Yanis Laïb

Kévin Berger

Stéphane Raël

Jean Lévêque

Christophe Viguier
email: christophe.viguier2@safrangroup.com

Abdelrahman El-Wakeel
email: abdelrahman.elwakeel@strath.ac.uk

Min Zhang
email: min.zhang@strath.ac.uk

Kévin Yanis Laïb

Stéphane Berger

Jean Raël

Lévêque

Static characterization on-state of an industrial Si Power MOSFET at cryogenic temperature

Keywords: Cryogenic characterization, MOSFET, power electronics, power applications, Silicon

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

I. INTRODUCTION

O reduce fuel consumption and CO2 emissions; the aviation industry is investigating the potential of superconducting applications such as motors or generators and cables. As these applications require a cryogenic system on board to operate, the question of a complete cryogenic electric chain, namely: turbine -generatorpower electronics -cable -power electronics -engine -fans, naturally arose in order to reduce losses.

Reducing switch losses is a key issue for power converters and the whole cryogenic electrical chain. However, cryogenic temperatures can modify the behavior of switches due to the contraction of materials and changes in the behavior of charge carriers, so it is important to determine the optimum operating temperature range. If it is not possible to use the component at this temperature, then it will be a question of finding a compromise between reducing losses and correct operation of the switch.

Among the switches generally used in the industry, one can mention MOSFETs and IGBTs. Planar power MOSFET's structure was chosen first for the tests because it has a simplest structure than IGBT's. Choosing a silicon-based MOSFET gives us a better understanding of how things work at cryogenic temperature. The static losses of MOSFET come from its RDSON drain-source resistance. To check whether the switch can still be used, the change in threshold voltage VTH as a function of temperature must also be determined.

In the literature [1]- [START_REF] Jurčo | MOSFET-based HTS flux pump[END_REF], studies are mainly carried out using cryogenic fluids such as helium and nitrogen, i.e. at almost fixed cryogenic temperatures. This means that the complete characterization of the components, and in particular the exact optimum operating temperature, cannot be observed. So-called signal MOSFETs have also been studied at cryogenic temperatures, but they cannot be compared with our work because their structure and doping are very different from those of power components with currents in excess of a hundred amperes.

First, this article describes the component used, citing the main quantities of interest. The cryogenic system is then presented in its entirety, together with the associated instrumentation. Finally, the experimental results from the characterization at cryogenic temperature are detailed.

II. MOSFET STE180NE10 PRESENTATION

The choice of a MOSFET as a switch is arbitrary. However, the component is chosen to be representative of power components. STMicroelectronics' STE180NE10 MOSFET is a planar power MOSFET, and therefore with an internal power structure, not a signal structure (see Fig. 1): the structure has a N-layer to increase the breakdown voltage and tens of thousands of MOSFET structure are in parallel to do a component. It has a rated current of 180 A, a nominal voltage of 100 V and a length of 38 mm. The MOSFET STE180NE10 is therefore size and power fully compatible with our characterization system.

Table I shows some static characteristics at room temperature of the component given by the manufacturer in its technical document [START_REF]NE10[END_REF], namely: RDSON, VTH, VGS and TJ. The manufacturer guarantees an operating temperature of the junction up to -55 °C, i.e., 218 K but not below.

Having presented the interesting static characteristics of the MOSFET, the system for characterizing it at cryogenic temperature will now be presented.

III. CHARACTERIZATION SYSTEM

A. Cryogenic system

The cryogenic system shown in Fig. 2 is composed of an ARS DE-202 cryocooler and a vacuum chamber. This system, combined with a Lakeshore temperature controller, can regulate and maintain the component temperature within a range of 10 K to 300 K.

B. Measurement system and methods

The measurement system can measure RDSON, VTH and ID(VDS) curves. To measure RDSON, a conventional 4-wire measurement technique is used: a current source injects a current ID of 1 A with an accuracy of a milliamp, and a voltmeter reads the value of the voltage VDS with an accuracy of a microvolt. To avoid too much heating by Joule's effect of the component, the current is maintained less than 2 seconds. In addition, a dSpace device makes it possible to control the voltage VGS with an accuracy of the order of millivolts.

To measure VTH, the voltage VDS is imposed at 10 V to the nearest millivolt by a voltage source. By varying the voltage VGS, VTH = VGS is obtained when the current ID is 1 mA.

The ID(VDS) curves are acquired thanks to a Tektronix oscilloscope module for TDS series and a current probe linked to an oscilloscope. A pulsed current with a maximum amplitude of 180 A is applied on the drain, and the voltage is measured between the drain and the source. The on-state duration is 0.85 ms.

The results are finally obtained by averaging 16 pulses. Each pulse is separated by 10 seconds to allow the component to cool down. These protocols were carried out for different gate voltage values and for temperatures between 300 K and 10 K.

IV. MEASUREMENT RESULTS AND DISCUSSIONS

Three quantities will be determined: RDSON to find the temperature where static losses are minimal, VTH to ensure that the component is not saturated and ID(VDS) curves to ensure that the component is in the correct operating range.

A. RDSON resistance measurement

The RDSON measurements shown in Fig. 3 is made for IDS = 1 A and for different values of VGS. They then reveal that the ideal temperature for Si-MOSFET is around 80 K, close to the temperature of liquid nitrogen, used in most hightemperature superconducting applications. At 80 K, the reduction in resistance and static losses is 79% compared with the value at 300 K. These measurements also show that the resistance does not tend towards infinity at very low temperature, as some theories predict [START_REF] Gui | Review of Power Electronics Components at Cryogenic Temperatures[END_REF], but towards a constant.

These measurements also show that there is an inversion from 25 K of the order of the curves in relationship to the gate voltage. Indeed, as illustrated in Fig. 4, at 300 K the higher is the gate voltage, the higher is the resistance, but at 20 K, the higher is the gate voltage the higher is the resistance.

Fig. 5 shows the structure of a power MOSFET and the onstate resistances schematic that can be expressed as:

𝑅 𝐷𝑆𝑂𝑁 = 𝑅 𝑁+ + 𝑅 𝐶𝐻 + 𝑅 𝑎 + 𝑅 𝐽𝐹𝐸𝑇 + 𝑅 𝑁-/𝐷𝑟𝑖𝑓𝑡 + 𝑅 𝑆𝑢𝑏 [START_REF] Jia | Experimental investigation of semiconductor losses in cryogenic DC-DC converters[END_REF] where RN+ is the source region's diffusion resistance, RCH the channel resistance, Ra the access resistance where the current change direction, RJFET the resistance that represents the parasitic JFET transistor, RN-/Drift the resistance of the Drift area and Rsub the resistance of the substrate. The wire bonds resistances are not included here. However, as these are metallic junctions, a Seebeck effect can occur and influence the measurements, but it is considered negligible.

The reversal of the curves shown in Fig. 4 and the asymptotic value of the RDSON resistance at low temperatures can be explained by two reasons.

The first reason that can explain this phenomenon is the saturation of the channel. Indeed, the higher the gate voltage, the more the depletion zone increases, decreasing the thickness of the channel and consequently the RCH resistance. The channel thickness is minimum when VGS is maximum. Thus, for low values of VGS the thickness of the channel is greater and allows electrons to pass more easily.

The second reason would be an influence of the RJFET resistance of the JFET transistor in combination with the access resistance Ra. The JFET tends to reduce the width of the current flow, and that effect can increase with temperature decreases. In addition, at cryogenic temperatures, the carriers start to freeze which could make difficult for them to change direction and thus, could increase the access resistance, Ra. If it's the case then a high gate voltage may saturate the area and increase furthermore the resistance for high value of VGS but not for lower value, explaining the curves. Measuring the RDSON of a power UMOSFET also called power Trench-MOSFET can invalidate this idea. Indeed, the power Trench-MOSFET don't have the RJFET and Ra resistances as shown in Fig 6 . So, if the reversal of the curves is still present, then those resistances are not responsible for it. As structure of power MOSFET is extremely complex, the ideas presented above remain very difficult to affirm.

