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Atmospheric particulate matter with an aerodynamic diameter < 2.5 µm (PM2.5) is associated with adverse effects on the climate system, the human health, vegetation and the ecosystems. The World Health Organization (WHO) lowered the guideline limit for PM2.5 in autumn 2021 and this is exceeded in many regions including rural and remote areas in mainland Europe. Measurements of the chemical composition of PM2.5 is essential to assess the sources which contribute to PM2.5 mass concentrations and to further design meaningful policies to tackle sources at their origin.Here we report 6 years (2014- 2020) of PM2.5 mass and chemical speciation at five remote sites across France belonging to the EMEP network (European Monitoring and Evaluation Programme). The seasonal and spatial variability of aerosol composition and source contributions based on the proximity of sources and long-range transport are discussed. Trends in PM2.5 and the main components at the five locations were evaluated by means of random-forest modelling coupled with a de-weathering algorithm. This approach is advantageous as resulting trends are driven by changes in emission or atmospheric processes and not by changes in weather conditions and/or long-range transport patterns. Random-forest regression modelling was built using meteorological data, backtrajectory information and temporal variables at each site and quantified the most important factors that explain PM2.5 concentrations at remote rural areas in France.All sites observed statistically significant downward trends in PM2.5 at a rate of -4 to -9% year-1 for the period 2014 – 2020. The decrease in PM2.5 concentrations was mostly explained by changes in the secondary inorganic species (sulphate, nitrate and ammonium) and not by changes in primary PM2.5 emissions. The variability in trends in PM2.5 and components observed across the sites is discussed with their implications for policy makers.

Portable sensors have emerged as a promising solution for personal exposure (PE) measurement. For the first time in Île-de-France, PE to black carbon (BC), particulate matter (PM), and nitrogen dioxide (NO2) was quantified based on three field campaigns involving 37 volunteers from the general public wearing the sensors all day long for a week. This successful deployment demonstrated its ability to quantify PE on a large scale, in various environments (from dense urban to suburban, indoor and outdoor) and in all seasons. The impact of the visited environments was investigated. The proximity to road traffic (for BC and NO2), as well as cooking activities and tobacco smoke (for PM), made significant contributions to total exposure (up to 34%, 26%, and 44%, respectively), even though the time spent in these environments was short. Finally, even if ambient outdoor levels played a role in PE, the prominent impact of the different environments suggests that traditional ambient monitoring stations is not a proper surrogate for PE quantification.

Particulate organic nitrate (pON) can be a major part of secondary organic aerosol (SOA) and is commonly quantified by indirect means from aerosol mass spectrometer (AMS) data. However, pON quantification remains challenging. Here, we set out to quantify and characterize pON in the boreal forest, through direct field observations at Station for Measuring Ecosystem Atmosphere Relationships (SMEAR) II in Hyytia''la'', Finland, and targeted single precursor laboratory studies. We utilized a long time-of-flight AMS (LToF-AMS) for aerosol chemical characterization, with a particular focus to identify CxHyOzN+ ("CHON+") fragments. We estimate that during springtime at SMEAR II, pON (including both the organic and nitrate part) accounts for similar to 10% of the particle mass concentration (calculated by the NO+/NO2+ method) and originates mainly from the NO3 radical oxidation of biogenic volatile organic compounds. The majority of the background nitrate aerosol measured is organic. The CHON+ fragment analysis was largely unsuccessful at SMEAR II, mainly due to low concentrations of the few detected fragments. However, our findings may be useful at other sites as we identified 80 unique CHON+ fragments from the laboratory measurements of SOA formed from NO3 radical oxidation of three pON precursors (beta-pinene, limonene, and guaiacol). Finally, we noted a significant effect on ion identification during the LToF-AMS high-resolution data processing, resulting in too many ions being fit, depending on whether tungsten ions (W+) were used in the peak width determination. Although this phenomenon may be instrument-specific, we encourage all (LTOF-) AMS users to investigate this effect on their instrument to reduce the possibility of incorrect identifications.

As part of the ChArMEx project (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr ), one year of continuous filter sampling was conducted from August 2012 to August 2013 at a rural (coastal) site in Algeria aiming to better document fine aerosol seasonal variability and chemical composition in the Southern part of the Mediterranean. Over 350 filters have been collected, weighted, and analyzed for the main ions and organic and elemental carbon. The obtained mass concentrations varied between 2.5 and 50.6 μg/m3 for PM2.5. The annual modulations of PM2.5 showed higher concentrations in the end summer 2012 and the early summer 2013 (28.50 μg/m3 in August 2012, 20.23 μg/m3 in September 2012, 20.19 μg/m3 in July 2013, and 17.88 μg/m3in August 2013). The particulate organic matter (POM) presented the greatest contribution (50%), followed by the secondary inorganic aerosols (SIA, 27%). The average organic carbon OC concentrations ranged from 1.66 to 6.05 μgC/m3. The average elemental carbon EC concentrations ranged from 0.92 to 3.49 μgC/m3 and contributed 7% of the PM2.5 mass to Bou-Ismail. The average value of the OC /EC ratio was close to 5.1 in Bou-Ismail, and was close to that found in Finokalia 4 (Greece 2004, 2006) but was lower than that of Montseny 11 (Spain 2002–2007) Western Mediterranean Basin (WMB). The concentrations of water-soluble organic carbon WSOC in the PM2.5 ranging from 0.66 to 3.70 μg/m3 recorded the minimum level in March 2013, and the maximum level in August 2012, with an average of 2.02 μg/m3.

Since early 2020, the COVID-19 pandemic has led to lockdowns at national scales. These lockdowns resulted in large cuts of atmospheric pollutant emissions, notably related to the vehicular traffic source where daily commuting of light-duty vehicles was almost completely stopped in numerous urban areas worldwide, especially during Spring 2020. As a result, air quality changed in manners that are still currently under investigation. Long-term in-situ monitoring of atmospheric composition provides, to this perspective, essential information. However, a robust quantitative assessment of the impact of lockdown measures on ambient concentrations is hindered by weather variability. Basic comparisons with previous years may thus be flawed, especially regarding secondary pollutants, whose concentrations strongly depends on meteorological conditions. In order to circumvent this difficulty, an innovative methodology has been developed. The Analog Application for Air Quality (A3Q) method is based on the comparison of each day of lockdown to a group of analog days having similar meteorological conditions. The A3Q method has been successfully evaluated and applied to a comprehensive in-situ dataset of primary and secondary pollutants obtained at the SIRTA observatory, a suburban background site of the Paris megacity (France). The overall slight decrease of PM1 concentrations (−14 %) compared to business-as-usual conditions conceals contrasting behaviours. Primary traffic tracers (NOx and traffic-related carbonaceous aerosols) dropped by 42–66 % during the lockdown period. Further, the A3Q method enabled us to characterize of changes triggered by NOx decreases. Particulate nitrate and secondary organic aerosols (SOA), two of the main springtime aerosol components in North-Western Europe, decreased by −45 % and −25 %, respectively. A NOx-relationship emphasizes the interest of NOx mitigation policies at the regional (i.e. city) scale, although long-range pollution advection sporadically overcompensated regional decreases. Variations of the oxidation state of SOA suggests discrepancies in SOA formation processes. At the same time, the expected ozone increase (+20 %) underlines the negative feedback of NO titration. These results provide a quasi-comprehensive observation-based insight on mitigation policies regarding air quality in future low-carbon urban areas.

