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In the context of climate change with increasingly pronounced impacts, year 2022 in France has been the warmest year ever observed. It has been the case more specifically during July, when a severe heatwave occurred across North-Western Europe. Sea-level temperature anomalies jumped over +12°C, especially in the Western half of France, pushing back all-time records. Associated to extreme temperature occurred a severe drought, with long-lasting precipitation deficit throughout the year, which was amplified during July. With around 80% deficit, July 2022 in France has also been the driest ever recorded. These singular meteorological conditions were therefore a fertile ground for forest fires. Around 70 000 ha of forest have burned in France during 2022. The South-West region has been particularly impacted during July 2022, as well as other areas which are not usually subject to this kind of events (Brittany, Center, Paris region). During July 2022 occurred the ACROSS field campaign within the Paris region, where several sites following a South-West to North-East transect provided comprehensive characterization of atmospheric composition. Namely Rambouillet station (forest, SW of Paris), SIRTA (peri-urban, SW of Paris), PRG (urban, Paris center) and Chatelet Les Halles (urban, Paris center). These sites were equiped with state-of-the-art instrumentations to characterize aerosols and reactive gases. On July 19th, an intense biomass burning plume went through the Paris region, with PM10 concentrations reaching more than 150µg/m3. The experimental effort during that period is therefore a unique asset in order to characterize the composition of this episode. Most of the sites, during that episode, record high concentrations of carbonaceous aerosols (organic matter and black carbon) and Volatile Organic Compounds tracers of biomass burning (eg acetonitrile, benzene, toluene). Temporality of the episode, atmospheric dynamics and air mass pathways, suggest the transport of a biomass burning plume from South-Western France, more than 600km away from Paris. However, aerosol size distribution surpringly reveals the influence of local fires occuring near some of the sites, at almost the same time. This work is therefore focusing on the different properties of different plumes mixing at the same time over a densely urbanized region. These differences can be highlighted by source apportionment, combined with size distribution, as well as oxydation state of organic aerosols.

International audience

Biosphere-atmosphere interactions play a key role in urban chemistry because of biogenic volatile organic compound (BVOC) emissions. Of the BVOC, isoprene is the most emitted compound; however, it also has anthropogenic origins in urban areas. In this study, we aimed to investigate the spatio-temporal variability and atmospheric impacts of biogenic and anthropogenic isoprene in the subtropical megacity of São Paulo (MASP), Brazil. Several measurement campaigns were conducted in three different urban Atlantic forests (Matão, PEFI, and RMG), and an urban background site (IAG); this equated to a total of 268 samples for the 2018-2019 period. For all sampling points, daytime average concentrations of isoprene were two to three times higher during the rainy season (IAG: 1.75 ± 0.93 ppb; Matão: 0.87 ± 0.35 ppb; PEFI: 0.50 ± 0.30 ppb; RMG: 0.37 ± 0.18 ppb), than those observed during the dry season (IAG: 0.46 ± 0.24 ppb; Matão: 0.31 ± 0.17 ppb; PEFI: 0.17 ± 0.11 ppb; RMG: 0.11 ± 0.07 ppb). Average isoprene concentrations were similar to those observed in other places worldwide, with the exception of the Amazon forest. Our results indicate differences in isoprene concentrations between sites, suggesting that environmental conditions such as the urban heat island and vegetation types, may play a role in spatial variability. Estimates of the isoprene fraction indicated that the biogenic fraction (85%) surpassed the anthropogenic fraction during the rainy season. By contrast, the anthropogenic fraction (52%) exceeded the biogenic fraction during dry periods. These fractions have an impact on potentially forming secondary pollutants gaseous (ozone formation potential: 7.19-33.32 μg m

We present here the results obtained during an intensive field campaign conducted in the framework of the French “BIO-MAÏDO” (Bio-physico-chemistry of tropical clouds at Maïdo (Réunion Island): processes and impacts on secondary organic aerosols’ formation) project. This study integrates an exhaustive chemical and microphysical characterization of cloud water obtained in March–April 2019 at Reunion Island (Indian Ocean). Fourteen cloud samples have been collected along the slope of this mountainous island. A comprehensive chemical characterization of these samples is performed, including inorganic ions, metals, oxidants, and organic matter (organic acids, sugars, amino acids, carbonyls, and low-soluble volatile organic compounds (VOCs)). Cloud water presents high molecular complexity with elevated water-soluble organic matter content partly modulated by microphysical cloud properties. As expected, our findings show the presence of compounds of marine origin in cloud water samples (e.g., chloride, sodium) demonstrating ocean–cloud exchanges. However, the non-sea salt fraction of sulphate varies between 38 and 91 %, indicating the presence of other sources. Also, the presence of amino acids and for the first time in cloud waters of sugars, clearly indicates that biological activities contribute to the cloud water chemical composition. A significant variability between events is observed in the dissolved organic content (25.5 ± 18.4 mgC L−1), with levels reaching up to 62 mgC L−1. This variability was not similar for all the measured compounds, suggesting the presence of dissimilar emission sources or production mechanisms. For that, a statistical analysis is performed based on back-trajectory calculations using the CAT (Computing Atmospheric Trajectory Tool) model associated with land cover registry. These investigations reveal that air mass origins and microphysical variables do not fully explain the variability observed in cloud chemical composition, highlighting the complexity of emission sources, multiphasic transfer, and chemical processing in clouds. Additionally, several VOCs (oxygenated and low-soluble VOCs) were analysed in both gas and aqueous phases. Significant levels of biogenic low-soluble VOCs were detected in the aqueous phase, indicating the cloud-terrestrial vegetation exchange. Cloud scavenging of VOCs is assessed and compared to Henry’s law equilibrium to evaluate potential super or sub saturation conditions. The evaluation reveals the supersaturation of low-soluble VOCs from both natural and anthropogenic sources. Our results depict even higher supersaturation of terpenoids, suggesting their importance in the aqueous phase chemistry in highly impacted tropical areas.

International audience; Road transport is a major source of anthropogenic emissions especially in the Middle East where the regulations enforcement is generally poor. This study aims to quantify the Emission Factors (EF) of traffic-related gaseous and particulate pollutants inside the Salim Slam urban tunnel in Beirut, Lebanon. The fuel-based emission factors of measured pollutants were from the carbon mass balance model. The EF determined showed general higher values than those reported in recent studies from European and American countries, even for speciated NMVOC. The average CO and NOx emission factors for the mixed fleet (HDV + LDV) were determined to be 10.52 ± 3.00 g km−1 and 2.20 ± 0.57 g km−1 respectively, while the EF for PM2.5 55 ± 27 mg km−1. Moreover, IVOC species from gaseous phase were reported for the first time in the region. A reduction trend was observed in comparison with the previous tunnel study from Lebanon, however there is still a need to have tougher regulations to control the local practices such as removal of catalytic converter, adjustment of engine parameters for inspection, etc. The comparison of the EF to those calculated through EMEP or IPCC methodologies shows the need to take local practices while establishing national emission inventories.