Having the RDSON evolution with temperature determined, and some explanation of the reversal of the curves given, it seems necessary to explain why the resistance does not tend towards infinity at low temperature. To be sure that the component is not saturated the measurement of the threshold voltage VTH is needed.

B. VTH threshold voltage measurement

The VTH measurements are plotted in Fig. 7 revealing an increase in threshold voltage as the temperature decreases. However, this is not significant to saturate the component nor in preventing the control of a power MOSFET in an inverter, as the control is often powered by 15 V. In addition, over the entire temperature range of the measurements, the lowest grid voltage of 5 V was always higher than the threshold voltage.

If the threshold voltage is not responsible for the resistance tending towards a constant, then the ID (VDS) curves must be plotted to ensure that the MOSFET is still working in the proper ohmic region.

C. ID(VDS) and ohmic region measurement

If the MOSFET works in the saturated region that would explain why the resistance tends toward a constant. The ID (VDS) curves were then measured from at a temperature ranging from 10 K to 300 K with a step of 10 K. For ease of reading and analysis, only a few temperatures are shown in Figure 8. What is interesting to observe is that the slopes of the curves are following the RDSON evolution with temperature: between 300 K and 80 K, the slope of the ID (VDS) curves is increasing, e.g. 300 K cyan, 200 K green, and 80 K purple, while below 80 K the slopes are decreasing, e.g. 50 K yellow, 30 K orange, and 10 K blue. Although the RDSON resistance shown in Fig. 3 has been determined at a low current of 1 A, which does not always reflect an operation in the Ohmic region, a similar behavior to Fig. 3 have been observed on the dynamic resistance determined by using the linear part of the ID (VDS) curves between 120 A and 170 A and reported in Fig. 9. Below 80 K, the dynamic resistance also increases as the temperature decreases, with a value at very low temperatures, i.e. below 10 K, which seems to tend towards a constant rather than infinity.

Because the MOSFET should normally operate in the ohmic region, the ID(VDS) curves are meant to be linear. But what can be seen are diode-shaped curves from 40 K and below, as shown in Fig. 10. By taking the slope of the 10 K curve to determine what would be the threshold voltage of this diode shape curved, the obtained threshold voltage is between 0.3 V and 0.4 V which is typically a diode Schottky's threshold voltage. The fact that the MOSFET acts as a gate piloted diode explains why the resistance does not tend towards infinity.

D. Explanation of the Schottky diode effect

The power MOSFET structure in Fig. 5 shows an N+ substrate layer just above the drain. One utility of this layer is to prevent a diode Schottky's effect. Indeed, a Schottky diode is made of a junction between a metal and a low doping semiconductor as the N-layer, so the presence of the substrate, the N+ layer, is preventing effect because the N+ is a high doping layer. Assuming that doping of N+ layer is virtually decreasing because of the freezing of the carrier; the substrate is then considered as a low doping semi-conductor in junction with a metal which creates a Schottky diode.

V. CONCLUSIONS

The work reported in this article clearly demonstrates the benefits of using cryogenics in power electronics, with a sharp reduction in RDSON resistance and associated losses of the order of 80% at 80 K.

Evolution of the RDSON with temperature and gate voltage have been observed in detail. The ID(VDS) curves were used to explain why the resistance does not tend towards infinity by the apparent diode effect from 40 K. In addition, a hypothesis linked to the MOSFET structure was proposed to explain the observed Schottky diode effect.

In the future, in order to assess the dynamic losses, a flyback converter will be built as a power application of the Si MOSFET at cryogenic temperatures. A next step will be to carry out cryogenic characterization on SiC MOSFETs to validate the influence of internal resistances and N+ zone doping. Tests on MOSFETs with higher voltage withstand will also be carried out to see the influence of the N-zone. IGBT, Si Diode and Schottky (Si and SiC) structures will be also studied at cryogenic temperatures, with the aim of sizing and building a converter with these structures.

TFig. 1 .

 1 Fig. 1. Presentation of the MOSFET component installed on the cold plate of the cryogenic system and its terminals: Drain (D), Source (S) and Gate (G) (left), the structure of the component (top right) and the electrical diagram of the component (bottom right).

Fig. 2 .

 2 Fig. 2. Presentation of the cryogenic system.

Fig. 3 .

 3 Fig. 3. RDSON evolution with temperature for ID = 1 A and different VGS.

Fig. 5 .

 5 Fig. 5. On-state resistances schematic of a MOSFET and its structure.

Fig. 6 .

 6 Fig. 6.On-state resistances schematic of a UMOSFET/Trench-MOSFET and its structure.

Fig. 7 .

 7 Fig. 7. Evolution of threshold voltage VTH with the temperature defined for ID = 1 mA.

Fig. 4 .

 4 Fig. 4. RDSON curves as a function of VGS for 300 K and 20 K.

Fig. 10 .

 10 Fig. 10. Evolution of the ID(VDS) curves into diode shape curves @ VGS= 15 V, starting at 40 K and below.

Fig. 8 .

 8 Fig. 8. Evolution of ID(VDS) with temperature @ VGS = 15 V.

Fig. 9 .

 9 Fig. 9. Resistance evolution with temperature for VGS = 15 V, estimated from the slope of the IDS(VDS) curves between 120 A and 170 A, i.e. in the Ohmic region.

TABLE I

 I

	STATIC CHARACTERISTICS OF THE MOSFET STE180NE10
		GIVEN BY THE MANUFACTURER IN [9]
	Symbol	Parameters	Test conditions	Value	Unit
	RDSON	Static drain-source on resistance	VGS = 10 V, ID = 40 A	4.5	mΩ
	VTH	Gate threshold voltage	VDS = VGS, ID = 250 µA	2 to 4	V
	VGS	Gate-source voltage	-	 20	V
	TJ	Operating junction temperature	-	-55 to 150	°C

This work has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 875006. This work is also supported in part by the French government via the Banque Publique d'Investissement (BPI) as part of the France 2030 plan.


César Ducruet

Barbara Polo Martin

Mame Astou Sene

Mariantonia Lo Prete

Ling Sun

Hidekazu Itoh

Yoann Pigne

Ports and their influence on local air pollution and public health: a global analysis

Keywords: health, maritime transport, air pollution, port region, vessel movements

Despite the skyrocketing growth of environmental studies in recent decades about ports and shipping, the local health impacts of ports remain largely under-researched. This article wishes to tackle this lacuna by statistically analyzing data on global shipping flows across nearly 5,000 ports in 35 countries between 2001 and 2018. The different traffic types, from containers to bulks and passengers, are analyzed jointly with data on natural conditions, air pollution, socio-economic features, and public health. Main results show that port regions pollute more than non-port regions on average, while health impacts vary according to the size and specialization of port regions. Three types of port regions are clearly differentiated, of which industrial, intermediate, and metropolitan port regions.

Introduction

The environmental impacts of ports and shipping have attracted a growing attention in recent decades. In 1993 already, the International Association Cities and Ports entitled its fourth international conference "port cities, actors of the environment". In the early 2000s, new research emerged on the integration of environmental values in port policies [START_REF] Chédot | Port et environnement, régulations et transitions dans les ports de commerce de l'Europe du Nord-Ouest[END_REF] and port legislation [START_REF] Ansaud | La Prise en compte de la protection de l'environnement par le droit portuaire[END_REF], to name but a few. Rising environmental concerns often motivated, alongside a wide range of other technical, technological, spatial, and socio-economic considerations, the separation between port and city by the relocation or closure of ports, and the redevelopment of old port areas for new urban uses such as culture and tourism [START_REF] Hoyle | The port-city interface: trends, problems, and examples[END_REF].

Pollution (such as measured by CO2 and PM2.5) is also driven by other activities in the port city [START_REF] Merk | The effectiveness of port-city policies: A comparative approach[END_REF]. The port is a transport node, but also a magnet for industrial and logistic activities, as illustrated by numerous growth pole and free-zone policies in the 1970s in Western countries and more evidently in Asia. Industrial and port activities serve traditional port cities by trucks at distance, while creating new pressures on suburban settlements.

