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© 2015 American Chemical Society. In the troposphere, the heterogeneous lifetime of an organic molecule in an aerosol exposed to hydroxyl radicals (OH) is thought to be weeks, which is orders of magnitude slower than the analogous gas phase reactions (hours). Here, we report an unexpectedly large acceleration in the effective heterogeneous OH reaction rate in the presence of NO. This 10-50 fold acceleration originates from free radical chain reactions, propagated by alkoxy radicals that form inside the aerosol by the reaction of NO with peroxy radicals, which do not appear to produce chain terminating products (e.g., alkyl nitrates), unlike gas phase mechanisms. A kinetic model, constrained by experiments, suggests that in polluted regions heterogeneous oxidation plays a much more prominent role in the daily chemical evolution of organic aerosol than previously believed.

The chemical composition of organic aerosols influences their impacts on human health and the climate system. Aerosol formation from gas-to-particle conversion and in-particle reaction was studied for the oxidation of limonene in a new facility, the Cambridge Atmospheric Simulation Chamber (CASC). Health-relevant oxidising organic species produced during secondary organic aerosol (SOA) formation were quantified in real time using an Online Particle-bound Reactive Oxygen Species Instrument (OPROSI). Two categories of reactive oxygen species (ROS) were identified based on time series analysis: a short-lived component produced during precursor ozonolysis with a lifetime of the order of minutes, and a stable component that was long-lived on the experiment timescale (∼ 4 h). Individual organic species were monitored continuously over this time using Extractive Electrospray Ionisation (EESI) Mass Spectrometry (MS) for the particle phase and Proton Transfer Reaction (PTR) MS for the gas phase. Many first-generation oxidation products are unsaturated, and we observed multiphase aging via further ozonolysis reactions. Volatile products such as C9H14O (limonaketone) and C10H16O2 (limonaldehyde) were observed in the gas phase early in the experiment, before reacting again with ozone. Loss of C10H16O4 (7-hydroxy limononic acid) from the particle phase was surprisingly slow. A combination of reduced C = C reactivity and viscous particle formation (relative to other SOA systems) may explain this, and both scenarios were tested in the Pretty Good Aerosol Model (PG-AM). A range of characterisation measurements were also carried out to benchmark the chamber against existing facilities. This work demonstrates the utility of CASC, particularly for understanding the reactivity and health-relevant properties of organic aerosols using novel, highly time-resolved techniques.

In this work we report the study of the ozonolysis of 2,5-dihydrofuran and 2,3-dihydrofuran and the reaction conditions leading to the formation of secondary organic aerosols. The reactions have been carried out in a Teflon chamber filled with synthetic air mixtures at atmospheric pressure and room temperature. The ozonolysis only produced particles in the presence of SO2. Rising relative humidity from 0 to 40% had no effect on the production of secondary organic aerosol in the case of 2,5-dihydrofuran, while it reduced the particle number and particle mass concentrations from the 2,3-dihydrofuran ozonolysis. The water-to-SO2 rate constant ratio for the 2,3-dihydrofuran Criegee intermediate was derived from the secondary organic aerosol (SOA) yields in experiments with different relative humidity values, kH2O/kSO2 = (9.8 ± 3.7) × 10-5. The experimental results show that SO3 may not be the only intermediate involved in the formation or growth of new particles in contrast to the data reported for other Criegee intermediate-SO2 reactions. For the studied reactions, SO2 concentrations remained constant during the experiments, behaving as a catalyst in the production of condensable products. Computational calculations also show that the stabilised Criegee intermediates from the ozonolysis reaction of both 2,5-dihydrofuran and 2,3-dihydrofuran may react with SO2, resulting in the regeneration of SO2 and the formation of low-volatility organic acids., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

We focused this research on the composition of the organic aerosols transported in the two main airflows of the subtropical North Atlantic free troposphere: (i) the Saharan Air Layer – the warm, dry and dusty airstream that expands from North Africa to the Americas at subtropical and tropical latitudes – and (ii) the westerlies – which flows from North America through the North Atlantic at mid and subtropical latitudes. We determined the inorganic compounds (secondary inorganic species and elemental composition), elemental carbon and the organic fraction (bulk organic carbon and organic speciation) present in the aerosol collected at Izaña Observatory, ~ 2400 m a.s.l. in Tenerife Island. This study was performed within the context of the projects AEROATLAN (CGL2015-66299-P; 15 MINECO/FEDER) and TEAPARTICLE (CGL2011-29621), supported by the Ministry of Economy and Competitiveness of Spain and the European Regional Development Fund (ERDF).

We focused this research on the composition of the organic aerosols transported in the two main airflows of the subtropical North Atlantic free troposphere: (i) the Saharan Air Layer - the warm, dry and dusty airstream that expands from North Africa to the Americas at subtropical and tropical latitudes - and (ii) the westerlies, which flow from North America over the North Atlantic at mid- and subtropical latitudes. We determined the inorganic compounds (secondary inorganic species and elemental composition), elemental carbon and the organic fraction (bulk organic carbon and organic speciation) present in the aerosol collected at Izaña Observatory, ∼2400m.a.s.l. on the island of Tenerife. The concentrations of all inorganic and almost all organic compounds were higher in the Saharan Air Layer than in the westerlies, with bulk organic matter concentrations within the range 0.02-4.0μ-3. In the Saharan Air Layer, the total aerosol population was by far dominated by dust (93% of bulk mass), which was mixed with secondary inorganic pollutants ( < 5%) and organic matter (∼1.5%). The chemical speciation of the organic aerosols (levoglucosan, dicarboxylic acids, saccharides, n-alkanes, hopanes, polycyclic aromatic hydrocarbons and those formed after oxidation of α-pinene and isoprene, determined by gas chromatography coupled with mass spectrometry) accounted for 15% of the bulk organic matter (determined by the thermo-optical transmission technique); the most abundant organic compounds were saccharides (associated with surface soils), secondary organic aerosols linked to oxidation of biogenic isoprene (SOA ISO) and dicarboxylic acids (linked to several primary sources and SOA). When the Saharan Air Layer shifted southward, Izaña was within the westerlies stream and organic matter accounted for 28% of the bulk mass of aerosols. In the westerlies, the organic aerosol species determined accounted for 64% of the bulk organic matter, with SOA ISO and dicarboxylic acids being the most abundant; the highest concentration of organic matter (3.6μ-3) and of some organic species (e.g. levoglucosan and some dicarboxylic acids) were associated with biomass burning linked to a fire in North America. In the Saharan Air Layer, the correlation found between SOA ISO and nitrate suggests a large-scale impact of enhancement of the formation rate of secondary organic aerosols due to interaction with anthropogenic NO emissions. © 2017 Author(s)., This study was performed within the context of the projects AEROATLAN (CGL2015-66299-P; MINECO/FEDER) and TEAPARTICLE (CGL2011-29621), supported by the Ministry of Economy and Competitiveness of Spain and the European Regional Development Fund (ERDF). The authors acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT back-trajectories used in this publication. The excellent work performed by the staff of the Atmospheric Research Centre (Concepción Bayo, Cándida Hernández, Fernando de Ory, Virgilio Carreño, Rubén del Campo and SIELTEC Canarias) and of the Institute of Environmental Assessment and Water Research (Roser Chaler, Dori Fanjul, and Bibiano Hortelano) is appreciated. M. Isabel García acknowledges the grant of the Canarian Agency for Research, Innovation and Information Society (ACIISI), co-funded by the European Social Funds. Measurements at Izaña Observatory are performed within the context Global Atmospheric Watch networks with the financial support of the State Meteorological Agency of Spain (AEMET).

Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern receptor site of Beijing, China. The samples were analyzed for total carbon (TC) and water-soluble dicarboxylic acids (C-2-C-12), oxocarboxylic adds (C-2-C-9), glyoxal and methylglyoxal to better understand the photochemical aging of organic aerosols in the vicinity of Beijing. Concentrations of TC are 50% greater in daytime when winds come from Beijing than in nighttime when winds come from the northern forest areas. Most diacids showed higher concentrations in daytime, suggesting that the organics emitted from the urban Beijing and delivered to the northern vicinity in daytime are subjected to photo-oxidation to result in diacids. However, oxalic acid (C-2), which is the most abundant diacid followed by C-3 or C-4, became on average 30% more abundant in nighttime together with azelaic, omega-oxooctanoic and omega-oxononanoic acids, which are specific oxidation products of biogenic unsaturated fatty acids. Methylglyoxal, an oxidation product of isoprene and a precursor of oxalic acid, also became 29% more abundant in nighttime. Based on a positive correlation between C-2 and glyoxylic acid (omega C-2) in nighttime when relative humidity significantly enhanced, we propose a nighttime aqueous phase production of C-2 via the oxidation of omega C-2. We found an increase in the contribution of diacids to TC by 3 folds during consecutive clear days. This study demonstrates that diacids and related compounds are largely produced in the northern vicinity of Beijing via photochemical processing of organic precursors emitted from urban center and forest areas. (C) 2014 Elsevier B.V. All rights reserved.

Biomass burning is a major source of greenhouse gases and influences regional to global climate. Pre-industrial fire-history records from black carbon, charcoal and other proxies provide baseline estimates of biomass burning at local to global scales spanning millennia, and are thus useful to examine the role of fire in the carbon cycle and climate system. Here we use the specific biomarker levoglucosan together with black carbon and ammonium concentrations from the North Greenland Eemian (NEEM) ice cores (77.49° N, 51.2° W; 2480 m a.s.l) over the past 2000 years to infer changes in boreal fire activity. Increases in boreal fire activity over the periods 1000–1300 CE and decreases during 700–900 CE coincide with high-latitude NH temperature changes. Levoglucosan concentrations in the NEEM ice cores peak between 1500 and 1700 CE, and most levoglucosan spikes coincide with the most extensive central and northern Asian droughts of the past millennium. Many of these multi-annual droughts are caused by Asian monsoon failures, thus suggesting a connection between low- and high-latitude climate processes. North America is a primary source of biomass burning aerosols due to its relative proximity to the Greenland Ice Cap. During major fire events, however, isotopic analyses of dust, back trajectories and links with levoglucosan peaks and regional drought reconstructions suggest that Siberia is also an important source of pyrogenic aerosols to Greenland.

Black carbon aerosols (BC) at a London urban site were characterised in both winter- and summertime 2012 during the Clean Air for London (ClearfLo) project. Positive matrix factorisation (PMF) factors of organic aerosol mass spectra measured by a high-resolution aerosol mass spectrometer (HR-AMS) showed traffic-dominant sources in summer but in winter the influence of additional non-traffic sources became more important, mainly from solid fuel sources (SF). Measurements using a single particle soot photometer (SP2, DMT), showed the traffic-dominant BC exhibited an almost uniform BC core size (Dc) distribution with very thin coating thickness throughout the detectable range of Dc. However, the size distribution of Dc (project average mass median Dc = 149 ± 22 nm in winter, and 120 ± 6 nm in summer) and BC coating thickness varied significantly in winter. A novel methodology was developed to attribute the BC number concentrations and mass abundances from traffic (BCtr) and from SF (BCsf), by using a 2-D histogram of the particle optical properties as a function of BC core size, as measured by the SP2. The BCtr and BCsf showed distinctly different Dc distributions and coating thicknesses, with BCsf displaying larger Dc and larger coating thickness compared to BCtr. BC particles from different sources were also apportioned by applying a multiple linear regression between the total BC mass and each AMS-PMF factor (BC–AMS–PMF method), and also attributed by applying the absorption spectral dependence of carbonaceous aerosols to 7-wavelength Aethalometer measurements (Aethalometer method). Air masses that originated from westerly (W), southeasterly (SE), and easterly (E) sectors showed BCsf fractions that ranged from low to high, and whose mass median Dc values were 137 ± 10 nm, 143 ± 11 nm and 169 ± 29 nm, respectively. The corresponding bulk relative coating thickness of BC (coated particle size/BC core – Dp/Dc) for these same sectors was 1.28 ± 0.07, 1.45 ± 0.16 and 1.65 ± 0.19. For W, SE and E air masses, the number fraction of BCsf ranged from 6 ± 2% to 11 ± 5% to 18 ± 10%, respectively, but importantly the larger BC core sizes lead to an increased fraction of BCsf in terms of mass than number (for W, SE and E air masses, the BCsf mass fractions ranged from 16 ± 6%, 24 ± 10% and 39 ± 14%, respectively). An increased fraction of non-BC particles (particles that did not contain a BC core) was also observed when SF sources were more significant. The BC mass attribution by the SP2 method agreed well with the BC–AMS–PMF multiple linear regression method (BC–AMS–PMF : SP2 ratio = 1.05, r2 = 0.80) over the entire experimental period. Good agreement was found between BCsf attributed with the Aethalometer model and the SP2. However, the assumed absorption Ångström exponent (αwb) had to be changed according to the different air mass sectors to yield the best comparison with the SP2. This could be due to influences of fuel type or burn phase., Atmospheric Chemistry and Physics, 14 (18), ISSN:1680-7375, ISSN:1680-7367

Atmospheric dicarboxylic acids (DCA) are a ubiquitous water-soluble component of secondary organic aerosols (SOA), which can act as cloud condensation nuclei (CCN), affecting the Earth's climate. Despite the high abundances of oxalic acid and related compounds in the marine aerosols, there is no consensus on what controls their distributions over the open ocean. Marine biological productivity could play a role in the production of DCA, but there is no substantial evidence to support this hypothesis. Here we present latitudinal distributions of DCA, oxoacids and -dicarbonyls in the marine aerosols from the remote Pacific. Their concentrations were found several times higher in more biologically influenced aerosols (MBA) than less biologically influenced aerosols. We propose isoprene and unsaturated fatty acids as sources of DCA as inferred from significantly higher abundances of isoprene-SOA tracers and azelaic acid in MBA. These results have implications toward the reassessment of climate forcing feedbacks of marine-derived SOA.

Organic aerosols (OA) are universally regarded as an important component of the atmosphere that have far-ranging impacts on climate forcing and human health. Many of these impacts are related to OA molecular characteristics. Despite the acknowledged importance, current uncertainties related to the source apportionment of molecular properties and environmental impacts make it difficult to confidently predict the net impacts of OA. Here we evaluate the specific molecular compounds as well as bulk structural properties of total suspended particulates in ambient OA collected from key emission sources (marine, biomass burning, and urban) using ultrahigh resolution mass spectrometry (UHR-MS) and proton nuclear magnetic resonance spectroscopy (1H NMR). UHR-MS and 1H NMR show that OA within each source is structurally diverse, and the molecular characteristics are described in detail. Principal component analysis (PCA) revealed that (1) aromatic nitrogen species are distinguishing components for these biomass burning aerosols; (2) these urban aerosols are distinguished by having formulas with high O/C ratios and lesser aromatic and condensed aromatic formulas; and (3) these marine aerosols are distinguished by lipid-like compounds of likely marine biological origin. This study provides a unique qualitative approach for enhancing the chemical characterization of OA necessary for molecular source apportionment.