Cloud droplets are able to trap many gaseous compounds and represent a very reactive media in the atmosphere. However, phase-partitioning of Volatile Organic Compounds (VOCs) between gaseous phase (interstitial air) and atmospheric liquid phase (cloud droplets) is still poorly characterized. In the present work, air samples and cloud water were collected simultaneously and hydrophobic organic compounds from anthropogenic and biogenic origins were quantified in order to evaluate their air/water partitioning. For this, cloud events were sampled at the puy de Dome station (PUY). A new analytical approach was optimized to explore dissolved VOCs in the aqueous phase by Stir Bar Sorptive Extraction (SBSE) and gaseous samples were collected using sorbent tubes. All samples were analyzed by Thermal Desorption (TD) Gas Chromatography (GC) coupled with Mass Spectrometry (MS). Extraction efficiencies by SBSE vary between 22% and 97% and the detection limit of VOCs in aqueous cloud samples lies between 1.0 and 8.7 ng L−1. Experimental partitioning is evaluated towards the theoretical one described by the Henry's Law constants. Our results show that observed concentrations of hydrophobic VOCs are supersaturated by a factor of 10–103 in comparison with Henry's law equilibrium. Calculations have been performed to evaluate the potential role of adsorption at the air/water interface and of sorption with non-dissolved organic carbon. However, the supersaturation in the cloud droplets requires more laboratory experiments to understand processes at the air/water interface and constrain cloud chemistry models.

The puy de Dôme (pdD) altitude research station is located in the centre of France (45° 46' N, 2° 57' E, 1465 m altitude a.s.l), 16 km from the town of Clermont-Ferrand. This station is a global GAW station (PUY), and is part of the ACTRIS-2 integrating activities (H2020). Long series of meteorological parameters such as wind speed and direction, temperature, pressure, relative humidity and radiation, atmospheric trace gases (O3, NOx, SO2, CO2, CO), and physical, optical and chemical properties of aerosols (particle size, black carbon, mass,..) are available.Cartridge sampling measurements are performed to link the observations of volatile organic compounds (VOCs) within ACTRIS and GAW. A selection of VOCs, including a large set of non-methane hydrocarbons and some terpenes (isoprene, α-pinene), was measured during summer 2010, spring and summer 2011, winter 2012, summer and winter 2013, summer 2015, and twice a week in 2017, 2018 and 2019. The analysis of VOCs collected off-line on Tenax/Carbosieve III or Tenax TA cartridges was carried out using gas chromatography coupled with thermo-desorption with mass spectrometry (GC-MS).In August 2018, a new gas chromatography (GC-FID) system was installed at the station. It allows the acquisition of non-methane hydrocarbons (C5-C10) with a temporal resolution of two hours.The reactive gas measurement series are analysed in terms of observed levels (i), diurnal and seasonal variability (ii), air mass origins (iii) and sources of these gaseous pollutants (iv).(i) The level observed at the PUY station is discussed and compared with two other stations: Monte Cimone (mainly in the free troposphere) and Hohenpeissenberg (mainly in the planetary boundary layer PBL).(ii) As the height of the PBL changes with a diurnal cycle and with the seasons, the PUY station is in the different layers of the troposphere during the year impacting the measured concentrations.(iii) In order to determine the transport pathways of the air masses before their arrival at the pdD site, the HYSPLIT (Hybrid Single Particle Lagrangian Trajectory) model was used. Trajectories were classified according to their predominant transport direction prior to measurement, either continental (C), marine (M), modified marine (Mod), Mediterranean (Med), or mixed according to their trajectories. In order to determine the influence of wind direction, the pollution wind rose was determined for the main pollutants.(iv) Comparison with temperature, air mass origins, boundary layer height are used to identify the main parameters influencing the variability of VOCs. The Principal Component Analysis (PCA) has been performed to deduce correlations between the main atmospheric species and their main determinants.

In South America, the observations of atmospheric pollutants are deficient, and few cities have implemented air quality monitoring programs. In addition, Volatile Organic Compounds (VOCs) observations are still missing, and little is known about their contributions to the atmospheric composition and impacts in a large ethanol usage context like Brazil. Here, we present a wide range of VOCs that have been measured for ten years in Sao Paulo Megacity (SPM) in different campaigns at traffic, urban and background sites. When compared with other cities worldwide, the average VOCs ambient concentrations in SPM were higher by factors of 2 to 10. However, the ambient VOCs distribution among these cities is homogeneous even for ethanol, aldehydes and alkenes species. Emission ratios (ER) were established related to carbon monoxide and acetylene, which did not depict strong seasonal and interannual variability in SPM. When compared with previous studies, ERs showed an enrichment from road-tunnel to background, suggesting the presence of other sources than traffic. A good agreement in ER was found with Los Angeles and Paris; but limited consistencies with Middle East and Asia cities. Our ethanol measurements show that contrasted ER can be obtained depending on the emission process involved, with a strong impact of evaporation on ethanol concentrations. The multiyear acetaldehyde analysis displayed that ER could be a valuable metric to assess the long-term changes in emissions sources. Finally, VOCs emissions were calculated from ER and compared with those estimated by the global emission inventory (Edgar). The total VOC emissions estimated by the global inventory agree very well with those from our observations up to 75%. Nevertheless, the VOCs speciation is misrepresented in the inventory, mainly for oxygenated and heavier alkanes compounds. These inconsistencies will also have an impact on the quantification of secondary atmospheric pollutants formation associated to road transport emissions.

Objective The poor outdoor air quality in megacities of the developing world and its impact on health is a matter of concern for both the local populations and the decision-makers. The objective of this work is to quantify the mortality attributable to long-term exposure to PM2.5, NO 2 , and O 3 in Greater Cairo (Egypt). Methods We analyze the temporal and spatial variability of the three pollutants concentrations measured at 18 stations of the area. Then, we apply the method recommended by the WHO to estimate the excess mortality. In this assessment, three different shapes (log-linear, linear, and log-log) of the concentration-response functions (CRF) are used. Results With PM2.5 concentrations varying from 50 to more than 100 µg/m 3 in the different sectors of the megacity, the spatial variability of this pollutant is found to be one important cause of uncertainty on the excess mortality associated with it. Also important is the choice of the CRF. With the average (75 µg/m 3 ) PM2.5 concentration and the most favorable log-log shape of the CRF, 11% (CI, 9–14%) of the non-accidental mortality in the population older than 30 years can still be attributed to PM2.5, which corresponds to 12520 (CI, 10240–15930) yearly premature deaths. Should the Egyptian legal 70 µg/m 3 PM10 limit (corresponding to approximately 37.5 µg/m 3 for PM2.5) be met, this number would be reduced to 7970, meaning that 4550 premature deaths could be avoided each year. Except around some industrial or traffic hot spots, NO 2 concentration is found to be below the 40 µg/m 3 air quality guideline of the WHO. However, the average concentration (34 µg/m 3 ) of this gas exceeds the stricter 10 µg/m 3 recommendation of the HRAPIE project and it is thus estimated that from 7850 to 10470 yearly deaths can be attributed to NO 2 . Finally, with the ozone concentration measured at one station only, it is found that, depending on the choice of the CRF, between 2.4% and 8.8% of the mortality due to respiratory diseases can be attributed to this gas. Conclusion In Greater Cairo, PM2.5 and NO 2 constitute major health risks. The best estimate is that in the population older than 30 years, 11% and 8% of the non-accidental mortality can be attributed to these two pollutants, respectively.

