartman has expressed the threshold surface electric field, the ionization length and the number of charges created along this length, versus the wire radius, down to 0.1 µm (close to the minimum jet diameter reported for water ES without discharge producing 0.2 µm droplets, see Figure 3b). More diverging fields around smaller electrode, allow higher voltages and related surface field without overcoming the Meek's criterion for pre-onset streamer development (see dashed blue field profile in Figure 3a for steady ES without discharge for d out < 50 µm). Moreover, the critical ionization length and the related surface field increase for radius smaller than a few micrometers (Figure 3b). Then, for jet diameter smaller than few µm from capillaries with outer diameters smaller than few tens of µm, the discharge threshold voltage is offset above the cone-jet mode one and steady water ES can be achieved in air without discharges (see 3.3.2).

 Electrical discharge regime versus spatial evolution of the total electric field in the gas: the pulse or pulseless discharge regime depends on the ionization length i.e. on the field profile in the gap (see Figure 3). For any gas composition and density, this length depends on the voltage and on the radius of the high field electrode (nozzle, liquid cone and jet) with respect to the field profile in the gap [START_REF] Hartman | Theoretical Evaluation of Peek's Law[END_REF]. The field profile 1 in Figure 3a applies for the dripping mode of ES (not presented on Fig. 2). It leads to a smaller ionization length than required to achieve the Meek's criterion for streamer development reported at discharge onset [START_REF] Hartman | Theoretical Evaluation of Peek's Law[END_REF]. Above the onset voltage of discharge (field profile 2), the ionization length overcomes tens of micrometers and pre-onset streamers are measured as current pulses, from 1 to 100 pC per pulse, depending on the space charge density related to the continuous corona current. For higher voltages, avalanches develop on longer lengths (field profile 3). The steady corona regime is then characterized by a continuous flux of ions from the axisymmetric corona-shaped ionization volume confined around the liquid cone-jet transition (see Figure 2b), to the grounded electrodes. The quasistationary space charge distributed symmetrically in the gas around the liquid cone-jet axis, retro controls the field on the anode liquid surface. As for point-to-plane gaps, no more pulse is reported. The continuous corona current evolves much less with the voltage and related Laplacian field than without corona space charge at lower voltage. This confirms the limited electrical field variation over large voltage range due to the corona space charge retro-controlling the Laplacian field in the high field region [START_REF] Goldman | Corona discharges In[END_REF]. At higher voltages (field profile 4) for unsteady ES depicted in fig. 2c, longer avalanches create enough charges leaving the confined corona to fulfill the Meek's criterion for streamer propagation further in the gap, in the low field region thanks to the transient local self-generated space charge field of streamers.

After the description of ES modes related to the discharge physics, working conditions are addressed below.

Operating conditions of the corona-assisted cone-jet mode in (, Q liq , V liq ) space

The nozzle-ring-plate configuration is commonly used to shield the polarized liquid cone above the production zone from electrical field variations that may arise with fluctuating surface potential when charged droplets are deposited on insulated surfaces [START_REF] Tatoulian | Deposition of poly(acrylic acid) films by EHDA in postdischarge at atmospheric pressure in air[END_REF][START_REF] Borra | Polymer surface processing by atmospheric pressure DBD for post-discharge grafting of washing-resistant functional coatings[END_REF][START_REF] Borra | Atmospheric Pressure Deposition of Thin Functional Coatings: Polymer Surface Patterning by DBD and Post-Discharge Polymerization of Liquid Vinyl Monomer from Surface Radicals[END_REF], or with space charge variations when charged particles are injected in the spray, as observed in bipolar ES coagulation for powder production (Borra et al., 1997a;Sigmund et al., 2014a;[START_REF] Sigmund | An Aerosol-Based Process for Electrostatic Coating of Particle Surfaces with Nanoparticles[END_REF] and bipolar-scrubbing (see next section). Operating conditions of pulseless corona-assisted cone-jet for steady water ES are thus depicted in the (, Q liq , V liq ) space for the same ES nozzle-to-plate, with or without a ring. In both configurations, impulse streamers induce "unsteady" ES modes, while the confined pulseless corona leads to steady water ES in pulseless corona-assisted cone-jet mode (cone-jet glow).

Effect of corona space charge on the minimum flowrate and voltage versus conductivity:

-For nozzle to plate ES configuration (Fig. 4a), the succession of spraying modes reported in Figure 2 is the same for water than for liquids with lower surface tension, but shifted to higher voltages, all the more for water with the opposed space charge field from corona ions implying higher voltage to reach the same total electric field profile along the liquid surface. However, contrary to the classical cone-jet mode, which for the minimum flowrate decreases for higher conductivities, higher flowrates are required to achieve the steady ES of more conductive water in the pulseless corona-assisted cone-jet. Indeed, higher electric and balancing capillary pressures result from faster polarization of more conductive liquid cone.

Then, for subcritical flowrate, the liquid is divided into unstable liquid jets before the cone formation due to excessive outward electric pressure [START_REF] Cloupeau | Electrohydrodynamic spraying functioning modes: a critical review[END_REF]. Larger cone and jet at higher flowrates reduce the surface charge density and the related electric pressure at constant voltage on larger liquid area

(E n, surface ≈  (C.m -²)/  0 (F.m -1
)). Higher flowrate thus leads to longer cone with lower electric pressure in the cone base to build the field profile along the cone surface required for cone-jet formation, as described in section 3.2.

With larger cones at larger flowrates, less diverging field profiles lead to streamer development with destabilizing asymmetric and transient local space charges rather than to pulseless corona with its quasistationary axisymmetric space charge. Then higher voltages and related smaller cone and jet are required to induce more diverging field favorable to the pulseless corona discharge.

-For shorter gaps with the ring (Fig. 4b), the domains of steady corona ES are shifted to lower voltages.

Reducing thus the energy cost of the process, rings are rather used for their stabilizing effect on the liquid cone to achieve the required steady "electrical conditions" discussed just above. Moreover, the ring with the same polarity as the liquid, lowers the normal component of the total electric field at the liquid surface to suppress the destabilizing streamer for steady water ES in air [START_REF] Borra | Destabilisation of sprays in the cone-jet mode by electrical dicharges on the jet[END_REF] as for spray focusing in ES Deposition devices for coating [START_REF] Jaworek | Electrospray application to powder production and surface coating[END_REF]. For detailed information on shielding and focusing rings, these "electrostatic extractor" have been commonly used for more than a century by Lord Kelvin in his electrical power supply based on water electro-dripping/spraying [START_REF] Kelvin | On a Self-Acting Apparatus for Multiplying and Maintaining Electric Charges, with Applications to Illustrate the Voltaic Theory Proceedings of the Royal Society[END_REF], for electron beam focusing/deflection and for pulsed ES drop-on-demand as in ink-jet printing devices (Sweet RG, 1965;[START_REF] Kamphoefner | Ink jet printing[END_REF][START_REF] Stachewicz | Single event electrospraying of water[END_REF] and for material production by spray drying [START_REF] Kodas | Aerosol processing of materials[END_REF][START_REF] Rulison | Synthesis of yttria powders by electrospray pyrolysis[END_REF][START_REF] Camelot | Bipolar coagulation process for the production of powders[END_REF]. The onset voltage of coronaassisted cone-jet increases with the conductivity in nozzle-plate configuration but evolves differently with the ring (see Figure 4). Both effects (higher minimum flowrate for higher conductivities and different evolution of the threshold voltage with and without a ring) result from the different distributions of the corona space charge in the gap, thus retro-controlling with different intensity and dynamics the total electric field profile along the cone and the jet surface. Indeed, the ring collects corona ions created around the liquid cone-jet or from edges of the nozzle independently of the charged droplets current, radially above the jet break-up, or as a concentric plume of ions around the droplet spray in nozzle to plate configuration.

Droplet properties and spray development in corona-assisted cone-jet mode of water ES

Thanks to Phase Doppler development in the 1990's, some spray characterization can be found in literature for the classical cone-jet mode without discharges to establish or/and confirm empirical scaling laws [START_REF] Gañán-Calvo | Current and droplet size in the electrospraying of liquids. Scaling laws[END_REF][START_REF] Hartmann | EHD atomization in the cone-jet mode physical modeling of the liquid cone and jet[END_REF]. Velocity, flux and diameter of droplet are usually measured to build radial profiles, which are then integrated over the section of the spray at different heights from the nozzle. The production frequency and related concentration and charge per drop can be calculated and the size distribution integrating all produced droplets is obtained, with a modal most frequently produced droplet size in these unimodal or even monodisperse size distributions. To highlight these unique droplet properties achieved in the less documented pulseless corona-assisted conejet mode, diameter and charge per drop are presented for this steady water ES in air with empirical scaling laws versus liquid conductivities, flowrates and corona current related to the applied voltage (Figure 5).

Droplet diameter (d droplet ):

The unimodal size distribution produced in pulseless corona-assisted cone-jet (Figure 2b) confirms the steady EHD conditions for droplet production. The geometric standard deviation of the size distribution (GSD≈ 1.3) is larger than for monodisperse spray produced by axisymmetric varicose fragmentation in cone-jet mode (< 1.15), as expected for water droplets produced by asymmetric kink fragmentation mode [START_REF] Hartmann | Jet break-up in electrohydrodynamic atomization in the cone-jet mode[END_REF], with the characteristic whipping motion of the jet for 0.1 mS.m -1 water ES at 100 mL.h -1 [START_REF] Ehouarn | Pulvérisation électro-hydrodynamique de liquide stabilisée par décharges électriques pour le traitement d'effluents particulaires[END_REF]. Then the modal diameter of droplet size distribution follows the empirical relation:

d droplet ≈ Q liq 0.5 •I corona -0.04 • liq -0.2
As for ES in cone-jet without discharge, in corona-assisted cone-jet, the droplet diameter evolves with the conductivity and the flowrate but as well with the corona current (see Figure 5a). Higher conductivity leads to smaller droplets at a given flow rate. Higher flow rates leads to larger droplets, as expected from classical scaling laws for the cone-jet without discharges. As for cone-jet without discharge, smaller conejet lead to smaller droplets at higher voltage and corona current [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF].

Spray current and droplet charge:

The spray current and the subsequent mean charge per drop follow the empirical fitted laws versus flowrate and corona current: [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF]). The 0.2 exponent of the flowrate is smaller than expected from scaling laws with a 1/3 or 1/4 exponent of the flowrate. This deviation probably arises from the different field profile along the cone surface induced by the corona space charge field. The higher specific charge per drop are derived for lower flow rates from 6 to 12 mC.kg -1 , following this empirical relation:

I spray ≈ Q liq 0.2 • I Corona 0.1 ,
q droplet / m≈ Q liq -0.8 •I Corona 0.1 .
The charge-to-mass ratio is close to the Rayleigh limit (q Rayleigh / m= (8/ m)•( 0  r 3 ) 1/2 ). Hence, the steady water ES in pulseless corona-assisted cone-jet mode produces unimodal size and charge distribution with modal diameter and specific charge of droplets from 40 to 70 % of this maximal charge.

