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Organic aerosol (OA) is a major part of atmospheric fine particulate matter (PM), accounting for approximately 20-60% w/w of PM in the continental mid-altitudes. However, ambient OA remains poorly understood due to mixed source origins and processes (anthropogenic and biogenic, primary and secondary). The objective of this study was to refine source apportionment of PM10 OA by Positive Matrix Factorization (PMF) using specific primary and secondary organic molecular markers. PM10 samples were collected over a one year period (2013) at an urban station in Grenoble (France) every third day (24 h-basis sampling) on quartz filters, and an extended chemical characterization was performed (~216 species quantified) including specific primary organic markers i.e. levoglucosan, polyols (arabitol, mannitol), 1-nitropyrene (diesel emission), PAHs, alkanes, hopanes, etc. and secondary markers i.e. nitro- and oxy-PAHs, hydroxyglutaric acid (α-pinene secondary organic aerosol SOA), α-methyl glyceric acid (isoprene SOA), DHOPA (toluene SOA), etc. together with other PM chemical species such as OC/EC, Humic Like Substances (HuLiS), ions/cations (Na+, Mg2+, NH4+, Cl-, SO42-, NO3-), metals (Ba, Cu, Ti, Zn, Sb,...). Results showed that a better source apportionment of PM10 OA fraction was achieved using specific organic markers with additional sources resolved such as biogenic SOA, anthropogenic SOA, primary biogenic (fungi) and plant debris by comparison to more traditional PMF. More than 50% of OC seemed secondary in nature, and a high contribution of anthropogenic SOA was noticed in winter during a specific PM pollution event. Primary and secondary sources of HuLiS were also investigated in this study. Discussion will further underline the details of the chemical and temporal/seasonal profiles of each factor, and their relative contributions.

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.

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 nitro- and 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, 7-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 (Figure 1). These substances were then used in sourcereceptor models such as positive matrix factorization (PMF) to apportion the SOA contribution from PAH oxidation on PM10 mass.

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.

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.

Airborne PM pollution has emerged out as a critical issue all across the world. Quantitative and qualitative source analysis is becoming imperative to imply effective emission control strategies to reduce ambient air pollutants. Receptor oriented models, based on the statistical approach, have been developed to analyze various characteristics of the pollutants measured at the receptor site and to estimate their contributions to the source. Among the multivariate statistical receptor models used for PM source apportionment, Positive Matrix Factorization (PMF) has been adopted world wide as one of the most convenient technique. PMF has a non negative constraint and is able to quantify the factor contribution directly without a subsequent use of multiple regression analysis. More than 40% of European source apportionment studies have applied PMF (Belis et al. 2013). Recent advancements have proposed the use of new organic molecular markers in PMF to better investigate the contribution of biogenic and/or secondary organic aerosols. It has been observed that the use of these compounds improves the efficacy of PM source apportionment (Waked et al. 2014). The main objective of this study was to apportion specific PM10 sources, by using a wide variety of such organic molecular markers as PMF input data, for samples collected at an urban station “Les Frenes” of a local air quality network (Air Rhône-Alpes), considered as representative of a densely populated urban area Grenoble (France). PM10 samples were collected every third day (24 h-basis sampling) on quartz filters over a one year period (2013) and extended chemical characterization was performed including the quantification of species such as OC/EC, ions/cations (Na+, Mg2+, NH4+, Cl-, SO42-, NO3-), Polycyclic Aromatic Hydrocarbon (PAH), oxy-PAH, nitro-PAH, polyols (arabitol, mannitol), Methane Sulfonic Acid (MSA), levoglucosan, sulfur-containing PAH (Benzo[b]naphtha[2,1-d]thiophene, BNT), oxalate, higher odd number alkanes (C27, C29, C31), metals (Ba, Cu, Cr, Zn, Sb, Ni, V, Al, Ti, Fe, Mn, Rb, Ca, K). Results showed that the 10-factor profiles have given the best fit in the PMF analysis including biogenic emissions (marine, soil, plant debris), secondary inorganic (nitrate and sulfate factors) and organic aerosols, dust and aged sea salt particles and anthropogenic sources (oil combustion, traffic exhaust, biomass burning, industry…) (Figure 1). The highest percentage contribution to PM is made by secondary inorganic aerosol (~20%). It is interesting to note that Secondary PAH-aerosol factor accounts for ~ 4%. Discussion will further underline the factor contribution on seasonal basis and the stability of the chosen solution.

In the atmosphere, polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds. They are mostly emitted into the troposphere by incomplete combustion processes, such as diesel exhaust, residential heating, and wood burning. PAHs may react with oxidants by either homogeneous or heterogeneous reactions to form nitro and/or oxy-PAHs known to be more carcinogenic and mutagenic than parent PAHs (IARC, 2010, 2013; Rosenkranz and Mermelstein, 1985). It has been recently shown that lighter PAHs such as naphthalene and methylnaphthalene are precursors of secondary organic aerosol (SOA) and could represent one of the missing sources of SOA in urban areas (Chan et al., 2009). The purpose of this study is to better understand the SOA formation from gaseous PAH oxidation under different experimental conditions. Photooxidation experiments were performed in the UNC outdoor smog chamber. Naphthalene and 2-methylnaphthalene were selected as the two most abundant PAHs emitted in the gas phase (Reisen and Arey, 2005). Experiments were performed in the presence of nitrogen oxides, varying the type of the seed aerosol (MgSO4 vs (NH4)2SO4), aerosol acidity and relative humidity inside the chamber, as these parameters are known to have an impact on SOA formation. A complete chemical characterization of the aerosol has been performed using three complementary high-resolution mass spectrometry techniques. The composition of the gas phase has been determined during the time course of the experiments using a chemical ionization time of flight mass spectrometer (ToF-CIMS) using iodide reagent ion chemistry and the composition of the condensed phase has been characterized using ultra-performance liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS) and gas chromatography coupled to a high-resolution quadrupole time-of-flight mass spectrometry (GC-QTOFMS)...