As numerous ports remain urban, research on environmental issues in port cities has been very dynamic in the last two decades [START_REF] Carpenter | Proposing a framework for anchoring sustainability relationships between ports and cities[END_REF][START_REF] Wagner | Sustainability in port cities: a bibliometric approach[END_REF][START_REF] Zheng | Port city sustainability: a review of its research trends[END_REF]. Specific aspects were explored, such as green industrial maritime transport transformation [START_REF] Comtois | Transformations de l'industrie maritime: portrait international de développement durable appliqué[END_REF], industrial ecology [START_REF] Cerceau | Implementing industrial ecology in port cities: international overview of case studies and cross-case analysis[END_REF], environmental conflicts (Lo [START_REF] Prete | Port de commerce et environnement : une relation en évolution. Ce que nous apprennent les recours contentieux dans les ports français et italiens en mer Méditerranée[END_REF][START_REF] Bartlomiejski | Environmental conflicts in port cities[END_REF], urban vulnerability in port cities [START_REF] Lo Prete | La vulnérabilité des villes portuaires méditerranéennes françaises et italiennes au prisme des contentieux[END_REF], sustainability of port and port-city plans [START_REF] Schipper | A sustainability assessment of ports and port-city plans: Comparing ambitions with achievements[END_REF], and stakeholder perspectives on port city sustainable development [START_REF] Lam | A stakeholder perspective of port city sustainable development[END_REF]. This surge of interest goes along with increasing efforts at all levels, from institutions such as the International Maritime Organization (IMO), the International Association of Ports and Harbors (IAPH), and the European Seaports Organization (ESPO), to promote sustainability in ports through a broader environmental vision that also encompasses health issues. Port city actors benefit from ever more advanced methods and precise measurement tools to quantify and map pollutions of all kinds [START_REF] Azarkamand | Review of initiatives and methodologies to reduce CO2 emissions and climate change effects in ports[END_REF][START_REF] Contini | Recent advances in studying air quality and health effects of shipping emissions[END_REF]. For seaport pollution and the correlated health concerns on the local population prevention, the set of technical and organizational solutions available to the port community is very diverse, to improve the fluidity and safety of passenger and goods flows and to lean towards renewable energies and cleaner fuels [START_REF] Sdoukopoulos | Energy efficiency in European ports: state-of-practice and insights on the way forward[END_REF][START_REF] Alamoush | Ports' technical and operational measures to reduce greenhouse gas emission and improve energy efficiency: a review[END_REF].

Nevertheless, two main questions remain largely unanswered: to what extent do ports contribute to local pollution? How much is this contribution detrimental to the health of local populations? The "health" dimension of port impacts/concerns has largely been left aside in the literature. Environmental and health studies are, in fact, drastically different in nearly all aspects (Table 1).

The literature on green ports is so vast that it has been the focus of entire books [START_REF] Bergqvist | Green Ports. Inland and Seaside Sustainable Transportation Strategies[END_REF] and dense review articles (Lam and Notteboom, 2014;[START_REF] Gonzalez-Aregall | A global review of the hinterland dimension of green port strategies[END_REF][START_REF] Iris | A review of energy efficiency in ports: operational strategies, technologies and energy management systems[END_REF]. In comparison, we have found only five journal articles dealing explicitly with ports, pollution, and health in the entire literature (Gianicolo et al., 2013;[START_REF] Vigotti | Mortality analysis by neighbourhood in a city with high levels of industrial air pollution[END_REF][START_REF] Bauleo | Longterm exposure to air pollutants from multiple sources and mortality in an industrial area: a cohort study[END_REF][START_REF] Viana | Estimated health impacts from maritime transport in the Mediterranean region and benefits from the use of cleaner fuels[END_REF][START_REF] Gillingham | Racial disparities in the health effects from air pollution: evidence from ports[END_REF]. Most of them deal with a port city in Italy, where the interplay between environmental assessment and risk for labor is significantly critical [START_REF] Attardi | Evaluating sustainability and democracy in the development of industrial port cities: some Italian cases[END_REF]. Although the recent review of the field by [START_REF] Mueller | Health impact assessments of shipping and port-sourced air pollution on a global scale: A scoping literature review[END_REF] includes more papers, most of them are in fact health impact assessments looking at health risk factors but without an explicit and direct analysis of actual health effects on the population [START_REF] Allen | From suspicious illness to policy change in petrochemical regions: Popular epidemiology, science, and the law in the U.S. and Italy[END_REF]. More likely are studies about the health impacts of shipping onboard, including the crew and passengers [START_REF] Mouchtouri | State of the art: public health and passenger ships[END_REF][START_REF] Akamangwa | Working for the environment and against safety: How compliance affects health and safety on board ships[END_REF][START_REF] Lloret | Environmental and human health impacts of cruise tourism: a review[END_REF].

The concept of "environmental health" (OMS Europe, 1994) includes all environmental concerns that can influence life quality such as air pollution (interconnection between local population and their environment), and the one of "vulnerability" refers to potential impacts or tangible effects on the local population [START_REF] Lo Prete | La vulnérabilité des villes portuaires méditerranéennes françaises et italiennes au prisme des contentieux[END_REF]. But, while environmental health focuses mainly on environmental factors that may affect health (e.g., air pollution causing respiratory diseases), the notion of vulnerability also focuses on people who would suffer from the threats or tangible effects of port development as a potential or real effect which would therefore affect public health. This distinction is important to understanding how, today, the health question in a port context cannot be separated from the environmental question and must be considered in an encompassing manner [START_REF] Jeanjean | Interdisciplinary communitybased participatory health research across the industrial region of the Étang de Berre: The EPSEAL Fos Crau study[END_REF] When it comes to health and ports, studies were conducted at the global scale dealing with ship emissions and mortality [START_REF] Corbett | Mortality from ship emissions: a global assessment[END_REF]. The literature includes several health impact studies of industrial activities but with no specific mention of ports [START_REF] Martuzzi | Industrially contaminated sites and health[END_REF][START_REF] Mudu | Human health in areas with industrial contamination[END_REF][START_REF] Domingo | Health risks for the population living near petrochemical industrial complexes. 1. Cancer risks: a review of the scientific literature[END_REF][START_REF] Domingo | Health risks for the population living near petrochemical industrial complexes. 1. Cancer risks: a review of the scientific literature[END_REF].

The same applies to health studies of port cities and regions that do not mention the port as a factor (on the case of Sydney, Australia, see [START_REF] Broome | The health benefits of reducing air pollution in Sydney, Australia[END_REF] for the Campania region in Italy, see [START_REF] Fusco | Mortality Atlas of the Campania Region. All-cause and cause-specific mortality at municipal level, 2006-2014[END_REF].

Our proposed research innovates in several ways. First, it provides an international perspective of the impact of ports on local air pollution and public health across the OECD area. Second, we use untapped data on global merchant vessel movements and a full set of environmental, socio-economic, geographic, and demographic indicators to run multivariate analyses of such impacts at the scale of small regions (of which cities) and large regions. Main results demonstrate whether possessing a port increases pollution, is detrimental to life expectancy, and/or aggravates mortality rates. We differentiate traffic types by their uneven effects on environment and health (e.g., passengers, containers, bulks, etc.) and conclude with a typology of port regions. This typology serves to identify critical cases and as a benchmark to pursue more qualitative research at thinner scales on actual environmental and health protection practices.

The remainders of this article are organized as follows. The second section provides a review of the recent literature on pollution and health impacts in port cities. Thirdly, we introduce the data and methodology. The fourth section displays the main results of the statistical analysis and the cartography of the typology. We conclude in the last section about the lessons learned and propose further research pathways.