Spray expansion

With such charge levels, close to the Rayleigh limit, the corona-assisted cone-jet mode is particularly well adapted for physical studies of electrical properties of suspended droplets as well as for the development of interfacial processes based on electrical forces, such as bipolar-scrubbing of particles for filtration. To highlight the interest of unimodal water sprays for self-dispersion of unipolar droplets due to electrostatic repulsion, droplet velocity (radial profiles at different heights-z-from the nozzle) are presented for the pulseless corona-assisted cone-jet mode. As reported and modelled for cone-jet without discharge, the spray development in the gas depends on the initial droplet velocity and related inertia balanced by drag and electrical forces from the total electric field including the Lagrangian one related to the voltage and the space charge fields [START_REF] Snarski | Experiments characterizing the interaction between 2 sprays of electrically charged liquid droplets[END_REF]Hartmann et al., 1999a;[START_REF] Deng | Influence of space charge on the scale-up of multiplexed electrosprays[END_REF][START_REF] Grifoll | Efficient Lagrangian simulation of electrospray droplets dynamics[END_REF]Yang WW et al., 2012). The latest arises here from positive droplets and corona ions. Axial velocities decrease within a few ms from a few to a fraction of m.s -1 on the spray axis over a few centimeters, while negative velocities of droplets flowing back to the ring are reported on the edges of the spray (see Figure 6). Droplet concentration (not presented here) decreases from a 10 4 -10 5 to 10 2 in the first few centimeters from the jet on the spray axis with specific surface up to 1000 m².m -3 [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF].

Steady water ES in cone-jet mode without discharge

Steady water ES in cone-jet can also be performed without discharges in ambient air by acting (i) on liquid surface tension (ii) on threshold field of discharge and (iii) on the field profile around the liquid cone-jet using fine spraying nozzles (< 100 µm).

(i) The water surface tension can be lowered by organic surfactants or organic solvents to decrease the onset voltage of cone-jet. For such aqueous solutions with surface tension below 50 mN.m -1 , the threshold voltage of cone-jet and multi-cone-jet modes are smaller than the discharge one and both modes can be induced in air without discharges [START_REF] Smith | The EHD atomization of liquids[END_REF][START_REF] Ehouarn | EHD atomization -Stability domains and scaling laws of the cone-jetglow mode[END_REF].

(ii) To increase the dielectric strength of the gas i.e. the threshold reduced field of discharge (E/N in V.m - 4, [START_REF] Nasser | Fundamentals of Gaseous Ionization and Plasma Electronics[END_REF])), water ES has been performed in CO 2 or SF 6 at atmospheric pressure or at higher pressure in air [START_REF] Smith | The EHD atomization of liquids[END_REF]Hayati et al., 1987b;[START_REF] Bailey | Electrostatic spraying of liquids[END_REF], [START_REF] Yamashita | NEGATIVE-ION PRODUCTION WITH THE ELECTROSPRAY ION-SOURCE[END_REF]Tang K et al., 1994b[START_REF] Tang | Generation of Monodisperse Water Droplets from Electrosprays in a Corona-Assisted Cone-Jet Mode[END_REF]. Then, the steady cone-jet is reported without discharge .

(iii) Otherwise, using smaller capillaries (<100 µm), the steady ES in cone-jet mode without discharges in ambient air has also been successfully tested by [START_REF] Lopez-Herrera | An experimental study of the electrospraying of water in air at atmospheric pressure[END_REF], as reported by [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF]. In this case, the faster decrease of the electric field in the gap quenches the development of transient plasma filament since the field never overcomes the threshold field of ionization, further than a few micrometers from the liquid surface (see Figure 3a, dashed blue field profile). Then, eventual shorter avalanches produce less concentrated space charges without streamer formation due to insufficient number of electrons created on this sub-critical length of ionization discussed above from Figure 3b. This is used in commercial ES aerosol generator [START_REF] Fu | A New ES Aerosol Generator with High Particle Transmission Efficiency[END_REF] with smaller capillaries and flowrates down to nL.h -1 on 4 µm capillaries [START_REF] Radionova | Dual nano-electrospray and mixing in the taylor cone[END_REF] and even less in [START_REF] Marginean | Picoelectrospray Ionization-MS using narrow-Bore chemically etched emitters[END_REF]. This applies to analytical methods based on mobility analysis either of droplets in atmospheric pressure ES-DMA [START_REF] Liu | An electrospray aerosol generator with X-ray photoionizer for particle charge reduction[END_REF][START_REF] Almaier | Nano ES coupled to DMA (GEMMA) for the characterization of proteinaceous nanoparticlesfrom small peptides to functional protein complexes: A review[END_REF] or of ions in low pressure ES-Ionization [START_REF] Gibson | Nanoelectrospray emitters: Trends and perspective[END_REF].

Operating conditions for steady Water ES in cone-jet mode with and without discharges

Steady production of droplets with constant size and charge distributions can be achieved in ambient air by water ES in cone-jet mode with pulseless corona or without discharges (see Figure 7). µL.min -1 µm mm [START_REF] Cloupeau | Electrostatic spraying of liquids in cone-jet mode[END_REF] water + 0..5% surfactant 0.5-1.5 600 120/ < 40 by lowering surface tension  d drop Vol. = 1µm (1.5 mS.m - 1 ) (Tang K et al., 1994b) in CO2 at 0.5 % vol 10 0.1 3 5-50 0.4/ 0.15  d drop = 2 µm 6 &10µm at 20 & 40µL.min -1 [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF]Borra 1997, 1999a-c, 2004) 0.04-5 500-3300 [0.4-1.8] / [0.25-0.2] [50-130] µm [START_REF] Jaworek | Studies of the corona discharge in ehd spraying[END_REF][START_REF] Jaworek | Classification of the modes of EHD spraying[END_REF]) 1 2000-3000 0.9/ 0.65 [START_REF] Lopez-Herrera | An experimental study of the electrospraying of water in air at atmospheric pressure[END_REF] In both cases, streamer and subsequent disruption of the EHD equilibrium are avoided, due to diverging fields induced on smaller radius, as in point-to-plane discharges [START_REF] Goldman | Corona discharges In[END_REF][START_REF] Hartman | Theoretical Evaluation of Peek's Law[END_REF]. Indeed, small discrepancies in nozzle geometry make big differences as far as corona discharge are involved due to the double constraint for EHD equilibrium with water in air. The first one on the onset voltage of cone-jet formation, as defined in 3.2. The second condition concerns the spatial evolution of the electric field around the liquid, defining the ionization length and the corresponding discharge regime.

As addressed in 3.3.1.2, smaller outer and inner nozzle diameters induce finer and longer jet, quenching the discharge on shorter ionization length than required for streamer development, even for liquid voltage higher than the threshold for cone-jet formation. In that case, the steady cone-jet mode is established without discharge.

The nozzle geometry affects the functioning flowrate and voltage of water ES in air, as depicted in Figure 7, for both steady cone-jet modes with and without discharges. Since the minimum flowrate depends on the conductivity, steady ES of more conductive water solutions can be achieved at lower flowrates with smaller capillaries for both steady cone-jet with and without discharges. Then, as a rule of thumb, for inner diameters larger than 0.1 mm, pulseless corona-assisted cone-jet can be performed down to 0.5 µL.min -1 flowrates, while steady water ES in cone-jet mode without discharges can be performed down to nL.min -1 for inner diameters smaller than 100µm, with even more diverging field to quench the discharge.

Steady ES in cone-jet mode can be used for the production of water droplets in ambient air with unimodal or even monodisperse size distributions. Monodisperse submicron-sized sprays are achieved at lower flowrates for higher conductivities with small capillaries in cone-jet mode without discharges. Larger droplets from a few micrometers at 3 µL.min -1 to 100 µm for a few mL.min -1 , with still unimodal size distributions are produced in pulseless corona-assisted cone-jet mode using capillaries with inner diameter from 0.12 to 0.5 mm and outer diameters smaller than 2mm, for water conductivities from 0.1 to 10 mS.m -1 . With charge levels close to the Rayleigh limit, the corona-assisted cone-jet mode is well adapted for physical studies of such suspended charged droplets and for the development of enhanced efficiencies interfacial processes, such as electro-scrubbing. This particular mode of steady ES in cone-jet mode stabilized by a corona discharge has thus been tested for filtration by bipolar-scrubbing for filtration of fumes or ambient aerosol at lab-scale with mL.h -1 water flow rate (see next section 4). Steady ES without discharge has impacted the rapidly growing market of high sensitivity analysis of biological aqueous solution by ESI-MS performed at much lower flowrates down to sub-nL.min -1 [START_REF] Gibson | Nanoelectrospray emitters: Trends and perspective[END_REF]. Otherwise, Water ES with electrical discharges and more generally plasma-droplets interaction are studied to take advantage of the large interfacial exchanges between self-dispersed droplets and the gaseous plasma species like electrons, radicals, excited species or ions, with ozone and other nitrogen oxides/acids, as discussed above for surface and water decontamination and in conclusions for the development of new plasma-based aerosol processes, especially for material coating and deposition processes .

Other modes than this steady mono cone-jet have recently been reinvestigated to achieve higher flowrate ES applications: the multi-jet first and the simple jet modes, described by Hayati, Cloupeau and others since the 1980', respectively for high added value applications of tailored monodisperse droplets [START_REF] Duby | Stabilization of monodisperse electrosprays in the multi-jet mode via electric field enhancement[END_REF] and for metal recovery from used water and as the evaporation step in desalination process to achieve ES of high conductivity water up to 600 mL.h -1 (Agostinho et al., 2018). In both cases, the monodispersity of droplets is conserved. In the first case, similar monodisperse micron-sized droplet are produced than in cone-jet ES with higher throughout, while in the second, bigger droplets are achieved (> 200 µm).

Other applications of steady cone-jet mode of ES could be achieved at lower voltages and higher flowrates even for "dirty" water with conductivity around S.m -1 , with higher corona current in the same configuration, or by playing with corona ion space charge location and density around the liquid for different geometries and locations of ring(s), collecting i.e. driving ions on defined pathways "drawn by field lines". Steady water ES in corona assisted cone-jet mode may advantageously be applied to water desalination by droplet evaporation, all the more efficient with smaller droplets than in the simple-jet mode, already used to achieve the production of "clean" condensed water (Agostinho et al., 2018). Nozzleless ES devices, with needles under the liquid surface, has been reinvestigated for multi-ES, selffed in pure de-ionized water condensed from air [START_REF] Pyrgiotakis | A chemical free, nanotechnology-based method for airborne bacterial inactivation using engineered water nanostructures[END_REF]. In terms of installation and maintenance cost, this system may find applications to avoid steps to control the water conductivity with a de-ionization step and the water feeding with flowrate retro-controlled by conductivity measurements.

