Noureddin Osseiran

Manolis N Romanias
email: emmanouil.romanias@imt-lille-douai.fr

Vincent Gaudion

Maria E Angelaki

Vassileios C Papadimitriou

Alexandre Tomas

Patrice Coddeville

Frederic Thevenet

Development and validation of a thermally regulated atmospheric simulation chamber (THALAMOS): A versatile tool to simulate atmospheric processes

Keywords:

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Air pollution is one of the major concerns of our society nowadays. The intense anthropogenic activities related to combustion, industrialization, agriculture and livestock, release a wide variety of pollutants in the atmosphere affecting air quality. Furthermore, in the context of climate change and the anticipated global temperature change, as well as the increasing urbanization rate observed within the last 70 years (in 2015 around 80% of the population was living in urban areas in developed countries (United Nations, 2018)), the effects on air quality have been a top priority issue in the agenda of many countries. Therefore, a strong effort has been made by the atmospheric science community through multidisciplinary actions involving laboratory, field and modeling studies aiming to elucidate the important processes that lead to air pollution, to propose solutions and to make predictions regarding the future Earth's climate.

Hence, the thorough study of chemical processes occurring during night time or daytime in the atmosphere, is of great importance in order to (i) elucidate the fate of pollutants and investigate their impact to the physicochemical properties of the atmosphere, e.g., formation of organic aerosols and tropospheric O3, stratospheric ozone depletion as well as to (ii) determine the lifetimes of pollutants and thus their impact on the future climate. However, the atmosphere is an open chemical reactor and thus the direct control or isolation of chemical processes is challenging. Alternatively, in laboratory scale the investigation of key atmospheric phenomena can occur inside Atmospheric Simulation Chambers (ASC). ASC provide a controlled, yet realistic environment, aiming to simulating atmospheric conditions without any meteorological or emissive influences that occur in real atmosphere. Since the first ASC development [START_REF] Akimoto | Design and characterization of the evacuable and bakable photochemical smog chamber[END_REF][START_REF] Leone | An outdoor smog chamber and modeling study of toluene-NOx photooxidation[END_REF] in the mid-1980s, several small to large-scale facilities have been developed worldwide aiming to study (i) gas phase reactions between the major atmospheric oxidants and both anthropogenic and biogenic volatile organic compounds (VOCs), (ii) secondary organic aerosol (SOA) formation and (iii) nucleation phenomena, and/or processes related with air-quality and climate. In Europe, most of these facilities are integrated in the Eurochamp-2020 project and are accessible to the scientific community [START_REF] Huang | DFT study on the abstraction and addition of Cl atom with toluene[END_REF].

Generally, there are two types of simulation chambers: indoor and outdoor. They are also present in a wide range of volumes and forms, and can be constructed by several materials including Teflon, Pyrex glass, stainless steel etc. However, till today, the majority of simulation chambers studies, especially the ones related to gas-phase chemistry, have been conducted close to ambient temperature and sea level pressure conditions. Atmospheric pressure and temperature though vary with the altitude.

Particularly, temperature variation can strongly affect physicochemical phenomena (i.e. kinetics, reaction mechanism, nucleation processes, etc.) and plays a key role in several atmospheric studies.

Therefore, the objective of this study was to develop and validate an atmospheric simulation chamber, named THALAMOS (thermally regulated atmospheric simulation chamber), that can be used as a reference tool for temperature dependent studies simulating both outdoor and indoor environment. In this paper, we introduce THALAMOS to the scientific community presenting a detailed description of chambers' characteristics and capabilities. To the best of our knowledge, THALAMOS is the first ASC, in national level that allows temperature dependent studies, and one of very few facilities globally, with such a wide accessible temperature range, 233 -373 K that fully covers relevant to the troposphere temperature range and can also be operated at higher temperatures either to study extreme indoor conditions or to investigate reaction mechanism. Within this framework, a series of results that demonstrate both THALAMOS validity as a versatile tool for temperature dependent kinetics and endproducts determination as well as the extent of its capabilities are presented herein. First, THALAMOS was validated by measuring the kinetics of the well documented gas phase reactions of OH radicals and Cl atoms with ethanol and dichloromethane (DCM), over a wide temperature range.

Next, the Cl atoms rate coefficients for the gas phase reaction of Cl atoms with toluene were measured and the reaction mechanism was investigated, as a function of temperature. Finally, the obtained results are discussed. Toluene is an aromatic compound mainly emitted by anthropogenic activities and concentrations that can reach up to several hundreds of ppbV in outdoor [START_REF] Hazrati | Benzene, toluene, ethylbenzene and xylene concentrations in atmospheric ambient air of gasoline and CNG refueling stations[END_REF] or working indoor environments [START_REF] Can | Indoor air quality assessment in painting and printmaking department of a fine arts faculty building[END_REF].

Materials and methods

1.1 THALAMOS description and characteristics THALAMOS is an indoor, atmospheric simulation chamber with a volume of 0.6 m 3 (Fig. 1) that consists of three main parts, (i) a climatic thermostatic cage (VT-4100, Vötsch industrietechnik, Germany), (ii) a Teflon chamber of cuboid shape attached on an aluminum frame (see Fig. 1) and (iii) multiple inline complementary detection techniques, such as Fourier transform infrared spectroscopy (FTIR), selective ion flow tube mass spectrometry (SIFT-MS), and gas chromatography mass spectrometry (GC-MS) that they are assembled externally to the Teflon-chamber. The thermostatic cage (or climatic box) has an effective volume of 1200 L and the temperature can be regulated between 231 and 453 K. The climatic box is equipped with a platinum temperature sensor (PT-100, Pico technology, France) to measure the temperature and two fans to transfer and homogenize the heated/cooled air in the thermostatic cage (Fig. 1). Fig. 2 displays the temperature change rate inside the climatic box illustrating the facility efficiency to achieve extreme cold or hot conditions in a relatively short time window and to adequately simulate the relevant to the Troposphere conditions, in a very well-controlled environment inside the Teflon-chamber.

The Teflon chamber volume was experimentally determined via absolute concentration measurement of ethylbenzene by employing Beer-Lambert low and using in-line infrared spectroscopy. Particularly, multiple titrated volumes of liquid ethyl-benzene (C6H5CH2CH3) were introduced via micro-syringe into the chamber, i.e., 0.1 -0.5 mL, and the infrared (IR) spectra were recorded using 1 cm -1 resolution and 128 co-added scans. IR spectra were integrated between 2493 and 3492 cm -1 . Using an integrated band strength of 3.36 × 10 -17 cm 2 /(molecule•cm), and a density of 0.8626 g/cm 3 for ethylbenzene, chamber volume was determined to be 601 ± 6 L [START_REF] Lide | Physical Constants of Organic Compounds[END_REF]. A temperature and pressure sensor were assorted in the center and back side of the Teflon chamber (see Fig. 1) and the gas mixture temperature/pressure were monitored in real-time. Both measurements were digitized and recorded and stored in a lab computer for further analysis.

The Teflon chamber is also equipped with four fans to ensure (i) the temperature homogeneity of the gas mixture and (ii) the efficient mixing of reagents. Particularly, the two fans are placed at the front and bottom-right side of the chamber, right after the inlet port and installed with a 45 degrees angle allowing the efficient transport of the injected compounds to the main body of the chamber. Two more fans are placed at the back and up-left side (Fig. 1). The temperature inside the thermostatic cage and the Teflon chamber were measured via two thermocouples and the readings comparison over a wide range are comparatively depicted in Appendix A Fig. S1. An excellent agreement -differences are lower than 1% in Kelvin scale, validating that the gas mixture in the Teflon chamber is effectively thermally-equilibrated throughout the reactor volume.

Admission and mixing of compounds

A multi-inlet port placed in the front and bottom-right side of the chamber was used for compounds introduction (Fig. 1). Depending on the physical state and volatility of compounds, different injection methods were applied.