Literature review on ports, pollution, and health impacts

Most activities taking place in the port city environment are in some way linked to the shipping activity [START_REF] Coomber | Description of the vessel traffic within the North Pelagos Sanctuary: Inputs for Marine Spatial Planning and management implications within an existing international Marine Protected Area[END_REF]). Yet, some can be found in any city, such as manufacturing, logistics, and heavy industries, while others are specific to ports, such as loading and unloading of goods, oil jetties, shipyards, fishing fleets, marinas, and dredging and building of port infrastructures. Various forms of pollution, including air, noise, visual, olfactory and water pollution, can result from such activities, bringing negative consequences for human health and the environment [START_REF] Sakib | Addressing the pollution control potential of marine spatial planning for shipping activity[END_REF].

Port and port-related activities not only consume various resources, such as water, electricity, coal and land, but also inevitably damage the urban environment [START_REF] Li | The analysis of a simulation of a port-city green cooperative development, based on system dynamics: A case study of Shanghai port, China[END_REF]. Maritime transport noticeably contributes to the degradation of air quality in coastal areas [START_REF] Ledoux | Influence of ship emissions on NOx, SO2, O3and PM concentrations in a North-Sea harbor in France[END_REF][START_REF] Mwase | Health impact of air pollution from shipping in the Baltic Sea: effects of different spatial resolutions in Sweden[END_REF][START_REF] Merico | Comparison of the impact of ships to size-segregated particle concentrations in two harbour cities of northern Adriatic Sea[END_REF]Gregoris et al., 2021). Air pollutants such as sulphur oxides (SOx), nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), and volatile organic compounds (VOCs) are emitted to the atmosphere as a direct result of shipping activities [START_REF] Sorte | Impact of harbour activities on local air quality: a review[END_REF]. Exposure to PM and nitrogen dioxide (NO2) is particularly harmful to health [START_REF] Eea | Healthy environment, healthy lives: how the environment influences health and well-being in Europe[END_REF]. Annual NOx ship emissions can reach 5-10% of total global emissions, and even 30-40% at the regional level [START_REF] Ramacher | Contributions of traffic and shipping emissions to city-scale NOX and PM2.5 exposure in Hamburg[END_REF]. Before the launch of sulfur limit and emission control areas (SECAs) by the IMO designed under Marpol convention, annual SOx emissions from ships accounted for 4-9% of the total global emissions. In Europe, according to [START_REF] Merico | Shipping and air in Italian port cities: State-of-the-art analysis of available results of estimated impacts[END_REF], PM2.5 and PM10 emissions represented 45% and 28% of shipping-related emissions, respectively. In particular, ultrafine particles from cruise ships and ferries (especially at ports such as Barcelona, Palma de Mallorca, Venice, Civitavecchia, Southampton, Lisbon, etc.) may cause specific problems both to occupational health for dockworkers and for coastal residents.

Worldwide, 14,500-37,500 premature deaths were attributed to PM2.5 related to shipping, with the highest values in areas recording both high PM concentration and population density.

But such global averages must not hide that pollution from ships concentrates near the coast and within ports [START_REF] Jahangiri | An improved emission inventory method for estimating engine exhaust emissions from ships[END_REF]. In the latter case, ships pollute more at berth than during maneuvering [START_REF] Fameli | Estimation of the emissions by transport in two port cities of the northeastern Mediterranean, Greece[END_REF], so that their turnaround time is a crucial factor of pollution, especially concerning NOX [START_REF] Sorte | Assessment of source contribution to air quality in an urban area close to a harbor: Case-study in Porto, Portugal[END_REF], but also PM concentration, which may culminate to 7-26% in Asian ports [START_REF] Chen | Ship emission impacts on air quality and human health in the Pearl River Delta (PRD) region, China, in 2015, with projections to 2030[END_REF][START_REF] Zhang | Modelling driving factors of PM2.5 concentrations in port cities of the Yangtze River Delta[END_REF]. The terminal area itself, port-related industries and logistics also participate to local air pollution, although their contribution is not always clearly measured [START_REF] Mueller | Health impact assessments of shipping and port-sourced air pollution on a global scale: A scoping literature review[END_REF]Rowangould et al., 2020). [START_REF] Merico | Comparison of the impact of ships to size-segregated particle concentrations in two harbour cities of northern Adriatic Sea[END_REF] and [START_REF] Sorte | Assessment of source contribution to air quality in an urban area close to a harbor: Case-study in Porto, Portugal[END_REF] quantified the contribution of these emissions to ambient air quality (i.e., ship, terminal, road traffic, refineries), and in the latter study it was found that the combination of trucks, railways, cargo handling equipment and bulk material storage contributed the most to surface PM10 concentrations over the study area. A study on the port of Felixstowe (UK) demonstrated that inland transport emissions were double the size of port emissions [START_REF] Gibbs | The role of sea ports in endto-end maritime transport chain emissions[END_REF].

Air pollution in ports also varies according to traffic types. At liquid bulk terminals, the main concern is the emission of volatile organic compounds (VOCs) during the storage and turnover of oil and chemicals [START_REF] Yuan | Spatiotemporal distribution characteristics and potential sources of VOCs at an industrial harbor city in southern Taiwan: three-year VOCs monitoring data analysis[END_REF]. Solid bulks (e.g., grain, coal, ores, cement) may produce dust during ship loading and unloading or when carried via uncovered conveyor belts and unfiltered silos. Cereals in particular are mixed with earth residuals contaminated by agricultural fertilizers and pesticides. The study by [START_REF] Morin | Particules urbaines et céréalières, micro-organismes, mycotoxines et pesticides[END_REF] on Rouen, Europe's largest port for cereals, was motivated by the fact that ship loading with food grains emits important amounts of PM, representing potential danger for populations living in the close vicinity of the harbor (e.g., fertilizers, pesticides, mycotoxins and microflora).

Cruise shipping, which has been a fast-growing sector in the last decade or so, produces emissions that harm the health of not only tourists and residents [START_REF] Chatzinikolau | Health externalities of ship air pollution at port-Piraeus port case study[END_REF][START_REF] Perdiguero | Cruise activity and pollution: The case of Barcelona[END_REF], but also crew members [START_REF] Lloret | Environmental and human health impacts of cruise tourism: a review[END_REF]. When it comes to container vessels, not all port cities use rail or river as an alternative to road, which represents 75% of all intra-EU freight movements (Eurostat, 2019). Ports such as Le Havre in France have a much imbalanced modal split, with more than 90% of hinterland traffic occurring by road. Even in multimodal ports such as Antwerp in Belgium, where barges carry about 40% of hinterland traffic, road congestion may reach extreme levels, due to the combination of transnational and national trucking flows with urban commuting flows, especially at peak hours.

Currently, methodologies on how ship emissions impact air quality and human health are well established and used in cost-benefit analyses of policy proposals [START_REF] Nazmus | Addressing the pollution control potential of marine spatial planning for shipping activity[END_REF]. The effect of large-scale air pollution emission changes on ecosystem, human health, and economic impacts can be modelled with reasonable accuracy. However, there is no unified framework to assess the environmental and socioeconomic impacts of ports and shipping [START_REF] Ytreberg | Valuating environmental impacts from ship emissions -The marine perspective[END_REF]. Existing studies use a wide variety of methods, including experimental observations, numerical modelling, and emission inventory analysis (Merico et al., 2017). Some scholars conducted on-site sampling campaigns and quantitatively evaluated the impact of ship emissions on port air quality based on the measured data [START_REF] Wang | Atmospheric pollution from ships and its impact on local air quality at a port site in Shanghai[END_REF][START_REF] Peng | Optimal site selection for the remote-monitoring sulfur content of ship fuels in ports[END_REF]. [START_REF] Steffens | Near-port air quality assessment utilizing a mobile measurement approach[END_REF] used the mobile measurement method to assess the air quality of the port, which is more flexible than the fixed monitoring station. Mainstream methods to estimate ship emissions in ports are either top-down (i.e., fuel-based) or bottom-up (i.e., activitybased) (Nunes et al., 2017a;[START_REF] Yang | An AIS-based emission inventory and the impact on air quality in Tianjin port based on localized emission factors[END_REF][START_REF] Gregoris | Chemical characterization and source apportionment of size-segregated aerosol in the port-city of Venice (Italy)[END_REF]. The bottom-up approach for instance was adopted by [START_REF] Sorte | Emission inventory for harbour-related activities: comparison of two distinct bottom-up methodologies[END_REF] in their detailed emissions inventory covering shipping and cargo handling (see also [START_REF] Kara | Estimation of land-based emissions during container terminal operations in the Ambarlı Port, Turkey[END_REF][START_REF] Sorte | Impact of harbour activities on local air quality: a review[END_REF].