Water ES for high efficiency bipolar-scrubbing of submicron-sized particles from gases

With charge levels close to the Rayleigh's limit, the steady water ES in the corona-assisted cone-jet mode is adapted for physical studies of electrical properties of charged droplets as well as for the development of efficient interfacial processes based on electrical forces. This section addresses such ES application for gas filtration by bipolar scrubbing to remove suspended particles from fume, smoke or ambient aerosols flows.

Filtration: goals, means and limits

The removal of particles suspended in gases was already a concern in the 1900's to prevent smog formation next to urban areas [START_REF] Hinds | Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles[END_REF]. Since then, air quality has become a priority, with ever more accurate aerosol characterization tools and epidemiological studies of respiratory diseases. New tools for the missing range of size measurements down to sub-nanometer clusters [START_REF] Intra | An overview of aerosol particle sensors for size distribution measurement[END_REF], just confirmed high concentration of nanoclusters in towns "loaded" with combustion aerosols [START_REF] Rönkkö | Traffic: major source of atmospheric nanocluster[END_REF]. Fabrics filters and wet scrubbers collect particles from gas stream on fibers or droplets mainly by mechanical forces. Both are based on efficient diffusion of particles smaller than 100 nm, on inertial impaction of particles larger than 1 µm eventually combined with less efficient hydrodynamic interception for the intermediate size range. As a result, these mechanical filters lack of efficiency from 0.1 to 1 µm, for the Most Penetrating Particle Size -MPPS-around 0.3 µm [START_REF] Baron | Aerosol measurement: principles, techniques, and applications[END_REF]. In this size range, electrical forces are larger than gravity and thermophoresis and thus control the kinematics of particles suspended in gases and subsequent particle trajectories. More efficient electrofiltration devices have been developed [START_REF] Parker | Applied Electrostatic Precipitation[END_REF][START_REF] Jaworek | Modern electrostatic devices and methods for exhaust gas cleaning: A brief review[END_REF]Borra et al., 2009;[START_REF] Jidenko | Self-cleaning, maintenance-free aerosol filter by non-thermal plasma at atmospheric pressure[END_REF]. In Electro-Static Precipitators -ESP-particles are charged by corona ions and collected from the gas by electrical forces with lower pressure drop than in fabric filters [START_REF] Cross | Electrostatics : principles, problems and applications[END_REF][START_REF] Parker | Applied Electrostatic Precipitation[END_REF]. However, lower efficiencies in the same submicron size range arises from lower electrical mobility and related terminal velocities, with respect to the charging mechanisms, either by ion drift along field lines intercepting the surface of particles, or by ion diffusion, which is the unique charging process below 0.1 µm [START_REF] Wu | Continuum field-diffusion charging of particles possessing nonzero initial charge[END_REF][START_REF] Biskos | Unipolar diffusion charging of aerosol particles in the transition regime[END_REF][START_REF] Park | Real-time measurement of submicron particles with log-normal size distribution by unipolar diffusion and field charger[END_REF]. Filtration efficiencies are then reduced from 0.1 to 1 µm, since neither mechanical nor electrical collection are fully efficient, when used alone [START_REF] Hinds | Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles[END_REF]. Fabric filters induces high-pressure drop and usually works below 100 °C while ESP with lower pressure drop can be used for filtration of "hot" exhaust gases (incinerator, combustion power plants…). However, ESP requires maintenance and regulation since the surface potential of the collected dust layer increases and lowers the field in the gap. The voltage has to be raised to achieve stable corona discharge for continuous aerosol charging and collection. Then, to prevent from sparking due to back-discharges in the collected dust layer [START_REF] Cross | Electrostatics : principles, problems and applications[END_REF][START_REF] Czech | Optical emission spectroscopy of point-plane corona and backcorona discharges in air[END_REF], different options have been developed, first by cyclic cleaning of electrodes, then with multi-step ESP, splitting charging and collection steps [START_REF] Parker | Applied Electrostatic Precipitation[END_REF][START_REF] Asbach | Development of a highly efficient electrostatic partitioner of gas and particles with minimal effect on the gas phase[END_REF][START_REF] Jaworek | Dust particles removal by a novel two-stage electrostatic precipitator[END_REF]. As an alternative to fabric filters and ESP, unipolar wet ESP were first developed to clean the collection electrode of particles charged with the same polarity as droplets [START_REF] Eyraud | Study of a New Dust Collector Using Electrostatically Sprayed Water[END_REF][START_REF] Lear | Charged droplet scrubbing for fine particle control[END_REF]Xu DX et al., 2003).

Wet electro-scrubbers have then been tested as hybrid systems combining advantages of wet scrubbers, for low pressure drop and simultaneous scrubbing of soluble gases (SO X , NO X ) and ESP for efficient electro-collection in the submicron size range on larger surface of suspended droplets than in ESP [START_REF] Pilat | Collection of aerosol particles by electrostatic droplet spray scrubbers[END_REF][START_REF] Melcher | Electrostatic devices for controll of submicrometer particles[END_REF][START_REF] Ehouarn | Electro-pulvérisation de gouttelettes d'eau microniques et chargées électriquement[END_REF][START_REF] Borra | Moyens de pulverisation electrohydrodynamique: Google Patents[END_REF][START_REF] Unger | Filtration of submicron sized particles by electrocoagulation[END_REF]Jaworek et al., 2006a;Carotenuto et al., 2010b). With no more need to clean the electrodes as in ESP and reduced waste water per unit volume of filtered gas compared to wet scrubbing on neutral droplets, wet electroscrubbers is a continuous on-line process for gas velocities in the order of m.s -1 , typical of large scale ESP, see 4.3.1.3.

Bipolar wet electro-scrubbers

Principle, mechanisms and models

Based on Coulombian coagulation of oppositely charged particles and drops, wet electro-scrubbing is a continuous multi-step process for the removal of sub-micron sized atmospheric and combustion aerosol, depicted in Figure 8: suspended particles to be removed from the gas flow are first charged on-line by negative DC corona, injected in positive collecting water sprays dispersed in the scrubber by selfrepulsions of unipolar droplets, collected from the gas by gravity and self-repulsion losses to the earthed walls.

Several wet electro-scrubber concepts are reviewed with one or both charged particle and collector either with the same or with opposite polarities respectively in unipolar and bipolar scrubbers [START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF][START_REF] Jaworek | Multi-nozzle electrospray system for gas cleaning processes[END_REF][START_REF] Zhao | Modeling of Gravitational Wet Scrubbers with Electrostatic Enhancement[END_REF]. Different charge-to-mass ratio of the collecting droplets (see next section 4.2.2) and different concentrations from mg to g.m -3 of sub-micron and micron sized particles, as discussed in section 4.3.2, have been tested over large range of exhaust aerosol flowrates.

Wet electro-scrubbers have first been tested at higher flowrates up to 1700 Nm 3 .h -1 on exhaust aerosols from spark furnace, industrial boilers, diesel marine engines and other combustion sources [START_REF] Penney | Electrified liquid spray dust precipitator: Google Patents[END_REF][START_REF] Eyraud | Study of a New Dust Collector Using Electrostatically Sprayed Water[END_REF][START_REF] Pilat | Collection of aerosol particles by electrostatic droplet spray scrubbers[END_REF][START_REF] Pilat | Effect of diffusiophoresis and thermophoresis on overall particle collection efficiency of spray droplet scrubbers[END_REF][START_REF] Metzler | Electrostatic enhancement of dust separation in a nozzle scrubber[END_REF][START_REF] Jaworek | Submicron charged dust particle interception by charged drops[END_REF][START_REF] Krupa | Dust particle removal by wet-type electrostatic scrubber[END_REF]Jaworek et al., 2006a;[START_REF] Jaworek | Modern electrostatic devices and methods for exhaust gas cleaning: A brief review[END_REF][START_REF] Ha | Enhancement of diesel particulate matter collection in an electrostatic water-spraying scrubber[END_REF]Jaworek et al., 2011;Di Natale et al., 2013;[START_REF] Di Natale | Capture of particles in a wet electrostatic scrubber[END_REF][START_REF] Krupa | Diesel nanoparticles removal by charged spray[END_REF]. The total collection efficiency, defined in Figure 8, increases with electrical forces, especially for bipolar coagulation of oppositely charged particles and collecting droplets. Lab-scale systems have been tested at low flowrates (~ m 3 .h -1 ) for model validation [START_REF] D'addio | A lab-scale system to study submicron particles removal in wet electrostatic scrubbers[END_REF] or to highlight the interest of ES for bipolar scrubbing [START_REF] Borra | Electro-hydrodynamic pulverisation of charged water droplets for the reduction of particulate plasma by-products in Progress in Plasma Processing of Materials[END_REF][START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF]. The total collection efficiency, defined in Figure 8, is used for comparison with other devices, including all collection mechanisms by mechanical, thermal and electrical forces, i.e. including diffusion, impaction and interception, as well as electro-coagulation by image and Coulombian forces. The Coulombian coagulation efficiency ( -/+ Coulombian coag. ) is either derived from measured collection efficiencies of neutral and charged particles on positive droplets ( °/+ neutral coll. and  -/+ tot. coll. ), or calculated by theoretical analysis of Coulombian interaction between oppositely charged particles and droplets.

The theoretical analysis of electro-coagulation of oppositely charged particles was formalized by Fuchs [START_REF] Fuchs | The Mechanics of Aerosols[END_REF]. Models to account for collection of particles on a charged drop are reviewed in [START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF]Jaworek et al., 2006a;Carotenuto et al., 2010b). Three approaches have been used. Melcher discussed the scrubbing in terms of time constants of unipolar droplets repulsion and Coulombian coagulation [START_REF] Melcher | Electrostatic devices for controll of submicrometer particles[END_REF]. The two other approaches rely on unitary or "single drop collection rate", then time integrated with respect to heterogeneous droplet concentration and evolving particle concentration along the scrubber (see 4.3.1). Here should be noted that it is most often assumed that the collecting field between a drop and a particle is not influenced by the background space charge field [START_REF] Jaworek | Submicron particles removal by charged sprays[END_REF]. Indeed, bipolar referred as Coulombian coagulation efficiencies have first been calculated for single falling or fixed drop [START_REF] Kraemer | Collection of Aerosol Particles in Presence of Electrostatic Fields[END_REF]Nielsen et al., 1976a, b;[START_REF] Prem | Calculated particle collection efficiencies by single droplets considering inertial impaction brownian diffusion and electrostatics[END_REF][START_REF] Hara | Fundamental processes of fine particle collection by charged water droplets[END_REF][START_REF] Sumiyoshitani | Three-dimensional model for analyzing charge carrier motion around a charged spherical object in the presence of flow and electric field[END_REF][START_REF] Zuo | Numerical study of particle motion near a charged collector[END_REF]. When considered as independent, the total single drop efficiency is defined as the sum of single drop collection efficiencies for each mechanism, if much smaller than unity [START_REF] Kasper | Penetration of a multistage diffusion battery at various temperatures[END_REF][START_REF] Brown | Air Filtration: An Integrated Approach to the Theory and Applications of Fibrous Filters[END_REF]. Otherwise, additional coupling terms are included for combined actions [START_REF] Alonso | Deposition of ultrafine aerosol particles on wire screens by simultaneous diffusion and image force[END_REF], as for electro-collection by interparticles image and Coulombian forces, eventually under additional Laplacian electric field imposed by polarized electrodes [START_REF] Kraemer | Collection of Aerosol Particles in Presence of Electrostatic Fields[END_REF]. At first, based on process engineering analysis, simple semi-empirical expressions of the grade efficiency (i.e. efficiency per size range), were used for optimization and eventual scale up of lab-scale device.