(i) Injection of gas phase compounds

Gases are introduced in the chamber either using gas syringes or via controlled flow through mass flow controllers.

(ii) Injection of liquid phase compounds

For the injection of liquid phase compounds two different methods were applied. In the first method, liquid compounds were injected inside the chamber via a septum inlet using syringes, under a stream of zero-air. To facilitate the evaporation of the liquid, the introduction line was heated at 323 K by using heating taped inlets to control the temperature. Nevertheless, to ensure complete vaporization of the injected compounds, inlet-line's temperature can be increased up to 423 K, when needed, in the case of very low-volatile compounds. In the second method, gas mixtures of known concentrations were prepared in zero air and injected using mass flow controllers. In particular, compounds in the liquid phase were transferred to a glass tube that could be thermostated. Then using gas handling system equipped with Baratron pressure gauges compounds' were either collected in 10 L glass bulb or to a 6 L Silonite canister (both were previously evacuated to a pressure of 10 -3 mbar) and further diluted to a total pressure of 1300 mbar for the glass bulb and 2070 mbar for Silonite canister using zero air as bath gas. The manometrically prepared mixtures were injected in the chamber using mass flow controllers under zero air stream.

(iii) Mixing of compounds Gas mixture homogenization inside THALAMOS, at 296 K, is achieved within ~1 min, but in general, it is also dependent on compound volatility, potent adsorption, hydrolysis or condensation onto chamber's surface and THALAMOS temperature. To ensure steady-state concentrations for all the species in the chamber, gas mixture was fan-mixed for, at least, 20 min before reaction's initiation, and the gas phase concentrations of the organic compounds were continuously monitored to warrant steady-state using the analytical instrumentation described below.

Bath gas and Teflon chamber cleaning

In the majority of the THALAMOS runs, zero air is being used as bath gas, generated from an oil-free air-compressor, coupled with an inline water removal system. Then, zero air could be further purified and is provided to the chamber under a regulated constant flow. Depending on the purification process, two different zero air flows can be used. In the first case, the air produced is driven through a zero air generator (AZ-2020, Claind, Italy) operated at 673 K to catalytically convert the organics present in the air flow to CO2. The exact relative humidity (RH) in the gas flow at room temperature, 293 K, was determined to be 2% using a temperature and relative humidity probe (HQ 210, Kimo, France) with an accuracy ± 1% as stated by the manufacturer. Alternatively, the air flow from the compressor is sent to a high purification system (zero-air generator equipped with a pressure swing adsorption (PSA) device), where volatile organic compounds (VOCs), CO2, CO and H2O are removed.

The remaining impurity levels in the air stream are always lower than the analytical system detection limits: VOCs < 0.1 ppbV, CO2 < 10 ppbV, CO < 80 ppbV and H2O ~ 2 ppmV at 293 K. We estimate that NOx and O3 concentration levels in the chamber are below 50 and 500 pptV respectively (detection limits of NOx analyzer (T200 UP, Teledyne, USA) and ozone analyzer (APOA 370, Horiba, France)). In addition, it is important to mention that when measurements in the presence of NOx are carried out in THALAMOS, right after their completion the Teflon film of the chamber, the tubing's and even the diaphragm in the Teflon pump are replaced to ensure that our system is clean and free of any memory effects in the future experiments.

Prior to each experiment, THALAMOS is flushed-out for at least 2 hours, using a constant flow of zero-air, i.e., 20 L/min and a similar pumped-out rate. The cleaning process is necessary in order to avoid any side reaction or accumulation of different reactants inside the chamber or dead-volumes, eliminating memory effects during sequential experiments.

Light sources and radicals/atoms precursors and production

In order to induce photo-oxidation reactions, the thermostatic cage has been equipped with a light irradiation system capable to host 20 lamps. More specifically, the attached broad-band emission light sources are (i) 10 ultraviolet (UV) lamps emitting in the A region of electromagnetic spectrum, i.e.

UV-A lamps (PL-L 24W/10/4P, Philips, Netherlands) with a maximum wavelength (λmax) at 365 nm, and (ii) 10 mercury lamps (HNS-L 24W 2G11, Osram, UK) emitting UV radiation in the C region of the electromagnetic spectrum, i.e. UV-C lamps, with a λmax at 254 nm. Therefore, THALAMOS can be used to study any induced processes in the gas phase (e.g. photolysis of compounds of interest, or cross section measurements) or involving heterogeneous phase (e.g., TiO2 photocatalysis). It should be noted that the heat released from the lamps (when switched on) does not impact the temperature inside THALAMOS. In particular, the response of the climatic box to temperature variations has been settled to a minimum of ±1 K, which is feasible due to the high performance of our heating/cooling system.

Gas mixture temperature inside THALAMOS is maintained stable (±1 K) and any variations are continuously monitored, both inside and outside the Teflon chamber, during the course of all the photochemical experiments.

In the current study, UV-A lamps were used to generate Cl atoms via Cl2 photolysis:

Cl2 + hν → 2 Cl (1)
Similarly, the UV-C lamps were used to photolyze H2O2 and produce OH radicals via the reaction:

H2O2 + hν → 2 • OH (2)
where hν corresponds to the light source photon-energy. loop between the chamber and the analytical instruments. In the case that solely SIFT-MS is used, reaction mixture was continuously sampled-out with a flow rate of 5 to 25 mL/min. Given that experiments duration was less than two hours, a negligible gas-mixture volume was lost <0.5%, taking into account experimental uncertainties. FTIR optical cell is part of the closed-loop and thus does not alter the gas volume. Finally, although it was not used in the present study, it is worth to note that GC-MS could be also used simultaneously in THALAMOS, since the amount of the required reaction mixture for the analysis is insignificant (~200 mL/min), compared to THALAMOS volume. It is also worth mentioning that in all cases results were cross-validated using simultaneously at least two independent detection methods, and the required sampling did not result in any measurable alteration of reactants concentrations, within the precision of the measurements.

The SIFT-MS is a tandem chemical ionization mass spectrometer based on the chemical ionization of the analytes. A microwave discharge is used for the simultaneous generation of three precursor ions, H3O + , NO + and O2 + , which are sequentially selected by a first quadrupole mass filter [START_REF] Smith | Selected ion flow tube mass spectrometry (SIFT-MS) for on-line trace gas analysis[END_REF][START_REF] Spanel | Advances in on-line absolute trace gas analysis by SIFT-MS[END_REF]. Then, the precursor ions are injected inside a flow tube reactor operated at mTorr pressure using N2, as carrier gas. At the same time, the sample is injected at the upstream-end of the reactor. The precursor ions react with the analytes along the flow tube to produce new characteristic ionized molecules [START_REF] Smith | Selected ion flow tube mass spectrometry (SIFT-MS) for on-line trace gas analysis[END_REF][START_REF] Spanel | Advances in on-line absolute trace gas analysis by SIFT-MS[END_REF]. It is worth mentioning that both the sampling port and the flow tube of the instrument are heated to 393 K to eliminate contaminations of the sampling line and wall reactions along the flow tube. Subsequently, the gas flow passes through a pinhole orifice of 0.3 mm diameter, located at the downstream end of the flow tube reactor to create a molecular beam. The molecular beam enters a differentially-pumped high vacuum chamber and both the precursor and reaction product-ions are focused, via electrostatic lenses, into a second quadrupole mass spectrometer for mass analysis and ion counting for identification and quantification, respectively. The mass spectrometer is internally calibrated on a daily basis, by flowing a standard mixture of 9 compounds provided by the supplier. The internal calibration procedure and the known reaction rate coefficients of the precursor ions with the analytes, allow estimating the theoretical concentrations of any organic compound. Nevertheless, to obtain accurate concentration measurements, the instrument was regularly calibrated by passing standards of the compounds of interest. Although in kinetic measurements the absolute concentrations are not used, it is worth mentioning that the difference between estimated theoretical concentrations and the ones determined experimentally were in fairly reasonable agreement with the observed differences never being higher than 30%. Instrument's time resolution depends on the number of mass spectral peaks monitored, as well as on the number of the averaging counts. For instance, the real time monitoring of 20 mass spectral intensities with a limit of 10000 counts for each mass, time resolution was ca. 10 sec. Under these conditions the detection limits for ethanol, dichloromethane and toluene were 1, 0.8, and 0.9 ppbV, respectively.