International audience; During the summers of 2013 and 2014, two three-week intensive campaigns took place over the western Mediterranean in order to investigate the origins of photo-oxidants as well as the sources and processes of formation of organic aerosols in this region. Within the frame of the MISTRAL/ChArMEx program, an extensive number of chemical compounds were investigated by means of ground-based and also airborne measurements. The objective of this paper is to investigate the sources of organic aerosols in the western Mediterranean basin. There can be a multitude of sources (continental vs. local, anthropogenic vs. biogenic …) and they have not yet been quantified accurately neither by measurements nor model simulations. Modelling of the organic aerosols is still uncertain and needs to be improved. The large observational data set obtained during the ChArMEx intensive campaign for the period of July to August 2013 presents an opportunity to evaluate new secondary aerosol schemes within the CHIMERE chemistry-transport model. To verify the robustness of the simulations, simulation-observation comparisons were performed and also the representativeness of the simulations was investigated where the ground-based measurements were performed (Ersa, Cape Corsica). The model has been configured in a way to fit the specificities of this unique region. The largest domain covers the entire Europe as well as the northern Africa with a low resolution (30 km), nested domains go down to a resolution of 1 km to resolve representativeness issues due to the complex orography of Cape Corsica. Multiple configurations of recent organic aerosol schemes based on the Volatility Basis Set (VBS) were implemented into CHIMERE .In order to evaluate the consistency of each configuration, the results are compared to the base simulations and a large pool of observational data (organic concentration in PM1, oxidation state, modern versus fossil carbon measurements, AirBase stations, EMEP stations …). This comparison shows that fragmentation processes and the formation of non-volatile organic aerosol are two critical factors to be included in the simulation of organic aerosols. Also, the simulation-observation comparisons show a good agreement between the concentration of organic aerosols, the oxidation stages (PMF measurements) and also the distribution of fossil/non-fossil sources for the scheme containing the aforementioned processes in the western Mediterranean area. In figure 1, a 2D image of organic aerosols concentrations in the western Mediterranean basin is shown for this scheme (Shrivastava et al., 2015). Systematic budget simulations will be presented to determine the origin of organic aerosol over the western Mediterranean basin. The uncertainty of these simulations will be assessed from comparing results from different aerosol schemes which best fit with the available measurements.

Bisphenol A (BPA) is a suspected endocrine disruptor in the environment. However, little is known about its distribution and transport in the atmosphere. Here, the concentrations of BPA in the atmospheric aerosols from urban, rural, marine, and the polar regions were measured using solvent extraction/derivatization and gas chromatography/mass spectrometry technique. The concentrations of BRA (1-17,400 pg m^[-3]) ranged over 4 orders of magnitude in the world with a declining trend from the continent (except for the Antarctica) to remote sites. A positive correlation was found between BPA and 1,3,5-triphenylbenzene, a tracer for plastic burning, in urban regions, indicating that the open burning of plastics in domestic waste should be a significant emission source of atmospheric BRA. Our results suggest that the ubiquity of BRA in the atmosphere may raise a requirement for the evaluation of health effects of BRA in order to control its emission sources, for example, from plastic burning.

A case study of atmospheric aerosol measurements exploring the impact of the vertical distribution of aerosol chemical composition upon the radiative budget in North-Western Europe is presented. Sub-micron aerosol chemical composition was measured by an Aerodyne Aerosol Mass Spectrometer (AMS) on both an airborne platform and a ground-based site at Cabauw in the Netherlands. The examined period in May 2008 was characterised by enhanced pollution loadings in North-Western Europe and was dominated by ammonium nitrate and Organic Matter (OM). Both ammonium nitrate and OM were observed to increase with altitude in the atmospheric boundary layer. This is primarily attributed to partitioning of semi-volatile gas phase species to the particle phase at reduced temperature and enhanced relative humidity. Increased ammonium nitrate concentrations in particular were found to strongly increase the ambient scattering potential of the aerosol burden, which was a consequence of the large amount of associated water as well as the enhanced mass. During particularly polluted conditions, increases in aerosol optical depth of 50–100% were estimated to occur due to the observed increase in secondary aerosol mass and associated water uptake. Furthermore, the single scattering albedo was also shown to increase with height in the boundary layer. These enhancements combined to increase the negative direct aerosol radiative forcing by close to a factor of two at the median percentile level. Such increases have major ramifications for regional climate predictions as semi-volatile components are often not included in aerosol models. The results presented here provide an ideal opportunity to test regional and global representations of both the aerosol vertical distribution and subsequent impacts in North-Western Europe. North-Western Europe can be viewed as an analogue for the possible future air quality over other polluted regions of the Northern Hemisphere, where substantial reductions in sulphur dioxide emissions have yet to occur. Anticipated reductions in sulphur dioxide in polluted regions will result in an increase in the availability of ammonia to form ammonium nitrate as opposed to ammonium sulphate. This will be most important where intensive agricultural practises occur. Our observations over North-Western Europe, a region where sulphur dioxide emissions have already been reduced, indicate that failure to include the semi-volatile behaviour of ammonium nitrate will result in significant errors in predicted aerosol direct radiative forcing. Such errors will be particularly significant on regional scales.

The numerical analysis of a dynamic constrained optimization problem is presented. It consists of a global minimization problem that is coupled with a system of ordinary differential equations. The activation and the deactivation of inequality constraints induce discontinuity points in the time evolution. A numerical method based on an operator splitting scheme and a fixed point algorithm is advocated. The ordinary differential equations are approximated by the Crank-Nicolson scheme, while a primal-dual interior-point method with warm-starts is used to solve the minimization problem. The computation of the discontinuity points is based on geometric arguments, extrapolation polynomials and sensitivity analysis. Second order convergence of the method is proved when an inequality constraint is activated. Numerical results for atmospheric particles confirm the theoretical investigations.

Aerosol particles (PM2.5) were collected during the day (n=6) and nighttime (n=9) from a tropical pasture site in Rondônia, Brazil during an intensive biomass burning period (16-26 September, 2002). Higher normalized (by K+, levoglucosan, or apparent elemental carbon, ECa) mass concentrations of SO4^[2-] and CH3SO3- in daytime suggest their photochemical production, while the opposite trend for NO3- suggests its transfer to the aerosol phase at lower temperatures and higher humidities, as well as possibly production through hydrolysis of N2O5 on aqueous aerosol particles. About 4.2-7.5% of OC (5-13% of water-soluble organic carbon (WSOC)) could be characterized at the molecular level using GC-MS and GC-FID. Among the detected organic compound classes, the relative abundances of anhydrosugars and aromatics were higher in night samples, but sugars/sugar alcohols, diacids, oxoacids and α-dicarbonyls were more abundant in day samples. Consecutive day and night samples showed that δ13C values of total carbon (TC) were lower in daytime samples, which can be interpreted as resulting from higher contributions of refractory TC depleted in 13C due to predominantly flaming combustion. The δ15N values of total nitrogen (TN) ranged from +23.5‰ to +25.7‰, however, there was no trend in day and night samples. Higher values of δ13C and δ15N for biomass burning particles than those of unburned vegetation reflect positive isotopic enrichment either during the formation of particles or after the emission of particles in the atmosphere.