Collection efficiency of large scale bipolar-scrubber has been defined [START_REF] Pilat | Collection of aerosol particles by electrostatic droplet spray scrubbers[END_REF][START_REF] Calvert | Evaluation of four novel fine particulate collection devices[END_REF][START_REF] Prem | Calculated particle collection efficiencies by single droplets considering inertial impaction brownian diffusion and electrostatics[END_REF][START_REF] Bertinat | Charged-droplet scrubbing for controlling sub-micron particle emissions[END_REF][START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF] using the macroscopic approach, by analogy to ESP efficiency calculations from Deutch-Andersen formalism [START_REF] Hinds | Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles[END_REF]. Assuming that particles are first homogeneously distributed in the gas at the same velocity and then collected at its terminal electrical velocity (see 4.2.2 and 4.3.2), when approaching the droplet within the coagulation sphere (usually considered as one diameter away from the surface of the drop, [START_REF] Jaworek | Submicron particles removal by charged sprays[END_REF]). The single drop bipolar coagulation efficiency is related to the cylinder of gas swept by a drop per unit time, defined as the cross section of the coagulation sphere around each drop within which any particle with opposite polarity is collected, time the relative velocity between particle and drop [START_REF] Kraemer | Collection of Aerosol Particles in Presence of Electrostatic Fields[END_REF][START_REF] Melcher | Electrostatic devices for controll of submicrometer particles[END_REF][START_REF] Bertinat | Charged-droplet scrubbing for controlling sub-micron particle emissions[END_REF]. Replacing the collection surface of the ESP electrode by the surface of suspended droplets related to droplet concentration, the expression of the collection efficiency for ESP can be converted, as follows for collection by bipolar coagulation in electro-scrubbers [START_REF] Bertinat | Charged-droplet scrubbing for controlling sub-micron particle emissions[END_REF][START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF]. The Coulombian coagulation efficiency ( -/+ ) is defined, neglecting other forces and losses to the walls, versus the mean product <N drop t scrubbing >, so averaged over the whole scrubber to account for variable droplet concentrations met along the scrubber, with respective transit times: [START_REF] Bertinat | Charged-droplet scrubbing for controlling sub-micron particle emissions[END_REF] with N drop and q drop , respectively the collecting water droplet number concentration (m -3 ) and charge (C), µ p , the electrical mobility of particles (m².V -1 .s -1 ), and t, the aerosol transit time in the scrubber. This expression cannot be used for the design of electro-scrubbers as Deutsch equation for ESP, since the terms of the exponent are interdependent and do not include other collection mechanisms nor losses to the wall. However, a parameter (A) specific to each scrubber can be added to account for the spatial distribution of droplets defining the active volume of the scrubber for electro-coagulation [START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF]. This parameter is defined by fitting Bertinat's law with defined charge per drop versus particle mobility and aerosol flowrate, i.e. versus mixing conditions and related <N.t> products, to Coulombian coagulation efficiencies defined from measured total and neutral collection efficiencies. Despite the critical assumption of stationary particles swept by moving droplets, Bertinat's law is useful to define optimal conditions for collection of submicron particles [START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF][START_REF] Cross | Electrostatics : principles, problems and applications[END_REF] as detailed in 4.3.1 for ES application to bipolar scrubbing.

Otherwise, at last, Eulerian and Lagrangian methods (Carotenuto et al., 2010b;[START_REF] Jaworek | Submicron particles removal by charged sprays[END_REF]Di Natale et al., 2016a) can be combined to describe trajectories of micron-sized particles and water droplets [START_REF] Beard | Experimental and numerical collision efficiencies for sub-micron particles scavenged by small raindrops[END_REF]Nielsen et al., 1976a;[START_REF] Prem | Calculated particle collection efficiencies by single droplets considering inertial impaction brownian diffusion and electrostatics[END_REF] and single drop collection efficiency [START_REF] Bozorgi | Simulation of spray scrubber with Eulerian/Lagrangian approach in aerosol removal[END_REF][START_REF] Goniva | Towards efficient simulation of off-gas scrubbing by a hybrid Eulerian Lagrangian model[END_REF][START_REF] Jȩdrusik | Collection of low resistivity fly ash in an electrostatic precipitator[END_REF]. This has been done first for neutral scrubbers (Wang A et al., 2016a, b) and atmospheric scavenging by falling droplets, adapted to ventury scrubbers (Yang HT et al., 2003;[START_REF] Bozorgi | Simulation of spray scrubber with Eulerian/Lagrangian approach in aerosol removal[END_REF]Jaworek et al., 2006a;Carotenuto et al., 2010b;Di Natale et al., 2016a;[START_REF] Li | Study of gas-liquid two-phase flow patterns of self-excited dust scrubbers[END_REF]. Numerical calculation of single drop collision efficiency and related scavenging parameter have been performed [START_REF] Zhao | Modeling of Gravitational Wet Scrubbers with Electrostatic Enhancement[END_REF], for each collection mechanism with detailed numerical evaluation of these collisional efficiencies with references in (Carotenuto et al., 2010b). Fractional efficiency have first been calculated for different size and charge distributions [START_REF] Eliasson | Bipolar Coagulation -Modeling and Applications[END_REF] and improved with discrete (for each diameter), sectional size intervals) or continuous log normal size distributions, compared in (Park SH et al., 2005). Stochastic Monte Carlo methods can be used to define the single drop scavenging efficiency by population balance for time integration to account for actual droplet concentration and for decreasing concentration of particles along the scrubber [START_REF] Zhao | Modeling of Gravitational Wet Scrubbers with Electrostatic Enhancement[END_REF]Carotenuto et al., 2010b).

Methods for the production of charged water droplets for bipolar scrubbing

Charged droplets can be produced by different processes with variable charge-to-mass ratio [START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Vaaraslahti | Spray charging of droplets in a wet scrubber[END_REF][START_REF] Pilat | Droplet charging for wet scrubbers[END_REF][START_REF] Krupa | Charged spray generation for gas cleaning applications[END_REF]. Charged droplets may be produced without liquid polarization, by charge separation during breakup of the liquid double layer. First observed during the fragmentation of liquid films and jets with bursting bubbles [START_REF] Iribarne | Electrification accompanying the bursting of bubbles in water and dilute aqueous solutions[END_REF] and with pneumatic nebulizers, specific charge from 1 to 100 nC.kg -1 are reported for 100 µm droplets produced at a few L.min -1 [START_REF] Vaaraslahti | Spray charging of droplets in a wet scrubber[END_REF]. Such scrubber supplied by sea water have been tested [START_REF] Ha | Enhancement of diesel particulate matter collection in an electrostatic water-spraying scrubber[END_REF].

Water droplets can also be charged by Corona ions (Xu DX et al., 2003) to lower levels than by the simplest induction charging by liquid polarization in mechanical nebulizers, achieving up to 10 % of the Rayleigh charge limit [START_REF] Bailey | Electrostatic spraying of liquids[END_REF]. Charge-to-mass ratio from 10 -3 to 1 mC.kg -1 have been measured for 50 µm water droplets from pressure nebulizers where the liquid is pressurized across an orifice [START_REF] Pilat | Droplet charging for wet scrubbers[END_REF][START_REF] Krupa | Charged spray generation for gas cleaning applications[END_REF] and from pneumatic nebulizers [START_REF] Metzler | Electrostatic enhancement of dust separation in a nozzle scrubber[END_REF]Yang HT et al., 2003).

ES is used to achieve tunable and higher charge per drop -by induction charging as well-, but without dilution of the aerosol to be filtered by additional gas flow for the production of charged droplets [START_REF] Lear | Charged droplet scrubbing for fine particle control[END_REF][START_REF] Hara | Fundamental processes of fine particle collection by charged water droplets[END_REF]. Electro scrubbing has been tested with water ES in other modes than the cone-jet mode, with less charged and larger drops, from 0.1 to 0.2 mC.kg -1 for millimeter droplets produced in the dripping mode for model validation [START_REF] D'addio | A lab-scale system to study submicron particles removal in wet electrostatic scrubbers[END_REF].

The same EHD break up of jets as for ES in cone-jet mode is used to achieve higher charge per drop:

-from 1 mC.kg -1 for 100 µm droplets from a rotary cup nebulizer with multiple jets [START_REF] Bailey | Electrostatic spraying of liquids[END_REF][START_REF] Balachandran | Efficiency of smoke removal by charged water droplets[END_REF], to a few mC.kg -1 for 80 µm droplets assumed to carry half of the Rayleigh charge limit from ES in precession mode (Jaworek et al., 2006a), for static scrubbing in closed room. -up to 12 mC.kg -1 for 100 µm drop i.e. up to 70% of the Rayleigh charge limit, measured in steady corona-assisted cone-jet mode, ( §3. 3.1.4, (Ehouarn P. et al., 2001;[START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF]. As expected for Coulombian coagulation, higher efficiencies are achieved for similar test aerosol collected by droplets with charge-to-mass ratio higher than by any other process by steady water ES, depicted below.

Electro-scrubbing by steady water ES in the corona-assisted cone-jet mode

Since no other data are available on the topic, here are presented results from two PhD researchers [START_REF] Ehouarn | Pulvérisation électro-hydrodynamique de liquide stabilisée par décharges électriques pour le traitement d'effluents particulaires[END_REF][START_REF] Unger | Charge d'aérosol par décharge électrique pour la filtration d'effluents particulaires[END_REF][START_REF] Unger | Filtration of submicron sized particles by electrocoagulation[END_REF] with total collection efficiencies of this ES bipolar scrubber versus the aerosol mobility in Figure 9a with related Coulombian coagulation efficiencies on Figure 9a-b. Properties of collecting water droplets and test aerosols (diameter, electrical charge, concentration), have been controlled independently from 0 to 10 -6 m².V -1 .s -1 for electrical mobilities of sub-micron aerosol charged by a wire-cylinder corona charger [START_REF] Unger | Unipolar field charging of particles by electrical discharge: effect of particle shape[END_REF] and from 30 to 70 % of the Rayleigh charge limit for water drop, see section 3 [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF]. A set of conditions to achieve steady water ES in corona assisted cone-jet (100 mL.h -1 , 200 µS.m -1 water) is used to produce 90 µm droplets with 3.6 pC per drop (9.4 mC.kg -1 ). The charged aerosol is mixed with droplets of opposite polarity produced by a line of four ES on top of an horizontal pipe of 7 cm diameter for 10 cm inter nozzle distance (appendix A1 and Fig. 8).