Complementary to the SIFT-MS, the reaction mixture was simultaneously analyzed employing an FTIR spectrometer equipped with a 10 m path length White-cell, with anti-reflected coated zinc selenide transmission windows. A liquid-N2 cooled mercury cadmium telluride (MCT) detector was attached and 64 co-added IR spectra were recorded between 650 and 4000 cm -1 , with 1 cm -1 resolution, using Result-3 software. Quantification and data processing was performed using a thermos scientific software, TQ-Analyst TM , and internally developed routines for kinetic analysis. The optical path was also experimentally calibrated using compounds with well-known IR cross-sections and it was determined to be 10 ± 0.1 m, that is in excellent agreement with manufacturer technical data. The detection limits for ethanol, dichloromethane and toluene were in the ppmV range (~ 1 ppmV).

Background IR spectra were collected before compounds injection in the chamber. Note that a Teflon circulating pump was used in a closed loop to ensure gas phase mixture homogeneity between chamber and FT-IR cell. After recording the background, reaction mixture was introduced in the chamber left until it was well-mixed. Well-mixing was verified by recording sequential IR spectra.

The stabilization of the concentrations in the Teflon chamber was achieved after a few minutes and was verified by observing stable. The reactants characteristic IR absorption bands reached a steady absorbance (±1 %) within a few minutes and that was also cross-checked by monitoring the compounds concentration profiles using the SIFT-MS.

1.1.5 THALAMOS first-order losses n-Pentane (C5H12) was used as probe molecule aiming to evaluate possible leaks of THALAMOS. In this series of experiments, 30 ppmV of n-pentane was injected in the chamber and its temporal profile was monitored for several hours using the SIFT-MS. A typical plot, 293 K, is shown in Appendix A

Fig. S2.

The first order loss of pentane was measured to be ~10 -6 sec -1 and it is not expected to affect the kinetic measurements. Similar tests were carried-out between 253 and 353 K leading to identical results. However, since wall-loss and on surface hydrolysis is also an intrinsic variable of the compound used (volatility, functionality, chemical affinity, etc.), dark-loss tests were carried-out in a case-by-case basis, before every experimental series runs.

Relative rate measurements

In this section THALAMOS validation approach is presented. Two well-studied gas phase reactions, i.e., OH radicals with ethanol (C2H5OH) and Cl atoms with dichloromethane (DCM, CH2Cl2), were studied between 253 and 363 K at 760 Torr, in the presence of zero air. Further, kinetics and endoxidation products for the reaction of Cl atoms with toluene (C7H8) were also determined. In all cases, the kinetic measurements were performed applying the relative rate method (RR).

In RR method the temporal loss of the under study compound (M) is measured relative to that of a reference compound (REF) ensuring that the observed changes are solely due to their reaction with the oxidant of interest X (X: OH, Cl, NO3, O3). RR method is a widely used method [START_REF] Atkinson | Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II -gas phase reactions of organic species[END_REF][START_REF] Burkholder | Chemical kinetics and photochemical data for use in atmospheric studies[END_REF] and the relative rate coefficient is derived by the expression [START_REF] King | The relative-rate technique for determining rate constants[END_REF]:

ln = ln ( ) (3)
where [START_REF] King | The relative-rate technique for determining rate constants[END_REF].

[M]0, [REF]0, [M]t ,
Dark loss and photolysis tests were always conducted before rate coefficient measurements to ensure that both reactants are only lost via the reaction with the reactive species, while reactants well-mixing was verified before irradiation. In all measurements presented herein, UV-A and UV-C lamps photolysis loss was negligible for all the compounds the study involves, within the time frame of the experiment, while no measurable dark loss were observed.

Experimental protocol

Prior to each relative rate experiment, the chamber was continuously flushed with zero air (cleaning process). Next, the background concentrations of the compounds of interest were measured using all the employed detection techniques. In kinetics determinations and at temperatures above 293 K, reactants and radical precursors were introduced in the chamber once the desired chamber temperature had been reached. At lower temperatures than 293 K the reaction mixture was introduced at room temperature and then the desired temperature was set. Reactants concentration was monitored through the whole time until the final temperature adjustment of the chamber to ensure that no wall loss processes were occurred. Two criteria need to be fulfilled before initiating the reaction: (i) the temperature in the climatic box to be equal to ±1 K with that of the gas mixture recorded inside the Teflon chamber, and (ii) the concentration profiles of organic compounds to be stable. Then, the reaction is initiated by switching on the UV-A or UV-C lamps, which photolyzes the OH radicals or Cl atoms precursors, respectively. Reactants consumption and products formation is then continuously recorded, as a function of time.

Materials

All chemicals used in the current study are commercially available and listed in Appendix A Table S1 along with their stated purities. The mass spectrometric ion peaks selected to monitor the concentration profiles of reference and target molecules are listed in Table 1.

Results and discussion

THALAMOS validation for kinetic measurements

In this section, OH radicals and Cl atoms kinetics for their reaction with ethanol and DCM, respectively, are presented. There were multiple reasons for choosing the abovementioned reactions.

First, both reactions are of atmospheric interest; in particular, the study of atmospheric relevant reactions initiated by OH radicals (the major tropospheric oxidant) and Cl atoms (important tropospheric oxidant in coastal and urban areas) is of significant importance in order to determine the fate of pollutants in the atmosphere and thus their impact on air quality and climate change. Secondly, the rate coefficients of both reactions have been extensively studied and the kinetic data have been evaluated by both International Union of Pure and Applied Chemistry (IUPAC) and the National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) Panels. Therefore, these reactions were selected to evaluate THALAMOS reliability to measure relative rate coefficients over a wide temperature range, 253 -353 K and thus its capability to provide accurate kinetic data of atmospheric relevant reactions.