9 pages, 3 figures, 1 table, supporting information http://pubs.acs.org/doi/suppl/10.1021/acs.est.5b02922, A number of field observations employing aerosol mass spectrometers (AMS) have demonstrated that organic matter rich in monocarboxylic acids and aliphatic carbonyls originating from cooking activities (the COA factor) contributes significantly to ambient organic matter (OM) in urban environments. Little is known about the contribution and nature of COA in rural localities. We studied the correlation of COA with chemical tracers at a rural site in the Po Valley, Italy. Our statistical approach, based on positive matrix factorization (PMF) shows that the COA factor was clearly linked to local emissions of chloride and methanesulfonic acid (MSA), chemical tracers not associated with cooking emissions, or with combustion sources. While the association with Cl is not understood at this stage, the emission of reduced sulfur compounds, aliphatic carbonyls and monocarboxylic acids is consistent with several agricultural practices (e.g., manure storage) and waste disposal systems (e.g., landfills) which characterize the suburban and rural areas of the Po Valley and of other many populated environments. It is concluded that the nature and origins of the AMS COA factor measured at a rural site are complex and include far more than the emissions from food cooking, This work was funded by European integrated project on aerosol cloud climate and air quality interactions (no. 036833-2, EUCAARI). Manuel Dall’Osto and Roy M. Harrison thank the UK National Centre for Atmospheric Science for financial support. We acknowledge funding from the EU FP7-ENV-2013 programme “impact of Biogenic vs. Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding” (BACCHUS), project no. 603445. Programme Ramon y Cajal (RYC-2012-11922) also provided financial support

Trace element measurements in PM10–2.5, PM2.5–1.0 and PM1.0–0.3 aerosol were performed with 2 h time resolution at kerbside, urban background and rural sites during the ClearfLo winter 2012 campaign in London. The environment-dependent variability of emissions was characterized using the Multilinear Engine implementation of the positive matrix factorization model, conducted on data sets comprising all three sites but segregated by size. Combining the sites enabled separation of sources with high temporal covariance but significant spatial variability. Separation of sizes improved source resolution by preventing sources occurring in only a single size fraction from having too small a contribution for the model to resolve. Anchor profiles were retrieved internally by analysing data subsets, and these profiles were used in the analyses of the complete data sets of all sites for enhanced source apportionment. A total of nine different factors were resolved (notable elements in brackets): in PM10–2.5, brake wear (Cu, Zr, Sb, Ba), other traffic-related (Fe), resuspended dust (Si, Ca), sea/road salt (Cl), aged sea salt (Na, Mg) and industrial (Cr, Ni); in PM2.5–1.0, brake wear, other traffic-related, resuspended dust, sea/road salt, aged sea salt and S-rich (S); and in PM1.0–0.3, traffic-related (Fe, Cu, Zr, Sb, Ba), resuspended dust, sea/road salt, aged sea salt, reacted Cl (Cl), S-rich and solid fuel (K, Pb). Human activities enhance the kerb-to-rural concentration gradients of coarse aged sea salt, typically considered to have a natural source, by 1.7–2.2. These site-dependent concentration differences reflect the effect of local resuspension processes in London. The anthropogenically influenced factors traffic (brake wear and other traffic-related processes), dust and sea/road salt provide further kerb-to-rural concentration enhancements by direct source emissions by a factor of 3.5–12.7. The traffic and dust factors are mainly emitted in PM10–2.5 and show strong diurnal variations with concentrations up to 4 times higher during rush hour than during night-time. Regionally influenced S-rich and solid fuel factors, occurring primarily in PM1.0–0.3, have negligible resuspension influences, and concentrations are similar throughout the day and across the regions.

2005年度日本地球化学会賞受賞記念論文, I started a study of polar organic compounds in the atmosphere of Los Angeles and its vicinity in early 1980s, when acid rain problems became an important environmental issue. In late 1980s, another two problems were recognized to be serious; i.e., global warming due to the increased greenhouse gases and depletion of stratospheric ozone discovered over Antarctica. I have developed GC and GC/MS methods to determine various organic compounds in the atmosphere including water-soluble mono- (C1-C10) and di-carboxylic (C2-C10) acids. Using those methods, formic and acetic acids were found as major monoacids in rainwater and in gas phase, followed by propionic acid. Total monoacids were found to account for up to 12% of total organic carbon in the Los Angeles rainwater. Their concentrations were equal to 1/4 to 1/2 of those of inorganic acids (sulfate and nitrate). Similarly, oxalic acid (C2) was found as the most abundant diacid species followed by malonic (C3) and succinic (C4) acids in aerosols and rainwater. Studies of diacids in the atmosphere of urban Tokyo showed a diurnal variation with daytime maximum, indicating that secondary photochemical production of small diacids is more important than the primary emission from fossil fuel combustion (motor exhausts). Although diacids (C2-C10) account for < 2% of total aerosol carbon in the urban atmosphere, the values increased up to 9% in the Arctic and 26% in the marine aerosols from the Pacific. Polar sunrise experiments conducted at Alert in the high Arctic further confirmed a significant secondary production of small diacids in early spring when sun returns on the horizon. Based on the spatial distributions of diacids over the Pacific, photochemical transformation (aging) of organic aerosols was characterized by an enrichment of oxalic acid in the marine atmosphere. Because dicarboxylic acids are water-soluble and can act as cloud condensation nuclei (CCN) in the atmosphere, they likely contribute to the formation of cloud droplets and thus affect indirectly on radiation balance of the Earth and the climate changes. Recent advances in the organic aerosol studies are also reviewed together with the studies on their hygroscopic properties (CCN activity) with a scope for the future study.

Understanding sources, concentrations, and transformations of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere is important because of their potent mutagenicity and carcinogenicity. The measurement of particle-bound PAHs by three different methods during the Mexico City Metropolitan Area field campaign in April 2003 presents a unique opportunity for characterization of these compounds and intercomparison of the methods. The three methods are ( 1) collection and analysis of bulk samples for time-integrated gas- and particle-phase speciation by gas chromatography/ mass spectrometry; ( 2) aerosol photoionization for fast detection of PAHs on particles' surfaces; and ( 3) aerosol mass spectrometry for fast analysis of size and chemical composition. This research represents the first time aerosol mass spectrometry has been used to measure ambient PAH concentrations and the first time that fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH measurements suggest that motor vehicles and garbage and wood burning are important sources in Mexico City. The diurnal concentration patterns captured by aerosol photoionization and aerosol mass spectrometry are generally consistent. Ambient concentrations of particle-phase PAHs typically peak at similar to 110 ng m(-3) during the morning rush hour and rapidly decay due to changes in source activity patterns and dilution as the boundary layer rises, although surface-bound PAH concentrations decay faster. The more rapid decrease in surface versus bulk PAH concentrations during the late morning suggests that freshly emitted combustion-related particles are quickly coated by secondary aerosol material in Mexico City's atmosphere and may also be transformed by heterogeneous reactions. NSF Atmospheric Chemistry Program, Grants ATM-0308748, ATM-0528634 DOE Atmospheric Sciences Program, Grant DE-FG02-05ER63981

Tropical aerosols of PM 2.5 and PM 10 were collected at a rural site in Morogoro, Tanzania (East Africa), and analysed for stable carbon isotopic composition (δ 13 C) of dicarboxylic acids (C 2 –C 9 ), glyoxylic acid (ωC 2 ) and glyoxal (Gly) using gas chromatography/isotope ratio mass spectrometer. PM 2.5 samples showed that δ 13 C of oxalic (C 2 ) acid are largest (mean, −18.3±1.7‰) followed by malonic (C 3 , −19.6±1.0‰) and succinic (C 4 , −21.8±2.2‰) acids, whereas those in PM 10 are a little smaller: −19.9±3.1‰ (C 2 ), −20.2±2.7‰ (C 3 ) and −23.3±3.2‰ (C 4 ). The δ 13 C of C 2 –C 4 diacids showed a decreasing trend with an increase in carbon numbers. The higher δ 13 C values of oxalic acid can be explained by isotopic enrichment of 13 C in the remaining C 2 due to the atmospheric decomposition of oxalic acid or its precursors. δ 13 C of ωC 2 and Gly that are precursors of oxalic acid also showed larger values (mean, −22.5‰ and −20.2‰, respectively) in PM 2.5 than those (−26.7‰ and −23.7‰) in PM 10 . The δ 13 C values of ωC 2 and Gly are smaller than those of C 2 in both PM 2.5 and PM 10 . On the other hand, azelaic acid (C 9 ; mean, −28.5‰) is more depleted in 13 C, which is consistent with the previous knowledge; that is, C 9 is produced by the oxidation of unsaturated fatty acids emitted from terrestrial higher plants. A significant enrichment of 13 C in oxalic acid together with its negative correlations with relative abundance of C 2 in total diacids and ratios of water-soluble organic carbon and organic carbon further support that a photochemical degradation of oxalic acid occurs during long-range transport from source regions. Keywords: PM 2.5 and PM 10 , stable carbon isotope ratios, oxalic acid, diacids, glyoxylic acid, glyoxal, organic aerosols, Tanzania, East Africa (Published: 1 October 2014) Citation: Tellus B 2014, 66 , 23702, http://dx.doi.org/10.3402/tellusb.v66.23702