Mixing conditions

The ideal bipolar scrubber would consist of an injection of charged particles in spray with the highest droplet concentration, both being charged to maximal level with a large excess of charges with the polarity of collecting droplets. Then, with such unipolar net space charge, the spatial dispersion of droplets in the scrubber has to be optimized for efficient interfacial processes, as electro-scrubbing of cross flow aerosol. Indeed, one limit of electro-scrubbers results from repulsive losses to the walls increasing with the charge densities related to higher charge per drop. Nevertheless, large co-and reverse flow unipolar scrubbers have first been used for collection to the wall of aerosol with the same polarity as droplets with high efficiency in the sub-micron size range, using either ES in precession mode [START_REF] Lear | Charged droplet scrubbing for fine particle control[END_REF] or induction charging in ventury scrubber [START_REF] Vicard | Resultats et Experience Acquise avec un Nouveau Depoussiereur Electrique á Grande Vitesse: Le Venturi Electro-Dynamique[END_REF]. Even for bipolar scrubbing, electrostatic repulsions lowers the concentration of collecting droplets and the electro-coagulation efficiency [START_REF] Melcher | Electrostatic devices for controll of submicrometer particles[END_REF].

Positive droplet space charge density in ES bipolar scrubber

The dispersion of droplets in the scrubber depends on the total electric field including the space charge and eventual additional external field (Tang J et al., 1994a;Hartmann et al., 1999a;[START_REF] Deng | Influence of space charge on the scale-up of multiplexed electrosprays[END_REF][START_REF] Wei | Numerical simulation of cone-jet formation and current in ES -Modeling of space charge[END_REF]. As a rule of thumb, ES can be considered as independent for larger inter nozzle distance than the pipe diameter, when the development of ES is unaltered by others. This is achieved in this water ES scrubber with space charge from 10 11 , close to the spray injection to 10 8 e.cm -3 (droplet charge of a few pC per droplet (~ 10 7 e) and densities from 10 4 to 10 cm -3 ). Actually, the spatial development of such unipolar sprays is self-induced by space charge (see section 3.3.1.5), unaffected up to gas velocities of a few m.s -1 . The injection of negative particles with eventual ions from the charger affects the space charge field and subsequent losses to the wall of unipolar particles before mixing in the scrubber, as well as the interparticle field for coagulation in bipolar volumes, where both populations are mixed (see . The coaxial ring used to shield the liquid cone-jet i.e. the production zone from variable space charge field in the scrubber, can be polarized with the same polarity than the nozzle to avoid the recollection of droplet on the ring and to disperse all droplets over the entire cross section of this earthed tubular scrubber, for cross flow mixing of charged aerosol and collecting droplets [START_REF] Gan | Effect of a ring electrode on the conejet characteristics of ethanol in small-scale electro-spraying combustors[END_REF]. Besides, additional electrodes can be polarized in the scrubbers as well to control the electric field profile, intensity and dynamics necessarily affecting the bipolar coagulation [START_REF] Kraemer | Collection of Aerosol Particles in Presence of Electrostatic Fields[END_REF]Nielsen et al., 1976a;[START_REF] Bertinat | Charged-droplet scrubbing for controlling sub-micron particle emissions[END_REF][START_REF] Sumiyoshitani | Three-dimensional model for analyzing charge carrier motion around a charged spherical object in the presence of flow and electric field[END_REF]Park SH et al., 2005). The field controls relative velocities for mixing initial unipolar space charges but also the transit time of particles around the coagulation (b) (a) sphere to reach it (with 100% collection efficiencies). Depending on its intensity and frequency, it is beneficial for less charged particles and drops, but not anymore for more mobile particles and/or more charged droplets.

Co-, cross-or reverse-flows

Scrubbing has been tested with different spatial development of sprays and mixing conditions. Full or hollow conical sprays from pressure nebulizers have been compared for high flow applications [START_REF] Jaworek | Multi-nozzle electrospray system for gas cleaning processes[END_REF]. Different scrubber geometries have also been compared for theoretical evaluation of optimal scrubbing conditions versus relative velocities of positive and negative species [START_REF] Bertinat | Charged-droplet scrubbing for controlling sub-micron particle emissions[END_REF][START_REF] Eliasson | Bipolar Coagulation -Modeling and Applications[END_REF]Jaworek et al., 2006a). When both populations are produced by positive and negative DC ES ("Symmetric case" in [START_REF] Eliasson | Bipolar Coagulation -Modeling and Applications[END_REF]), Coulombian coagulation efficiencies of droplets with similar charge and size distributions decrease from 53 % for face-to-face to less than 20 % for parallel injection of unipolar sprays of both polarities (Borra et al., 1997a;Borra et al., 1999a). Despite a bit lower efficiency in cross than in reverse flow with "face-to-face" injections of charged droplets [START_REF] Camelot | Bipolar coagulation for the production of controlled powders[END_REF][START_REF] Chou | Synthesis of multicomponenoxides by means of bipolar mixing[END_REF][START_REF] Fu | Performance study of a twin-head electrospray system[END_REF], cross flow has been selected for the bipolar scrubber [START_REF] Unger | Filtration of submicron sized particles by electrocoagulation[END_REF]. Actually, ES is more stable with vertical nozzles injecting sprays from the top of horizontal pipes. Counter flow is complex to handle when injectors of positive droplets and negative particles from the charger, have to be close for injection of particles in the highest concentration of droplets, as supported by Figure 9b for aerosol injection in the spray at different heights from the nozzle. Moreover, the parallel injection of oppositely charged species with different size and charge distributions of particles and droplets (asymmetric case) leads to smaller efficiencies than the cross one due to self-repulsion before mixing [START_REF] Ehouarn | Pulvérisation électro-hydrodynamique de liquide stabilisée par décharges électriques pour le traitement d'effluents particulaires[END_REF].

Gas velocity (< m.s -1 ) and aerosol dispersion

Most filtration devices works at exhaust velocity around 1 m.s -1 in scrubbers, fabric filters and ESP [START_REF] Parker | Applied Electrostatic Precipitation[END_REF][START_REF] Baron | Aerosol measurement: principles, techniques, and applications[END_REF]. Electro-scrubbing tests are thus often performed in this sub m.s -1 range. Moreover, steady ES in cone-jet is undisturbed up to gas velocities of 15 m.s -1 (Allaf- [START_REF] Allaf-Akbari | An electrospray in a gaseous crossflow[END_REF]. Sprays are used for mixing of gases and gas scrubbing [START_REF] Malet | Gas entrainment by one French PWR spray, SARNET-2 spray benchmark[END_REF]. With ES as well, the injection of aerosol perpendicularly to ES nozzle axis with droplets velocities from 8 to 1 m.s -1 (see 3.3.1.5) along the diameter of the pipe induces cross flow due to the momentum transfer between droplets and gas (Hartmann et al., 1999a;[START_REF] Jaworek | Submicron particles removal by charged sprays[END_REF]. In turns, this leads to turbulent mixing of particles within the droplets flux and probably accounts for the high efficiency achieved despite successive independent ES necessarily implying dead volumes in the scrubber with smaller droplet concentrations. For faster velocities, the spray dispersion and the related collection efficiency evolve (e.g. in venturi [START_REF] Ali | Dust particle removal efficiency of a venturi scrubber[END_REF] and electro-scrubbers (Carotenuto et al., 2010a;[START_REF] Di Natale | Capture of particles in a wet electrostatic scrubber[END_REF]Di Natale et al., 2016b)). With highly charged droplets produced by steady water ES in pulseless corona-assisted cone-jet and dispersed in the exhaust pipe with cross flow, sub m.s -1 inlet velocities are used so that the spray expansion and deposition to the wall of the earthed pipe are unaffected by the aerosol flow.

Aerosol properties

Electrical mobility: In constant conditions of particle production, ES and mixing, the measured collection efficiencies increase with the electrical mobility of particles, as expected from Bertinat's law, above 5.10 - 8 m².V -1 .s -1 . Longer transit times lead to higher efficiency all the more for lower mobilities. This is due to larger relative part of other collection mechanisms (diffusion, thermophoresis, impaction and interception, images forces and self repulsion losses) not included in Bertinat's law for bipolar coagulation alone (see Figure 9a, measured total collection efficiency > Coulombian efficiency). For mobilities above 10 -7 m².V - 1 s -1 , the expected Coulombian coagulation efficiencies, fits to the measured collection efficiencies, over 95 % from 15 to 5 L.min -1 , even for sub-second transit times. The size integrated number efficiency overcomes 99.2 %, without pressure drop and only 0.4 water L.m -3 of filtered aerosol. Neglecting first, the turbulent mixing in this cross flow arrangement and the effect of decreasing particle concentration addressed in 4.3.1 and 4.3.2, the droplet concentration profile for this water ES [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF] has been discretized in different volumes with respective droplet concentrations and transit times of aerosol. Scrubbing efficiencies have then been calculated with respect to heterogeneous droplet concentration met across one spray, as detailed in [START_REF] Ehouarn | Pulvérisation électro-hydrodynamique de liquide stabilisée par décharges électriques pour le traitement d'effluents particulaires[END_REF]. Despite numerous assumptions, the total collection efficiency follows roughly Bertinat's law for on-line particles removal from an aerosol flow versus particle mobility, aerosol flowrate, number of ES and position of injection in the spray for different Nt products at constant charge per drop, with expected deviation between experimental data and calculations from these assumptions (see Figure 9b). When working with defined aerosol mobility and charge per drop as well as with a known profile of droplet concentration in the scrubber, this law enables one to define optimal mixing conditions (aerosol velocity, relative injection position in the spray, diameter of the exhaust pipe) for the selected cross flow scrubber. However, it is useless for other geometries and does not account for higher efficiencies with more concentrated industrial exhausts (from 0.1 to 100 g.m -3 ). To do so, readers should use other approaches for efficiency calculation through single drop scavenging efficiency, to account for the related enhanced collision probability,(see 4.2.1). Aerosol concentration, size and charge: Coagulation of submicron sized bipolar aerosol is known to limit the maximum inlet concentration to 10 6 cm -3 for size distribution measurements without coagulation using radioactive neutralizers (Adachi M. et al., 1981;[START_REF] Maisels | Coagulation in bipolar aerosol chargers[END_REF][START_REF] Alonso | Particle size distribution evolution during and after electrical charging: comparison of a corona ionizer and a radioactive neutralizer[END_REF] and to increase the ESP collection efficiency by shifting the inlet aerosol size from the MPPSize range to larger diameters [START_REF] Zevenhoven | An evaluation of the Masuda "boxer charger[END_REF][START_REF] Watanabe | Submicron particle agglomeration by an electrostatic agglomerator[END_REF]. [START_REF] Hara | Fundamental processes of fine particle collection by charged water droplets[END_REF] More concentrated aerosol generally leads to unimodal self-preserving size distribution by fast coagulation [START_REF] Goudeli | Coagulation-Agglomeration of Fractal-like Particles: Structure and Self-Preserving Size Distribution[END_REF] which, in turns affects the charge of particles i.e. the negative current injected in the scrubber and the related droplet charge with subsequent spray dispersion. Indeed, injection of larger negative current lowers the collection efficiencies from 97 % without, to 91 % with co-injection of negative corona ions with charged particles (from sub-nA current for charged particles alone to -500 nA with ions, compared to +300 nA per ES, [START_REF] Unger | Charge d'aérosol par décharge électrique pour la filtration d'effluents particulaires[END_REF]). This may account for the dispersion of Coulombian coagulation efficiencies reported in Figure 9b, from measured collection efficiencies for neutral and charged particles at different flowrates, as well as assumptions on mixing conditions (see 4.2.1). Finally, the current of negative particles injected in the scrubber (kept here below 0.1% of the spray current for maximal particle concentration 0.1 g.m -3 ), also depends on the size-charge relation specific to the selected corona charger, with respect to particle concentrations and sizes i.e. with respect to the aerosol source [START_REF] Biskos | Unipolar diffusion charging of aerosol particles in the transition regime[END_REF][START_REF] Intra | Progress in unipolar corona discharger designs for airborne particle charging: A literature review[END_REF].