The source apportionment literature is vast and diverse, examining ship emissions and air quality alongside effects of emission regulations [START_REF] Anastasopolos | Evaluating the effectiveness of low-sulphur marine fuel regulations at improving urban ambient PM2.5 air quality: Source apportionment of PM2.5 at Canadian Atlantic and Pacific coast cities with implementation of the North American Emissions Control Area[END_REF]. There is a strong difficulty to disentangle the contribution of each source to total local pollution, due to complex interactions among them and rapidly changing meteorological conditions [START_REF] Lang | Investigating the contribution of shipping emissions to atmospheric PM2.5 using a combined source apportionment approach[END_REF]. To simulate urban-scale pollutant concentrations, [START_REF] Ramacher | Contributions of traffic and shipping emissions to city-scale NOX and PM2.5 exposure in Hamburg[END_REF] used the coupled prognostic meteorological and chemistry transport model (TAPM) to measure the contribution of road traffic and shipping related emissions to total air quality and annual mean population exposure in Hamburg. [START_REF] Merico | Development of an integrated modellingmeasurement system for near-real-time estimates of harbour activity impact to atmospheric pollution in coastal cities[END_REF] proposed a system integrating dispersion modelling and measures issued from both meteorological stations and traffic data inside the harbor.

Despite their regular advances, such experiments still have limitations due to the complexity of chemical processes in the atmosphere, the difficulty of source attribution, and limited spatiotemporal data resolution.

Quantitative studies with an explicit focus on health impacts are usually done at the intra-urban level. In Civitavecchia, [START_REF] Bauleo | Longterm exposure to air pollutants from multiple sources and mortality in an industrial area: a cohort study[END_REF] showed that people living in areas with higher concentrations of PM10 or NOx were younger and had a lower socioeconomic status than in less polluted areas, while residents near the port had higher mortality from all cancers and neurological diseases. In Brindisi, Gianicolo et al. ( 2013) found that health risks (i.e., unplanned hospital admissions) increased for people living under prevailing winds carrying PM10 and NO2 and coming from port and industrial areas. In Taranto, the district most affected by the port and steelworks (i.e., young age, low socioeconomic status, high deprivation index, and highest SO2 mean concentration) located at distance due to topography [START_REF] Vigotti | Mortality analysis by neighbourhood in a city with high levels of industrial air pollution[END_REF]. According

to [START_REF] Viana | Estimated health impacts from maritime transport in the Mediterranean region and benefits from the use of cleaner fuels[END_REF] in their study of eight Mediterranean cities, shipping caused fewer premature deaths than vehicular traffic, though emissions from both remained comparable in magnitude. [START_REF] Gillingham | Racial disparities in the health effects from air pollution: evidence from ports[END_REF] used vessel tonnage and patient-level administrative data over the period 2001-2016 to demonstrate that air pollution from U.S. ports affects health outcomes but differ by race, as respiratory hospital visits, heart-related visits, and psychiatric visits are three times higher for Black people than for whites.

The level of detail and diversity of measures offered by these studies largely explain the rarity of comparative analyses internationally and even within the same country. This is also due to the relative uniqueness of port sites, urban morphologies, and climatic conditions from one place to the other. Therefore, we present in the next section the data and methodology capable, for the first time, of running an international and comparative analysis of the environmental and health impacts of ports.

Data and methodology for an international study

3.1 Hypotheses Based on the above, our main hypotheses are as follows:

H1a: the presence of a port aggravates air pollution and health conditions H1b: port regions witness heavier environmental and health impacts than non-port regions This can be verified by a statistical analysis, first willing to test whether ports regions exhibit a specific profile compared with other regions. Ports may significantly affect pollution and health, but local environmental and health conditions are influenced by other activities and a number of natural and human factors. Impacts may come from activities distinct from the port itself (i.e., terminals) but strongly related to it, like industries, logistics, and the concentration of population. However, numerous new terminals have been developed in the periphery, at greenfield sites, so that a port region is not necessarily more polluting than a non-port region. Given that ports are very diverse across the globe, traffic volume and specialization should also be considered:

H2: impacts are higher for larger ports than for smaller ports H3: impacts are differentiated across traffic types While the quantity of traffic passing through ports should inevitably result in more air pollution, this is less evident when it comes to differentiate traffic types. Those act as "supply chains" each having its own rationale. As mentioned above, solid bulks like cereals provoke dust clouds in port cities, while container traffic pollutes mainly when carried onshore between the terminal and the hinterland, especially in a dense urban environment for trucks to go through. The consideration of traffic types is also important because of their particular regional branching and industrial relatedness [START_REF] Ducruet | Regions and material flows: investigating the regional branching and industry relatedness of port traffics in a global perspective[END_REF]. Bulks shall be produced or consumed more locally by heavy industries, compared with containers that feed more distant customers or concentrate in dense urban regions [START_REF] Guerrero | Deep-sea hinterlands: Some empirical evidence of the spatial impact of containerization[END_REF]. Cruise shipping, which takes place within port cities, implies long turnaround times for vessels during port stay, as well as important road traffic for tourists [START_REF] Tichavska | Port-city exhaust emission model: An application to cruise and ferry operations in Las Palmas Port[END_REF].

3.2) Global database

The proposed international perspective uses the port region as the spatial unit of analysis. The OECD territorial database (OECD, 2023), which covers about 2,000 regions in 36 countries, is the main data source, which provides socio-economic, environmental, and health indicators at two regional levels, namely small regions (TL3)

and large regions (TL2). While we are aware that administrative boundaries and port hinterlands are often mismatched, administrative regions remain relevant spatial units as they constitute the "captive" part of the hinterland [START_REF] Ducruet | Port regions and globalization[END_REF][START_REF] Notteboom | Port Economics, Management and Policy[END_REF]. We combine this database with the one from Lloyd's List on global shipping, which main advantage is to palliate the absence of a global database on actual port throughput (Lloyd's List Intelligence, 2023).

As seen in Table 2, Lloyd's data allows calculating ship traffic at ports in total and by type of ship, which corresponds to the product between ship capacity (gross registered tons) and number of calls on a yearly basis. We excluded non-commercial vessels, like navy ships and hospital ships for instance. After several trials and errors, it was decided to exclude vessels performing port services (i.e., towage, pilotage, dredging) as well as general cargo, and to keep other categories at an aggregated level, like liquid bulk (i.e., chemicals, crude oil, gas, oil tanker), solid bulk (i.e., coal, cement, grain, ores), and passenger/vehicles (i.e., ferry, cruise, roll-on/roll-off, and vehicles), while containers is a category on its own. Traffic was summed for regions containing more than one port.

As high ship turnaround time is recognized as a factor of pollution in the literature, it was calculated as an average for the whole fleet by region and by year.