Atmospheric aerosols are responsible for adverse health effects and uncertain climate forcing. Depending on their composition, they can directly affect climate by scattering or absorbing solar radiation and they can also indirectly affect by serving as cloud condensation nuclei (CCN). While the chemistry and physical properties of the inorganic components of the aerosols are more or less known, the same does not stand for the organic components. Hygroscopic water soluble organic material can enhance the water absorption of the particles, affecting their climate forcing. This dissertation explores the hygroscopic properties of atmospheric organic aerosol, the first part of the thesis is dedicated to the development and analysis of methods for the measurement of water soluble organic aerosol, while the second part investigates the hygroscopic properties and CCN activity of organic particulate matter emitted by different sources or produced in the atmosphere through oxidation of volatile organic compounds. Τα ατμοσφαιρικά σωματίδια έχουν αρνητικές επιδράσεις στην ανθρώπινη υγεία αλλά και αβέβαιες επιπτώσεις στο κλίμα. Ανάλογα με τη σύστασή τους, μπορούν να επιδράσουν άμεσα στο κλίμα, σκεδάζοντας ή απορροφώντας ηλιακή ακτινοβολία, ενώ μπορούν ακόμα να δράσουν ως πυρήνες συμπύκνωσης συννέφων. Παρόλο που η χημεία και οι φυσικές ιδιότητες των ανόργανων συστατικών των αεροζόλ είναι γενικά γνωστές, δε συμβαίνει το ίδιο για τα οργανικά συστατικά. Υγροσκοπικά υδατοδιαλυτά οργανικά συστατικά μπορούν να αυξήσουν την απορρόφηση νερού από τα σωματίδια, επηρεάζοντας την επίδραση αυτών στο κλίμα. Αυτή η διατριβή διερευνά τις υγροσκοπικές ιδιότητες των ατμοσφαιρικών οργανικών σωματιδίων: Το πρώτο μέρος ασχολείται με την ανάπτυξη και την ανάλυση μεθόδων για τη μέτρηση των υδατοδιαλυτών ατμοσφαιρικών οργανικών σωματιδίων, ενώ στο δεύτερο διερευνώνται οι υγροσκοπικές ιδιότητες και η δράση ως πυρήνων συμπύκνωσης συννέφων οργανικών σωματιδίων που εκπέμπονται από διαφορετικές πηγές ή παράγονται στην ατμόσφαιρα μέσω οξείδωσης πτητικών οργανικών ενώσεων.

Organic particles are either emitted directly into the atmosphere by fossil fuel or biomass combustion thus forming primary organic aerosols or are formed by gas-to-particle conversion from gaseous precursors leading to secondary organic aerosols. Surface active substances (SAS) as atmospheric organic compounds contribute significantly their water soluble organic carbon (WSOC) pool [1, 2]. Atmospheric composition is of unquestionable importance in the study of the damage produced on building materials of artistic interest [3]. Thus, atmospheric aerosols are known to accumulate on the stone surfaces of the historical buildings forming black crusts. Newly formed layers tend to have higher concentrations of organic carbon (OC) than elemental carbon (EC) as a result of recent atmospheric increase in organics [4].This work is focused on investigation of organic carbon (OC) present in the black crust of historic buildings from two urban sites: Zagreb (Croatia) and Jajce (Bosnia and Herzegovina). The black crusts were analyzed for total organic carbon (TOC), and the sub–fractions: WSOC and SAS. Characterization of water soluble organic surfactants was carried out by adsorption study at the mercury electrode/solution interface using electrochemical methods (phase sensitive alternating current voltammetry). For quantification of the SAS content a calibration plot of the non-ionic surfactant Triton-X-100 was used. The results will be supported by data showing the temporal distributions of organic aerosols (PM10) over the urban site of Zagreb, Croatia during one year (2011-2012) were estimated. We found that the mean organic carbon (OC) concentrations in autumn, winter, spring and summer, were 11.29 ± 8.2, 9.10±.4.40, 4.03 ±1.58, and 3.41±1.42 μg C m−3, respectively. The average OC/EC ratio was 6.6. Results show that humic-like matter (HULIS) may be an important surface active matter in atmospheric aerosols during warm seasons. Moreover, the presence of HULIS was also detected in the investigated samples of the black crust.

In the atmosphere, aerosol particles play a key role on both climate change and human health due to their effect on air quality. These particles are made of a complex mixture of organic and inorganic species emitted from several sources. Although the sources and the production mechanisms for inorganic species are now quite well understood, the characterization of the organic fraction is much more difficult to study. Indeed, particulate organic matter comes from primary organic aerosols directly emitted to the atmosphere and secondary organic aerosols (SOA), which are formed from gas-to-particle conversion of Volatile Organic Compounds (VOC). Three-dimensional chemistry-transport models are developed to better understand the organic aerosol formation processes. However, these models underestimate the organic aerosol concentrations. The aim of this thesis is to study the transport, the emissions and the chemical transformations involved in the formation of the organic aerosols using the WRF-Chem chemistry-transport model (Weather Research and Forecasting – Chemistry; Grell .et al., 2005). Model outputs are compared to measurements performed at the puy de Dôme station (France) during three campaigns. These measurements allow for characterizing various air masses and different seasonal behaviours (in autumn, winter and summer). The station hosts many probes for controlling meteorological parameters, gas phase species and aerosol properties. In particular, a mass spectrometer (AMS: Aerosol Mass Spectrometer) provides detailed time evolution of the chemical composition and mass concentration of the particulate matter. The comparisons between model results and observations have shown that seasonal variations of the aerosol chemical composition are captured by the WRF-Chem model. However, the organic aerosols mass concentrations are strongly underestimated and this underestimation is more important for the polluted summer case. The calculated origins of air masses are comparable to the results of the lagrangian model HYSPLIT currently used for atmospheric dispersion. The top of the puy de Dôme is observed to be either in the boundary layer or above depending on the season and these observations are correctly reproduced by the WRF-Chem model. As the anthropogenic VOC concentrations are underestimated by WFR-Chem model, sensitivity tests on the anthropogenic VOC emissions and SOA yields, used in the VBS secondary organic aerosols parameterisation, are done to better reproduce the organic aerosol concentrations observed at the puy de Dôme station., Dans l’atmosphère, les particules d’aérosol jouent un rôle clef sur le climat et, par leur action sur la qualité de l’air, ont un impact néfaste sur la santé publique. Ces particules sont composées d’un mélange complexe d’espèces inorganiques et organiques formées à partir d’une grande variété de sources. Si les sources et mécanismes de production des espèces inorganiques sont désormais relativement bien connus, la caractérisation de la fraction organique des aérosols est beaucoup plus complexe : elle est constituée d’aérosols organiques primaires, émis directement dans l’atmosphère, et d’aérosols organiques secondaires (AOS) produits par la conversion gaz-particules de Composés Organiques Volatils (COV). Afin de comprendre les processus de formation des aérosols organiques, des modèles tridimensionnels de chimie-transport sont mis en œuvre. Or, à ce jour, les concentrations en aérosols organiques observées dans l’atmosphère demeurent sous-estimées par ces modèles. L’objectif de cette thèse est d’étudier les différents processus de transport, d’émissions et de transformations chimiques intervenant dans la formation des aérosols organiques à partir du modèle de chimie-transport WRF-Chem (Weather Research and Forecasting – Chemistry). Les sorties du modèle ont été comparées à des mesures effectuées à la station du puy de Dôme au cours de trois situations correspondant à trois saisons (automne, hiver, été) durant lesquelles des masses d’air de diverses origines ont été échantillonnées. Ces mesures documentent les conditions météorologiques, les propriétés des espèces chimiques gazeuses et des particules d’aérosol. En particulier, les mesures fournies par un spectromètre de masse (AMS : Aerosol Mass Spectrometer), fournissent de informations détaillées sur la variabilité temporelle de la composition chimique des aérosols et notamment sur leur concentration en masse. Les comparaisons modèle/mesures ont montré que les variations saisonnières de la composition chimique des aérosols observées au puy de Dôme étaient bien capturées par le modèle. Cependant, il s’est avéré que les concentrations en aérosols organiques étaient fortement sous-estimées par le modèle et plus particulièrement lors de la situation d’été. La confrontation des origines des masses d’air simulées par le modèle WRF-Chem à celles déterminées par le modèle lagrangien HYSPLIT reconnu pour l’étude de la dispersion atmosphérique et l’analyse des variations de la localisation du sommet du puy de Dôme vis-à-vis de la couche limite atmosphérique ont mis en évidence que le transport était correctement reproduit par le modèle. Les mesures de gaz disponibles au puy de Dôme ont mis en évidence une forte sous-estimation des concentrations en COV d’origine anthropique simulées par le modèle. Des tests de sensibilité ont été réalisés sur les émissions de ces espèces pour restituer les niveaux de concentration observés. Les émissions et les rendements en AOS des COV d’origine anthropique implémentés dans la paramétrisation VBS dédiée aux aérosols organiques dans le modèle ont pu être modifiés afin de reproduire les niveaux de concentration en aérosols organiques observés au puy de Dôme.