We performed a case study of the organic aerosol (OA) budget during the MEGAPOLI campaign during summer 2009 in Paris. We combined aerosol mass spectrometer, gas-phase chemistry and atmospheric boundary layer (ABL) data, and applied the MXL/MESSy column model. We find that during daytime, vertical mixing due to ABL growth has opposing effects on secondary organic aerosol (SOA) and primary organic aerosol (POA) concentrations. POA concentrations are mainly governed by dilution due to boundary layer expansion and transport of POA-depleted air from aloft, while SOA concentrations are enhanced by entrainment of SOA-rich air from the residual layer (RL). Further, local emissions and photochemical production control the diurnal cycle of SOA. SOA from intermediate volatility organic compounds (fSOA-iv) constitutes about half of the locally formed SOA mass. Other processes that previously have been shown to influence the urban OA budget, such as aging of semi-volatile and intermediate volatility organic compounds (S/IVOC), dry deposition of S/IVOCs and IVOC emissions, are found to have minor influences on OA. Our model results show that the modern carbon content of the OA is driven by vertical and long-range transport, with a minor contribution from local cooking emissions. SOA from regional sources and resulting from aging and long-lived precursors can lead to high SOA concentrations above the ABL, which can strongly influence ground-based observations through downward transport. Sensitivity analysis shows that modeled SOA concentrations in the ABL are equally sensitive to ABL dynamics as to SOA concentrations transported from the RL.

International audience; The relative importance of eastern Mediterranean emissions is suspected to be largely underestimated compared to other regions worldwide. Here we use detailed spe-ciated measurements of volatile organic compounds (VOCs) to evaluate the spatial heterogeneity of VOC urban emission composition and the consistency of regional and global emission inventories downscaled to Lebanon (European Monitoring and Evaluation Programme, EMEP; Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP; and MACCity, Monitoring Atmospheric Composition and Climate and megaCITY Zoom for the Environment). The assessment was conducted through the comparison of the emission ratios (ERs) extracted from the emission inventories to the ones obtained from the hourly observations collected at a suburban site in Beirut, Lebanon, during summer and winter ECOCEM (Emissions and Chemistry of Organic Carbon in the Eastern Mediterranean) campaigns. The observed ERs were calculated using two independent methods. ER values from both methods agree very well and are comparable to the ones of the road transport sector from near-field measurements for more than 80 % of the species. There is no significant seasonality in ER for more than 90 % of the species, unlike the seasonality usually observed in other cities worldwide. Regardless of the season, ERs agree within a factor of 2 between Beirut and other representative cities worldwide , except for the unburned fuel fraction and ethane. ERs of aromatics (except benzene) are higher in Beirut compared to northern post-industrialized countries and even the Middle Eastern city Mecca. The comparison of the observed ER to the ones extracted from the ACCMIP and MACCity global emission inventories suggests that the overall speciation of anthropogenic sources for major hydrocarbons that act as ozone and secondary organic aerosol (SOA) precursors in ACCMIP is better represented than other species. The comparison of the specific road transport ERs, relative to acetylene derived from near-field measurements, to ERs from ACCMIP and EMEP emission inventories for the road transport sector showed that ERs of more reactive species are usually consistent within a factor of 2 with EMEP, while xylenes and toluene are underestimated by over a factor of 2 by ACCMIP. The observed heterogeneity of anthropogenic VOC emission composition between Middle Eastern cities can be significant for reactive VOCs but is not depicted by global emis-Published by Copernicus Publications on behalf of the European Geosciences Union. 194 T. Salameh et al.: Composition of gaseous organic carbon during ECOCEM in Beirut, Lebanon sion inventories. This suggests that systematic and detailed measurements are needed in the eastern Mediterranean Basin in order to better constrain emission inventory.

For the last twenty-five years, CO-PDD (Cézeaux-Aulnat-Opme-puy de Dôme) has evolved to become a full instrumented platform for atmospheric research. It is nationally accredited by CNRS, the French national center for scientific research, and recognized as a global station in the GAW network (Global Atmospheric Watch). It is a reference site of the European and national research infrastructures ACTRIS (Aerosol Cloud and Trace gases Research Infrastructure) and ICOS (Integrated Carbon Observing System). The site located on-top of the puy de Dôme mountain (1465 m a.s.l.) is completed by additional sites located at lower altitudes and adding the vertical dimension to the atmospheric observations: Opme (660 m a.s.l.), Cézeaux (410 m) and Aulnat (330 m). On the sites has been developed a unique combination of in-situ and remote sensing measurements capturing and documenting the variability of particulate and gaseous atmospheric composition, but also the optical, biochemical and physical properties of aerosol particles, clouds and precipitations. Given its location far away from any major emission sources, its altitude and the mountain orography, the puy de Dôme station is ideally situated to sample different air masses in the boundary layer or in the free troposphere depending on time of day and seasons. It is also an ideal place to study cloud properties with frequent presence of clouds at the top in autumn and winter. As a result of the natural conditions prevailing at the site and of the very exhaustive instrumental deployment, scientific studies at puy de Dôme strongly contribute to improving the knowledge in atmospheric sciences including the characterization of trends and variability, the understanding of complex and interconnected processes (microphysical, chemical, biological, chemical and dynamical) and providing a reference point for climate models. In this context, CO-PDD is a pilot site to conduct instrumental development inside its wind tunnel for testing liquid/ice cloud probes in natural conditions, or in-situ systems to collect aerosol and cloud. This paper reviews 25 years (1995–2020) of atmospheric observation at the station, and related scientific research contributing to atmospheric and climate science.

Several field campaigns were deployed in the framework of the project Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) to measure a broad range of atmospheric constituents. Here, we present the analysis of an unprecedented and comprehensive dataset integrating up to fifty-six VOC from ambient sites and emission sources. VOCs were collected on sorbent tubes in the coastal city of Abidjan, Côte d'Ivoire, in winter and summer 2016 and analysed by gas chromatography coupled with flame ionization and mass spectrometer detectors (GC-FID and GC-MS) at the laboratory. The comparison between VOC emission source profiles and ambient profiles suggests the substantial impact of two-wheelers and domestic fires on the composition of Abidjan's atmosphere. However, despite the high VOC concentrations near-source, moderate ambient levels were observed (by a factor of 10 to 4000 lower) and similar to the ones observed in northern mid-latitude urban areas. Beyond photochemistry, reported high wind speeds suggest that meteorology is an essential factor that regulates air pollution in Abidjan. Emission ratios (ΔVOC / ΔCO) were established based on real-world measurements achieved on a selected number of representative combustion sources. Maximal molar mass contributions were observed from two-wheeler (TW) emissions, overpassing other regional sources by two orders of magnitude. This source also largely governs the VOC atmospheric impacts in terms of OH reactivity, secondary aerosol formation (SOAP) and ozone production (POCP). While the contribution of aromatics dominates the atmospheric impact, our measurements reveal the systematic presence of anthropogenic terpenoids in all residential combustion sectors. Finally, emission factors were used to retrieve and quantify VOC emissions from the main anthropogenic source sectors at national level. Our detailed VOC emissions estimation suggests that the road transport sector is the dominant source in Cote d'Ivoire by emitting around 1200 Gg yr−1 of gas-phase VOCs. These new estimations are 100 and 160 times larger than previous global inventory estimations like MACCity or Edgar (v4.3.2). Additionally, the residential sector is also largely underestimated by a factor of 13 to 43. For the only Cote d'Ivoire, these new estimates for VOCs are three to six times higher than the whole Europe. Given the significant underestimation of VOC emissions from transport and residential sectors for Côte d'Ivoire country there is an urgent need for such an effort in the whole West Africa region for building more realistic and region-specific emission inventories. This is not only true for VOCs but all atmospheric pollutants. The dearth of waste burning, fuelwood burning and charcoal representation in regional inventories need also to be addressed, particularly in low-income areas where these types of activities are essential sources of VOC emissions.