OECD data include two main pollutions, namely PM2.5 concentration (µg/m 3 ) and Greenhouse Gases (GHG) emissions (million tons CO2 equivalent). These PM2.5 concentration estimates (outdoor and ambient) were derived "by integrating satellite observations, chemical transport models and measurements from ground monitoring station networks" (OECD, 2023). They were population-weighted using gridded population datasets. Fine particulate matter was chosen as it is the pollutant which poses the greatest risk to health globally, especially as it increases the risk of respiratory and cardiovascular diseases [START_REF] Who | Source identification of PM2.5 at a port and an adjacent urban site in a coastal city of China: impact of ship emissions and port activities[END_REF]. GHG is the sum of seven gases with direct effects on climate change: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6), and nitrogen trifluoride (NF3). The data are expressed in CO2 equivalents and refer to gross direct emissions from human activities. We also documented natural conditions locally. Those were collected from the website

Copernicus1 , a dataset providing daily surface meteorological data for the period from 1979 to present. Among all possible indicators, we retained the most relevant to study port pollution, namely temperature, wind speed, and precipitations. The method has been to calculate the yearly average for each region from individual station data, using QGIS and the shapefiles of regions. While temperature is known to increase pollution [START_REF] Zhao | PM2.5 and O3 pollution during 2015-2019 over 367 Chinese cities: Spatiotemporal variations, meteorological and topographical impacts[END_REF], wind speed and precipitations reduce it by dispersion and dilution [START_REF] Liu | The effect of natural and anthropogenic factors on haze pollution in Chinese cities: A spatial econometrics approach[END_REF][START_REF] Zhang | Spatiotemporal characteristics and influencing factors of Air pollutants over port cities of the Yangtze River Delta[END_REF]. Such effects were tested via several control variables, scoped to those shown in Table 2. The retained health indicators are life expectancy at birth and mortality rate. Among all possible socio-economic variables, population density and Gross Value Added (GVA) per capita are retained as potential factors of increased pollution.

Analyses are compared between large and small territorial units to investigate the potential effects of geographic scale on the relationship between vessel activity, pollution, and health. Depending on the scope of the hinterland, relationships may vary between the variables, as shown in a recent study on employment and traffic specialization in French port cities [START_REF] Amdaoud | The mutual specialization of port and urban functions: The case of France[END_REF]. Descriptive statistics for the retained indicators are provided in Appendix 1.

Statistical analysis

As a cross-sectional and time-series study (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), the best method to verify the hypotheses was a regression analysis of panel data. The main reason was because this model could mitigate the effect of omitted variable bias when there is a lack of information on variables that are associated with both the regressors of interest and the dependent variable, and if these variables are constant in the time dimension or across entities. We ran two models: a) fixed effects regression using time and entity fixed effects and b) random effects. A Hausman test led us to choose the fixed effects model.

Due to the inclusion of a time-invariant variable (ECA zone dummy), we selected a variant of the model called the Least-Squares Dummy Variable (LSDV) model, equivalent to the demeaning approach. The detailed statistical results are provided in the appendices, while in-text tables provide the estimates and significance only.

A factor analysis as well as a hierarchical cluster analysis (HCA) were applied to the most recent year (2018) in order to describe general (static) trends and delineate distinct classes of port regions. In these analyses and like for regressions, several variables were transformed into natural logarithms to attenuate the influence of extreme values (GHG, total traffic, population density, and GVA per capita). For the factor analysis and the HCA, a number of other variables were transformed into location quotients to avoid the geographic or national bias when comparing regions (mortality rate, life expectancy, PM2.5, wind speed, temperature, precipitation). Location quotients are calculated as the regional value divided by the national average.

Results

The effect of having a port

The first analysis focuses on the port dummy to verify its effect on environmental and health conditions. For the main environmental, health, and socio-economic variables, we calculated the ratio between the average score of port regions and the average score of all regions (Figure 1). This allows to answer positively the fundamental question about whether port regions are more polluted than non-port regions, in terms of GHG emissions. This is the case for both large and small regions, but the gap between port and non-port regions is much wider in the case of small regions (1.5-1.6 compared with 1.1-1.2). Although such results cannot account for a direct and causal effect of ports, environmental issues are more critical for smaller territories having a port. This is not the case of the exposure to PM2.5 emissions, given that the ratios are lower than 1 for both large and small regions. Small port regions are also characterized by a higher population density and GDP per capita on average, which accentuate GHG emissions and at the same time, the exposure to such emissions.

However, health indicators show no specificity, except the mortality rate that is lower than average for small port regions, while life expectancy is more or less the same between port and non-port regions. At this stage, it is only possible to establish links between GHG emissions and the concentration of population and economic activities when a region has a port. The relationship with health conditions needs further investigation using other methodologies. Interestingly, the bottom part of Figure 1 shows that in maritime countries 2 , non-port coastal regions are nearly identical to nonport inland regions in all aspects (ratio around 1), except for population density. The latter is much lower in non-port coastal regions, and this is principally due to the specialization of these regions in other activities than trade, like agriculture, culture and tourism. Mortality rate is also slightly lower (around 0.9 on average) in coastal nonport regions, as verified in earlier studies comparing coastal vs. inland areas as well as densely vs. sparsely populated areas [START_REF] Fusco | Mortality Atlas of the Campania Region. All-cause and cause-specific mortality at municipal level, 2006-2014[END_REF]. The model results show that the port dummy is significant and has the expected sign for GHG emissions, for both large and small regions (Table 3) 3 . However, it is significant and negative for PM2.5 concentration. This may be explained by the fact that despite the high absolute emissions of PM2.5 in port cities, inland regions may have even greater concentration of such sources. One reason is that PM2.5 emissions in port regions are, at least partly, blown away by stronger winds along the coast 4 . This is well apparent in Table 3 as wind speed is significantly and negatively influencing PM2.5 concentration. Higher temperatures foster GHG emissions, in accordance with the literature [START_REF] Zhao | PM2.5 and O3 pollution during 2015-2019 over 367 Chinese cities: Spatiotemporal variations, meteorological and topographical impacts[END_REF]. Lastly, population density amplifies GHG emissions and PM2.5 concentration at both territorial levels. The concentration of population, especially in port regions, amplifies the probability for port-related traffic (e.g., heavyduty vehicles) and urban traffic to create bottlenecks, especially at peak hours along the most frequented road arteries.

3 See appendices 2 and 3 for full statistical results. 4 We calculated that wind speed, on average, is 1.3 to 1.4 faster in port regions than in non-port regions.

GHG emissions PM2_5

GDP_hab Population_density

Table 3: Model results with port dummy

Secondly, the port dummy is confronted with health indicators. For mortality rate, it is positive but not significant, while for life expectancy it is always positive and significant. What looks like a contradiction could signify that the port effect will differ according to more complex phenomena than just the presence or absence of such an infrastructure. Besides, Gross Value Added (GVA) per capita lowers mortality and increases life expectancy at both regional scales. It is worthy of investigation to include air pollution indicators in the model. GHG emissions significantly lower life expectancy, while PM2.5 concentration has the opposite effect 5 . The respective influences of GHG emissions and PM2.5 concentration on mortality rates are opposed between large and small regions. It shows that the aggravating effect of GHG on health is more "local" (small regions) while the one of PM2.5 is more spread inland (large regions). Such results can be linked with the fact that wind speed significantly reduces mortality at small regions. However, the unavailability of additional data, such as about medical care (e.g., number of doctors, hospital beds), hampers the models' results. This motivates us to enrich the analysis with more information about ports, which can be differentiated by their traffic size and specialization.

5 It should be noted that GHG emissions and PM2.5 concentration are used both as dependent and independent variables in our analyses. Therefore, it is not possible to directly compare the parameters of other variables, such as GVA per capita, as their influence on health is underestimated due to the inclusion of GHG and PM2.5.