OH radical reaction rate coefficients with ethanol

The gas phase reaction of OH radicals with ethanol has been the subject of interest for more than 3 decades [START_REF] Campbell | Rate constants for reactions of hydroxyl radicals with alcohol vapours at 292 K[END_REF][START_REF] Dillon | Kinetics of the reactions of HO with methanol (210-351 K) and with ethanol (216-368 K)[END_REF][START_REF] Greenhill | The rate-constant of the reaction of hydroxyl radicals with methanol, ethanol and (D3)methanol[END_REF][START_REF] Jiménez | Kinetics of the reactions of the hydroxyl radical with CH3OH and C2H5OH between 235 and 360 K[END_REF][START_REF] Kovács | Absolute rate constants for the reactions ofOHradicals withCH3CH2OH, CF2HCH2OH and CF3CH2OH. React[END_REF][START_REF] Nelson | Absolute and relative rate constants for the reactions of hydroxyl radicals and chlorine atoms with a series of aliphatic alcohols and ethers at 298 K[END_REF][START_REF] Oh | Kinetics of the gas-phase reactions of hydroxyl radicals with C1-C6 aliphatic alcohols in the presence of ammonium sulfate aerosols[END_REF][START_REF] Orkin | High-accuracy measurements of OH• reaction rate constants and IR and UV absorption spectra: Ethanol and partially fluorinated ethyl alcohols[END_REF][START_REF] Overend | Rates of hydroxyl radical reactions. 4. Reactions with methanol, ethanol, 1-propanol, and 2-propanol at 296[END_REF][START_REF] Picquet | Kinetics of the reactions of OH radicals with some oxygenated volatile organic compounds under simulated atmospheric conditions[END_REF][START_REF] Ravishankara | Kinetic rate constants for the reaction of hydroxyl with methanol, ethanol, and tetrahydrofuran at 298 K[END_REF][START_REF] Sørensen | Do aerosols act as catalysts in the OH radical initiated atmospheric oxidation of volatile organic compounds?[END_REF][START_REF] Wallington | The gas phase reactions of hydroxyl radicals with a series of aliphatic alcohols over the temperature range 240-440 K[END_REF][START_REF] Wayne | Catalytic conversion of alcohols to alkenes by OH[END_REF][START_REF] Wu | Relative rate constants for the reactions of hydroxyl radicals and chlorine atoms with a series of aliphatic alcohols[END_REF]. For the determination of the bimolecular rate coefficient, both absolute and relative rate methods have been employed. Early published data were in large disagreement between each other [START_REF] Campbell | Rate constants for reactions of hydroxyl radicals with alcohol vapours at 292 K[END_REF][START_REF] Greenhill | The rate-constant of the reaction of hydroxyl radicals with methanol, ethanol and (D3)methanol[END_REF][START_REF] Overend | Rates of hydroxyl radical reactions. 4. Reactions with methanol, ethanol, 1-propanol, and 2-propanol at 296[END_REF][START_REF] Wallington | The gas phase reactions of hydroxyl radicals with a series of aliphatic alcohols over the temperature range 240-440 K[END_REF][START_REF] Wayne | Catalytic conversion of alcohols to alkenes by OH[END_REF] with the problem to become even more intense between the temperature dependent kinetic studies [START_REF] Greenhill | The rate-constant of the reaction of hydroxyl radicals with methanol, ethanol and (D3)methanol[END_REF][START_REF] Wallington | The gas phase reactions of hydroxyl radicals with a series of aliphatic alcohols over the temperature range 240-440 K[END_REF][START_REF] Wayne | Catalytic conversion of alcohols to alkenes by OH[END_REF].

Nevertheless, the latest temperature dependent studies by Jimenez et al. ( 2003), [START_REF] Dillon | Kinetics of the reactions of HO with methanol (210-351 K) and with ethanol (216-368 K)[END_REF] and [START_REF] Orkin | High-accuracy measurements of OH• reaction rate constants and IR and UV absorption spectra: Ethanol and partially fluorinated ethyl alcohols[END_REF] are in excellent agreement. It is worth mentioning that, to the best of our knowledge, all the temperature dependent studies have been carried out using absolute rate methods and thus the present work is the first temperature dependent study using relative rate methods.

Literature data have been reviewed by both NASA/JPL and IUPAC kinetics panels [START_REF] Atkinson | Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II -gas phase reactions of organic species[END_REF][START_REF] Burkholder | Chemical kinetics and photochemical data for use in atmospheric studies[END_REF]. In particular, IUPAC panel has adopted two different expression depending on the temperature region of interest: (210 -300 ) = 3.2 × 10 ! exp( [START_REF] Burkholder | Chemical kinetics and photochemical data for use in atmospheric studies[END_REF]) is recommended between 210 and 298 K.

In the current study, the kinetics of OH reaction with ethanol were studied in THALAMOS within the temperature range of 263 to 353 K, using OH + n-pentane as reference reaction. The SIFT-MS was employed for the real time monitoring of ethanol and the reference compound using the mass peaks 45 (C2H5O + ) and 42 (C3H6 + ) employing NO + and O2 + precursor ions chemistry, respectively (see also

Table 1). The temperature dependent rate coefficients for the reference reaction have been adopted

from the recent review study from [START_REF] Morin | Experimental study of the reactions of OH radicals with propane, n-pentane, and n-heptane over a wide temperature range[END_REF] and was (/012 3456754) = 9.0 × 10 8 × , .+ exp( Therefore, it is evidenced that THAMALOS is capable of determining the rate coefficient of OH initiated reactions as a function of temperature.

Cl atoms reaction rate coefficients with DCM.

The rate coefficient for the reaction of Cl atoms with DCM has been widely studied and kinetic data are very well-established [START_REF] Beichert | Rate constants for the reactions of chlorine atoms with some simple alkanes at 298 K: Measurement of a self-consistent set using both absolute and relative rate methods[END_REF][START_REF] Bryukov | Kinetics of reactions of Cl atoms with ethane, chloroethane, and 1,1-dichloroethane[END_REF][START_REF] Catoire | Kinetics and mechanisms of the self-reactions of CCl3O2 and CHCl2O2 radicals and their reactions with HO2[END_REF][START_REF] Clyne | Absolute rate constants for elementary reactions in the chlorination of CH4, CD4, CH3Cl, CH2Cl2, CHCl3, CDCl3 and CBrCl3[END_REF][START_REF] Davis | Reactions of Cl2P 3/2 : Absolute rate constants for reaction with H2, CH4, C2H6, CH2Cl2, C2Cl4, and c-C6H12[END_REF][START_REF] Niki | An FTIR study of the Cl atom-initiated oxidation of CH2Cl2 and CH3Cl[END_REF][START_REF] Orlando | Temperature dependence of the rate coefficients for the reaction of chlorine atoms with chloromethanes[END_REF][START_REF] Sarzyński | Kinetic study of the reaction of chlorine atoms with dichloromethane and D-dichloromethane in the gas phase[END_REF][START_REF] Tschuikow-Roux | Kinetics of photochlorination of mono-and disubstituted fluoro-, chloro-, and bromomethanes[END_REF]. Both absolute and relative rate measurements have been carried out to determine the temperature dependent rate coefficient (see Fig. 5). The reported data have been reviewed by IUPAC and NASA/JPL kinetics evaluation panels and the recommended expressions are (220 -300 K) = 5.9 × 10 ! exp(-

+-% & ) cm 3 /(molecule•sec) (IUPAC) and (273 -790 K) = 7.4 × 10 ! exp(- ; % & ) cm 3 /(molecule•sec) (NASA/JPL) .
In the current study, the rate coefficient for the gas phase reaction of Cl atoms with DCM was measured as a function of temperature using two reference compounds, i. ) cm 3 /(molecule•sec), recommended by NASA/JPL panel [START_REF] Burkholder | Chemical kinetics and photochemical data for use in atmospheric studies[END_REF]). Furthermore, a series of experiments were carried out at room temperature using 2,2,2-trifluoroethanol (CF3CH2OH) as reference, an average value of k(trifluoroethanol + Cl) = 6.85 ± 0.8 × 10 ? cm 3 /(molecule•sec) was calculated from literature studies at 298 K [START_REF] Garzón | Atmospheric reactions of (H)-and (D)-fluoroalcohols with chlorine atoms[END_REF][START_REF] Papadimitriou | Absolute reaction rates of chlorine atoms with CF3CH2OH, CHF2CH2OH, and CH2FCH2OH[END_REF][START_REF] Sellevåg | Atmospheric gas-phase degradation and global warming potentials of 2-fluoroethanol, 2,2difluoroethanol, and 2,2,2-trifluoroethanol[END_REF] to cross validate the rate coefficients measured using SIFT-MS and FTIR as detection techniques. The SIFT-MS mass peaks used to monitor the reactants are summarized Table 1. FTIR kinetics analysis was carried out employing the subtraction method in which the recorded spectra during reactions progress were subtracted from scaled to the initial compounds concentration reference spectra recorded, separately, for each compound. In all the cases, multiple bands for DCM and CH3C(O)CH3

or CF3CH2OH were monitored and it was ensured that the selected peaks were zeroed. Products contribution was either subtracted, where possible, or taken into account in cases where interference was intense and hard to resolve. Experiments at which differential IR spectroscopy was employed were also carried out. In that case products appeared as positive peaks, while reactants as negative.