In the framework of the TRANSport Emissions and Mitigation in the East Mediterranean (TRANSEMED/ChArMEx) program; Volatile Organic Compound (VOC) measurements were performed for the first time in Istanbul (Turkey) at an urban site in September 2014. One commercial gas-chromatograph coupled to a flame ionization detector (GC-FID) and one proton transfer mass spectrometer (PTR-MS) were deployed. In addition, sorbent tubes and canisters were implemented within the megacity close to major emission sources. More than 70 species including non-methane hydrocarbons (NMHC), oxygenated VOCs (OVOC) and organic compounds of intermediate volatility (IVOC) have been quantified. Among these compounds, 23 anthropogenic and biogenic species were continuously collected at the urban site. VOC concentrations show a great variability with maxima exceeding 10 ppb (i.e. n-butane, toluene, methanol, and acetaldehyde) and mean values between 0.1 (methacrolein + methylvinylketone) to 4.9 ppb (methanol). OVOC represents 43.9 % of the total VOC concentrations followed by alkanes (26.3 %), aromatic compounds (20.7 %), alkenes (4.8 %), terpenes (3.4 %) and acetonitrile (0.8 %). However, on average, the atmospheric composition of anthropogenic alkanes and aromatics is similar to the ones of European megacities like Paris and London, suggesting the impact of traffic emissions for those compounds. Unusual diurnal profiles of anthropogenic VOC, different from the one of traffic derived products like NOx, reveal the complex interaction between emissions and meteorology. Multiple evidences of the impact of sources other than traffic like industrial activities under continental and south–southwesterly wind regimes or ship emissions on IVOC loads was found. Five factors have been extracted from the PMF model (EPA/PMF 5.0) and have been compared to source profiles established by near-field measurements and other external variables (meteorological parameters, NOx, CO, SO2 ...). Surprisingly, road transport is not the dominant source by only explaining 15.8 % of measured VOC concentrations contrary to the local emission inventory. Other factors are toluene from solvent use (14.2 %), biogenic terpenes (7.8 %), natural gas evaporation (25.9 %), composed of butanes, and a last factor characterized by mixed regional emissions and composed of most of the species (36.3 %). The PMF results point out the influence of industrial emissions while there is no clear evidence of the impact of ship emissions on the measured VOC distribution. One reason might be the absence of IVOC in the input matrix; these compounds should be considered in future studies dealing with coastal urban areas. The sensitivity of PMF results on input data (time resolution, meteorological period, peak episode, uncertainty) was tested. While some PMF run are statistically less performant than the reference run, sensitivity tests show that same factors (number and type) are found with slightly different factor contributions (up to 15 % of change). Finally, the emission ratios (ER) of VOC relative to carbon monoxide (CO) were established. These ratios are consistent with those observed in Los Angeles within a factor of 2. These ER and the road transport factor from PMF were used to estimate VOC emissions and to evaluate three downscaled global emissions inventories (EDGAR, ACCMIP and MACCity). It was found that OVOC emissions were underestimated by a factor of 10 to 26 depending on the inventory. NMHC emission estimations were most of the time within the same range or overestimated by a 3 to 26-fold. In the road transport emission evaluation, EDGAR inventory was found to be better than ACCMIP inventory with most of the compounds within a range of 3 except for Like in TRANSEMED–Beirut (Lebanon), our work stresses the inadequacy of global emission inventories in the East Mediterranean and discrepancies between emission inventories themselves. There is an urgent need to better represent VOC emissions in this region including non-traffic sources, OVOC and lower volatility organic compounds. VOC emissions are expected to be much larger than expected and larger than Europe and North America.

Egypt, located in the Middle East and North Africa region, is considered to be a potential hot-spot of climate change where the warming and increase of the frequency of extreme temperatures could occur faster than at global scale. Precipitation is also expected to decrease in the region. In this work, our aim is to quantify the past and future temperature and precipitation trends at 8 locations selected for being representative of the variety of Egyptian climates. For the past period (1950–2017), we show that the decadal temperature trends derived from the analysis of the assimilated ERA-Interim (ERA-Int) and downscaled CORDEX (Historical and Evaluation) data are consistent. Relative to 1960, the daily maximal and minimal temperatures have increased by 1.3 ± 0.1 and 1.3 ± 0.3 °C, respectively, at the 8 selected locations. However, at the shorter yearly time scale, sub-regional differences of climate variability can be evidenced: this variability is less at the coastal and Nile Delta sites than at the drier inland locations. For the future, we use an ensemble of 6 CORDEX Africa models. Under the RCP45 scenario, the temperatures are predicted to increase at a rate ranging from 0.28 ± 0.04 °C/decade (Alexandria) to 0.38 ± 0.09 °C/decade (Hurghada and Aswan) between 2010 and 2040, and to abate afterwards (0.12 ± 0.08 °C/decade). Under the RCP85 scenario, the rates of temperature increase before 2040 are similar to those under RCP45 (from 0.24 ± 0.14 to 0.40 ± 0.12 °C/decade) but considerably larger afterwards (from 0.48 ± 0.18 °C to 0.72 ± 0.11 °C/decade between 2050 and 2100). As compared to the 2006–2015 reference period, the extreme temperatures analysis performed with the CLIMDEX software shows that the hot days and nights will become more frequent at all sites, but that the increase will occur at larger rates at the Red Sea (Hurghada) and upper Egypt (Aswan) sites than at the other ones. These inter-site differences are more pronounced with RCP45 than with RCP85. Considering the latter scenario, in the last decade of this century about 80% of the days in a year would be hotter than the 90th percentile of the 2006–2015 reference period. Regarding the annual precipitation, the analysis of ERA-Interim data of the 1980–2017 period does not reveal any significant trend, but in both RCP45 and RCP85 a significant decrease (from −0.48 to −0.9 mm/y, and from −0.95 to −1.40 mm/y, respectively) is predicted to occur from 2010 to 2100 in the north of Egypt where rain is currently the most abundant. Keywords: Egypt, Daily temperature trends, Extreme daily temperatures, Precipitation trends