The effect of traffic size and specialization

As shown in Table 4, total port traffic has a significant and positive effect on GHG emissions for both small and large regions. The quantity of cargo and passengers 6 handled at ports is thus contributing to local air pollution. It is not the case for PM2.5, which confirms the prior findings of Table 3. Interestingly, the average ship turnaround time (ATT) significantly and positively accentuates both GHG emissions and PM2.5 concentration at all territorial levels. For all regions, this goes along with a significant and positive effect of population density and GVA per capita on GHG emissions, and a negative effect of the belonging to an ECA zone for small regions only. This confirms the findings of [START_REF] Ducruet | Spatial Network Analysis of Container Port Operations: The Case of Ship Turnaround Times[END_REF] about the evolution and determinants of ATT at world container ports between 1977 and 2016, whereby city size accentuates ship times and therefore pollution. On the offshore side, solutions such as virtual arrival, vessel speed reduction, inter-terminal barge shuttles, and berth allocation systems are used to lower ATT [START_REF] Alamoush | Ports' technical and operational measures to reduce greenhouse gas emission and improve energy efficiency: a review[END_REF], just like underground transport, urban area bypass, modal split, automated door systems, truck appointment systems, and connectivity platforms on the onshore side to avoid queuing and congestion. Like for the port dummy analysis (Table 3), wind speed significantly reduces PM2.5 concentration at small and large regions, while GVA per capita decreases it.

The use of cold ironing 7 is a widely applied remedy to air pollution [START_REF] Gonzalez-Aregall | A global review of the hinterland dimension of green port strategies[END_REF], alongside improvements in the productivity of cargo handling vehicles.

The results by traffic types are much contrasted according to the territorial level and the type of air pollution. Solid bulk traffic fosters GHG emissions in small and large regions, however, although it is more recognized as a source of PM2.5 in the literature and in practice. Liquid bulk and passenger traffic reinforce PM2.5 concentration in 6 In this study, the use of ship tonnage capacity allows measuring cargo and passenger traffic based on the same unit (Gross Registered Tons, GRT).

7 Cold ironing is known by a variety of names, including shore power, shore-side power, shore-side electricity (SSE), high-voltage shore connection (HVSC), onshore power supply (OPS), shore-to-ship power, and alternative maritime power.

small regions only. This is in accordance with practice, since such traffics produce Volatile Organic Compounds (VOCs) like from bulks during handling and storage.

Especially during the loading and unloading of tanker ships, VOCs (methane and nonmethane) contribute to GHG emissions. Among them, the heavier components (nonmethane VOCs) contribute to low-level photochemical oxidants, such as ozone, which affect human health, food production and the environment. Additional pollutants include oil itself (accidental discharge, loss from deposit tankers and pipeline), oil and rubber (spill from bulk-handling device), oily and toxic sludges (fuel deposits), as well as polychlorinated biphenyls (PCBs), hydrofluorocarbons (HFCs) and hydrocarbons (updated from [START_REF] Trozzi | Environmental impact of port activities[END_REF].

Table 4: Model results with traffic size and specialization

Cruise shipping is one notable cause of PM2.5 emissions [START_REF] Lloret | Environmental and human health impacts of cruise tourism: a review[END_REF], which increased by 25% between 2019 and 2023 in Europe, compared with 9% in SOx and 18% in NOx emissions [START_REF] Day | Cruise ship air pollution around ports is getting worse[END_REF]. The EU has made it mandatory for Member States to install shore power facilities in ports by 2025. There are many initiatives in several port cities: cold ironing for ferries (Gothenburg, Hamburg), cruise liners (Amsterdam, Barcelona, Marseille, Le Havre, Livorno), passenger service vessels (Oslo, Venice), barges and other cargo vessels (Antwerp) [START_REF] Bergqvist | Green Ports. Inland and Seaside Sustainable Transportation Strategies[END_REF]. As underlined by [START_REF] Iris | A review of energy efficiency in ports: operational strategies, technologies and energy management systems[END_REF], cold ironing can have a crucial role given that numerous passengers stay onboard large cruise ships during hoteling.

When it comes to health, total traffic accentuates mortality and life expectancy for large regions, while it accentuates mortality and reduces life expectancy for smaller regions, which is a reasonable result since populations in small regions are more exposed to ports. Average turnaround time increases mortality and decreases life expectancy, which is also conform with experience. GVA per capita and population density increase life expectancy, but for mortality the results are opposed between large and small regions. This indicates that economic development may promote environmental awareness and medical levels, thereby improving health. Another important result is that GHG emissions generally reduce life expectancy, and increase mortality in large regions only.

All traffic types lower both mortality and life expectancy in large regions, while for small regions, bulks (solid and liquid) increase mortality. The same goes for container traffic, the only category to lower life expectancy in small regions. Thus, and based on the literature, the role of specific transport chains seems to be more apparent at a thinner geographic scale.

Towards a typology of port regions

General trends

A factor analysis provides a global view of all regions and variables (Figure 2).

Interestingly, the scatter plot of variables along the two main factor sis highly similar between large and small regions. It is important, as it demonstrates the quality and robustness of data and trends, which are stable across geographic scales. Groups of variables emerge, like in the upper-right quadrant with total traffic, container share, GDP per capita, and ATT, together with GHG emissions and population density. This confirms that container traffic concentrates in large port-city regions as key nodes in the supply chain notably from the demand side [START_REF] Ducruet | Regions and material flows: investigating the regional branching and industry relatedness of port traffics in a global perspective[END_REF]. PM2.5 concentration, especially for small regions, is also projected on the right/positive side of the first axis (horizontal), thereby comforting this profile of "port metropolis".

Natural elements only have a marginal role on pollution and health in the figure. In terms of health, mortality rate and life expectancy are opposed in a logical manner.

Moreover, mortality is close to liquid and solid bulks in the upper-left quadrant.

Although there is no possibility to establish a causal relationship, such a result confirms that bulks produce VOCs during cargo handling (coal, grain, ores, oil) that spread throughout the city's atmosphere and get mixed with urban pollution. Without protection, conveyor belts carrying coal or iron ore between port and plants provoke leaks and emissions during loading and unloading. For tankers, VOCs (methane and nonmethane) contribute to GHG emissions. Among them, the heavier components (nonmethane) contribute to photochemical oxidants like ozone, which affects human health, food production, and the environment.

Despite intermodalism permitted by containerization, container traffic generates important flows of heavy-duty vehicles within the port, across the city, and with the hinterland. In Europe, 75% of cargo flows occur by road (Eurostat, 2019), due to the geographic, logistical, and political difficulties implementing a modal shift towards short-sea shipping. These flows generate congestion, against which it is possible to fight through the use of various systems to track trucks and better regulate traffic, but also booking systems, automated door systems, as well as inter-terminal barge or rail shuttles [START_REF] Gonzalez-Aregall | A global review of the hinterland dimension of green port strategies[END_REF]. For inland navigation, modal shift is an important option, but also the bypass of urban areas with a dedicated freight line or underground freight transport (Visser, 2018). At container terminals, "green concessions" (Notteboom and Lam, 2018) between port and operators may include modal split obligations to favor green modes (van den Berg and de Langen, 2014).

Average ship turnaround time (ATT) is close to total traffic and GHG emissions in a logical way, since the bigger the demand (population density, GVA per capita), the bigger the traffic and pollution. This explains the launch of automated mooring systems to reduce ATT, during which ships continue to burn fuel. In the case of ro-ro terminals, [START_REF] Alamoush | Ports' technical and operational measures to reduce greenhouse gas emission and improve energy efficiency: a review[END_REF] estimated that such systems allow to reduce CO2 emissions due to mooring by 97%. In addition, berth allocation and planning can also contribute to lower ATT. According to Styhre and Winnes (2019), this reduction applies well to containerships, which operate on a regular basis contrary to bulk ships (Styhre et al., 2017).

Clusters of port regions

The great similarity of our results for small and large regions made it possible to categorize them in the same way, regardless of tiny differences (Table 5). We define "metropolitan port regions" the ones with the lowest mortality rate and highest life expectancy, while they rank high for population density and GDP per capita. They carry the largest traffic volumes and specialize in the most valued traffic, i.e., containers, far ahead other regions. Their ATT is the longest, probably due to their role as market concentrations and important settlements, and they have the highest average number of regions belonging to an ECA zone.