Differential analysis also led to indiscernible results. The experimental conditions and the rate coefficient values determined are given in Table 2. Typical relative rate profiles are presented in Appendix A Fig. S3 and rate coefficients are summarized in the Arrhenius plot (Fig. 5). Kinetic results from the present study are in excellent agreement with the corresponding recommended literature data from both IUPAC and NASA/JPL kinetics evaluation panels within 4%.

To conclude, in this section has been evidenced that THALAMOS is capable of measuring accurate gas phase rate coefficients of atmospheric relevant reactions as a function of temperature. To the best of our knowledge, on European level there is no other simulation chamber that has been used for gas phase kinetic studies in such a wide temperature range. Therefore, THALAMOS appears to be an innovative reference tool for temperature dependent investigation of atmospheric relevant processes extending and completing the capabilities of ASCs. Finally, we also present the kinetic and mechanistic investigation of Cl atoms initiated reaction with toluene, as a function of temperature.

Cl atoms reaction rate coefficients with toluene

In this section, temperature dependent Cl kinetics and reaction products with toluene, a common anthropogenic pollutant, are presented. Besides kinetics, product yields of benzaldehyde and benzyl alcohol -primary oxidation products -as a function of temperature were also determined, and a detailed mechanistic scheme is proposed.

Rate coefficient measurements

To the best of our knowledge, there are only room temperature kinetics studies for the reaction of Cl atoms with toluene in the literature [START_REF] Atkinson | Kinetics of the gas phase reaction of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure[END_REF][START_REF] Fantechi | Reactions of Cl atoms with selected VOCs: Kinetics, products and mechanisms[END_REF][START_REF] Markert | UV spectra and kinetics of radicals produced in the gas phase reactions of Cl, F and OH with toluene[END_REF][START_REF] Noziere | A kinetic and mechanistic study of the self-reaction and reaction with HO2 of the benzylperoxy radical[END_REF][START_REF] Shi | Kinetic studies of Cl-atom reactions with selected aromatic compounds using the photochemical reactor-FTIR spectroscopy technique[END_REF][START_REF] Wallington | Kinetics of the gas phase reaction of chlorine atoms with a series of alkenes, alkynes and aromatic species at 295 K[END_REF]. In this work, the rate coefficients of the Cl reaction with toluene were determined between 253 and 333 K, at 1 atm (zero air) employing relative rate methods. Cl reaction with ethane, methanol, and butanone were used as references, and their temperature dependent rate coefficients were taken from IUPAC kinetic database [START_REF] Atkinson | Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II -gas phase reactions of organic species[END_REF] Reactants loss and stable products formation were monitored via SIFT-MS. In particular, toluene, methanol and butanone, were monitored using all the three precursor ions of the MS, i.e. H3O + , NO + and O2 + , and the characteristic mass intensities of each compound are given in Table 1. Consequently, the relative rate ratios were determined for each pair of precursor ions for toluene ( 6@AB454 3C4DBCE@C F@5 ) and the reference compound ( C4G4C45D4 3C4DBCE@C F@5 ) i.e., 6@AB454 0 H / I / C4G4C45D4 0 H / I , 6@AB454 J/ I / C4G4C45D4 J/ I and 6@AB454 / K I / C4G4C45D4 / K I , respectively. The reported relative rate ratio represents the averaged value of the ions' precursor ratio. However, in the cases that ethane was used as reference ( 46M754 3C4DBCE@C F@5 )and due to the low proton transfer affinity of the H3O + and NO + (low detection sensitivity), only O2 + precursor ion was selected to monitor its concentration. Therefore, the relative rate ratios are given by the

expressions 6@AB454 0 H / I / 46M754 / K I , 6@AB454 J/ I / 46M754 / K I and 6@AB454 / K I / 46M754 / K I
, while the mean relative rate coefficients were obtained by averaging the values of the aforementioned fractions. Table 3 summarizes the conditions that experiments carried out, the relative rate ratios and the obtained rate coefficients at each temperature. Typical relative rate kinetic profiles at 293 K are presented in Fig. 6.

The lines are linear least-squares fits of the data and the fit results are given in Table 3. It should be pinpointed that as shown in Fig. 6 a slight deviation from straight line fitting was observed, when butanone was used as reference compound. This trend is a model-example that demonstrates vulnerability of RR methods when compounds or references might be involved in secondary processes (e.g photolysis, on-surface or gas phase hydrolysis, polymerization etc.). Therefore, although the measurements, in which butanone was used as reference, lead to reasonable kinetic results, within the measurements uncertainties, the number of the experiments were limited.

The results from this study are comparatively given in Fig. 7, along with the existing literature data. It is evident that our room temperature values are in excellent agreement with the ones in the literature.

Averaged rate coefficient at 295 ± 3 K was measured to be (5.82 ± 0.19) × 10 -11 cm 3 /(molecule•sec). In addition, no temperature dependence of the reaction rate coefficient was measured for the reaction of Cl atoms with toluene between 253 and 333 K, leading to a value (5.85 ± 0.12) × 10 -11 cm 3 /(molecule•sec). The latter suggests a complex reaction mechanism that proceeds via adduct formation. Although no temperature dependent experimental data exist in the literature Huang et al.

(2012) have theoretically studied the reaction using ab-initio calculations reporting a strong positive temperature dependence of the rate coefficient in the range 298 -1000 K. However, there are no data available at lower temperatures. The authors propose that the reaction mainly proceeds through -H atom abstraction from the methyl group of toluene [START_REF] Huang | DFT study on the abstraction and addition of Cl atom with toluene[END_REF].

Product Study and proposed reaction mechanism

The mechanistic investigation and product analysis of the Cl atoms reaction with toluene was carried out in the temperature range 273 -333 K using SIFT-MS as detection technique. Benzaldehyde and benzyl alcohol were identified as primary degradation products. Traces of benzyl hydroperoxide were also observed. The precursor ions and the mass spectral intensities used for the products detection with the MS are given in Table 1. All products were quantified using MS that was calibrated by (i) flowing a standard reference gas mixture, e. g., known concentration for each compound (toluene, benzaldehyde and benzyl alcohol) or (ii) by injecting known amount of the compounds (in the liquid or gas phase as mixture diluted in air as discussed in section admission and mixing of compounds)

inside THALAMOS and following their concentration with SIFT-MS. The second calibration method was applied in order to account for the impact of temperature on the calibration factor of the compounds. It should be noted that at sub-ambient temperatures, benzyl alcohol was not calibrated, since it was very lossy on the wall surfaces due to the low vapor pressure (<0.2 Torr at 293 K and ca.

1.6 Torr at 333 K). Therefore, the calibration factor determined at room temperature was used to estimate the corresponding product-yields. The estimated error to the concentration measurements was ~7% for toluene and benzaldehyde, and ~15% for benzyl alcohol due to its sticky nature. Benzyl hydroperoxide was not available and the MS calibration was not feasible. Therefore, the theoretical concentrations included in the instrument's software were used instead. In addition, separate photolysis tests for benzaldehyde and benzyl alcohol in the chamber were carried out leading to negligible photolysis rates (kphot ~10 -5 sec -1 ) in the temperature range 273 -333 K.

Typical temporal profiles for toluene consumption and benzaldehyde and benzyl alcohol formation are presented in Appendix A Fig. S4, at 333 K. It is worth to note that although benzaldehyde was rapidly produced, benzyl alcohol was appeared to be formed at delayed times when substantial toluene consumption took place. This delayed production of Benzyl alcohol suggests either that benzyl alcohol is a secondary reaction product or/and, less importantly, delayed mixing due to its low volatility. In order to further look into benzyl alcohol formation, separate measurements carried out, in which the reaction mixture was irradiated for ~ 10 min and then lights were off until benzyl alcohol reach a steady state. The above cycle was repeated several times, until toluene consumption due to its reaction with Cl atoms to be at least 50%.