Sao Paulo Megacity (MASP), with more than 20 million inhabitants, is among the world's most populous cities. Brazil is the only area in the world where fuel with a high ethanol content has been used since 1975 and its usage have increased in the last decade with the development of flex-fuel vehicles. Here, the biofuel effect on VOCs burden and composition it is discussed by a crossed analysis of long-term ambient data and emission data over the last decades in MASP. The most abundant NMHCs in ppbv were propane (5.02 ± 5.94), ethylene (3.97 ± 4.55), ethane (2.28 ± 1.89), acetylene (1.98 ± 2.11), 2,2,4-trymethylpentane (2.05 ± 1.48), i-propylbenzene (1.96 ± 1.85), n-butane (1.97 ± 2.24), toluene (1.62 ± 2.02), i-pentane (1.30 ± 1.61) and propylene (1.26 ± 1.54). The comparison with studies performed in MASP over the last 15 years showed a decrease in the NMHC concentration levels, in spite of the growth of the vehicular fleet and fuel consumption. Nevertheless, NMHCs mean concentrations were higher in MASP compared to those in other megacities worldwide (Beijing, London, Los Angeles and Paris) by a factor of 1.1 to 10, although showing similar composition. This suggests that NMHC distribution is dominated by traffic emissions regardless of regional characteristics like fuel usage and composition. Diurnal profiles of NMHC in MASP confirm these findings by all showing the same patterns as CO and acetylene, both recognized as combustion emission tracers. Finally large-scale ethanol usage would not affect the distribution of NMHCs in MASP and gasoline vehicular emissions seem to be the most important source of hydrocarbons in urban areas.

Long-term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel-based emission inventory approach that diverges from conventional bottom-up inventory methods explains 1970–2015 trends in NOx/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. cities demonstrates that motor vehicle emissions controls were largely responsible for U.S. urban NOx/CO trends in the past half century. Differing NOx/CO enhancement ratio trends in U.S. and European cities over the past 25 years highlights alternative strategies for mitigating transportation emissions, reflecting Europe's increased use of light-duty diesel vehicles and correspondingly slower decreases in NOx emissions compared to the U.S. A global inventory widely used by global chemistry models fails to capture these long-term trends and regional differences in U.S. and Europe megacity NOx/CO enhancement ratios, possibly contributing to these models' inability to accurately reproduce observed long-term changes in tropospheric ozone.

International audience; Measurements of 31 non-methane hydrocarbons (NMHCs) were carried out at three urban (Paris, 2003-2014, Strasbourg, 2002-2014 and Lyon, 2007-2014) sites in France over the period of a decade. A trend analysis was applied by means of the Mann-Kendall non-parametric test to annual and seasonal mean concentrations in order to point out changes in specific emission sources and to assess the impact of emission controls and reduction strategies. The trends were compared to those from three rural sites (Peyrusse-Vieille, 2002-2013, Tardière, 2003-2013 and Donon, 1997-2007). The results obtained showed a significant yearly decrease in pollutant concentrations over the study period and for the majority of species in the range of -1 to -7% in accordance with the decrease of NMHC emissions in France (-5 to -9%). Concentrations of long-lived species such as ethane and propane which are recognized as tracers of distant sources and natural gas remained constant. Compounds associated with combustion processes such as acetylene, propene, ethylene and benzene showed a significant decline in the range of -2% to -5% yr-1. These trends are consistent with those recently described at urban and background sites in the northern mid-latitudes and with emission inventories. C7-C9 aromatics such as toluene and xylenes as well as C4-C5 alkanes such as isopentane and isobutane also showed a significant decrease in the range of -3% to -7% yr-1. The decreasing trends in terms of % yr-1 observed at these French urban sites were typically higher for acetylene, ethylene and benzene than those reported for French rural sites of the national observatory of Measurement and Evaluation in Rural areas of trans-boundary Air pollution (MERA). The study also highlighted the difficult choice of a long term sampling site representative of the general trends of pollutant concentrations.

NitroMAC (French acronym for continuous atmospheric measurements of nitrogenous compounds) is an instrument which has been developed for the semi-continuous measurement of atmospheric nitrous acid (HONO). This instrument relies on wet chemical sampling and detection using high performance liquid chromatography (HPLC)-visible absorption at 540 nm. Sampling proceeds by dissolution of gaseous HONO in a phosphate buffer solution followed by derivatization with sulfanilamide/N-(1-naphthyl)-ethylenediamine. The performance of this instrument was found to be as follows: a detection limit of around 3 ppt with measurement uncertainty of 10% over an analysis time of 10 min. Intercomparison was made between the instrument and a long-path absorption photometer (LOPAP) during two experiments in different environments. First, air was sampled in a smog chamber with concentrations up to 18 ppb of nitrous acid. NitroMAC and LOPAP measurements showed very good agreement. Then, in a second experiment, ambient air with HONO concentrations below 250 ppt was sampled. While NitroMAC showed its capability of measuring HONO in moderate and highly polluted environments, the intercomparison results in ambient air highlighted that corrections must be made for minor interferences when low concentrations are measured.

International audience; Trends of long-term observations and emission inventories suggest that traffic emissions will no longer dominate the concentrations of monoaromatic compounds (i.e., TEX - toluene, xylenes, and ethylbenzene) in European urban areas. But the split limit between traffic and other emission sector contributions such as solvent use remains tenuous. Here long-term observations of an extensive set of hydrocarbons, including TEX, at traffic and urban background sites in London, Paris and Strasbourg were combined to estimate the relative importance of traffic emissions on TEX in every city. When analyzing the urban enhancement emission ratios of TEX-to-benzene on a seasonal basis, two potential source signatures other than traffic could be differentiated in all cities (1) summertime evaporation from fuel and/or solvent and (2) wintertime domestic heating. However, traffic emissions still unambiguously dominate the concentration levels of TEX in every city despite the reduction of their emissions at exhaust pipe over the last two decades. Traffic explains between 60% and 96% (at ±20%) of TEX levels while it is less clear for xylenes at some locations. Our results provide a basis to evaluate regional emission inventories. The method is applicable at any urban area where speciated hydrocarbon monitoring is available.

International audience; Large world's urban areas are important pollutant emission sources. Several studies in mid-northern latitudes megacities characterized the importance and potential impacts of these emissions at larger scale, however, there are still missing observations in sensitive places like South America and Africa. The unplanned growth of urban conglomerations is the main issue in West Africa, aggravating health problems due to unregulated emissions and producing effects on atmospheric chemistry. Hence, the characterization, quantification and fate of these emissions, is a key input to improve the comprehension about the role of local sources over this region and to assess their impact on regional climate and air quality conditions. During the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) project, an intensive airborne campaign was performed in summer 2016 with the purpose to quantify a large range of atmospheric components for the better understanding on the effect of African emissions on regional climate. This study presents the results obtained on-board the French ATR42 French aircraft by a comprehensive suite of airborne measurement techniques, whereby volatile organic compounds (VOCs) together with simultaneous trace gas and aerosols measurements were analysed. Here we examine primary VOCs emissions, their photochemical aging processes and their potential impacts on the local atmospheric composition near coastal urban agglomerates. Moreover, trace gases and VOCs contributions were compared with previous campaigns performed in the region. Differences and communalities are evaluated regarding the expected changes in regional emissions over the last decade. Finally, the comparison with previous airborne campaigns in other urban areas worldwide will be performed with the purpose of understand the implications of human emissions in this highly populated area of the developing world.