At the opposite side of the coin, "industrial port regions" have the most important GHG emissions and mortality rates, together with the lowest life expectancy. They do handle important traffic volumes, but this traffic is mainly composed of solid and liquid bulks, i.e., lower-valued and more polluting traffic. What is more, such regions are not so much part of ECA zones, given their lowest score in this category. Industrial port regions are also characterized by a low population density, given the location of plants and factories away from major urban settlements. They rank relatively high for GDP per capita given their role as transformation and production centers. These two regional types can both be considered "critical" for two main reasons. First, it is important to note that be they small or large, metropolitan port regions score only slightly under industrial ones in terms of pollution; they even exceed them for PM2.5 concentration when considering small spatial units. Thus, while environmental impacts should be more severe in industrial regions, a lot more population is exposed to pollution in metropolitan port regions due to high density. This is particularly salient when considering that container traffic reinforces congestion within and across large agglomerations.

( (1) highest values for each regional scale / indicator are in bold and italics

(2) location quotient (LQ)8 , natural logarithm (LN), share (%), raw number (RN)

Between those two types, intermediate port regions do not witness a specific profile.

They rank high only for a few variables, such as passenger and vehicle traffic. More importantly, they have the lowest GHG and PM2.5 emissions, traffic volume, GDP per capita, and ATT of all regions. Given their low population density, it is possible to infer that such a profile corresponds to peripheral regions using passenger transport to connect with the "core" regions. However, their relatively high score for mortality may be related to a specific activity like cruise shipping. Compared with other regions, this also means that health impacts are clearly associated with the concentration of populations and economic activities. The following cartography allows us to identify which regions compose these clusters on the map, and possible spatial regularities. For small regions (Figure 4), data was available only for parts of Europe, New Zealand, and Japan. This explains at least in part the country bias whereby most industrial port regions concentrate in Japan. The rest of Japan is composed of metropolitan port regions situated along the so-called megalopolis from Fukuoka to Tokyo. Such a pattern for Japan is likely to be explained by the ageing population, which accentuates mortality rates outside of the megalopolis.

In Europe, the industrial port region with the maximum traffic is Alejento in Portugal, with the port of Sines having developed a container hub in 2004 out of a heavy industrial growth pole. Most traffic goes to metropolitan regions, such as Marseille-Fos (Bouchesdu-Rhône), Le Havre and Rouen (Seine-Maritime), France's two largest industrial and container ports. Other cases include Gothenburg (Västra Götaland), Malmö and Stockholm in Sweden, Tallinn in Estonia, and Klaipeda in Lithuania. Italy concentrates a sheer number of metropolitan port regions, containing the large ports of Genoa, Savona and La Spezia (Liguria), but also Lazio (Civitavecchia), Naples and Salerno.

Discussion and conclusion

This research provides the first-ever empirical analysis of the between port activities, environment, and health from an international perspective. A thorough review of the existing literature revealed that only a few studies actually measured the health impacts of ports (and their industrial areas) at the local level, compared with studies of environmental impacts. This work is challenging due to the fact that it does not measure actual port pollution, but rather, considers the presence of port(s) and the level and diversity of port activities. Local measures of pollution are, in turn, not specific to ports, as they encompass the whole territory around the port rather than the port itself. Finding a link between port activities and local pollution/health thus makes the study successful in many ways.

By putting together data from the OECD and the Lloyd's List at the level of subnational regions, main results confirm that port regions pollute more than non-port regions, in particular for GHG emissions. The analysis based on the port dummy confirms that the presence of port(s) increases GHG emissions but not PM2.5 emissions, mainly due to winds. Beyond the port dummy, traffic size and longer ship turnaround time increase pollution, in accordance with expectations. Belonging to an Emission Control Area (ECA) lowers local pollution as predicted, a trend which is valid at both territorial levels.

The analysis of pollutions (GHG and PM2.5) together with traffic volume and traffic types corroborate practice in many ways, as GHG emissions increase mortality in all cases, and PM2.5 lowers life expectancy, although it is not proved that such pollutions come from the port itself. It is one future task of further research to complement traffic with ship pollution data, at the condition that we access additional information on ship engines and fuel types.

This research detected similar types of regions at both territorial levels, small and large regions, thereby confirming the robustness of data and spatial patterns. The class of "metropolitan port regions" depicts the concentration of population, socio-economic activities, traffic volume (notably containers), and GHG emissions. Such regions also witness the lowest mortality rates and often situate within Emission Control Areas (ECAs), namely in Europe and North America. They stand in direct opposition with "industrial port regions", which specialize in bulk traffic, have the worst sanitary scores, and pollute the most. Such a category includes Australian mining regions and U.S.

regions specialized in the oil and agri-food business (Gulf of Mexico and Great Lakes / Midwest). The "intermediary port regions" stand in between with no particular profile except from a specialization in vehicle and passenger traffic.

The main implication of those findings is that the port factor is an essential component of local socio-economic activity, pollution, and public health despite the high level of aggregation (i.e., subnational regions) and the administrative -rather than functionalnature of the spatial units under consideration. Given the limited literature on ports and health, and the fact that over 80% of world trade volumes are carried via sea transport, this calls for further research in this particular field, which is still small and scattered.

Three main directions for improvement are proposed to refine and deepen current results.

First, the population under study may be described in more detail. One possibility is to look at social fragility and deprivation [START_REF] Allen | From suspicious illness to policy change in petrochemical regions: Popular epidemiology, science, and the law in the U.S. and Italy[END_REF]. But related data like the unemployment rate in particular was not available across the whole OECD area. This dimension is important, as the social and economic insecurity engendered by port development concerns above all the precarious classes (De Lara, 2018), and the impact of air pollution is larger among the poorest [START_REF] Suarez-Castillo | Air pollution and health: causal approaches and inequalities[END_REF]. As health indicators are very sensitive to the age structure of population, their decomposition by age groups would be a prerequisite to better check the impact of air pollution. Data about the access to and availability of medical healthcare, such as the number of doctors and hospital beds, would greatly enhance the analysis.

Second, Lloyd's List Intelligence data on vessel movements may be combined with engine and fuel type data to calculate actual port/shipping pollution and compare it with OECD figures. As more precise pollution and health data is provided by the OECD, we shall also run separate analyses by GHG emission source (i.e., transport in general, road transport, and industry) and by cause of mortality (i.e., respiratory system, circulatory system, and transport). Port activities can be further disaggregated by ship types to have a clearer view of traffic specialization (i.e., crude oil, chemicals, tanker, general cargo, port services, cruise, ferries, etc.).

Third, another avenue of research is to work at the level of metropolitan areas. The OECD metropolitan database includes socio-economic and environmental indicators at this particular level, which is more functional than the administrative region. This shall make it possible to integrate new variables on port city topography and morphology for instance, wind direction, and use data on urban congestion, such as the Tom-Tom Index 9 . At this level, information on environmental-friendly measures and equipment (ISO certifications, cold ironing, modal split) can be made available through a survey towards the relevant local authorities.

Figure 1 :

 1 Figure 1: Comparison of port and non-port regions, 2001-2018

Figure 2 :

 2 Figure 2: Factor analysis and classification in 2018 N.B. 245 large regions (left) and 164 small regions (right)

Figure 3 :

 3 Figure 3: Typology of large port regions in 2018

Figure 4 :

 4 Figure 4: Typology of small port regions in 2018

  .

Table 1 : Comparison between environmental and health studies in a port context

 1

Table 2 : List of regional variables

 2

Table 5 : Results of the hierarchical clustering analysis, 2018

 5

https://cds.climate.copernicus.eu/

This specific analysis is applied to France, Italy, New Zealand, and Portugal only.

Location quotient: regional share / national share was used to avoid the country bias when comparing regions.

Acknowledgements

This research received funding from the Agence Nationale de la Recherche (ANR -French National Agency for Research) via the research project MAGNETICS (Maritime Globalization, Network Externalities, and Transport Impacts on Cities).

Authors would like to thank Nadine Levratto, Messaoud Zouikri, Magali Dumontet (Paris-Nanterre University), and Florence Jusot (Paris School of Economics) for their very useful comments.