Volatile Organic Compounds (VOCs) have direct influences on air quality and climate. They also play a key role in atmospheric chemistry, as they are precursors of secondary pollutants, such as ozone (O3) and secondary organic aerosols (SOA).Long-term datasets of in-situ atmospheric measurements are crucial to characterize the variability of atmospheric chemical composition. Online and continuous measurements of O3, NOx and aerosols have been achieved at the SIRTA-ACTRIS facility (Paris region, France), since 2012. Regarding VOCs, they have been measured there for several years thanks to bi-weekly samplings followed by offline Gas Chromatography analysis. However, this method doesn’t provide a good representation of the temporal variability of VOC concentrations. To tackle this issue, online VOC measurements using a Proton-Transfer-Reaction Quadrupole Mass-Spectrometer (PTR-Q-MS) have been started in January 2020.The dataset acquired during the first year of online VOC measurements is analyzed, which gives insights on VOC seasonal variability. The additional long-term datasets obtained from co-located measurements (O3, NOx, aerosol physical and chemical properties, meteorological parameters) are also used for the sake of this study.Due to Covid-19 pandemic, the year 2020 notably comprised a total lockdown in France in Spring, and a lighter one in Autumn. Therefore, a focus can be made on the impact of these lockdowns on the VOC variability and sources. To this end, the diurnal cycles of VOCs considered markers for anthropogenic sources are carefully investigated. Results notably indicate that markers for traffic and wood burning sources behave quite differently during the Spring lockdown in comparison to the other periods. A source apportionment analysis using positive matrix factorization allows to further document the seasonal variability of VOC sources and the impacts on air quality associated with the lockdown measures.

Secondary organic aerosol (SOA) accounts for a significant fraction of particulate matter (PM) in the atmosphere. Source identification, including the SOA fraction, is critical for the effective management of air pollution. Molecular SOA markers (tracers) are key compounds allowing the source apportionment of SOA using different methodologies. Therefore, accurate SOA marker measurements in ambient air PM are important. This study determined the concentrations of 12 key SOA markers (biogenic and anthropogenic) in the urban dust standard reference material available from the National Institute of Standards and Technology (NIST) (SRM 1649b). Two extraction procedures, sonication and QuEChERS-like (quick easy cheap effective rugged and safe), have been compared. Three research laboratories/institutes using two analytical techniques (gas chromatography/mass spectrometry (GC/MS) and ultra-high-pressure liquid chromatography/tandem mass spectrometry (HPLC/MS-MS)) carried out the analyses. The results obtained were all in good agreement, except for 2-methylerythritol. The analysis of this compound still seems to be challenging by both GC/MS (large injection repeatability) and HPLC/MS-MS (separation issues of both 2-methyltetrols: 2-methylthreitol and 2-methylerythritol). Possible inhomogeneity in the SRM for this compound could also explain the large discrepancies observed. Sonication and QuEChERS-like procedures gave comparable results for the extraction of the SOA markers showing that QuEChERS-like extraction is suitable for the analysis of SOA markers in ambient air PM. As this study provides, for the first time, indicative values in a reference material for typical SOA markers, the analysis of SRM 1649b (urban dust) could be used for quality control/assurance purposes. Graphical abstract.

Twenty-five biogenic and anthropogenic secondary organic aerosol (SOA) markers have been measured over a one-year period in both gaseous and PM10 phases in the Paris region (France). Seasonal and chemical patterns were similar to those previously observed in Europe, but significantly different from the ones observed in America and Asia due to dissimilarities in source precursor emissions. Nitroaromatic compounds showed higher concentrations in winter due to larger emissions of their precursors originating from biomass combustion used for residential heating purposes. Among the biogenic markers, only isoprene SOA marker concentrations increased in summer while pinene SOA markers did not display any clear seasonal trend. The measured SOA markers, usually considered as semi-volatiles, were mainly associated to the particulate phase, except for the nitrophenols and nitroguaiacols, and their gas/particle partitioning (GPP) showed a low temperature and OM concentrations dependency. An evaluation of their GPP with thermodynamic model predictions suggested that apart from equilibrium partitioning between organic phase and air, the GPP of the markers is affected by processes suppressing volatility from a mixed organic and inorganic phase, such as enhanced dissolution in aerosol aqueous phase and non-equilibrium conditions. SOA marker concentrations were used to apportion secondary organic carbon (SOC) sources applying both, an improved version of the SOA-tracer method and positive matrix factorization (PMF) Total SOC estimations agreed very well between both models, except in summer and during a highly processed Springtime PM pollution event in which systematic underestimation by the SOA tracer method was evidenced. As a first approach, the SOA-tracer method could provide a reliable estimation of the average SOC concentrations, but it is limited due to the lack of markers for aged SOA together with missing SOA/SOC conversion fractions for several sources.

The CARA program has been developed since 2008 by the French reference laboratory for air quality monitoring (LCSQA) and the regional monitoring networks to gain a better knowledge at the national level on the particulate matter (PM) chemistry and its diverse origins in urban environments. It results of strong collaborations with international-level academic partners, allowing to bring state-of-the-art, straightforward and robust results and methodologies within operational air quality stakeholders (and subsequently, decision makers). Here, we illustrate some of the main outputs obtained over the last decade thanks to this program, regarding methodological aspects (both in terms of measurement techniques and data treatment procedures) as well as acquired knowledge on the predominant PM sources. Offline and online methods are used following well-suited quality assurance and quality control procedures, notably including inter-laboratory comparison exercises. Source apportionment studies are conducted using various receptor modeling approaches. Overall, the results presented herewith underline the major influences of residential wood burning (during the cold period) and road transport emissions (exhaust and non-exhaust ones, all along the year), as well as substantial contributions of mineral dust and primary biogenic particles (mostly during the warm period). Long-range transport phenomena, e.g., advection of secondary inorganic aerosols from the European continental sector and of Saharan dust into the French West Indies, are also discussed in this paper. Finally, we briefly address the use of stable isotope measurements (δ15N) and of various organic molecular markers for a better understanding of the origins of ammonium and of the different organic aerosol fractions, respectively.

International audience; The field of small air quality sensors is of growing interest within the scientific community, especially because this new technology is liable to improve air pollutant monitoring as well as be used for personal exposure quantification. Amongst the myriad existing devices, the performances are highly variable; this is why the sensors must be rigorously assessed before deployment, according to the intended use. This study is included in the Polluscope project; its purpose is to quantify personal exposure to air pollutants by using portable sensors. This paper designs and applies a methodology for the evaluation of portable air quality sensors to eight devices measuring PM, BC, NO2 and O3. The dedicated testing protocol includes static ambient air measurements compared with reference instruments, controlled chamber and mobility tests, as well as reproducibility evaluation. Three sensors (AE51, Cairclip and Canarin) were retained to be used for the field campaigns. The reliability of their performances were robustly quantified by using several metrics. These three devices (for a total of 36 units) were deployed to be worn by volunteers for a week. The results show the ability of sensors to discriminate between different environments (i.e., cooking, commuting or in an office). This work demonstrates, first, the ability of the three selected sensors to deliver data reliable enough to enable personal exposure estimations, and second, the robustness of this testing methodology.