International audience; As part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx), a series of aerosol and gas-phase measurements were deployed aboard the SAFIRE ATR42 research aircraft in summer 2014. The present study focuses on the four flights performed in late June early July over two forested regions in the south of France. We combine in situ observations and model simulations to aid in the understanding of secondary organic aerosol (SOA) formation over these forested areas in the Mediterranean and to highlight the role of different gas-phase precursors. The non-refractory particulate species measured by a compact aerosol time-of-flight mass spectrometer (cToF-AMS) were dominated by organ-ics (60 to 72 %) followed by a combined contribution of 25 % by ammonia and sulfate aerosols. The contribution from nitrate and black carbon (BC) particles was less than 5 % of the total PM 1 mass concentration. Measurements of non-refractory species from off-line transmission electron mi-croscopy (TEM) showed that particles have different mixing states and that large fractions (35 %) of the measured particles were organic aerosol containing C, O, and S but without inclusions of crystalline sulfate particles. The organic aerosol measured using the cToF-AMS contained only evidence of oxidized organic aerosol (OOA), without a contribution of fresh primary organic aerosol. Positive matrix factorization (PMF) on the combined organic-inorganic matrices separated the oxidized organic aerosol into a more-oxidized organic aerosol (MOOA), and a less-oxidized organic aerosol (LOOA). The MOOA component is associated with inorganic species and had higher contributions of m/z 44 than the LOOA factor. The LOOA factor is not associated with inorganic species and correlates well with biogenic volatile organic species measured with a proton-transfer-reaction mass spectrometer, such as isoprene and its oxidation products (methyl vinyl ketone, MVK; methacroleine, MACR; and iso-prene hydroxyhydroperoxides, ISOPOOH). Despite a significantly high mixing ratio of isoprene (0.4 to 1.2 ppbV) and its oxidation products (0.2 and 0.8 ppbV), the contribution of specific signatures for isoprene epoxydiols SOA (IEPOX-SOA) within the aerosol organic mass spectrum (m/z 53 and m/z 82) were very weak, suggesting that the presence of Published by Copernicus Publications on behalf of the European Geosciences Union. 7042 E. Freney et al.: Aerosol composition and the contribution of SOA formation isoprene-derived SOA was either too low to be detected by the cToF-AMS, or that SOA was not formed through IEPOX. This was corroborated through simulations performed with the Polyphemus model showing that although 60 to 80 % of SOA originated from biogenic precursors, only about 15 to 32 % was related to isoprene (non-IEPOX) SOA; the remainder was 10 % sesquiterpene SOA and 35 to 40 % monoter-pene SOA. The model results show that despite the zone of sampling being far from industrial or urban sources, a total contribution of 20 to 34 % of the SOA was attributed to purely anthropogenic precursors (aromatics and intermediate or semi-volatile compounds). The measurements obtained during this study allow us to evaluate how biogenic emissions contribute to increasing SOA concentrations over Mediterranean forested areas. Directly comparing these measurements with the Polyphemus model provides insight into the SOA formation pathways that are prevailing in these forested areas as well as processes that need to be implemented in future simulations.

SSCI-VIDE+CARE+ABO:YDU:CGO; International audience; Emission factors (EFs) of pollutants emitted by light-duty vehicles (LDV) were investigated in the Leopold II tunnel in Brussels city center (Belgium), in September 2011 and in January 2013, respectively. Two sampling sites were housing the instruments for the measurements of a large range of air pollutants, including non-methane volatile organic compounds (NMVOCs), nitrogen oxides (NOx) and carbon dioxide (CO2). The NMVOCs and NOx traffic EFs for LDV were determined from their correlation with CO2 using a single point analysis method.The emission factor of NOx is (544 ± 199) mg vehicle−1 km−1; NMVOCs emission factors vary from (0.26 ± 0.09) mg vehicle−1 km−1 for cis-but-2-ene to (8.11 ± 2.71) mg vehicle−1 km−1 for toluene. Good agreement is observed between the EFs determined in the Leopold II tunnel and the most recent EFs determined in another European roadway tunnel in 2004, with only a slight decrease of the EFs during the last decade. An historical perspective is provided and the observed trend in the NMVOCs emission factors reflect changes in the car fleet composition, the fuels and/or the engine technology that have occurred within the last three decades in Europe.

Ambient particle number size distributions were measured in Paris, France, during summer (1–31 July 2009) and winter (15 January to 15 February 2010) at three fixed ground sites and using two mobile laboratories and one airplane. The campaigns were part of the Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation (MEGAPOLI) project. New particle formation (NPF) was observed only during summer on approximately 50 % of the campaign days, assisted by the low condensation sink (about 10.7 ± 5.9 × 10−3 s−1). NPF events inside the Paris plume were also observed at 600 m altitude onboard an aircraft simultaneously with regional events identified on the ground. Increased particle number concentrations were measured aloft also outside of the Paris plume at the same altitude, and were attributed to NPF. The Paris plume was identified, based on increased particle number and black carbon concentration, up to 200 km away from the Paris center during summer. The number concentration of particles with diameters exceeding 2.5 nm measured on the surface at the Paris center was on average 6.9 ± 8.7 × 104 and 12.1 ± 8.6 × 104 cm−3 during summer and winter, respectively, and was found to decrease exponentially with distance from Paris. However, further than 30 km from the city center, the particle number concentration at the surface was similar during both campaigns. During summer, one suburban site in the NE was not significantly affected by Paris emissions due to higher background number concentrations, while the particle number concentration at the second suburban site in the SW increased by a factor of 3 when it was downwind of Paris.

A number of campaigns have been carried out to establish the emission factors of pollutants from fuel combustion in West Africa, as part of work package 2 (‘Air Pollution and Health’) of the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) FP7 program. Emission sources considered here include wood and charcoal burning, charcoal making, open waste burning, and vehicles including trucks, cars, buses and two-wheeled vehicles. Emission factors of total particulate matter, black carbon, primary organic carbon and non-methane volatile organic compounds (NMVOC) have been established. In addition, emission factor measurements were performed in combustion chambers in order to reproduce field burning conditions for tropical hardwood, and obtain particulate emission factors by size (PM0.25, PM1, PM2.5 and PM10). Aerosol samples were collected on quartz filters and analysed using gravimetric and thermal methods. The emission factors of 50 NMVOC species were determined using systematic off-line sampling. Emission factors from wood burning for black carbon, organic carbon and total particulate matter were 0.8 ± 0.4 g/kg of dry matter (dm), 9.29 ± 3.82 g/kg dm and 34.54 ± 20.6 g/kg dm, respectively. From traffic sources, the highest emission factors for all particulate species were emitted from two wheeled vehicles with two-stroke engines (2.74 g/kg fuel for black carbon, 65.11 g/kg fuel for organic carbon and 496 g/kg fuel for total particulate matter). The emissions of NMVOCs were lower than those of particles for all sources aside from traffic. The largest NMVOC emissions were observed for two-stroke two-wheeled vehicles, which were up to three times higher than emissions from light-duty and heavy-duty vehicles. Isoprene and monoterpenes, which are usually associated with biogenic emissions, were present in almost all anthropogenic source categories and could be as significant as aromatic emissions in wood burning (1 g/kg dm). Black carbon was primarily emitted in the ultrafine fraction, with 77 % of the total mass being emitted as particles smaller than 0.25 µm. This study observed higher particle and NMVOC emission factors than those in the current literature. This study underlines the important role of in-situ measurements in deriving realistic and representative emission factors.