Fractional efficiencies (vs d p ) of bipolar scrubbers

Fractional collection efficiency is calculated from number or mass concentration measurements versus particle size [START_REF] Hinds | Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles[END_REF][START_REF] Baron | Aerosol measurement: principles, techniques, and applications[END_REF], to depict size dependent properties of aerosol, e.g. with the Coulombian force for bipolar scrubbing (Carotenuto et al., 2010b;Chen TM et al., 2014). Fractional efficiencies are presented in Figure 10 for different bipolar-scrubbers using ES or induction charging for the production of charged water droplets from pressure and pneumatic nebulizers. Higher efficiencies are achieved by lab-scale electro-scrubbing on highly charged droplets produced by ES in corona assisted cone-jet mode, than by induction charging. However, different objectives were targeted either for physical studies up to m 3 .h -1 or for applied scrubber optimization up to 100 times higher flowrates and 10 times higher aerosol concentrations. For comparison with emission limits from 10 to 100 mg.Nm -3 , efficiencies are often calculated as the ratio of final to initial mass concentrations. Bipolar scrubbing was developed for high flowrate (238 m 3 .h -1 ) particle removal from steel furnace exhaust (0.1 to 1 g.m -3 ) with 94 % mass removal efficiency achieved by induction charging of 50 µm water drops from pressure nebulizer, with 2 L.m -3 at 10 W.m -3 [START_REF] Pilat | USA Patent No[END_REF]. For similar flowrates of a few hundred m 3 .h -1 , most bipolar scrubbers were designed with characteristic lengths of a few meters first to achieve transit times of at least a few seconds with aerosol velocities up to m.s -1 , as well as to reduce losses of droplets to the walls [START_REF] Allen | Electrostatically Augmented Wet Dedusters[END_REF]. To do so, classical pressure and pneumatic nebulizers with large gas flow rate and subsequent less diverging sprays dispersed in larger volumes than ES, (due to less charged, larger and faster droplets than with ES), are adapted for efficient collection at large flow rate. In large flowrate scrubbers, only few studies address fractional efficiencies for removal of sub-micron particles by droplets charged by induction (from 0.1 to 1 mC.kg -1 , Figure 10). Minimum collection efficiency above 80 % were achieved for submicron test aerosol with MPPS around 0.2 to 0.3 µm with 2 and 1.6 L.m -3 of waste water per unit volume of filtered gas, respectively for pressure [START_REF] Pilat | Collection of aerosol particles by electrostatic droplet spray scrubbers[END_REF] and pneumatic nebulizers [START_REF] Calvert | Evaluation of four novel fine particulate collection devices[END_REF] (see apendix A1). For real exhaust aerosol concentration from diesel engines, up to 10 6-7 cm -3 (~g.m -3 ), similar pressure nebulizer with a full cone spray achieve 93% efficiency with 290 µm droplets (0.135 mC.kg -1 ) for 0.2µm combustion aerosol with half the water consumption [START_REF] Krupa | Charged spray generation for gas cleaning applications[END_REF][START_REF] Di Natale | Capture of particles in a wet electrostatic scrubber[END_REF]Di Natale et al., 2016b). For similar aerosol, the reader can also refer to [START_REF] Ha | Enhancement of diesel particulate matter collection in an electrostatic water-spraying scrubber[END_REF] with sea water droplets. With higher charge per drop from ES, faster self-repulsions lower the droplets concentration on smaller lengths, a few cm from the ES nozzle, than from other nebulisers, as depicted in 3.3.1.5. ES bipolar scrubbing is thus more efficient in smaller horizontal pipes to achieve particle injection in the spray above a minimal droplet concentration for efficient Coulombian coagulation (see section 4.3.1.2). 99.2% number efficiencies are achieved by bipolar scrubbing with 4 water ES in corona assisted cone-jet, for aerosol concentrations up to 10 6 cm -3 , with a minimum efficiency for the MPPS around 0.4 µm of 97%. Higher exhaust gas flowrates, for real applications, are thus filtered with pressure and pneumatic nebulizers consuming more water for lower charge-to-mass ratio of droplets charged by induction, than in more efficient lab-scale ES scrubbers. Higher charge-to-mass ratio lowers the volume of waste water per cubic meter of filtered gas, at lower energetic cost (~ 0.03 kWh.m -3 ), using steady water ES in corona assisted cone-jet than with induction charging of droplets from pressure or pneumatic nebulizers.

Conclusion

Bipolar wet scrubber using highly charged droplets produced by steady water ES in pulseless corona assisted cone-jet is more efficient (> 99 %) than other means to produce charged droplets for the removal of sub-micron particles from aerosol flows. Indeed, the selected cross flow configuration leads to turbulent mixing of particles within the droplet flux related to spray expansion (self-induced and unaffected up to 15 m.s -1 ) and probably accounts for the high efficiency achieved despite successive independent ES necessarily implying dead volumes in the scrubber with smaller droplet concentrations. With continuous production of self-dispersed charged droplets with low liquid consumption per unit gas volume, low-pressure drop, maintenance and exploitation cost, such ES scrubbing devices with a row of a few nozzles could be used in parallel for removal of particles from gases at higher flow rates than used for lab-scale proof of concept. Such ES bipolar scrubber could thus be considered not only as an additional last step downstream electrostatic precipitator to remove submicron particles but may be tested as High Efficiency Particulate Air (HEPA) Filter. This is all the more true that test were performed with immiscible oil droplet in water from ambient gas temperature for intermediate aerosol concentration from 1 to 10 mg.m -3 . Better efficiencies are expected on more concentrated particle in hot gases since the total collection efficiency is expected to increase for hotter exhaust aerosol due to thermophoresis pushing particles from hot gas to cool droplet surface (Di Natale et al., 2016a) and for higher concentrations than tested (> 2.10 6 cm -3 , 100 mg.m -3 ). Water consumption can also be reduced with smaller droplets produced by ES at lower water flowrate and/or higher conductivities leading to larger collecting surface per unit water volume. Horizontal ES bipolar scrubber has proved to be efficient and can still be optimized using curtain-like sprays for cross flow injection of particles in more concentrated collecting droplets. It has to be emphasized that larger flow rates can be treated in co-/reverse-flow, suitable for larger scale scrubbers, as already performed with success in the first unipolar ES scrubber [START_REF] Lear | Charged droplet scrubbing for fine particle control[END_REF], still to be tested for bipolar ES scrubbing. The spray current has to be larger than the current of charged particles injected with eventual post-corona ions to be taken into account to avoid the reduction of the droplet charge, critical for electro collection. Corona field chargers, where aerosol are injected in the discharge gap as used here for test on aerosol concentration from 0.1 mg to 100 mg.m -3 , are useless at higher concentrations with respect to deposition on electrodes and subsequent unsteady corona and charge of particles [START_REF] Parker | Applied Electrostatic Precipitation[END_REF][START_REF] Unger | Influence of aerosol deposition on the charging efficiency of a corona charger[END_REF][START_REF] Unger | Unipolar field charging of particles by electrical discharge: effect of particle shape[END_REF]. Reliable post-discharge diffusion charger are available for lab-scale studies [START_REF] Unger | Charge d'aérosol par décharge électrique pour la filtration d'effluents particulaires[END_REF] up to commercial devices for low flow rate application to size distribution measurement [START_REF] Biskos | Unipolar diffusion charging of aerosol particles in the transition regime[END_REF] and scaled-up for industrial two-steps ESP at larger flow rates [START_REF] Asbach | Development of a highly efficient electrostatic partitioner of gas and particles with minimal effect on the gas phase[END_REF]. The development of these efficient bipolar scrubbers implies to achieve efficient particle charging up to 10 -7 m².s -1 .V -1 mobilities, for higher flowrate and concentration of suspended submicron particles, ideally up to m 3 .s -1 and g.m -3 . The critical size-mobility relation from different DC corona and/or AC Dielectric Barrier Discharges for bipolar charging still has to be addressed for high aerosol flowrate applications. Then, high flowrate and particle loading could be studied taking into account the evolution of the sizemobility relation with concentration, expected from self-repulsion losses of such unipolar aerosol clouds reported for charge density higher than 10 7 e.cm -3 [START_REF] Whitby | Generator for Producing High Concentrations of Small Ions[END_REF][START_REF] Whitby | Charging and decay of monodispersed aerosols in presence of unipolar ion sources[END_REF][START_REF] Kasper | Electrostatic dispersion of homopolar charged aerosols[END_REF][START_REF] Mcmurry | Aerosol Wall Losses in Electrically Charged Chambers[END_REF][START_REF] Stratmann | Theoretical investigation of ion and particle transport in space charge fields[END_REF][START_REF] Bouarouri | Ion current density profiles in negative corona gaps versus EHD confinements[END_REF].