Furthermore, to complement and cross validate the results obtained with the MS, an experiment was carried out at room temperature coupling the FTIR to the chamber. The concentrations of toluene and molecular chlorine used were rather high, in the range of 55 ppmV each. Benzaldehyde and benzyl alcohol were also identified by FTIR. HCl was also observed to be formed. The reference spectra of toluene and the formed organics were recorded in separate experiments after introducing a known concentration of each compound in the FTIR cell. Toluene and benzaldehyde concentrations were determined using the well-established cross section values at 739.8 and 1731 cm -1 for toluene and benzaldehyde, respectively. Although benzyl alcohol was observed FTIR detection sensitivity was not adequate to accurately measure its concentration. Toluene total loss was approximately 45%. Typical IR spectra recorded during the reaction, as well as reference spectra of toluene, benzaldehyde and benzyl alcohol are given in Appendix A Fig. S5.

Table 4 summarizes the experimental conditions and the yields of the major products in the temperature range 273 -333 K. The yield of the detected products (YDP) was determined as the ratio of the product concentration formed to the concentration of toluene consumed during the course of the reaction:

YDP = Δ[product]/Δ[toluene] (3)
where Δ[product] correspond to the concentration of the product formed and Δ[toluene] the consumed concentration of toluene.

It should be noted that product yields determination was based on the initial data of the photooxidation experiment, where Cl atoms are principally consumed by toluene and side reactions of the products formed with Cl atoms are negligible compared to formation rate, within the experimental uncertainties. Benzaldehyde was found to be the major product formed. Typical plots displaying the consumption of toluene and the formation of benzaldehyde with the SIFT-MS and the FTIR are given in Fig. 8. The total yield of benzaldehyde was independent of temperature with an average value of 0.80 ± 0.05 (Fig. 8). The yield of benzyl alcohol was measured to be ~0.11 at 293 K (Appendix A Fig. S6). At 273 K the yield of benzyl alcohol was decreased by a factor of 2 compared to the room temperature value, but this might be an artifact of the system due to the high sticky efficiency and the significantly decreased vapor pressure of the compound at lower temperatures. Regarding benzyl hydroperoxide, an upper limit of 0.001 can be given based on the theoretical concentrations measured with SIFT-MS.

There is a large disagreement between literature studies regarding the absolute yield of the products formed from the Cl initiated oxidation of toluene. Nozière et al. (1994) conducted experiments in a 140 L Pyrex reactor using relatively high concentrations of toluene (6-33 ppmV) and Cl2 (132 ppmV), and they observed benzaldehyde, as the major product, with a yield of 0.41 ± 0.04. The formation of benzyl alcohol, and benzyl hydroperoxide was also reported with yields 0.15 ± 0.03 and 0.18 ± 0.04, respectively [START_REF] Noziere | A kinetic and mechanistic study of the self-reaction and reaction with HO2 of the benzylperoxy radical[END_REF]. On the contrary, [START_REF] Fantechi | Reactions of Cl atoms with selected VOCs: Kinetics, products and mechanisms[END_REF] did not detect either benzyl alcohol or benzyl hydroperoxide. According to these authors, the major end-oxidation product was benzaldehyde with a yield of 0.62 ± 0.30. [START_REF] Wang | Reactions of chlorine atoms with a series of aromatic hydrocarbons[END_REF], recently, reported product-yields for benzaldehyde and benzyl alcohol of 0.84 ± 0.07 and 0.11 ± 0.02, respectively. The benzyl hydroperoxide formation was not included in Wang et al.'s analysis [START_REF] Wang | Reactions of chlorine atoms with a series of aromatic hydrocarbons[END_REF]. However, under their experimental conditions (i.e. atmospheric pressure and 296 K) benzyl hydroperoxide concentration is expected to be very low, especially since the total products yield is almost unity (0.95 ± 0.08). The product yields measured in the current study at 293 K for benzaldehyde and benzyl alcohol are in excellent agreement with those of [START_REF] Wang | Reactions of chlorine atoms with a series of aromatic hydrocarbons[END_REF]. In addition, no temperature dependence of the yields was observed. although the upper limit for benzyl hydroperoxide (0.001) is significantly lower than the reported value by Nozière et al. (1994), it is in agreement with the observations from [START_REF] Fantechi | Reactions of Cl atoms with selected VOCs: Kinetics, products and mechanisms[END_REF] and [START_REF] Wang | Reactions of chlorine atoms with a series of aromatic hydrocarbons[END_REF]. Although [START_REF] Wang | Reactions of chlorine atoms with a series of aromatic hydrocarbons[END_REF] suggested that dark reactions in Nozière et al.'s system (1994) might be responsible for the observed discrepancy, there are no evidence and the issue is currently unresolved (due to high initial concentrations of toluene and Cl2 used) .

Taking into account that the major products formed from the Cl initiated oxidation of toluene preserved the aromatic structure and that no chlorinated organic compounds were observed, it seems that reaction proceeds via direct or indirect -H atom abstraction and not by addition of Cl to the aromatic ring. The formation of HCl observed in our FTIR experiment, as well as in other studies [START_REF] Fantechi | Reactions of Cl atoms with selected VOCs: Kinetics, products and mechanisms[END_REF] provide with further indications that enhance the latter statement's validity.

Further, a comparison between benzene (k = 1.3 × 10 -15 cm 3 /(molecule•sec) at 295 K [START_REF] Shi | Kinetic studies of Cl-atom reactions with selected aromatic compounds using the photochemical reactor-FTIR spectroscopy technique[END_REF] or < 5.0 × 10 -16 [START_REF] Noziere | A kinetic and mechanistic study of the self-reaction and reaction with HO2 of the benzylperoxy radical[END_REF]) and toluene determined in this work (k = 5.82 ×10 -11 cm 3 /(molecule•sec) at 298 K) was conducted, and reactivity towards Cl atoms reveals that association mechanism is a highly unlikely reaction pathway and the replacement of one hydrogen with a methyl group drastically increases toluene's reactivity, since -CH3 hydrogen metathesis does not affect ring's aromaticity. However, it is worth to mention that in order to further investigate if the hydrogen metathesis proceeds via adduct formation in a stepwise process or via direct abstraction quantomechanical molecular calculations could be of use, although it was beyond the scope of the present study. Theoretical calculations performed by [START_REF] Huang | DFT study on the abstraction and addition of Cl atom with toluene[END_REF] also support the experimental observations. In particular, it is proposed that the -H atom is mainly abstracted from the -CH3 group of toluene, while the rest of the potent -H atom elimination sites, such as ortho, meta and para positions have a negligible contribution if any. The latter is also consistent with previously reported experimental studies [START_REF] Fantechi | Reactions of Cl atoms with selected VOCs: Kinetics, products and mechanisms[END_REF][START_REF] Markert | UV spectra and kinetics of radicals produced in the gas phase reactions of Cl, F and OH with toluene[END_REF][START_REF] Wang | Reactions of chlorine atoms with a series of aromatic hydrocarbons[END_REF]. Thus in Fig. 9, a mechanistic scheme is proposed for the oxidation of toluene from Cl atoms.