International audience; Agricultural activities highly contribute to atmospheric pollution, but the diversity and the magnitude of their emissions are still subject to large uncertainties. A field measurement campaign was conducted to characterize gaseous and particulate emissions from an experimental farm in France containing a sheep pen and a dairy stable. During the campaign, more than four hundred volatile organic compounds (VOCs) were characterized using an original combination of online and off-line measurements. Carbon dioxide (CO2) and ammonia (NH3) were the most concentrated compounds inside the buildings, followed by methanol, acetic acid and acetaldehyde. A CO2 mass balance model was used to estimate NH3 and VOC emission rates. To our knowledge, this study constitutes the first evaluation of emission rates for most of the identified VOCs. The measurements show that the dairy stable emitted more VOCs than the sheep pen. Despite strong VOC and NH3 emissions, the chemical composition of particles indicates that gaseous farm emissions do not affect the loading of fine particles inside the farm and is mainly explained by the low residence time inside the buildings. The experimental dataset obtained in this work will help to improve emissions inventories for agricultural activities.

As part of the ChArMEx project (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr), one year of continuous filter sampling was conducted from August 2012 to August 2013 at a rural (coastal) site in Algeria aiming to better document fine aerosol seasonal variability and chemical composition in the Southern part of the Mediterranean. Over 350 filters have been collected, weighted, and analyzed for the main ions and organic and elemental carbon. The obtained mass concentrations varied between 2.5 and 50.6 μg/m

Wood burning is widely used for domestic heating and has been identified as a ubiquitous pollution source in urban areas, especially during cold months. The present study is based on a three and a half winter months field campaign in the Paris region measuring Volatile Organic Compounds (VOCs) by Proton Transfer Reaction Mass Spectrometry (PTR-MS) in addition to Black Carbon (BC). Several VOCs were identified as strongly wood burning-influenced (e.g., acetic acid, furfural), or traffic-influenced (e.g., toluene, C8-aromatics). Methylbutenone, benzenediol and butandione were identified for the first time as wood burning-related in ambient air. A Positive Matrix Factorization (PMF) analysis highlighted that wood burning is the most important source of VOCs during the winter season. (47%). Traffic was found to account for about 22% of the measured VOCs during the same period, whereas solvent use plus background accounted altogether for the remaining fraction. The comparison with the regional emission inventory showed good consistency for benzene and xylenes but revisions of the inventory should be considered for several VOCs such as acetic acid, C9-aromatics and methanol. Finally, complementary measurements acquired simultaneously at other sites in Île-de-France (the Paris region) enabled evaluation of spatial variabilities. The influence of traffic emissions on investigated pollutants displayed a clear negative gradient from roadside to suburban stations, whereas wood burning pollution was found to be fairly homogeneous over the region.

International audience; An original source apportionment study was conducted on atmospheric particles (PM 10) collected in Metz, one of the largest cities of Eastern France. A Positive matrix factorization (PMF) analysis was applied to a sampling filter-based chemical dataset obtained for the April 2015 to January 2017 period. Nine factors were clearly identified, showing mainly contributions from anthropogenic sources of primary PM (19.2% and 16.1% for traffic and biomass burning, respectively) as well as secondary aerosols (12.3%, 14.5%, 21.8% for sulfate-, nitrate-, and oxalate-rich factors, respectively). Wood-burning aerosols exhibited strong temporal variations and contributed up to 30% of the PM mass fraction during winter, while primary traffic concentrations remained relatively constant throughout the year. These two sources are also the main contributors during observed PM 10 pollution episodes. Furthermore, the dominance of the oxalate-rich factor among other secondary aerosol factors underlines the role of atmospheric processing to secondary organic aerosol loadings which are still poorly characterized in this region. Finally, Concentration-Weighted Trajectory (CWT) analysis were performed to investigate the geographical origins of the apportioned sources, notably illustrating a significant transport of both nitrate-rich and sulfate-rich factors from Northeastern Europe but also from the Balkan region.

National audience

This work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Center (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulfate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artifacts in individual instruments, such as the overestimation of m/z 44 from organic aerosol. This effect was quantified by the m/z (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artifact was applied to the measurements acquired during this study. For some instruments (those with high artifacts), this fragmentation table adjustment led to an “overcorrection” of the f44 (m/z 44/Org) signal. This correction based on measurements made with pure NH4NO3, assumes that the magnitude of the artifact is independent of chemical composition. Using data acquired at different NH4NO3 mixing ratios (from solutions of NH4NO3 and (NH4)2SO4) we observe that the magnitude of the artifact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO3 mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artifact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry. © 2019, © 2019 Author(s). Published with license by Taylor & Francis Group, LLC., Funding text #1 aLaboratoire de Météorologie Physique (LaMP), Aubiere, France; bInstitut National de l’Environnement Industriel et des Risques (INERIS), Verneuil-en-Halatte, France; cLaboratoire des Sciences du Climat et de l’Environnement (LSCE), CNRS-CEA-UVSQ, Gif-sur-Yvette, France; dAerodyne Research, Inc, Billerica, Massachusetts, USA; eEnvironment Energy and Water Research Center, The Cyprus Institute, Nicosia, Cyprus; fEstonian Environmental Research Center (EERC), Tallinn, Estonia; gFinnish meteorological institute (FMI), Helsinki, Finland; hIERSD, National Observatory of Athens, Athens, Greece; iDepartment of the Environment, Centre for Energy, Environment and Technology Research (CIEMAT), Madrid, Spain; jDeutscher Wetterdienst, Meteorologisches Observatorium Hohenpeißenberg, Hohenpeißenberg, Germany; kInstitute for Atmospheric and Earth System Research (INAR)/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland; lLeibniz Institute for Tropospheric Research, Leipzig, Germany; mEnvironmental Research Group, MRC-HPA Centre for Environment and Health, King’s College London, London, United Kingdom; nInstitute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain; oLaboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen PSI, Switzerland; pNational Institute of R&D for Optoelectronics (INOE), Ilfov, Romania; qProambiente S.c.r.l CNR Research Area, Bologna, Italy Funding text #2 This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654109. The US Department of Energy Small Business Innovative Research program (award number DE-SC0017041) provided support for development of ACSM calibration procedures. CNRS, CEA, and INERIS are acknowledged for financial support of the ACMCC. The intercomparison campaign and the following data treatment have been conducted in collaboration with the French reference laboratory for air quality monitoring (LCSQA), funded by the French Ministry of Environment. COST action CA16109 Chemical On-Line cOmpoSition and Source Apportionment of fine aerosoLs COLOSSAL grant is gratefully acknowledged for the support of data workshops. M.C. Minguillón acknowledges the Ramón y Cajal fellowship awarded by the Spanish Ministry of Economy, Industry and Competitiveness. The CIEMAT participation has been partially funded by MINECO/AEI/FEDER, UE (CGL2017-85344-R and CGL2017-90884-REDT) and TIGAS-CM (Y2018/EMT- 5177) Project. PSI is grateful for financial support by the Federal Office for the Environment in Switzerland.