Health risks posed by ambient air pollutants to the urban Lebanese population have not been well characterized. The aim of this study is to assess cancer risk and mortality burden of non-methane hydrocarbons (NMHCs) and particulates (PM) based on two field-sampling campaigns conducted during summer and winter seasons in Beirut. Seventy NMHCs were analyzed by TD-GC-FID. PM2.5 elemental carbon (EC) components were examined using a Lab OC-EC aerosol Analyzer, and polycyclic aromatic hydrocarbons were analyzed by GC-MS. The US EPA fraction-based approach was used to assess non-cancer hazard and cancer risk for the hydrocarbon mixture, and the UK Committee on Medical Effects of Air Pollutants (COMEAP) guidelines were followed to determine the PM2.5 attributable mortality burden. The average cumulative cancer risk exceeded the US EPA acceptable level (10−6) by 40-fold in the summer and 30-fold in the winter. Benzene was found to be the highest contributor to cancer risk (39–43%), followed by 1,3-butadiene (25–29%), both originating from traffic gasoline evaporation and combustion. The EC attributable average mortality fraction was 7.8–10%, while the average attributable number of deaths (AD) and years of life lost (YLL) were found to be 257–327 and 3086–3923, respectively. Our findings provide a baseline for future air monitoring programs, and for interventions aiming at reducing cancer risk in this population.

International audience; As part of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) project, airborne campaigns were designed to measure a large range of atmospheric constituents focusing on the improvement of our current understanding on the effect of anthropogenic emissions on regional climate. The targeted region, Southern West Africa, holds currently a population of over 340 million people, and is predicted by the United Nations to reach about 800 million by 2050. The climate in the region is characterized by a large-scale atmospheric circulation system which controls precipitation over a land area of about 6 million km2, directly impacting the water resources, agriculture and power generation of hundreds of millions of people. Besides its large natural variability, the West African monsoon system is also expected to be significantly affected by global and regional climate change, with large uncertainties on the role of local pollution. An important aspect assessing the impact of human activities on the local climate is thereby the understanding of aerosol sources and properties. The presented study details results of the DACCIWA measurement campaign using the French ATR42 research aircraft, which in combination with the German Falcon 20 and British Twin Otter aircraft, aimed to characterize physico-chemical properties of aerosols in the region using a suite of aerosol measurement techniques (e.g. C-TOF AMS, APITOF, SMPS, etc.) and supporting information from simultaneous trace gas measurements (e.g. PTRMS). This large dataset has been used to assess how anthropogenic emission (NOx, SO2, SO4) is impacting formation of biogenic secondary organic aerosol formation, in particular through the formation of isoprene epoxydiols (IEPOX). The recently collected data will certainly help understanding the coupling between human activities and regional climate in a sensitive, highly populated area.

The ChArMEx (Chemistry and Aerosol Mediterranean Experiment) SOP2 (Special Observation Period 2) field campaign took place from 15 July to 05 August 2013 in the western Mediterranean basin, at Ersa a remote site in Cape Corsica. During the campaign more than 80 Volatile Organic Compounds (VOCs), including oxygenated species were measured by different online and offline techniques. At the same time an exhaustive description of the chemical composition of fine aerosols was performed. First we combined a back-trajectory analysis and an estimation of photochemical age to characterize air mass origins and chemical processing times, which confirmed the remote nature of the site. Therefore, low levels of anthropogenic VOCs (typically tens to hundreds of ppt for individual species) and black carbon (0.1–0.9 μg m

Secondary organic aerosol (SOA) is a major component of atmospheric fine particle mass. Intermediate-volatility organic compounds (IVOCs) have been proposed to be an important source of SOA. We present a comprehensive analysis of atmospheric IVOC concentrations and their SOA production using measurements made in Pasadena, California during the California at the Nexus of Air Quality and Climate Change (CalNex) study. The campaign-average concentration of primary IVOCs was 6.3 ± 1.9 μg m(-3) (average ± standard deviation), which is comparable to the concentration of organic aerosol but only 7.4 ± 1.2% of the concentration of speciated volatile organic compounds. Only 8.6 ± 2.2% of the mass of the primary IVOCs was speciated. Almost no weekend/weekday variation in the ambient concentration of both speciated and total primary IVOCs was observed, suggesting that petroleum-related sources other than on-road diesel vehicles contribute substantially to the IVOC emissions. Primary IVOCs are estimated to produce about 30% of newly formed SOA in the afternoon during CalNex, about 5 times that from single-ring aromatics. The importance of IVOCs in SOA formation is expected to be similar in many urban environments.

International audience; Measurements of gaseous and particulate organic carbon were performed during the MEGAPOLI experiments, in July 2009 and January–February 2010, at the SIRTA observatory in suburban Paris. Measurements comprise primary and secondary volatile organic compounds (VOCs), of both anthropogenic and biogenic origins, including C 12 –C 16 n-alkanes of intermediate volatility (IVOCs), suspected to be efficient precursors of secondary organic aerosol (SOA). The time series of gaseous carbon are generally consistent with times series of particulate organic carbon at regional scale, and are clearly affected by meteorology and air mass origin. Concentration levels of anthropogenic VOCs in urban and suburban Paris were surprisingly low (2–963 ppt) compared to other megacities worldwide and to rural continental sites. Urban enhancement ratios of anthropogenic VOC pairs agree well between the urban and suburban Paris sites, showing the regional extent of anthropogenic sources of similar composition. Contrary to other primary anthropogenic VOCs (aromatics and alkanes), IVOCs showed lower concentrations in winter (< 5 ppt) compared to summer (13– 27 ppt), which cannot be explained by the gas-particle partitioning theory. Higher concentrations of most oxygenated VOCs in winter (18–5984 ppt) suggest their dominant primary anthropogenic origin. The respective role of primary anthropogenic gaseous compounds in regional SOA formation was investigated by estimating the SOA mass concentration expected from the anthropogenic VOCs and IVOCs (I / VOCs) measured at SIRTA. From an integrated approach based on emission ratios and SOA yields, 38 % of the SOA measured at SIRTA is explained by the measured concentrations of I / VOCs, with a 2 % contribution by C 12 –C 16 n-alkane IVOCs. From the results of an alternative time-resolved approach, the average IVOC contribution to SOA formation is estimated to be 7 %, which is half of the average contribution of the traditional aromatic compounds (15 %). Both approaches, which are based on in situ observations Published by Copernicus Publications on behalf of the European Geosciences Union. 10440 W. Ait-Helal et al.: Volatile and intermediate volatility organic compounds in suburban Paris of particular I / VOCs, emphasize the importance of the intermediate volatility compounds in the SOA formation, and support previous results from chamber experiments and mod-eling studies. They also support the need to make systematic the IVOCs' speciated measurement during field campaigns.

Nitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NOx, O3, photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity, wind speed and wind direction), black carbon concentration, total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h−1 and 0.25 ppb h−1, during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J(NO2) and the product between J(NO2) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground., Atmospheric Chemistry and Physics, 14 (6), ISSN:1680-7375, ISSN:1680-7367

Besides their impacts on health, BTEX play an important role in the formation of secondary organic aerosols and ozone for which limit values are regularly exceeded in Paris megacity and Ile de France region. An enrichment by a factor of 3 in the C7C9 aromatic fraction in the Paris atmosphere compared to other northern mid-latitude cities was shown in 2013. Here, we combined different approaches to investigate the role of transport-related sources in such enrichment (gasoline composition and vehicle fleet composition): a statistical analysis of a large BTEX dataset including multi-year and multi-site measurements (traffic, background, tunnel) and a coupled experimental and modelling analysis of liquid and headspace composition of representative fuels distributed in Ile de France region (SP95, SP95 E10, and SP98). For the latter the experimental set-up was designed to analyze the composition of 87 VOCs from C2 to C17 in both liquid and headspace phases. The model is able to predict the headspace composition at ± 15% and with an R2 > 0.9. First a strong positive spatial gradient in BTEX composition at traffic stations is observed, with higher TEX-to-benzene ratio in Paris center compared to the suburbs and outskirts up to a factor of 2. This gradient reflects differences in fleet composition especially gasoline powered vehicles in Paris with a larger proportion of two-wheelers (15% in 2012). This gradient is also consistent with the inter-annual increase of TEX-to-benzene ratios along with the doubling of two-wheelers use and the decrease in the number of passenger cars. The gasoline evaporation model cannot solely explain the observed spatial variability. Finally, we investigated the potential contribution of two-wheelers to the aromatic enrichment in IdF region by introducing an additional unburned gasoline term to the model. The results support the suggestion that two-wheelers are a potential contributor to this enrichment. Considering the high use of two-wheelers in other European cities such as London or Barcelona if Europe is to decrease transport-related air pollution and inner city traffic, policy makers should consider finding alternatives to the conventionally-powered two-wheelers and supporting electric two-wheelers for example. Keywords: Urban air quality, Megacity, VOC, BTEX, Fuel composition, Two-wheelers, Emission ratios

International audience; Fine organic aerosols were collected at a semi-urban site in Beirut, Lebanon, from 28 January to 12 February 2012 as part of the Emission and Chemistry of Organic Carbon in East Mediterranean-Beirut (ECOCEM-Beirut). A total of 20 quartz filter samples were collected on a 12 h basis using a high-volume sampler and were analyzed using a GC/MS technique. Levoglucosan was the major most abundant single component with an average value of 306 ng.m -3, followed by saturated and unsaturated carboxylic acids and sugars with average values of 234 and 118 ng.m-3, respectively. Reported values for other carboxylic acids, polycyclic aromatic hydrocarbons, and biogenic secondary organic aerosols (BSOA) were 87, 33 and 21 ng.m-3, respectively. Compared to a similar field campaign conducted in summer 2011, levoglucosan concentrations were lower in summer by a factor of 6, due to the use of wood burning for residential heating in winter. Concentrations of saturated and unsaturated carboxylic acids, other carboxylic acids, and BSOA were higher in summer by a factor of 3, 2, and 7, respectively. Higher concentrations observed for BSOA and other dicarboxylic acids during summer are due to higher biogenic emissions and greater photochemical activity in summer. Copyright © American Association for Aerosol Research.

Airborne measurements of aerosol composition and gas phase compounds over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico in June 2010 indicated the presence of high concentrations of secondary organic aerosol (SOA) formed from organic compounds of intermediate volatility. In this work, we investigated SOA formation from South Louisiana crude oil vapors reacting with OH in a Potential Aerosol Mass flow reactor. We use the dependence of evaporation time on the saturation concentration (C*) of the SOA precursors to separate the contribution of species of different C* to total SOA formation. This study shows consistent results with those at the DWH oil spill: (1) organic compounds of intermediate volatility with C* = 10(5)-10(6) μg m(-3) contribute the large majority of SOA mass formed, and have much larger SOA yields (0.37 for C* = 10(5) and 0.21 for C* = 10(6) μg m(-3)) than more volatile compounds with C*≥10(7) μg m(-3), (2) the mass spectral signature of SOA formed from oxidation of the less volatile compounds in the reactor shows good agreement with that of SOA formed at DWH oil spill. These results also support the use of flow reactors simulating atmospheric SOA formation and aging.

[1] Ground-based and airborne volatile organic compound (VOC) measurements in Los Angeles, California, and Paris, France, during the Research at the Nexus of Air Quality and Climate Change (CalNex) and Megacities: Emissions, Urban, Regional and Global Atmospheric Pollution and Climate Effects, and Integrated Tools for Assessment and Mitigation (MEGAPOLI) campaigns, respectively, are used to examine the spatial variability of the composition of anthropogenic VOC urban emissions and to evaluate regional emission inventories. Two independent methods that take into account the effect of chemistry were used to determine the emission ratios of anthropogenic VOCs (including anthropogenic isoprene and oxygenated VOCs) over carbon monoxide (CO) and acetylene. Emission ratios from both methods agree within ±20%, showing the reliability of our approach. Emission ratios for alkenes, alkanes, and benzene are fairly similar between Los Angeles and Paris, whereas the emission ratios for C7–C9 aromatics in Paris are higher than in Los Angeles and other French and European Union urban areas by a factor of 2–3. The results suggest that the emissions of gasoline-powered vehicles still dominate the hydrocarbon distribution in northern mid-latitude urban areas, which disagrees with emission inventories. However, regional characteristics like the gasoline composition could affect the composition of hydrocarbon emissions. The observed emission ratios show large discrepancies by a factor of 2–4 (alkanes and oxygenated VOC) with the ones derived from four reference emission databases. A bias in CO emissions was also evident for both megacities. Nevertheless, the difference between measurements and inventory in terms of the overall OH reactivity is, in general, lower than 40%, and the potential to form secondary organic aerosols (SOA) agrees within 30% when considering volatile organic emissions as the main SOA precursors.

International audience

During summers 2013 and 2014, two three weeks intensive campaign took place over the western Mediterranean basin in order to investigate photo-oxidant and aerosol sources over the region. Within the frame of the MISTRALS/ChArMEx (Chemistry-Aerosol Mediterranean Experiment) program and the ANR/SAFMED (Secondary Aerosol Formation in the MEDiterranean) project, this campaign included an extensive experimental set-up based on ground-based, balloon-borne, aircraft and satellite measurements. In this paper, a modeling perspective of the campaign is given, based on simulations with the regional chemistry-transport model, CHIMERE, in a configuration shaped for the Mediterranean region. Major sources of photo-oxidants, and aerosols are addressed: long range transport from continental Europe, pollution build-up from shipping emissions, marine emissions, organic aerosol formation from biogenic and anthropogenic VOC emissions, dust emissions.