Assuming that toluene is mainly removed from the atmosphere via the gas phase reactions with OH radicals and Cl atoms, and reactions with O3 and NO3 are expected to be negligible, the atmospheric lifetime (τx, where x is the corresponding oxidant) can be estimated using the expressions:

τ /0 = OP × /0 (4)
and

τ QA = RS × QA (5)
where /0 and QA are the bimolecular rate coefficients for the corresponding reactions of toluene with OH radicals (i.e. 6.12 × 10 -12 cm 3 /(molecule•sec) at 300 K) and Cl atoms (i.e. 5.82 × 10 -11 cm 3 /(molecule•sec) at 295 ± 3 K average value of all studies) and [OH] and [Cl] are the diurnally averaged concentrations of OH radicals and Cl atoms in the environment of reference. Assuming an average tropospheric concentration of OH, i.e. 2 × 10 6 radical/cm 3 and an average boundary layer concentration of Cl, i.e. 10 4 atom/cm 3 respectively, [START_REF] Hein | An inverse modeling approach to investigate the global atmospheric methane cycle[END_REF], OH radicals are expected to be the dominant sink, leading to an estimated lifetime of about one day (1 day). In urban and coastal areas though, where Cl atoms abundance is significant higher (Spicer et al., 1998), Cl chemistry will substantially reduce the globally averaged lifetime of toluene, even locally, in the troposphere (Table 5), which might be important for such short-lived compounds. On the contrary, in indoor environments where OH radical concentrations are significant lower, e.g., 10 4 to 10 5 molecule/cm 3 [START_REF] Carslaw | A new detailed chemical model for indoor air pollution[END_REF][START_REF] Sarwar | Hydroxyl radicals in indoor environments[END_REF] and Cl levels substantially increased due to the use of Clcontaining cleaning products and other indoor materials, Cl atoms might dominate over OH radicals.

Conclusions

In the current study, we present a recently designed and developed photochemical chamber, THALAMOS, with a wide temperature range thermostatic ability, 233 -373 K. THALAMOS is equipped with in-line FTIR, SIFT-MS and GC-MS complementary detection techniques that allow internal cross-validation of various type of quantitative measurements, such as kinetics and product yields studies. A detailed description of the facility, the instrumentation and the characterization of the conditions has been realized. The first kinetic results employing relative rate methods obtained during THALAMOS validation are also presented. Applying the relative rate method, and studying the temperature dependence of two well documented reactions it was evident that THALAMOS is capable of producing highly precise and accurate temperature kinetic data for atmospheric relevant OH and Cl reactions. Furthermore, the kinetics and the mechanism for the Cl reaction with toluene was studied within a wide temperature range. The kinetic measurements carried out in THALAMOS revealed that the degradation of toluene from Cl atoms is important in coastal areas and/or indoor environments.

Benzaldehyde and benzyl alcohol were identified as the major Cl initiated end-oxidation products and the yields were measured to be 0.80 ± 0.05 and 0.11 ± 0.04, respectively. The present results are in excellent agreement with the ones from Wang et al. 43 THALAMOS is oriented to be a unique tool for temperature dependent studies in the gas or heterogeneous phases, targeted to elucidate the impact of temperature to secondary organic aerosol formation, as well as to simulate extreme temperatures and humidity conditions (i.e. T > 25 o C, RH > 60%, typical for Southern countries). The latter aims to test the efficiency of depolluting materials and to assist in sensors calibrations under extreme indoor or outdoor conditions. Average k (± 2σ) over the temperature range 258-333 K 5.85±0.15 d a Errors represent the 2σ fit precision and do not include systematic uncertainties b Variation denotes the difference between the highest and the lowest relative rate ratios of the compound of interest and the reference, 6@AB454 / C4G4C45D4 , values between the different precursor ions. c Uncertainties quoted to the mean values are the 2σ standard deviations.

d Quoted uncertainty is the 2σ precision of the average value obtained from the linear fit of all measurements (see Fig. 7). The relative rate ratios determined for each pair of precursor ions (H3O + , NO + and O2 + ) for toluene ( 6@AB454 3C4DBCE@C F@5 ) and the reference compound ( C4G4C45D4 3C4DBCE@C F@5 ) are given in the table as 6@AB454 0 H / I / C4G4C45D4 . The reported relative rate ratio represents the averaged value of the ions' precursor ratio. 80±5 b 11±4 b a Errors represent the 2σ fit precision and includes the uncertainty to concentrations determination b Uncertainties quoted to the mean values are the standard deviation. nd: not determined; Yield 0 H / I , Yield J/ I and Yield / K I : the yield of the products formed deploying selective ion flow tube mass spectrometry (SIFT-MS) for each of the precursor ions H3O + , NO + and O2 + ; Average yield of all ions: the average yield of each product formation using SIFT-MS; Yield FTIR: the yield of benzaldehyde demined deploying Fourier transformed infrared spectroscopy (FTIR).

)

  cm 3 /(molecule•sec)[START_REF] Atkinson | Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II -gas phase reactions of organic species[END_REF]. On the other hand, NASA/JPL panel preferred values are based on the comprehensive absolute rate coefficient measurements at sub-ambient temperatures by[START_REF] Jiménez | Kinetics of the reactions of the hydroxyl radical with CH3OH and C2H5OH between 235 and 360 K[END_REF],[START_REF] Dillon | Kinetics of the reactions of HO with methanol (210-351 K) and with ethanol (216-368 K)[END_REF] and[START_REF] Orkin | High-accuracy measurements of OH• reaction rate constants and IR and UV absorption spectra: Ethanol and partially fluorinated ethyl alcohols[END_REF]. Therefore, a temperature independent reaction rate coefficient ( (210 -298 ) = 3.35 × 10 ! cm 3 /(molecule•sec)

)

  cm 3 /(molecule•sec). The initial concentrations of ethanol and reference compound were between 3 -4.5 ppmV, while H2O2 was ranged between 90-500 ppmV. The summary of the experimental conditions and the rate coefficients values obtained are given in Table2. Typical relative rate kinetic profiles are shown in Fig.3, the NO + and O2 + precursor ions were selected to monitor the concentrations of ethanol and pentane respectively. The lines are linear least-squares fits of the data and the fit results are given in Table2. The rate coefficient values determined in the current study, along with the recommended literature values from IUPAC and NASA/JPL are depicted in Fig.4. One can notice an excellent agreement between the measured rate coefficients and the IUPAC and NASA/JPL recommended values (±3%) within the entire temperature range experiments performed.

  e., methane (CH4) (k(methane + Cl) = 7.1 × 10 ! exp(-1270/,) cm 3 /(molecule•sec), NASA/JPL recommended over 181-1550 K) and acetone (CH3C(O)CH3) (k(acetone + Cl) = 1

FiguresFig. 1

 1 Figures

  Fig. 1 General description of THALAMOS (thermally regulated atmospheric simulation chamber) facility. UV: ultraviolet; FTIR: Fourier transformed infrared spectroscopy; GC-MS: gas chromatography mass spectrometry; SIFT-MS: selective ion flow tube mass spectrometry.

Fig. 2 .Fig. 2

 22 Fig. 2.

Fig. 3 .Fig. 3

 33 Fig. 3.

Fig. 4 .Fig. 4

 44 Fig. 4.

Fig. 5 .Fig. 5

 55 Fig. 5.

Fig. 6 .Fig. 6 40 Fig. 7 .Fig. 7

 664077 Fig. 6.

Fig. 8 .Fig. 8

 88 Fig. 8.

Fig. 9 Fig. 9

 99 Fig. 9

  and [REF]t are the initial concentrations of the compound of interest and that of the reference, at reaction time t = 0, and at discrete times (t) after reaction mixture irradiation and kM and kREF are the corresponding second order rate coefficients, respectively. A relative rate plot,

	ln([M]0/[M]t) versus ln([REF]0/[REF]t), should be linear, with a slope equal to rate coefficients ratio,

kM/kREF, and a zero intercept. Therefore, the rate coefficient for the reaction of interest can be determined from the relative rate data fitting relative to the known rate coefficient of the reference reaction (kREF)

Table 1

 1 Mass spectral ions intensities selected to monitor the concentration profiles of the compounds used in the current study.