Conclusions and perspectives

Some applications of electrosprays of Water or aqueous solutions have been reviewed with special attention for material production and bio-applications and a focus on particle filtration. As a continuous process, water ES in cone-jet mode (with and without discharge) can be used for the production of monodisperse/unimodal size distributions of self-dispersed unipolar water droplets. Means to achieve these two steady modes of water ES in ambient air have been presented with respect to electrical discharges in the gas around the liquid cone and jet. Filamentary streamer discharges with transient and asymmetric space charges disrupt the EHD equilibrium required for steady cone-jet mode, while the axisymmetric and quasi-stationary space charge is required to achieve steady water electrospray in ambient air in the pulseless corona-assisted cone-jet mode. Subsequent conditions to achieve steady water ES in cone-jet mode without discharge are then related (i) to lower onset electric field of cone-jet formation for aqueous mixtures with smaller surface tension than pure water and/or (ii) to higher discharge onset by playing either on the dielectric strength and density of the gas or on the electric field profile around the liquid cone-jet using fine spraying nozzles (< 100 µm). Scaling laws between regulation parameters and droplet properties are reminded for steady water ES in cone-jet mode with pulseless corona and without discharge. Unimodal droplet size and charge distributions are achieved with modal diameters over three orders of magnitude from 0.2 µm droplets without discharge from nano-emitters at 5.10 -12 L.s -1 , to 10-150 µm droplets in pulseless corona-assisted cone-jet at 10 -4 L.s -1 . Other than the cone-jet modes tested for application of electrical properties of monodisperse droplets to filtration by electro-scrubbing from tens to hundreds mL.h -1 or used for rapidly growing market of high sensitivity analysis by ESI-MS down to sub-nL.min -1 flowrates, the multi-jet first and the simple jet modes, have recently been reinvestigated to achieve higher liquid flowrate ES applications. High filtration efficiencies by wet bipolar-scrubbing (> 99%) reported for classical pollutant concentration in lab-scale prototype supports that Water ES could be applied to air cleaning with low water and energy consumptions., mainly conditioned by the development of plasma charger to overcome 5.10 -8 m².V -1 .s -1 , independently of the inlet concentration and of the nature of particles to be removed from the gas. New ES facilities will emerge with new applications of bipolar coagulation for droplets neutralization to reduce self-repulsion and losses, for controlled kinetics in micro-reactor droplets as in micro-fluidic devices and more generally for interfacial processes as bipolar scrubbing, as well as for electric field driven deposition for coating, 3D printing and pulsed drop-on demand.

Based on the well-controlled ES current versus electric field, ES with micrometer gap has been tested as a scanning microscopy to measure the surface topography with resolution in the µm range, linking the ES current evolution with the electric field i.e. with the gap length above surface defaults [START_REF] Yuill | Scanning Electrospray Microscopy with Nanopipets[END_REF]. Moreover, ES has been tested with magnetic fluids, as a tunable current source from simultaneous ES and electrical discharge versus the magnetic field intensity to control the shape of cones, the subsequent discharge regimes and related ozone production for gas depollution purposes [START_REF] Uehara | Discharge and flow characteristics using magnetic fluid spikes for air pollution control[END_REF]. In terms of applications, ES with electrical discharges, proposed for plasma-based aerosol production and coating processes are studied to take advantage of the high interfacial exchange surface between the droplets and the plasma gaseous by-products (radicals, excited species, and electron or ions as well as ozone and other nitrogen oxides and corresponding acids with hydrogen peroxide). Similar species are formed in gas phase in humid air and in liquid water droplets, and can advantageously be produced simultaneously by ES with different discharges (corona, streamers and sparks) depicted in section 3.3.1. Chemical reactions can be induced in droplets, e.g. with bio decontamination of water droplets (see section 2.3 and 3.3.3). Plasma-based aerosol processes with droplet injection in plasma are developed for SiO X or polymer particle production and deposition, as coating processes [START_REF] Fanelli | Aerosol-assisted atmospheric cold plasma deposition of superhydrophobic organic-inorganic nanocomposite thin films[END_REF][START_REF] Brunet | Deposition of homogeneous carbon-TiO2 composites by atmospheric pressure DBD[END_REF], to trigger either the polymerization of organic monomer precursor (Ward et al., 2003a;[START_REF] Tatoulian | Deposition of poly(acrylic acid) films by EHDA in postdischarge at atmospheric pressure in air[END_REF] or sol-gel reactions for oxide formation from organo-metal precursor, as reported by droplet injection in [START_REF] Ward | Atmospheric pressure glow discharge deposition of polysiloxane and SiOx films[END_REF][START_REF] Jacopo | Interaction of atomized colloid with acDBD for deposition of nanocomposite coating[END_REF] and downstream atmospheric pressure plasmas [START_REF] Borra | Atmospheric Pressure Deposition of Thin Functional Coatings: Polymer Surface Patterning by DBD and Post-Discharge Polymerization of Liquid Vinyl Monomer from Surface Radicals[END_REF][START_REF] Post | Post-Plasma SiOx Coatings of Metal and Metal Oxide Nanoparticles for Enhanced Thermal Stability and Tunable Photoactivity Applications[END_REF]. For more details, the reader can refer to a special session on the topic held in EAC 2016. ES is well adapted for such interfacial reactive plasma process, as just performed in microfluidic plasma devices (Zhang et al., 2017). In that respect, turbulent mixing from cross flow injection of ES into the gas, downstream a plasma, may be used to induce any chemical reaction in droplets. Coupled with controlled drying and eventual coating steps, these plasmas with interfacial suspended exchange surfaces for plasma-based reactivity with controlled kinetics will probably soon emerge as large-scale continuous production processes of tailored particles, powders and coatings. At last, despite abundant literature on the structures and properties of water, water drop deformation still is triggering curious minds since the first observation. No doubt that the best is yet to come in terms of ES applications for material production with finely tuned properties (composition, size, structure) in association with plasma, or in small portable units possibly achieved with "nano-emitters" at low voltages, but more probably for larger production units at enhanced production rates from high interfacial exchange surface of self-dispersed droplets, as already started for patch production.

ACKNOWLEDGEMENTS: Here are acknowledged (i) the French ministry of Research and Education for the salary of one of both PhD devoted to this project, (ii) EDF and (iii) CNRS with ECODEV-ADEME for the financial support as part of an ARC research program from 1996 to 2003, and CNRS alone for the international patent. For their confidence to support the first study of the Bipolar wet scrubber, I thank Professors Fauchais and Amouroux. I take advantage of this review to acknowledge Gildas Hartman, Max and Alice Goldman, Emmanuel Marode for sharing their experience on dc corona, streamers and sparks. Denis Boulaud from IRSN, Brian Scarlett and Jan Marijnissen from TU Delft on aerosol science and technology. I thank Damien Camelot, Rob Hartmann, Najim Benali, Djamal Djermoun, Pascale Ehouarn, Lomig Unger, the PhD students who contribute to this work, and especially Nicolas Jidenko for his help for this review. At last, I am grateful to Professor Weber for proposing the special issue.

LIST of FIGURES

Figure 1: DBVtechno's ES Deposition device for deposition of controlled amounts of dried allergenic proteins homogeneously distributed over the patch surface, (a) Single ES in the cone-jet mode of the aqueous solution of proteins deposited after evaporation and drying along the transit to surface of the patch and (b) the multi nozzle electro-spraying machine for the large scale production of bio-functionalized skin compatible patches. Figure 2: correlation between discharge regime and ES modes with related size distributions (a) and ( c) with (preonset) streamers and related transient and asymmetric surface field variations leading to unstable EHD conditions and multimodal size distributions or (b) with the stationary and axisymmetric corona space charge to achieve steady water ES in pulseless corona-assisted cone-jet, with unimodal droplet size distributions and geometrical standard deviation around 1.3 and daylight or 60s dark pictures of the nozzle-to-plane gap. Figure 3: Electric field profiles along the curvilinear field line from the liquid surface at increasing liquid voltages leading to different ionization lengths with impulse or pulseless discharges correlated to unsteady or steady ES modes: the blue bold profile leads to steady water ES in pulseless corona-assisted cone-jet for nozzles with outer diameters from 0.4 to a 1.8 mm, liquid flow rate from 30 to 200 mL.h -1 at 0.1 to 10 mS.m -1

, while the dashed blue one leads to steady cone-jet mode without discharge on smaller capillary down to 4 µm; (b) Critical ionization length versus the radius of curvature of the positive liquid electrode, [START_REF] Hartman | Theoretical Evaluation of Peek's Law[END_REF] Figure 4: Steady water ES in corona-assisted cone-jet in (, Q Liq , V Liq ) space for a 4 cm gap with the nozzle (d out /d in = 0.5/ 0.25 mm) for (a) nozzle-plate and (b) nozzle-ring-plate configurations, [START_REF] Borra | Destabilisation of sprays in the cone-jet mode by electrical dicharges on the jet[END_REF]Borra et al., 1999d;[START_REF] Borra | Electrohydrodynamic atomisation of water stabilised by glow discharge -operating range and droplet properties[END_REF], with a ring (d in = 10 mm) a few millimeters from the nozzle above the jet tip. Figure 5: (a) Modal diameter and (b) Charge-to-mass ratio of droplets and corresponding Rayleigh charge limit, versus flow rate in pulseless corona-assisted cone-jet (110 µS.m -1 water). The diameter are represented for different conductivities, and a 15% envelop for the additional variation that can be achieved with the corona ion space charge density controlled by the voltage and the related corona current [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF] Figure 6: Radial profiles of droplet velocity in pulseless corona-assisted cone-jet [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF] Figure 7: conditions for water ES in steady cone-jet modes with (white) and without discharges (blue) in air Figure 8: Mean number concentration of particles (integrated on the cross section) along the Bipolar-scrubber Figure 9: in constant reference ES conditions, (a) Comparison of total collection and Coulombian coagulation efficiencies (points and line, respectively) of 10 6 cm -3 -i.e. 10-100 mg.m -3 -0.44 µm monodisperse negative aerosol versus the electrical mobility for different flow rates with a line of 4 ES and (b) Coulombian coagulation efficiency versus the adimensional parameter A•q g •µ a •c g •dt/ 0 (line with A=2•10 30 from [START_REF] Ehouarn | Pulvérisation électro-hydrodynamique de liquide stabilisée par décharges électriques pour le traitement d'effluents particulaires[END_REF][START_REF] Unger | Charge d'aérosol par décharge électrique pour la filtration d'effluents particulaires[END_REF]), i.e. versus the mean <N drop .t> product, controlled by injection of aerosol with constant mobility of 10 -7 m².V -1

.s -1 at 10 L.min Properties of collecting water droplets and test aerosols (diameter, electrical charge, concentration), have been controlled independently from 0 to 10 -6 m².V -1 .s -1 for electrical mobilities of sub-micron aerosol by a wire-cylinder corona charger [START_REF] Unger | Unipolar field charging of particles by electrical discharge: effect of particle shape[END_REF] and from 30 to 70 % of the maximum Rayleigh charge limit for water drop, see section 3 [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF]. A set of conditions to achieve steady water ES in corona assisted cone-jet (100 mL.h -1 , 200 µS.m -1 water) is used to produce 90 µm droplets with 3.6 pC per drop (9.4 mC.kg -1 ). The charged aerosol is mixed with droplets of opposite polarity produced by a line of four ES on top of an horizontal pipe of 7 cm diameter for 10 cm inter nozzle distance The experimental set-up is classical for aerosol filtration studies (see Fig. A1) with: -aerosol production: A Sinclair-Lamer Generator is used to produce a monodisperse aerosol of Di-Ethyl-Hexyl-Sebacate with tunable modal diameters from 0.4 to 1.1 µm and a pneumatic nebulizer to achieve unimodal size distribution of 0.3 µm DEHS droplets or NaCl dissolved in water droplet leading to 30 to 70 nm salt crystals after evaporation versus the initial salt concentration in water, before nebulization). These aerosols generators are fed with dry filtered compressed air, with controlled relative humidity, critical in terms of corona charger stability with subsequent control of a steady charge diameter relation.