International audience; he present study proposes an advanced methodology to refine the source apportionment of organic aerosol (OA). This methodology is based on the combination of offline and online datasets in a single Positive Matrix Factorization (PMF) analysis using the multilinear engine (ME-2) algorithm and a customized time synchronization procedure. It has been applied to data from measurements conducted in the Paris region (France) during a PM pollution event in March 2015. Measurements included OA ACSM (Aerosol Chemical Speciation Monitor) mass spectra and specific primary and secondary organic molecular markers from PM10 filters on their original time resolution (30 min for ACSM and 4 h for PM10 filters). Comparison with the conventional PMF analysis of the ACSM OA dataset (PMF-ACSM) showed very good agreement for the discrimination between primary and secondary OA fractions with about 75% of the OA mass of secondary origin. Furthermore, the use of the combined datasets allowed the deconvolution of 3 primary OA (POA) factors and 7 secondary OA (SOA) factors. A clear identification of the source/origin of 54% of the total SOA mass could be achieved thanks to specific molecular markers. Specifically, 28% of that fraction was linked to combustion sources (biomass burning and traffic emissions). A clear identification of primary traffic OA was also obtained using the PMF-combined analysis while PMF-ACSM only gave a proxy for this OA source in the form of total hydrocarbon-like OA (HOA) mass concentrations. In addition, the primary biomass burning-related OA source was explained by two OA factors, BBOA and OPOA-like BBOA. This new approach has showed undeniable advantages over the conventional approaches by providing valuable insights into the processes involved in SOA formation and their sources. However, the origins of highly oxidized SOA could not be fully identified due to the lack of specific molecular markers for such aged SOA.

As part of the European ACTRIS project, the first large Quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM) intercomparison study was conducted in the region of Paris for 3 weeks during the late-fall - early-winter period (November-December 2013). The first week was dedicated to the tuning and calibration of each instrument, whereas the second and third were dedicated to side-by-side comparison in ambient conditions with co-located instruments providing independent information on submicron aerosol optical, physical, and chemical properties. Near real-time measurements of the major chemical species (organic matter, sulfate, nitrate, ammonium, and chloride) in the non-refractory submicron aerosols (NR-PM1) were obtained here from 13 Q-ACSM. The results show that these instruments can produce highly comparable and robust measurements of the NR-PM1 total mass and its major components. Taking the median of the 13 Q-ACSM as a reference for this study, strong correlations (r2 > 0.9) were observed systematically for each individual Q-ACSM across all chemical families except for chloride for which three Q-ACSMs showing weak correlations partly due to the very low concentrations during the study. Reproducibility expanded uncertainties of Q-ACSM concentration measurements were determined using appropriate methodologies defined by the International Standard Organization (ISO 17025, 1999) and were found to be 9, 15, 19, 28, and 36 % for NR-PM1, nitrate, organic matter, sulfate, and ammonium, respectively. However, discrepancies were observed in the relative concentrations of the constituent mass fragments for each chemical component. In particular, significant differences were observed for the organic fragment at mass-to-charge ratio 44, which is a key parameter describing the oxidation state of organic aerosol. Following this first major intercomparison exercise of a large number of Q-ACSMs, detailed intercomparison results are presented, along with a discussion of some recommendations about best calibration practices, standardized data processing, and data treatment.

The present study proposes a novel approach to combine online and offline measurements in statistical source-receptor model such as Positive matrix factorization (PMF). Offline measurements include here POA (primary organic aerosol) and SOA (secondary organic aerosol) molecular markers. Their combination with data obtained using an Aerosol Chemical Speciation Monitor (ACSM) notably allowed for a better deconvolution of SOA fractions - at short time resolution (30min) - of SOA fractions than usually not obtained with online measurements only.; Ces travaux proposent une nouvelle approche permettant de combiner des mesures automatiques et manuelles de la composition chimique des aérosols à l’aide d’un modèle statistique de type “Positive Matrix Factorization” (PMF). Les mesures manuelles incluent des marqueurs moléculaires spécifiques des aérosols organiques primaires et secondaires (AOP et AOS). La combinaison de ces mesures avec les données issues d’un Aerosol Chemical Speciation Monitor (ACSM) a notamment permis d’obtenir une meilleure discrimination des différentes fractions de l’AOS - sur un pas de temps court (30min) – que ce qu’il est générallement réalisé à l’aide des seules mesures automatiques.

International audience; The present study aimed at performing PM10 source apportionment, using positive matrix factorization (PMF), based on filter samples collected every 4 h at a sub-urban station in the Paris region (France) during a PM pollution event in March 2015 (PM10 > 50 μg m−3 for several consecutive days). The PMF model allowed to deconvolve 11 source factors. The use of specific primary and secondary organic molecular markers favoured the determination of common sources such as biomass burning and primary traffic emissions, as well as 2 specific biogenic SOA (marine + isoprene) and 3 anthropogenic SOA (nitro-PAHs + oxy-PAHs + phenolic compounds oxidation) factors. This study is probably the first one to report the use of methylnitrocatechol isomers as well as 1-nitropyrene to apportion secondary OA linked to biomass burning emissions and primary traffic emissions, respectively. Secondary organic carbon (SOC) fractions were found to account for 47% of the total OC. The use of organic molecular markers allowed the identification of 41% of the total SOC composed of anthropogenic SOA (namely, oxy-PAHs, nitro-PAHs and phenolic compounds oxidation, representing 15%, 9%, 11% of the total OC, respectively) and biogenic SOA (marine + isoprene) (6% in total). Results obtained also showed that 35% of the total SOC originated from anthropogenic sources and especially PAH SOA (oxy-PAHs + nitro-PAHs), accounting for 24% of the total SOC, highlighting its significant contribution in urban influenced environments. Anthropogenic SOA related to nitro-PAHs and phenolic compounds exhibited a clear diurnal pattern with high concentrations during the night indicating the prominent role of night-time chemistry but with different chemical processes involved.

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

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds emitted by all combustion sources. They are of major health concern because of their toxic properties and are therefore, regulated pollutants in ambient air. In the atmosphere, PAH oxidation through homogeneous and heterogeneous reactions may lead to the formation of oxy- and nitro-PAHs. These latter species are also emitted concomitantly with PAHs during incomplete combustion processes. Oxy- and nitro-PAHs are potentially more toxic than their parent PAHs. The identification of the origins of oxy- and nitro-PAHs is challenging, due to the coexistence of their primary and/or secondary sources. These species are also of prime interest because they are, typically part of the secondary organic aerosol (SOA) generated from gaseous PAH oxidation, which is significant in urban environments. Based on ambient air field observations, the objective of this work is to better understand the chemical processes involved in the formation of nitro- and oxy-PAHs, their sources and to identify specific molecules that could further be used as molecular markers of PAH oxidation and SOA formation. Field measurements were performed at both locations in France (Grenoble, 2013 and at the SIRTA station, 2015 (25 km SW from Paris)) over 1 year with samplings, every third day, of the gaseous and particulate (PM10) phases. Intensive observations at SIRTA have been also performed with PM10 samples collected every 4-hour during a period of severe PM pollution event (PM>50 µg m-3 for several days) in March 2015, concomitantly with online measurements (e.g. ACSM, 7λ-Aethalometer). The study of the occurrence of nitro-, -oxy and parent PAHs in the atmosphere, the seasonal and diurnal variations of their concentrations and substance patterns and the assessment of the cancer risk induced by these compounds have been performed. Based on these observations combined with literature knowledge and an extended aerosol chemical characterization, specific molecules of PAH oxidation have been identified. These substances were then used in source-receptor models such as positive matrix factorization (PMF) to apportion the SOA contribution from PAH oxidation on PM10 mass.