			Mass to
	Compound	Product ions used monitored	charge ratio	Precursor ion
			(m/z)
	Ethanol	C2H5O +	45	NO +
	n-Pentane	C3H6 +	42	O2 +
	Dichloromethane (DCM)	CH( 35 Cl) ( 35 Cl) +	83	NO +
	Acetone	C3H6O +	58	O2 +
	2,2,2-Trifluoroethanol	[CF3CH2OH]H +	101	H3O +
	Methane	CH3O2 +	47	O2 +
		C7H8H +	93	H3O +
	Toluene	C7H8 +	92	NO +
		C7H8 +	92	O2 +
	Ethane	C2H4 +	28	O2 +
		CH5O +	33	H3O +
	Methanol	NO + CH3OH	62	NO +
		CH3O +	31	O2 +
		C4H9O +	73	H3O +
	Butanone	NO + C4H8O	102	NO +
		C4H8O +	72	O2 +
		C7H7O +	107	H3O +
	Benzaldehyde	C7H5O +	105	NO +
		C7H5O +	105	O2 +
		C7H7 +	91	H3O +
	Benzyl alcohol	C7H8O +	108	NO +
		C7H8O +	108	O2 +
	Benzyl hydroperoxide	C7H8O2 + NO + C7H8O2 +	124 154	H3O + NO +

Table 2

 2 Experimental conditions and kinetics results for the gas phase reaction of OH radicals with ethanol and Cl atoms with DCM.DCM and the three reference compounds used (i.e. methane, acetone, trifluoroethanol), respectively; k(methane + Cl), k(acetone + Cl), and k(trifluoroethanol + Cl): the rate coefficients of methane, acetone and trifluoroethanol with Cl atoms as proposed in literature; k: is the final value of the rate coefficient of the compound of interest; NASA/JPL: National Aeronautics and Space Administration/Jet Propulsion Laboratory.

	C2H5OH + OH

[M]0: initial concentration of the compound M; T: temperature; kethanol / kpentane: the experimentally determined relative rate coefficient ratios of the ethanol and the reference compound; kDCM / kmethane, kDCM / kacetone, and kDCM / ktrifluoroethanol: the experimentally determined relative rate coefficient ratios of

Table 3

 3 Summary of the experimental conditions and rate coefficients obtained in this work for the gas phase reaction of toluene with Cl atoms.

	Reference: Ethane. k(ethane + Cl) = 7.05 × 10 -11 exp(-60/T), IUPAC recommended over 180-330 K
	T (K)	[Toluene]0 (ppmV)	[Ethane]0 (ppmV)	[Cl2]0 (ppmV )	6@AB454 0 H / I / 46M754 / K I	a		6@AB454 J/ I	/ 46M754 / K I	a		6@AB454 / K I	/ 46M754 / K I	a	Variation b	6@AB454 / 46M754 of all ions c	k (×10 -11 cm 3 /(molecule•sec) ) c
	253	3.3	3.3	22	1.14±0.08			1.16±0.08			1.19±0.04	4%	1.16±0.03	6.45±0.17
	273	3.6	3.6	20	1.00±0.01			1.00±0.01			0.98±0.01	2%	0.99±0.01	5.60±0.06
	293 293	3.8 5.6	3.8 5.6	15 15	1.02±0.02 1.03±0.02			1.01±0.01 1.01±0.01			1.03±0.01 1.02±0.01	2% 2%	1.02±0.01 1.02±0.01	5.86±0.06
	313	4.1	4.1	11	0.98±0.02			1.00±0.02			1.02±0.01	4%	1.00±0.02	5.82±0.12
	333	4.3	4.3	17	0.99±0.04			1.00±0.04			0.99±0.02	1%	1.00±0.01	5.89±0.06
	Reference: Methanol. k(methanol + Cl) = 7.10 × 10 -11 exp(-75/T), IUPAC recommended over 200-500 K
	T (K)	[Toluene]0 (ppmV)	[Methanol]0 (ppmV)	[Cl2]0 (ppmV )	6@AB454 0 H / I / T46M75@A 0 H / I	a	6@AB454 J/ I	/ T46M75@A J/ I	a	6@AB454 / K I	/ T46M75@A / K I a	Variation	6@AB454 / T46M75@A of all ions c	k (×10 -11 cm 3 /(molecule•sec) ) c
	253	3.4	3.4	33	1.02±0.01			0.97±0.01			1.08±0.02	10%	1.02±0.06	5.38±0.32
	268	3.3	4.1	17	1.20±0.01			1.07±0.02			1.18±0.01	11%	1.15±0.07	6.17±0.38
	278 278	1.7 3.5	1.8 4.5	10 20	1.11±0.01 1.06±0.01			0.97±0.02 1.04±0.02			1.12±0.01 1.10±0.01	13% 5%	1.07±0.08 1.07±0.03	5.80±0.43
	293	1.9	2.0	11	1.08±0.01			0.96±0.02			1.07±0.01	11%	1.04±0.07	5.72±0.38
	333	2.1	2.2	12	0.99±0.01			0.95±0.02			1.05±0.01	10%	1.00±0.05	5.68±0.28
	Reference: Butanone. k(butanone + Cl) = 3.05 × 10 -11 exp(80/T), IUPAC recommended over 200-450 K T (K) [Toluene]0 (ppmV) [Butanone]0 (ppmV) [Cl2]0 (ppmV ) 6@AB454 0 H / I / UB675@54 0 H / I a 6@AB454 J/ I / UB675@54 J/ I a 293 1.9 1.8 11 1.58±0.10 1.45±0.06 293 1.9 1.8 11 1.72±0.06 1.60±0.04	6@AB454 / K I / K I UB675@54 / 1.46±0.08 a 1.51±0.04	Variation 8% 12%	6@AB454 / UB675@54 of all ions c 1.50±0.07 1.61±0.10	k (×10 -11 cm 3 /(molecule•sec) ) c 6.22±0.31
	313	1.8	1.9	7.0	1.52±0.02			1.51±0.04			1.27±0.02	16%	1.43±0.14	5.63±0.55

Table 4

 4 Summary of experimental conditions and product yields for the gas phase reaction of toluene with Cl atoms.

	T (K)	(ppmV) [Toluene]0	) (ppmV [Cl2]0	Benzaldehyde

Table 5

 5 Toluene atmospheric lifetime include both OH and Cl initiated tropospheric oxidation.

		Scenario 1			Scenario 2
	τOH	τCl (hours) τeff (hours) τOH (hours) τCl (hours) τeff (hours)
	(hours)
	22.7	955	22.2	22.7	47.7	15.4

Acknowledgments

This article is dedicated to the memory of Dr. Ian Barnes from the Institute for Atmospheric and Environmental Research, University of Wuppertal, Germany, one among the leaders of chemical kinetics who inspired many scientists of our generation. This work is part of the chemical and physical properties of the atmosphere (CaPPA) project funded by the Agence Nationale de la Recherhe (ANR) through the programme d'investissements d'avenir PIA (No. ANR-11-LABX-0005-01), the "Hauts-de-France" Regional Council and the European Regional Development Fund (ERDF). A. Tomas and M. Romanias are thankful to the Institut National des Sciences de L'univers (INSU) les Enveloppes Fluides et L'environnement-Chimie de L'atmosphère (LEFE-CHAT) program for financial support. N. Osseiran acknowledges support from Labex CaPPA for his graduate fellowship. V.C Papadimitriou acknowledges support from Labex CaPPA for his short term visit at the institute mines telecom (IMT) Lille Douai. M. E. Angelaki acknowledges support from the project make our planet great again (MOPGA) for her short term visit at IMT Lille Douai, and the Greek sate scholarships foundation (IKY) program that funds her PhD.

linear fit of experimental results (not forced to pass through the origin). The slope corresponds to the product yield of benzaldehyde (±2σ precision).