Ambient wintertime background urban aerosol in Cork city, Ireland, was characterized using aerosol mass spectrometry. During the three-week measurement study in 2009, 93% of the ca. 1 350 000 single particles characterized by an Aerosol Time-of-Flight Mass Spectrometer (TSI ATOFMS) were classified into five organic-rich particle types, internally mixed to different proportions with elemental carbon (EC), sulphate and nitrate, while the remaining 7% was predominantly inorganic in nature. Non-refractory PM1 aerosol was characterized using a High Resolution Time-of-Flight Aerosol Mass Spectrometer (Aerodyne HR-ToF-AMS) and was also found to comprise organic aerosol as the most abundant species (62 %), followed by nitrate (15 %), sulphate (9 %) and ammonium (9 %), and chloride (5 %). Positive matrix factorization (PMF) was applied to the HR-ToF-AMS organic matrix, and a five-factor solution was found to describe the variance in the data well. Specifically, "hydrocarbon-like" organic aerosol (HOA) comprised 20% of the mass, "low-volatility" oxygenated organic aerosol (LV-OOA) comprised 18 %, "biomass burning" organic aerosol (BBOA) comprised 23 %, non-wood solid-fuel combustion "peat and coal" organic aerosol (PCOA) comprised 21 %, and finally a species type characterized by primary m/z peaks at 41 and 55, similar to previously reported "cooking" organic aerosol (COA), but possessing different diurnal variations to what would be expected for cooking activities, contributed 18 %. Correlations between the different particle types obtained by the two aerosol mass spectrometers are also discussed. Despite wood, coal and peat being minor fuel types used for domestic space heating in urban areas, their relatively low combustion efficiencies result in a significant contribution to PM1 aerosol mass (44% and 28% of the total organic aerosol mass and non-refractory total PM1, respectively).Ambient wintertime background urban aerosol in Cork city, Ireland, was characterized using aerosol mass spectrometry. During the three-week measurement study in 2009, 93% of the ca. 1 350 000 single particles characterized by an Aerosol Time-of-Flight Mass Spectrometer (TSI ATOFMS) were classified into five organic-rich particle types, internally mixed to different proportions with elemental carbon (EC), sulphate and nitrate, while the remaining 7% was predominantly inorganic in nature. Non-refractory PM1 aerosol was characterized using a High Resolution Time-of-Flight Aerosol Mass Spectrometer (Aerodyne HR-ToF-AMS) and was also found to comprise organic aerosol as the most abundant species (62 %), followed by nitrate (15 %), sulphate (9 %) and ammonium (9 %), and chloride (5 %). Positive matrix factorization (PMF) was applied to the HR-ToF-AMS organic matrix, and a five-factor solution was found to describe the variance in the data well. Specifically, "hydrocarbon-like" organic aerosol (HOA) comprised 20% of the mass, "low-volatility" oxygenated organic aerosol (LV-OOA) comprised 18 %, "biomass burning" organic aerosol (BBOA) comprised 23 %, non-wood solid-fuel combustion "peat and coal" organic aerosol (PCOA) comprised 21 %, and finally a species type characterized by primary m/z peaks at 41 and 55, similar to previously reported "cooking" organic aerosol (COA), but possessing different diurnal variations to what would be expected for cooking activities, contributed 18 %. Correlations between the different particle types obtained by the two aerosol mass spectrometers are also discussed. Despite wood, coal and peat being minor fuel types used for domestic space heating in urban areas, their relatively low combustion efficiencies result in a significant contribution to PM1 aerosol mass (44% and 28% of the total organic aerosol mass and non-refractory total PM1, respectively).

This work aims to demonstrate the ability of numerical simulations to mode] solid · and liquid interfaces. In the work on the solid interfaces, the GCMC method was used to sin:rnlatc the ads011Jtion isotherrn of acetaldehyde on ice under the conditions of the ·upper tropospherc and the molecular dynamics method was usecl to characterize the adsorption of difünctionalized organic compounds on ice, aiming at interpreting experimental results. Part of this work was devotcd to the simulation of the phase diagrarn (p, T) of organic aerosols (oxalic acid and malonic) in tropospberic conditions to study the ability of aerosols to act as condensation nuclei for icc particlcs. The work: on liquid interfaces concerned firstly the competitive adsorption of polymcrs and surfactants at the water surface. It is based on a very precise desc1iption, by mnncrical simulation, of the structure émd dynamics cif the surface of the considered systems. The second pari of the work on liquid interfaces bas focused on the characterization of ion transfer across a liquid/liquid interface through the calculations of the free energy variations of the system during the transfo·. To obtain a rigorous desc1iptio11 of the details of the corresponding processes, a specific method was developed in this thesis to calculate the free energy profile while taking into account tbe dynamics of the interface., Ce travail a pour objectif de montrer la capacité des simulations numériques à modéliser les phénomènes aux interfaces solides et liquides. Dans le travail sur les interfaces solides, la méthode GCMC a été utilisée pour simuler l'isotherme d'adsorption de !'acétaldéhyde sur la glace dans les conditions de la haute troposphère, puis l'adsorption de composés organiques bi-fonctionnalisés sur la glace a été caractérisée par dynamique moléculaire avec pour objectif d'interpréter des résl1ltats expérimentaux de la littérature. Une partie de ce travail a été consacrée à la circulation du diagramme de phase (p,T) d'aérosols organiques (acide oxalique et malonique) clans les conditions troposphériques afin d'étudier la capacité de ces aérosols à jouer le rôle de noyaux de condensation pour les particules de glace. Le travail sur les interfaces liquides a concerné tout d'abord l'adsorption compétitive de polymères et de smfactants à la surface de l'eau. Il s'appuie sur une description très précise, par simulation, de la structure et de la dynamique de la surface des systèmes considérés. La deuxième partie des travaux sur les interfaces liquides s'est intéressée à la caractérisation du transfert d'ions à travers une interface liquide/liquide par le biais du calcul des variations de l'énergie libre du système au cours du transfc1i. Afin d'obtenir une description très rigoureuse des détails des processus mis enjeu, une méthode spécifique a été développée dans cette thèse pour calculer le profil d'énergie libre en tenant compte directement du caractère très dynamique de l'interface.