During the last years the atmosphere of the Great Athens Area (GAA) and other Greek cities is burdened from extended residential biomass burning for heating purposes. In this work, a series of near real-time and off-line biomass burning tracers are analyzed during intense wood burning events in Athens. The measurements were conducted at an urban background site located in the center of Athens, and in the heart of wood burning activities (winter 2013–2014). The measured tracers include high resolution measurements of non-sea salt potassium (nss-K+), wood burning black carbon (BCwb), the m/z 60 fragment associated with levoglucosan and monosaccharide anhydrides (levoglucosan, mannosan and galactosan) determined on selected filter samples. The suitability of these tracers was evaluated when the prevailing meteorological conditions with low dispersion and deposition mechanisms (low wind speed, absence of precipitation) were associated with high biomass burning emissions at nighttime. During the severe smog periods, the levels of K+, BCwb, m/z 60 and levoglucosan were up to 2.2 μg m−3, 12.5 μg m−3, 3.4 μg m−3 and 8.6 μg m−3, respectively, higher by a factor of at least two, relatively to the non smog periods due to biomass burning. Correlations between biomass burning tracers as well as between monosaccharide anhydrides provided information about the type of material and wood being burned.

Understanding the sources and processes responsible for high-level atmospheric PM concentrations is required to implement effective PM control strategies. During the last decade, the use of AMS and ACSM instrumentations has successfully allowed real time measurements of particulate organic fraction. However, to profoundly understand the sources and formation processes of organic aerosol (OA), a comprehensive source apportionment analysis is still needed. The combination of different datasets from several measurements to refine the apportionment of OA sources, and notably secondary ones, is probably one of the best way to achieve this goal. In this study, we propose a novel approach combining online and offline measurements in Positive Matrix Factorization source-receptor model (PMF). An intensive campaign was performed at the SIRTA atmospheric research observatory, representing the suburban background air quality conditions of the Paris area (about 25 km SW from Paris). PM10 samples were collected every 4 hours over a period of intensive PM pollution events (PM > 50 µg m-3 over several days) on March 6-24 2015, concomitantly with online measurements including ACSM, PTRMS, 7λ Aethalometer, TEOM-FDMS, NOx and O3 analyzers. Regular PMF was first performed on organic matrix obtained from offline measurements using specific primary (e.g. levoglucosan (biomass burning), methane sulphonic acid (MSA) (marine), 1-nitropyrene (traffic)) and secondary organic molecular markers (e.g. hydroxyglutaric acid (α-pinene), 3-methyl,5-nitrocatechol (biomass burning), α-methyl glyceric acid (isoprene)) and on ACSM OA matrix. Results show that PMF performed on individual dataset is not truly viable to procure complete information about the different atmospheric processes involved. Here, the synergic approach proposes to combine traditional off-line PMF factors, such as primary biomass burning, primary biogenics, secondary biogenics, traffic, with OA matrix from ACSM measurements. The unified matrix was again deconvolved with PMF in order to retrieve factors such as HOA, BBOA, OOA, and to explore additional information about OA sources.

The role that soil, foliage, and atmospheric dynamics have on surface carbonyl sulfide (OCS) exchange in a Mediterranean forest ecosystem in southern France (the Oak Observatory at the Observatoire de Haute Provence, O3HP) was investigated in June of 2012 and 2013 with essentially a top-down approach. Atmospheric data suggest that the site is appropriate for estimating gross primary production (GPP) directly from eddy covariance measurements of OCS fluxes, but it is less adequate for scaling net ecosystem exchange (NEE) to GPP from observations of vertical gradients of OCS relative to CO2 during the daytime. Firstly, OCS and carbon dioxide (CO2) diurnal variations and vertical gradients show no net exchange of OCS at night when the carbon fluxes are dominated by ecosystem respiration. This contrasts with other oak woodland ecosystems of a Mediterranean climate, where nocturnal uptake of OCS by soil and/or vegetation has been observed. Since temperature, water, and organic carbon content of soil at the O3HP should favor the uptake of OCS, the lack of nocturnal net uptake would indicate that its gross consumption in soil is compensated for by emission processes that remain to be characterized. Secondly, the uptake of OCS during the photosynthetic period was characterized in two different ways. We measured ozone (O3) deposition velocities and estimated the partitioning of O3 deposition between stomatal and non-stomatal pathways before the start of a joint survey of OCS and O3 surface concentrations. We observed an increasing trend in the relative importance of the stomatal pathway during the morning hours and synchronous steep drops of mixing ratios of OCS (amplitude in the range of 60–100 ppt) and O3 (amplitude in the range of 15–30 ppb) after sunrise and before the break up of the nocturnal boundary layer. The uptake of OCS by plants was also characterized from vertical profiles. However, the time window for calculation of the ecosystem relative uptake (ERU) of OCS, which is a useful tool for partitioning measured NEE, was limited in June 2012 to a few hours after midday. This was due to the disruption of the vertical distribution of OCS by entrainment of OCS rich tropospheric air in the morning and because the vertical gradient of CO2 reverses when it is still light. Moreover, polluted air masses (up to 700 ppt of OCS) produced dramatic variation in atmospheric OCS ∕ CO2 ratios during the daytime in June 2013, further reducing the time window for ERU calculation.

Knowledge of the relative contribution of primary and secondary organic aerosol fractions is important in formulating effective control measurements for ambient particulate matter (PM), and the main part of Organic Aerosol (OA) in urban and rural atmospheres is found to be of secondary origin. However, its exact contribution still remains uncertain despite intensive efforts undertaken during the last decades to characterize and understand the chemistry leading to Secondary Organic Aerosol (SOA). Indeed, there is still no direct way to separate secondary to primary organic aerosol fractions. Quantification of Secondary Organic Carbon (SOC) is furthermore difficult because of our limited understanding of the molecular composition of SOC and because of the presence of a large, but unknown, number of secondary organic products. This study has been purposely carried out to estimate the contribution of SOC fraction to OA content, by using various semi-direct and indirect methodologies and evaluate associated uncertainties involved in the following outcomes. Measurements were conducted at SIRTA-LSCE, a well arranged atmospheric site in the vicinity of Paris (France), over a period from 6 to 24 March 2015. This was accomplished by utilizing information obtained from intensive filter measurements conducted at every 4 hours. SOC estimations were proposed using Positive Matrix Factorization applied to Aerosol Chemical Speciation Monitor (ACSM) measurements as well as using off-line data analyses, such as EC-, WSOC-, and SOA tracer-based methods. Results might also assert the photochemical origin of SOA, although the relative contribution to the OC and the SOA formation may differ during the chosen period. Large discrepancies were accounted for in the SOC estimations furnished using different techniques. Results imply that cautions should be taken while estimating SOC. Discussion will lead to profound information about the limitations and challenges associated to SOC estimations using different techniques.