Comprendre le devenir des composés organiques dans l'atmosphère est un enjeu majeur dans l'évaluation des impacts climatiques et sanitaires des émissions d'origines biotiques comme anthropiques. Ce travail propose une nouvelle approche analytique de la problématique en permettant d'accéder à la spéciation chimique à l'échelle moléculaire de la matière organique atmosphérique, notamment d'origine secondaire, simultanément en phases gazeuse et particulaire. L'objectif est de décrire la chimie multiphasique impliquée dans la formation et l'évolution des aérosols organiques secondaires (AOS) et d'améliorer la prise en compte des phénomènes de partition gaz/particules des composés organiques secondaires. Les phases gazeuse et particulaire sont simultanément prélevées, respectivement sur tubes d'adsorbant et sur filtres. La méthode adapte les techniques de dérivatisation des fonctions carbonylées et hydroxylées afin de les réaliser directement sur ces supports de prélèvement avant analyse des échantillons par thermo-désorption - chromatographie en phase gazeuse - spectrométrie de masse. La technique réduit l'utilisation de solvant, limite les pertes et contaminations et simplifie le traitement des échantillons. Potentiellement applicable à une large gamme de systèmes chimiques (précurseur/oxydant) et de type de sites (rural, urbain, trafic...), seront présentés ici les résultats de l'application de la méthode à l'étude de l'ozonolyse du limonène, l'un des terpènes les plus émis par la végétation à l'échelle globale et à fort rendement d'AOS.

International audience; Secondary Organic Aerosols (SOAs) are formed in the atmosphere by gas-to-particle conversion of organic gases

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.

Gas-particle partitioning is an important mechanism affecting the transport and fate of semi-volatile organic compounds (SOCs). The preferential partitioning of SOCs in the atmosphere depends on parameters such as the compound’s molecular structure as well as particulate matter physical and chemical properties. This can be explained by various empirical and theoretical models based on single- or poly-parameter linear free energy relationship (ppLFER). To explain the SOC partitioning, each model considers one or more of the compound’s physico-chemical properties or particulate matter characteristics. Despite the past efforts in determining the most appropriate model, discrepancies remain between the model prediction and observation because some models neglect certain intermolecular interactions. The aim of the present research was to apply a dual-phase as well as a multi-phase ppLFER model to predict gas-particle partitioning of nitro- and oxy- aromatic hydrocarbons. To this end, air samples (gas and particulate phase) were collected from urban and non-urban sites in Germany, France, and India. The poster will present the model predictions versus observations, and discuss their structural differences in details.

Gas-particle partitioning (GPP) is an important mechanism which affects the transport, fate, and bioavailability of semi-volatile organic compounds (SOCs). The preferential partitioning of SOCs in the atmosphere depends on parameters such as the compound’s molecular structure as well as particulate matter (PM) physical and chemical properties. The various organic and inorganic PM constituents interact with SOCs depending on their molecular structures. Previous studies considered PM as a homogenous bulk and used a typical organic solvent (i.e. octanol) as a surrogate to simulate such interaction. In the present study we applied polyparameter linear free energy relationship (ppLFER) to address this process following a multiphase aerosol scenario. ppLFER models have been developed for various organic solvents (Abraham et al., 2010) and inorganic surfaces (Goss et al., 2003). The models consider all types of molecular interactions (e.g. dispersion forces, hydrogen bonding) between solute and sorbent at equilibrium. We considered three different phases of particulate organic matter (OM): (A) high molecular mass organic soluble (OS) OM (mass mixing ratio in OM: 0.05), (B) low-mid molecular mass both water soluble (WS) and OSOM (0.55), and (C) high molecular mass organic polymers (OP) (0.40) (Rogge et al., 1993). An appropriate ppLFER model was used for each phase – i.e. hexadecane-air, dimethyl sulfoxide-air, and polyurethane ether-air, respectively. In addition, SOC adsorption to soot and soluble salt particles, namely ammonium sulphate and ammonium chloride, were included using corresponding ppLFER equations. Partitioning constants (KP; m3air g-1PM) determined with this model were corrected using the measured fractions of OM, soot, and the salts, and compared with the experimental KP for parent, oxy-, and nitro-PAHs, and nitrophenols from three central European sites - i.e. Košetice, Grenoble, and Mainz. As can be seen from Figure 1, the model made good predictions for semi-volatile pyrene (PYR), fluoranthene (FLT), 9,10-anthraquinone (9,10-ATQ), benzo(a)fluorenone (BAFLON), 9-nitroanthracene (9-NANT), and 3-nitrophenanthrene (3-NPHE), with 74 - 96% of the data points predicted within one order of magnitude accuracy (Table 1). The analysis indicated that absorption was the main process in the substance GPP, dominated by the contribution of low-mid molecular mass WSOSOM. Despite being assigned substantially different OM mass mixing ratios, OSOM and OP contributed less than 5% to the overall absorption process, although the contribution from OP was relatively higher. Finally, partitioning onto soot dominated the adsorption process, suggesting that the contributions from soluble salts may be neglected when studying the target analyte GPP. The PM phase state is an additional parameter to be included in future parameterizations of the GPP process.