The chemical composition of PM2.5 includes both organic and inorganic compounds. Organic compounds, which constitute a significant fraction of the PM2.5 mass, can be emitted directly as primary aerosol from sources such as fossil-fuel combustion, biomass burning, and natural biogenic emissions, or formed in the atmosphere via chemical reactions leading to secondary organic aerosol (SOA) formation. SOA, which account for 20 – 80 % of total organic aerosol, are currently a major source of uncertainty in air quality modeling. The identification and quantification of the chemical composition of the organic fraction of PM2.5 and its source apportionment are of great interest, especially in the Middle East region where data on organic aerosols are currently lacking. Lebanon, a small developing country in the Middle East region located on the eastern shore of the Mediterranean basin represents a good example for characterizing organic aerosols in this region. To address this issue, the air quality in Beirut (the capital city of Lebanon) was investigated with a focus on organic aerosols. First, an air pollutant emission inventory was developed for Lebanon with a spatial resolution of 5 km x 5 km and for Beirut with a spatial resolution of 1 km x 1 km. The results obtained show that the road transport sector is the major contributor to carbon monoxide (CO), nitrogen oxides (NOx) and non-methane volatile organic compounds (VOC) emissions, whereas fossil fuel-fired power plants and large industrial plants are the major contributors to sulfur dioxide (SO2) and primary particulate matter (PM) emissions. Then, two intensive 15-day measurement campaigns were conducted at a semi-urban site located in a Beirut suburb to characterize air pollutant concentrations. The first measurement campaign took place in July 2011 and the second in February 2012. Measurements included PM2.5, organic carbon (OC) and elemental carbon (EC) mass concentrations as well as a molecular characterization of organic aerosols. Using these data, a source apportionment of organic aerosols was conducted for summer and winter. In summer, biogenic precursors such as monoterpenes and sesquiterpenes were the major source of OC due to intensive solar radiation and high ambient temperatures that promote biogenic VOC emissions and photo-oxidation reactions. In winter, biomass burning was the major source of organic aerosols because of the intensive use of wood burning for heating. Finally, air pollutant concentrations in Beirut were simulated for July 2011 with the Polyphemus/Polair3D chemical-transport model (CTM). The emission inventory mentioned above was used as input to the model. Meteorological simulations were conducted with the Weather Research and Forecasting model (WRF) using different configurations and the configuration leading to the best agreement with the observations was used to drive the air quality simulations. The simulated air pollutant concentrations were compared to the measured concentrations collected during the summer measurement campaign. The results show that the model reproduces satisfactorily the concentrations of ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), and the major components of PM2.5. The differences obtained between the modeled and measured air pollutants concentrations are due in part to uncertainties in input data. Future studies should address the reduction of uncertainties such as those of the emission inventory. In addition, measurement campaigns involving several sites are needed to better characterize air pollution in Beirut and provide a more complete database to evaluate simulated air pollutant concentrations, La connaissance des sources primaires (combustion des énergies fossiles, combustion de la biomasse, éruptions des volcans, etc.) et secondaires (oxydation des composés organiques volatils (COV) suivie de la condensation formant des composés organiques particulaires) de l'aérosol organique ainsi que la caractérisation et la quantification de sa composition chimique restent un défit majeur, en particulier dans la région du Moyen Orient où les études de caractérisation de l'aérosol organique n'existent pas jusqu'à présent. Le Liban, un pays du Moyen Orient qui se situe au bord du bassin méditerranéen, représente un bon exemple pour la caractérisation des aérosols organiques dans cette région. Les travaux menés durant cette thèse s'inscrivent dans un objectif de l'étude de la qualité de l'air à Beyrouth (la capitale du Liban) en se concentrant plus spécifiquement sur les aérosols organiques. Tout d'abord, cette thèse a permis le développement d'un inventaire des émissions pour les gaz et les particules pour le Liban avec une résolution spatiale de 5 km x 5 km et pour la capitale Beyrouth avec une résolution spatiale de 1 km x 1 km. Les résultats obtenus indiquent que le transport routier est la source majoritaire responsable des émissions de monoxyde de carbone (CO), d'oxydes d'azote (NOX) et de composés organiques volatils non méthaniques (COVNM), tandis que les industries et les centrales électriques sont les principaux émetteurs des émissions de dioxyde de souffre (SO2) et des particules primaires. Ensuite, afin de caractériser les concentrations des polluants et plus spécialement la fraction organique des particules, deux campagnes de mesures intensives de 15 jours chacune ont été menées sur un site semi-urbain situé dans la banlieue de Beyrouth. Une première campagne estivale s'est déroulée en juillet 2011 et une deuxième campagne hivernale en février 2012. Ces campagnes, qui s'inscrivent dans le cadre du projet ECOCEM (Emission and Chemistry of Organic Carbon in East Mediterranean Beirut) ont permis une spéciation moléculaire et une catégorisation des sources en été et en hiver de l'aérosol organique au site de mesures où les campagnes ont été menées. En été, les précurseurs biogéniques tels que les monoterpènes et les sesquiterpènes qui aboutissent à la formation des aérosols organiques secondaires biogéniques sont la principale source à cause de l'insolation intensive et les températures élevées qui favorisent les émissions et les réactions de photo-oxydations. En hiver, la combustion de la biomasse est la principale source en raison de la combustion du bois dans le secteur résidentiel pour le chauffage. Enfin, les concentrations ambiantes des polluants à Beyrouth ont été simulées durant le mois de juillet 2011 à partir de données de l'inventaire des émissions développé dans le cadre de cette thèse en utilisant le modèle de chimie-transport Polyphemus/Polair3D. Les concentrations de polluants simulées avec le modèle ont été comparées aux concentrations mesurées durant la campagne estivale afin d'évaluer le modèle. Les résultats obtenus révèlent que le modèle est capable de simuler de manière satisfaisante les concentrations d'ozone (O3), de NOX et la plupart des composés présents dans les particules fines. Les différences entre le modèle et les mesures peuvent résulter des incertitudes dans les données d'entrée qui ont une très grande influence sur les sorties du modèle. Pour cela, une réduction des incertitudes engendrées par les données d'entrée et plus spécifiquement celles liées à l'inventaire des émissions est nécessaire. Par ailleurs, des mesures chimiques sur plusieurs sites sont aussi nécessaires dans le futur afin de mieux évaluer les simulations des concentrations de polluants