The carbonaceous fraction of aerosols is composed of many compounds which constitute the organic carbon (OC) and elemental carbon (EC) components. Within the organic carbon component, Polycyclic Aromatic Hydrocarbons (PAHs) are the prevalent contributor to atmospheric pollution and emitted by incomplete combustion processes. Atmospheric oxidation of PAHs induces the formation of oxidized compounds such as oxygenated-PAHs (oxy-PAHs) and nitrated-PAHs (nitro- PAHs). The study of these PAH derivatives have become a prime concern as most are known to be carcinogenic and potentially more mutagenic than PAHs. These compounds may also instigate the formation of secondary organic aerosol (SOA), which may represent a large source of SOA in urban areas. The main objective of this study was to investigate the primary and secondary processes leading to the formation of oxy-PAHs and nitro-PAHs. This was accomplished by utilizing information obtained from intensive filter measurements along with online monitoring. To the best of our knowledge, this unique approach has not been explored yet. Measurements were conducted at SIRTA-LSCE, which features, the suburban background conditions of Paris, France. Results highlight high concentrations of oxy-PAHs and nitro-PAHs during the period 14-21, March 2015, including specific secondary PAH derivatives as 6H-dibenz[b,d]pyran-6-one, acenaphthenequinone and 2-nitrofluoranthene. This suggests that such species could be generated through secondary processes related to high NO3 - and SO4 2- concentrations that can be explicitly observed considering ACSM results. Besides, the formation of 6H-dibenz[b,d]pyran-6-one seems to be highly influenced by the daytime chemistry while 2-nitrofluoranthene may be generated during nighttime (potentially involving NO3 radical chemistry). Interestingly, fossil-fuel-based Black Carbon (BCff) and 1-nitropyrene (1-NP, a promising marker for diesel emissions) present similar temporal concentration profiles. Discussion will further accentuate diurnal variations, information about the day- and nighttime chemistry, and also usefulness of combining off-line and on-line measurements to ensure a comprehensive understanding of the prevalent atmospheric processes.

A detailed knowledge of the sources, transformation, and fate of organic aerosols (OA) in the atmosphere has become essential because of their major impacts on climate change and air quality. A complete understanding is still hindered by the immense chemical complexity of the organic fraction emitted from both anthropogenic and biogenic sources (primary organic aerosols, POA) or formed into the atmosphere via the photochemical oxidation of (semi-) volatile organic compounds (secondary organic aerosols, SOA). The chemical speciation of OA and the identification of their major sources are then necessary. So far, detailed information on the chemical components is generally only available for 10–30% of OA. In the present study, the source apportionment of OA is presented based on the characterization of the water-soluble organic fraction of ambient air particles, collected onto conventional filters using offline-AMS analysis. An intensive campaign was performed at SIRTA-LSCE, which illustrates the suburban background conditions of Paris (France). Every 4 hour filter measurements were conducted over a period from 6 to 24, March 2015, concomitantly with online measurements, carried out using ACSM, Aethalometer, TEOM-FDMS, NOx and O3 analyzers. Source apportionment was performed on offline- AMS data by multi-linear engine (ME-2), using the newly developed Source Finder (SoFi) package. External markers (i.e. organic species like MSA, levoglucosan, oxalate and SOA molecular compounds) are used to substantiate the presence of primary and secondary factors. SoFi outputs indicate that some factors highlight different contribution over the first and second half of the sampling campaign, advocating the role of different chemical processes during these periods. Data analysis also provides more information about the different factors, their contribution to OA and existing major OA sources in Paris. Finally, results clearly illustrate the benefit of combining different measurements and the use of external markers, in aerosol source apportionment studies.

Electrospray ionization (ESI) and desorption electrospray ionization (DESI) mass spectrometry were for the first time compared to investigate degradation products resulting from radiolysis of polyurethane (PUR) irradiated using accelerated electrons. First, DESI optimization was performed to obtain the best results in terms of sensitivity for surface polymer analysis. Then, a comparison was performed between DESI-MS and ESI-MS characterization of the degradation products of irradiated PUR with different doses up to 10 MGy. Similar results were obtained despite a lower sensitivity of DESI. Finally, DESI results obtained by direct surface analysis of irradiated PUR films as a function of depth were compared to bulk analysis results obtained by ESI. This comparison shows that degradation products of PUR are very comparable at the surface or within the polymer, confirming the radio-oxidation homogeneity.

Experimental Emmental cheeses were analysed to evaluate the potential of mid-infrared spectroscopy to follow the ripening process. Cheeses were sampled at seven different ripening stages and were analysed. The infrared spectra were obtained by placing the cheese slices directly over the attenuated total reflectance crystal. Analysis of variance showed significant (P ≤ 0.05) absorbance changes between spectral sets in the regions assigned to vibrations of alcohol, amide and hydrocarbon chains. Principal component analysis (PCA) made it possible to describe four groups including samples ripened during 21, 27 and 34 days (G1), 51 and 58 days (G2), 65 days (G3) and the samples at the end of the ripening (mould opening, about 85 days) (G4). Using general discriminant analysis of spectral data, it is not possible to correctly distinguish samples according to seven dates of sampling, but samples belonging to the four groups identified by PCA are predicted well by the regression model.

As part of the European ACTRIS project, the first large Quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM) intercomparison study was conducted in the region of Paris for three weeks during the late fall–early winter period (November–December 2013). The first week was dedicated to tuning and calibration of each instrument whereas the second and third were dedicated to side-by-side comparison in ambient conditions with co-located instruments providing independent information on submicron aerosol optical, physical and chemical properties. Near real-time measurements of the major chemical species (organic matter, sulfate, nitrate, ammonium and chloride) in the non-refractory submicron aerosols (NR-PM1) were obtained here from 13 Q-ACSM. The results show that these instruments can produce highly comparable and robust measurements of the NR-PM1 total mass and its major components. Taking the median of the 13 Q-ACSM as a reference for this study, strong correlations (r2 > 0.9) were observed systematically for each individual ACSM across all chemical families except for chloride for which three ACSMs showing weak correlations partly due to the very low concentrations during the study. Reproducibility expanded uncertainties of Q-ACSM concentration measurements were determined using appropriate methodologies defined by the International Standard Organization (ISO 17025) and were found to be of 9, 15, 19, 28 and 36 % for NR-PM1, nitrate, organic matter, sulfate and ammonium respectively. However, discrepancies were observed in the relative concentrations of the constituent mass fragments for each chemical component. In particular, significant differences were observed for the organic fragment at mass-to-charge ratio 44, which is a key parameter describing the oxidation state of organic aerosol. Following this first major intercomparison exercise of a large number of ACSMs, detailed intercomparison results are presented as well as a discussion of some recommendations about best calibration practices, standardized data processing and data treatment.