-aerosol charging: These test aerosols are then charged in a wire-cylinder corona discharge, detailed in [START_REF] Unger | Influence of aerosol deposition on the charging efficiency of a corona charger[END_REF], to produce sub-micron negative particles hereafter referred as the "test aerosol", detailed in [START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF][START_REF] Unger | Unipolar field charging of particles by electrical discharge: effect of particle shape[END_REF].

Required ion collection downstream the corona charger to prevent competitive electro-scrubbing of negative gaseous ions and charged aerosol: As expected, lower efficacies were reported with than without gaseous ions injection, probably due to higher mobility and resulting electro-coagulation on positive water droplets, reducing thus the mean charge per collecting drop. This expected preliminary result leads to design a charged aerosol exhaust pipe from the corona charger within which gaseous ions were collected on the walls from the test charged aerosol with the same polarity before injection, mixing and electro-coagulation on water droplets charged in opposite polarity (see Fig. A2). Positive water droplets were produced by electrospray in the corona assisted cone-jet mode for liquid flow rates from a few tens to a few hundred mL/hour, as discussed in section 3 and detailed in Figure A3 (see Borra et al., 1999 and[START_REF] Ehouarn | Properties of water droplets produced by ehd pulverisation for the collection of particulate plasmas by-products[END_REF]. Water with conductivities from 100 to 5000 µS/m, is electro sprayed with nozzle diameter 0.4 mm. Doing so, droplets with charge levels close to the maximum Rayleigh limit (from 30 to 70%) were produced to enhance electro-coagulation efficiency. Wellcontrolled water droplets properties (diameter, electrical charge, concentration), were then tuned by simple operating parameters such as the nozzle voltage and the liquid flow rate, as depicted in the previous section 3 and detailed in Table 1. ES bipolar scrubbing has been performed in horizontal pipes to achieve particle injection in clouds of droplets above a minimal droplet concentration for efficient bipolar scrubbing (see section 4.3.1.2). Here for water ES, a pipe diameter of 7 cm with spray separated by a longer length to achieve self-induced development of the spray over a few cm.

The complete description of these experiments with additional results and detailed calculations on :

-droplet characteristics at different liquid flowrates, and then in reference test conditions for ES (100 mL/h 200 µS/m) versus the number of ES nozzles, the symmetry and the density of the net of ES production nozzles with lines, circles and hexagonal nets from 250 to 5000 Nozzle.m -²) -corona chargers with size-mobility relations for different aerosol nature and concentration -droplet density profiles in two types of scrubbers with parallel or crossflow injections Then in selected ES, corona and mixing test conditions, with one to four water ES nozzles (outer and inner diameters of 0.4/0.25 mm at 100 mL.h -1 of 200 µS.m -1 water), as the reference test conditions, filtration test have been performed versus:

-the electrical field profile in the scrubbers controlled by surface potential of walls and electrodes, positive and negative charge densities and distribution with different relative positions of injection of oppositely charged aerosol and droplets in the scrubber, aerosol flowrate, as well as with different ring voltages from 0 to 10 kV, focusing the spray and limiting its radial development, -the concentration of aerosol to be filtered that affects the negative currents of charged species from the corona charger into the scrubber, reducing the positive space charge created by scrubbing droplets in the scrubber by co-injection of negative corona ions (from 0 to 500 nA compared to the 300 nA of charged droplets per ES).

Figure 1 :

 1 Figure 1: DBVtechno's ES Deposition device for deposition of controlled amounts of dried allergenic proteins homogeneously distributed over the patch surface, (a) Single ES in the cone-jet mode of the aqueous solution

Figure 2 :

 2 Figure 2: correlation between discharge regime and ES modes with related size distributions (a) and (c) with (pre-onset) streamers and related transient and asymmetric surface field variations leading to unstable EHD conditions and multimodal size distributions or (b) with the stationary and axisymmetric corona space charge to achieve steady water ES in pulseless corona-assisted cone-jet, with unimodal droplet size distributions and geometrical standard deviation around 1.3 and daylight or 60s dark pictures of the nozzle-to-plane gap.



  Unimodal size dist.Water, Q Liq. = 100 mL.h -1 ,  = 200 µS.m

Figure 3 :

 3 Figure 3: Electric field profiles along the curvilinear field line from the liquid surface at increasing liquid voltages leading to different ionization lengths with impulse or pulseless discharges correlated to unsteady or

Figure 4 :

 4 Figure 4: Steady water ES in corona-assisted cone-jet in (, Q Liq , V Liq ) space for a 4 cm gap with the nozzle (d out /d in = 0.5/ 0.25 mm) for (a) nozzle-plate and (b) nozzle-ring-plate configurations, (Borra et al., 1996; Borra et al., 1999d; Borra et al., 2004), with a ring (d in = 10 mm) a few millimeters from the nozzle above the jet tip.

Figure 5 :

 5 Figure 5: (a) Modal diameter and (b) Charge-to-mass ratio of droplets and corresponding Rayleigh charge limit, versus flow rate in pulseless corona-assisted cone-jet (110 µS.m -1 water). The diameter are represented for different conductivities, and a 15% envelop for the additional variation that can be achieved with the corona ion space charge density controlled by the voltage and the related corona current (Ehouarn P. et al., 2001)

Figure 6 :

 6 Figure 6: Radial profiles of droplet velocity in pulseless corona-assisted cone-jet (Ehouarn P. et al., 2001)

Figure 7 :

 7 Figure 7: conditions for water ES in steady cone-jet modes with (white) and without discharges (blue) in air Steady cone-jet mode of ES Conductivity Flowrate d out / d in d drop (µm)

Figure 8 :

 8 Figure 8: Mean number concentration of particles (integrated on the cross section) along the Bipolarscrubber

Figure 9 :

 9 Figure 9: in constant reference ES conditions, (a) Comparison of total collection and Coulombian coagulation efficiencies (points and line, respectively) of 10 6 cm -3 -i.e. 10-100 mg.m -3 -0.44 µm monodisperse negative aerosol versus the electrical mobility for different flow rates with a line of 4 ES and (b) Coulombian coagulation efficiency versus the adimensional parameter A•q g •µ a •c g •dt/ 0 (line with A=2•10 30 from (Ehouarn P., 2001; Unger, 2001)), i.e. versus the mean <N drop .t> product, controlled by injection of aerosol with constant mobility of 10 -7 m².V -1 .s -1 at 10 L.min -1 , in different initial mixing conditions at different heights from the spay injection, with different numbers of ES, as well as with different mobilities and flowrates (see legend for tuned parameter)

Figure 10 :

 10 Figure 10: Collection efficiencies versus particle size for four bipolar-scrubbers with different charge levels of water droplets from 0.1 mC.kg -1 for induction charging of classical nebulizers at high liquid flowrates (200 L.h -1 ), to 12 mC.kg -1 for ES in corona assisted cone-jet at lower Liquid flowrate (0.4 L.h -1 )

  initial mixing conditions at different heights from the spay injection, with different numbers of ES, as well as with different mobilities and flowrates (see legend for tuned parameter) Figure 10: Collection efficiencies versus particle size for four bipolar-scrubbers with different charge levels of water droplets from 0.1 mC.kg -1 for induction charging of classical nebulizers at high liquid flowrates (200 L.h -1), to 12 mC.kg -1 for ES in corona assisted cone-jet at lower Liquid flowrate (0.4

  Figure A1: Set-up for the production of water droplets

Figure A2 :

 A2 Figure A2 : (a) Wire cylinder corona charger used to charge the submicron sized particles (b) measured and calculated charge versus particle diameter in reference conditions for electro-coagulation tests presented in the last section

-

  Mixing and coagulation conditions for experimental investigation of electro-scrubbers.Droplet are characterized in terms of particle diameter, charge and concentration profile in the scrubber. The charged aerosol is mixed with water droplets of opposite polarities downstream the corona charger in different scrubbers, with coaxial or cross flow of aerosol related to the axis of ES nozzles. Since most of particle filtration devices works at exhaust velocities in the order of meter per second in scrubbers, fabric filters and ESP, electro-scrubbing test are frequently performed in this sub m/s range, except in inertial Stokes impactor, cyclones and venturi scrubbers. Then, the continuous production of unipolar droplets is achieved in steady ES in pulseless corona assisted cone-jet mode for sub m/s inlet velocities, as reported up to cross flow velocities of 15 m/s, above which the gas flow interact with the liquid and modifies its shape affecting thus the capillary pressure and the cone-jet shape or even worst stability[START_REF] Allaf-Akbari | An electrospray in a gaseous crossflow[END_REF].

Table 1 : droplet and spray properties versus the water flow rate

 1

Adachi, M., Okuyama, K., & Kousaka, Y. (1981). Electrostatic coagulation of bipolarly charged aerosol particles.

Journal of Chemical Engineering of Japan, 14(6), 467-473. doi: 10.1252/jcej.14.467 Adachi, M., Okuyama, K., & Kousaka, Y. (1983). Electrical neutralization of charged aerosol-particles by bipolar ions. Journal of Chemical Engineering of Japan, 16(3), 229-235. doi: 10.1252/jcej.16.229 Adachi, M., Pui, D. Y. H., & Liu, B. Y. H. (1993). Aerosol Charge Neutralization by a Corona Ionizer. Aerosol Science and Technology, 18(1), 48 -58. Agostinho, L. L. F., Marijnissen, J. C. M., Kamau, A., & B., B. (2018). Simple-jet mode electrosprays with water.

Description, characterization and application in a single effect evaporation chamber. J. Aerosol Sci., present Special Issue, pp to be filled. Alasri, A., Roques, C., Michel, G., Cabassud, C., & Aptel, P. (1992). Bactericidal properties of peracetic acid and H2O2, alone and in combination, and chlorine and formaldehyde against bacterial water strains. . Can. J. Microbiol. ,[38][39][40][41][42].