The chemical composition of PM2.5 includes both organic and inorganic compounds. Organic compounds, which constitute a significant fraction of the PM2.5 mass, can be emitted directly as primary aerosol from sources such as fossil-fuel combustion, biomass burning, and natural biogenic emissions, or formed in the atmosphere via chemical reactions leading to secondary organic aerosol (SOA) formation. SOA, which account for 20 – 80 % of total organic aerosol, are currently a major source of uncertainty in air quality modeling. The identification and quantification of the chemical composition of the organic fraction of PM2.5 and its source apportionment are of great interest, especially in the Middle East region where data on organic aerosols are currently lacking. Lebanon, a small developing country in the Middle East region located on the eastern shore of the Mediterranean basin represents a good example for characterizing organic aerosols in this region. To address this issue, the air quality in Beirut (the capital city of Lebanon) was investigated with a focus on organic aerosols. First, an air pollutant emission inventory was developed for Lebanon with a spatial resolution of 5 km x 5 km and for Beirut with a spatial resolution of 1 km x 1 km. The results obtained show that the road transport sector is the major contributor to carbon monoxide (CO), nitrogen oxides (NOx) and non-methane volatile organic compounds (VOC) emissions, whereas fossil fuel-fired power plants and large industrial plants are the major contributors to sulfur dioxide (SO2) and primary particulate matter (PM) emissions. Then, two intensive 15-day measurement campaigns were conducted at a semi-urban site located in a Beirut suburb to characterize air pollutant concentrations. The first measurement campaign took place in July 2011 and the second in February 2012. Measurements included PM2.5, organic carbon (OC) and elemental carbon (EC) mass concentrations as well as a molecular characterization of organic aerosols. Using these data, a source apportionment of organic aerosols was conducted for summer and winter. In summer, biogenic precursors such as monoterpenes and sesquiterpenes were the major source of OC due to intensive solar radiation and high ambient temperatures that promote biogenic VOC emissions and photo-oxidation reactions. In winter, biomass burning was the major source of organic aerosols because of the intensive use of wood burning for heating. Finally, air pollutant concentrations in Beirut were simulated for July 2011 with the Polyphemus/Polair3D chemical-transport model (CTM). The emission inventory mentioned above was used as input to the model. Meteorological simulations were conducted with the Weather Research and Forecasting model (WRF) using different configurations and the configuration leading to the best agreement with the observations was used to drive the air quality simulations. The simulated air pollutant concentrations were compared to the measured concentrations collected during the summer measurement campaign. The results show that the model reproduces satisfactorily the concentrations of ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), and the major components of PM2.5. The differences obtained between the modeled and measured air pollutants concentrations are due in part to uncertainties in input data. Future studies should address the reduction of uncertainties such as those of the emission inventory. In addition, measurement campaigns involving several sites are needed to better characterize air pollution in Beirut and provide a more complete database to evaluate simulated air pollutant concentrations, La connaissance des sources primaires (combustion des énergies fossiles, combustion de la biomasse, éruptions des volcans, etc.) et secondaires (oxydation des composés organiques volatils (COV) suivie de la condensation formant des composés organiques particulaires) de l'aérosol organique ainsi que la caractérisation et la quantification de sa composition chimique restent un défit majeur, en particulier dans la région du Moyen Orient où les études de caractérisation de l'aérosol organique n'existent pas jusqu'à présent. Le Liban, un pays du Moyen Orient qui se situe au bord du bassin méditerranéen, représente un bon exemple pour la caractérisation des aérosols organiques dans cette région. Les travaux menés durant cette thèse s'inscrivent dans un objectif de l'étude de la qualité de l'air à Beyrouth (la capitale du Liban) en se concentrant plus spécifiquement sur les aérosols organiques. Tout d'abord, cette thèse a permis le développement d'un inventaire des émissions pour les gaz et les particules pour le Liban avec une résolution spatiale de 5 km x 5 km et pour la capitale Beyrouth avec une résolution spatiale de 1 km x 1 km. Les résultats obtenus indiquent que le transport routier est la source majoritaire responsable des émissions de monoxyde de carbone (CO), d'oxydes d'azote (NOX) et de composés organiques volatils non méthaniques (COVNM), tandis que les industries et les centrales électriques sont les principaux émetteurs des émissions de dioxyde de souffre (SO2) et des particules primaires. Ensuite, afin de caractériser les concentrations des polluants et plus spécialement la fraction organique des particules, deux campagnes de mesures intensives de 15 jours chacune ont été menées sur un site semi-urbain situé dans la banlieue de Beyrouth. Une première campagne estivale s'est déroulée en juillet 2011 et une deuxième campagne hivernale en février 2012. Ces campagnes, qui s'inscrivent dans le cadre du projet ECOCEM (Emission and Chemistry of Organic Carbon in East Mediterranean Beirut) ont permis une spéciation moléculaire et une catégorisation des sources en été et en hiver de l'aérosol organique au site de mesures où les campagnes ont été menées. En été, les précurseurs biogéniques tels que les monoterpènes et les sesquiterpènes qui aboutissent à la formation des aérosols organiques secondaires biogéniques sont la principale source à cause de l'insolation intensive et les températures élevées qui favorisent les émissions et les réactions de photo-oxydations. En hiver, la combustion de la biomasse est la principale source en raison de la combustion du bois dans le secteur résidentiel pour le chauffage. Enfin, les concentrations ambiantes des polluants à Beyrouth ont été simulées durant le mois de juillet 2011 à partir de données de l'inventaire des émissions développé dans le cadre de cette thèse en utilisant le modèle de chimie-transport Polyphemus/Polair3D. Les concentrations de polluants simulées avec le modèle ont été comparées aux concentrations mesurées durant la campagne estivale afin d'évaluer le modèle. Les résultats obtenus révèlent que le modèle est capable de simuler de manière satisfaisante les concentrations d'ozone (O3), de NOX et la plupart des composés présents dans les particules fines. Les différences entre le modèle et les mesures peuvent résulter des incertitudes dans les données d'entrée qui ont une très grande influence sur les sorties du modèle. Pour cela, une réduction des incertitudes engendrées par les données d'entrée et plus spécifiquement celles liées à l'inventaire des émissions est nécessaire. Par ailleurs, des mesures chimiques sur plusieurs sites sont aussi nécessaires dans le futur afin de mieux évaluer les simulations des concentrations de polluants

As part of the study of the evolution of Earth’s climate system, understanding the composition of gaseous and particulate atmospheric matter is a major issue in our understanding of Earth and its atmosphere, its past and its evolution. The secondary aerosols, i.e. formed from nucleation, represents the largest source in a number concentration of atmospheric particles but predicting, where, when and in what proportion these aerosols are formed in the atmosphere are still challenging. It is in this context that this study focused to complete our understanding of the process leading to the formation and growth of atmospheric secondary particles. Investigations conducted from long term field measurements at different altitude sites across Europe have made possible to highlight different vertical speciation of the nucleation process and that this phenomenon seems to be occur two times more frequently at the interface between the planetary boundary layer and the free troposphere than in the low planetary boundary layer. In addition these studies have been able to show that different nucleation path are enhanced according to the altitude, implicant a greater role in the process of formation induced by ions and volatile organic compounds at altitude sites. The contribution of this last family of compounds to the nucleation has also been examinated through numerous experimenal campaigns using reactive system as well as smog chambers experiments. Different behaviors of the new particle formation and nucleation parametrization depending on the chemical nature of the parent compound were pointed out. Finally, numerical studies based on both field and smog chamber experiments were conducted to confirm or explore, different numerical approaches to simulate the new secondary aerosol formation., Dans le cadre de l’étude de l’évolution du système climatique terrestre, comprendre la composition gazeuse et particulaire de l’atmosphère est un enjeu majeur dans notre compréhension de la Terre et de son atmosphère, de son passé et de son évolution à venir. Les aérosols secondaires, i.e. formés par nucléation, représentent la source la plus importante en nombre des aérosols atmosphériques mais prédire où, quand et en quelle proportion ces aérosols sont formés dans l’atmosphère demeure à ce jour un exercice peu fiable. C’est dans ce contexte que cette étude s’est attachée à compléter nos connaissances des processus conduisant à la formation et à la croissance des particules atmosphériques secondaires. Des études réalisées à partir de mesures de terrain à long terme sur différents sites d’altitude en Europe ont permis de mettre en évidence différentes spéciations verticales de la nucléation démontrant que ce phénomène semble être jusqu’à deux fois plus fréquents à la frontière avec la basse troposphère libre que dans la couche limite planétaire. D’autre part ces mêmes études ont pu mettre en évidence que les mécanismes conduisant à la nucléation de nouvelles particules se différencient avec l’altitude impliquant un rôle plus important de la voie de formation induite par les ions ainsi que des composés organiques volatils. La contribution de cette dernière famille de composés à la nucléation a été également testée durant plusieurs campagnes d’expérimentation en systèmes réactifs ainsi qu’en chambre de simulation atmosphérique. Différents comportements et paramétrisation de la nucléation selon la nature chimique du composé parent ont pu être mis en évidence. Enfin, des études numériques réalisées à partir de données de terrain et d’expérimentation ont permis d’explorer, d’infirmer, de confirmer et de proposer différentes approches numériques afin de simuler les évènements de formation des aérosols secondaires.