Aerosol mass spectrometer (AMS) measurements have been successfully used towards a better understanding of non-refractory submicron (PM1) aerosol chemical properties based on short-term campaigns. The recently developed Aerosol Chemical Speciation Monitor (ACSM) has been designed to deliver quite similar artifact-free chemical information but for low cost, and to perform robust monitoring over long-term periods. When deployed in parallel with real-time black carbon (BC) measurements, the combined data set allows for a quasi-comprehensive description of the whole PM1 fraction in near real time. Here we present 2-year long ACSM and BC data sets, between mid-2011 and mid-2013, obtained at the French atmospheric SIRTA supersite that is representative of background PM levels of the region of Paris. This large data set shows intense and time-limited (a few hours) pollution events observed during wintertime in the region of Paris, pointing to local carbonaceous emissions (mainly combustion sources). A non-parametric wind regression analysis was performed on this 2-year data set for the major PM1 constituents (organic matter, nitrate, sulfate and source apportioned BC) and ammonia in order to better refine their geographical origins and assess local/regional/advected contributions whose information is mandatory for efficient mitigation strategies. While ammonium sulfate typically shows a clear advected pattern, ammonium nitrate partially displays a similar feature, but, less expectedly, it also exhibits a significant contribution of regional and local emissions. The contribution of regional background organic aerosols (OA) is significant in spring and summer, while a more pronounced local origin is evidenced during wintertime, whose pattern is also observed for BC originating from domestic wood burning. Using time-resolved ACSM and BC information, seasonally differentiated weekly diurnal profiles of these constituents were investigated and helped to identify the main parameters controlling their temporal variations (sources, meteorological parameters). Finally, a careful investigation of all the major pollution episodes observed over the region of Paris between 2011 and 2013 was performed and classified in terms of chemical composition and the BC-to-sulfate ratio used here as a proxy of the local/regional/advected contribution of PM. In conclusion, these first 2-year quality-controlled measurements of ACSM clearly demonstrate their great potential to monitor on a long-term basis aerosol sources and their geographical origin and provide strategic information in near real time during pollution episodes. They also support the capacity of the ACSM to be proposed as a robust and credible alternative to filter-based sampling techniques for long-term monitoring strategies.

Measurements of CO2, CO, NOx and selected Volatile Organic Compounds (VOCs) mole fractions were performed continuously during a 10-day period in the Guy Môquet tunnel in Thiais, a peri-urban area about 15 km south of the centre of Paris, between 28 September and 8 October 2012. This data set is used here to identify the characteristics of traffic-emitted CO2 by evaluating its ratios to co-emitted species for the first time in the Paris region. High coefficients of determination (r2 > 0.7) are observed between CO2 and certain compounds that are characteristic of the traffic source (CO, NOx, benzene, xylenes and acetylene). Weak correlations (r2 < 0.2) are found with species such as propane, n-butane and i-butane that are associated with fuel evaporation, an insignificant source for CO2. To better characterise the traffic signal we focus only on species that are well-correlated with CO2 and on rush-hour periods characterised by the highest traffic-related mole fractions. From those mole fractions we remove the nighttime-average weekday mole fraction obtained for each species that we infer to be the most appropriate background signal for our study. Then we calculate observed Δspecies / ΔCO2 ratios, which we compare with the ones provided by the 2010 bottom–up high-resolved regional emission inventory from Airparif (the association in charge of monitoring the air quality in Île-de-France), focusing on local emission data for the specific road of the tunnel. We find an excellent agreement (2%) between the local inventory emission CO / CO2 ratio and our observed ΔCO / ΔCO2 ratio. Former tunnel experiments carried out elsewhere in the world provided observed ΔCO / ΔCO2 ratios that differ from 49 to 592% to ours. This variability can be related to technological improvement of vehicles, differences in driving conditions, and fleet composition. We also find a satisfactory agreement with the Airparif inventory for n-propylbenzene, n-pentane and xylenes to CO2 ratios. For most of the other species, the ratios obtained from the local emission inventory overestimate the observed ratios to CO2 by 34 to more than 300%. However, the emission ratios of NOx, o-xylene and i-pentane are underestimated by 30 to 79%. One main cause of such high differences between the inventory and our observations is likely the obsolete feature of the VOCs speciation matrix of the inventory that has not been updated since 1998, although law regulations on some VOCs have occurred since that time. Our study bears important consequences, discussed in the conclusion, for the characterisation of the urban CO2 plume and for atmospheric inverse modelling of urban CO2 emissions.

The present study aims at identifying and apportioning fine aerosols to their major sources in Paris (France) – the second most populated "larger urban zone" in Europe – and determining their geographical origins. It is based on the daily chemical composition of PM2.5 examined over 1 year at an urban background site of Paris (Bressi et al., 2013). Positive matrix factorization (EPA PMF3.0) was used to identify and apportion fine aerosols to their sources; bootstrapping was performed to determine the adequate number of PMF factors, and statistics (root mean square error, coefficient of determination, etc.) were examined to better model PM2.5 mass and chemical components. Potential source contribution function (PSCF) and conditional probability function (CPF) allowed the geographical origins of the sources to be assessed; special attention was paid to implement suitable weighting functions. Seven factors, namely ammonium sulfate (A.S.)-rich factor, ammonium nitrate (A.N.)-rich factor, heavy oil combustion, road traffic, biomass burning, marine aerosols and metal industry, were identified; a detailed discussion of their chemical characteristics is reported. They contribute 27, 24, 17, 14, 12, 6 and 1% of PM2.5 mass (14.7 μg m−3) respectively on the annual average; their seasonal variability is discussed. The A.S.- and A.N.-rich factors have undergone mid- or long-range transport from continental Europe; heavy oil combustion mainly stems from northern France and the English Channel, whereas road traffic and biomass burning are primarily locally emitted. Therefore, on average more than half of PM2.5 mass measured in the city of Paris is due to mid- or long-range transport of secondary aerosols stemming from continental Europe, whereas local sources only contribute a quarter of the annual averaged mass. These results imply that fine-aerosol abatement policies conducted at the local scale may not be sufficient to notably reduce PM2.5 levels at urban background sites in Paris, suggesting instead more coordinated strategies amongst neighbouring countries. Similar conclusions might be drawn in other continental urban background sites given the transboundary nature of PM2.5 pollution.

Studies describing the chemical composition of fine aerosol (PM2.5) in urban areas are often conducted during few weeks only, and at one sole site, giving thus a narrow view of their temporal and spatial characteristics. This paper presents a one-year (11 September 2009–10 September 2010) survey of the daily chemical composition of PM2.5 in the region of Paris, which is the second most populated "Larger Urban Zone" in Europe. Five sampling sites representative of suburban (SUB), urban (URB), northeast (NER), northwest (NWR) and south (SOR) rural backgrounds were implemented. The major chemical components of PM2.5 were determined including elemental carbon (EC), organic carbon (OC), and the major ions. OC was converted to organic matter (OM) using the chemical mass closure methodology, which leads to conversion factors of 1.95 for the SUB and URB sites, and 2.05 for the three rural ones. On average, gravimetrically determined PM2.5 annual mass concentrations are 15.2, 14.8, 12.6, 11.7 and 10.8 μg m−3 for SUB, URB, NER, NWR and SOR sites, respectively. The chemical composition of fine aerosol is very homogeneous at the five sites and is composed of OM (38–47%), nitrate (17–22%), non-sea-salt sulfate (13–16%), ammonium (10–12%), EC (4–10%), mineral dust (2–5%) and sea salt (3–4%). This chemical composition is in agreement with those reported in the literature for most European environments. On the annual scale, Paris (URB and SUB sites) exhibits its highest PM2.5 concentrations during late autumn, winter and early spring (higher than 15 μg m−3 on average, from December to April), intermediates during late spring and early autumn (between 10 and 15 μg m−3 during May, June, September, October, and November) and the lowest during summer (below 10 μg m−3 during July and August). PM levels are mostly homogeneous at the regional scale, on the whole duration of the project (e.g. for URB plotted against NER sites: slope = 1.06, r2 = 0.84, n = 330), suggesting the importance of mid- or long-range transport, and regional instead of local scale phenomena. During this one-year project, two third of the days exceeding the PM2.5 2015 EU annual limit value of 25 μg m−3 were due to continental import from countries located northeast, east of France. This result questions the efficiency of local, regional and even national abatement strategies during pollution episodes, pointing the need for a wider collaborative work with the neighbourhood countries on these topics. Nevertheless, emissions of local anthropogenic sources lead to higher levels at the URB and SUB sites compared to the others (e.g. 26% higher on average at the URB than at the NWR site for PM2.5, during the whole campaign), which can even be emphasised by specific meteorological conditions such as low boundary layer heights. OM and secondary inorganic species (nitrate, non-sea-salt sulfate and ammonium, noted SIA) are mainly imported by mid- or long-range transport (e.g. for NWR plotted against URB sites: slope = 0.79, r2 = 0.72, n = 335 for OM, and slope = 0.91, r2 = 0.89, n = 335 for SIA) whereas EC is primarily locally emitted (e.g. for SOR plotted against URB sites: slope = 0.27; r2 = 0.03; n = 335). This database will serve deepest investigations of carbonaceous aerosols, metals as well as the main sources and geographical origins of PM in the region of Paris.

International audience; Volatile organic compounds (VOCs) are key components in atmospheric chemistry. On a global scale, biogenic VOCs (BVOCs) constitute approximately 90 % of global VOC emissions. They participate in photochemical reactions and thus play a major role in the formation of tropospheric ozone and secondary organic aerosols. However, the impact of BVOCs on air quality is still characterized by large uncertainties, partly because emissions are not well quantified. As part of the Canopee project, a field campaign took place at the Oak Observatory of the Observatoire de Haute-Provence (O3HP), with the aim of quantifying BVOC emissions from a forest representative of the Mediterranean region.Measurements of concentrations and emission fluxes were carried out from the branch to the canopy level. Branch-level measurements enabled a better understanding of the environmental and physiological parameters of the plant that govern emissions. Fluxmeasurements above the top of the canopy enabled us to quantify the outgoing flow of BVOCs from the forest entering the troposphere. The results showed that white oak is a strong emitter of isoprene but a weak emitter ofmethanol andmonoterpenes. Isoprene emission fluxes were estimated at 7.2 mg m-2 h-1 (under standard conditions of temperature and solar radiation), thusmaking theO3HP forest one of the strongest isoprene emitting ecosystems worldwide; Les composés organiques volatils (COV) sont des composants clés en chimie atmosphérique. À l'échelle globale, on estime que 10 % ont une origine anthropique et 90 % une origine biogénique. L'impact des COV biogéniques (COVB), notamment sur la formation d'ozone (polluant et gaz à effet de serre) et d'aérosols organiques secondaires (à impact sanitaire et radiatif) en font un objet d'étude d'actualité. Toutefois, l'importance de l'impact des COVB sur la qualité de l'air est encore marquée par de larges incertitudes, en partie parce que les émissions demeurent mal quantifiées. Dans le cadre du projet Canopee, une campagne de mesure a eu lieu à l'O3HP, Observatoire du chêne pubescent à l'OHP (Observatoire de Haute-Provence), avec pour objectif de quantifier les émissions de COVB issues d'une forêt représentative de la région méditerranéenne. Des mesures de concentrations et de flux d'émission ont été réalisées à plusieurs échelles : de la branche à la canopée. L'étude des émissions à l'échelle du de la plante a permis une meilleure compréhension des paramètres environnementaux et physiologiques qui régissent les émissions. Les flux de COVB sortant de la canopée et exportés vers la troposphère ont pu être quantifiés. Les résultats montrent que le chêne blanc est un fort émetteur d'isoprène, mais un faible émetteur de méthanol et de monoterpènes. À l'échelle de la forêt, les flux d'émissions d'isoprène ont été estimés à 7,2 mg m-2 h-1 en conditions standard, ce qui fait de l'O3HP un des écosystèmes les plus fortement émetteurs d'isoprène à travers le monde.

Near real-time measurements of carbonaceous aerosols were performed in fine aerosols for a 10-day period during winter at a suburban site of Paris (France). These measurements were performed using an OCEC Sunset Field instrument for elemental carbon (EC) and organic carbon (OC); a Particle-Into-Liquid-Sampler coupled with a Total Organic Carbon (PILS-TOC) instrument for water-soluble OC (WSOC); and a 7-lambda aethalometer for absorption. A successful comparison was performed with filter sampling performed in parallel for EC, OC, and WSOC, providing further confidence on the results obtained by the online analyzers. A modified version of the aethalometer model was used to derive hourly concentrations of 3 organic aerosol (OA) sources: fossil fuel, wood burning, and secondary. This source apportionment was validated for primary OA (fossil fuel, wood burning) using time-resolved measurements of specific tracers (including levoglucosan, water-soluble potassium and methanol for wood burning) and showed that secondary organic aerosols (SOA) were the most abundant OA species during our study. Water-soluble properties of these different OA sources were investigated from the reconstruction of experimentally determined water-soluble/insoluble OC. About 23% of WSOC was found to be of a secondary (photochemical) origin. A large fraction of SOA was assigned as water-insoluble and could originate from semi-volatile primary OA from wood burning and/or anthropogenic emissions. These results have been obtained at a typical suburban site in France and may be then representative of a larger European area. They bring new light on the commonly accepted idea that SOA is mainly water-soluble.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds emitted by all combustion sources. They are of major health concern because of their carcinogenic, mutagenic and teratogenic properties and are therefore, regulated pollutants in ambient air. In the atmosphere, PAH oxidation through homogeneous and heterogeneous reactions may lead to the formation of oxy- and nitro-PAHs (Keyte et al., 2013). These latter species are also emitted concomitantly with PAHs during incomplete combustion processes. Oxy- and nitro- PAHs are potentially more toxic than their parent PAHs. The identification of the origins of oxy- and nitro- PAHs is challenging, due to the coexistence of their primary and/or secondary sources. These species are also of prime interest because they are, typically part of the secondary organic aerosol (SOA) generated from gaseous PAH oxidation, which is significant in urban environments (Chan et al., 2009). The objective of this work is to better understand the chemical processes involved in the formation of nitroand oxy-PAHs based on ambient air field observations, to better understand the sources of these toxic compounds and to identify specific molecules that could further be used as molecular markers of PAH oxidation and SOA formation. Field measurements were performed over 1 year with samplings, every third day, of the gaseous and particulate (PM10) phases in Grenoble (2013) and at the SIRTA station (25 km SW from Paris city center) (2015). Intensive observations at SIRTA have been also performed with PM10 samples collected every 4- hour during a period of severe PM pollution event (PM>50 μg m-3 for several days) in March 2015, concomitantly with online measurements (e.g. ACSM, 7λ-Aethalometer). The study of the occurrence of nitro-, -oxy and parent PAHs in the atmosphere, the seasonal and diurnal variations of their concentrations and substance patterns and the assessment of the cancer risk induced by these compounds have been performed. Based on these observations combined with literature knowledge and an extended aerosol chemical characterization, specific molecules of PAH oxidation have been identified. These substances were then used in source-receptor models such as positive matrix factorization (PMF) to apportion the SOA contribution from PAH oxidation on PM10 mass.