Etude simultanée de la composition chimique de la fraction organique des particules secondaires et de la phase gazeuse atmosphériques en site réel et en atmosphère simulée

National audienceSecondary Organic Aerosols (SOAs) are formed in the atmosphere by gas-to-particle conversion of oxygenated Semi-Volatile Organic Compounds (SVOCs). However, the community currently lacks data to describe these multiphase phenomena and assess their climate and health impacts. This analytical work intends to improve our understanding of SOA by an original study based on the development of a simultaneous sampling method for gaseous and particulate phases. Both phases are analyzed by the same sensitive and rapid analytical technique coupling thermal-desorption, gas chromatography and mass spectrometry (TD-GC-MS). The method involves derivatization of oxygenated SVOCs, in gas and particulate phases, on a solid support fitting with TD, to improve their analytical response and facilitate their identification. This work presents this development performed combining smog chamber experiments and the MEGAPOLI field campaign.Les Aérosols Organiques Secondaires (AOS) sont formés dans l'atmosphère par conversion de gaz organiques en particules ; ils sont issus de l'oxydation en phase gazeuse de Composés Organiques Volatils (COV) précurseurs, menant à la formation de Composés Organiques Semi-Volatils (COSV) oxygénés se partageant entre les phases gazeuse et particulaire. La communauté manque actuellement de données pour décrire ces phénomènes multiphasiques et évaluer leurs impacts climatiques et sanitaires. Ce travail analytique se propose ainsi d'améliorer notre connaissance des AOS par une étude originale basée sur la mise au point d'une méthode de prélèvement simultané des phases gazeuse et particulaire et leur analyse par une même technique analytique sensible et rapide, le couplage thermo-désorption/chromatographie en phase gazeuse/spectrométrie de masse (TD-GCMS). La méthode consiste en une dérivatisation indispensable des COSV oxygénés, prélevés en phase gazeuse comme en phase particulaire, sur un support solide thermo-désorbable afin d'améliorer leur réponse analytique et de faciliter leur identification. Ce travail présente le développement réalisé à partir d'expériences en chambres de simulation atmosphérique - dont CESAM, chambre spécialement conçue pour l'étude des phénomènes multiphasiques - et de la campagne de terrain du projet européen MEGAPOLI

Predicting indoor ozone and NOx concentrations

International audienceSimple modelling of indoor chemistry using FACSIMILE softwar

Radical-Initiated Brown Carbon Formation in Sunlit Carbonyl–Amine–Ammonium Sulfate Mixtures and Aqueous Aerosol Particles

Brown carbon (BrC) formed from glyoxal+ammonium sulfate (AS) and methylglyoxal+AS reactions photobleaches quickly, leading to the assumption that BrC formed overnight by Maillard reactions will be rapidly destroyed at sunrise. Here, we tested this assumption by reacting glyoxal, methylglyoxal, glycolaldehyde, or hydroxyacetone in aqueous mixtures with reduced nitrogen species at pH 4–5 in the dark and in sunlight (\u3e350 nm) for at least 10 h. The absorption of fresh carbonyl+AS mixtures decreased when exposed to sunlight, and no BrC formed, as expected from previous work. However, the addition of amines (either methylamine or glycine) allowed BrC to form in sunlight at comparable rates as in the dark. Hydroxyacetone+amine+AS aqueous mixtures generally browned faster in sunlight than in the dark, especially in the presence of HOOH, indicating a radical-initiated BrC formation mechanism is involved. In experiments with airborne aqueous aerosol containing AS, methylamine, and glyoxal or methylglyoxal, browning was further enhanced, especially in sunlight (\u3e300 nm), forming aerosol with optical properties similar to “very weak” atmospheric BrC. Liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analysis of aerosol filter extracts indicates that exposure of methylglyoxal+AS aqueous aerosol to methylamine gas, sunlight, and cloud processing increases incorporation of ammonia, methylamine, and photolytic species (e.g., acetyl radicals) into conjugated oligomer products. These results suggest that when amines are present, photolysis of first-generation, “dark reaction” BrC (imines and imidazoles) initiates faster, radical-initiated browning processes that may successfully compete with photobleaching, are enhanced in aqueous aerosol particles relative to bulk liquid solutions, and can produce BrC consistent with atmospheric observations

Brown Carbon from Photo-Oxidation of Glyoxal and SO2 in Aqueous Aerosol

Aqueous-phase dark reactions during the co-oxidation of glyoxal and S(IV) were recently identified as a potential source of brown carbon (BrC). Here, we explore the effects of sunlight and oxidants on aqueous solutions of glyoxal and S(IV), and on aqueous aerosol exposed to glyoxal and SO2. We find that BrC is able to form in sunlit, bulk-phase, sulfite-containing solutions, albeit more slowly than in the dark. In more atmospherically relevant chamber experiments where suspended aqueous aerosol particles are exposed to gas-phase glyoxal and SO2, the formation of detectable amounts of BrC requires an OH radical source and occurs most rapidly after a cloud event. From these observations we infer that this photobrowning is caused by radical-initiated reactions as evaporation concentrates aqueous-phase reactants and aerosol viscosity increases. Positive-mode electrospray ionization mass spectrometric analysis of aerosol-phase products reveals a large number of CxHyOz oligomers that are reduced rather than oxidized (relative to glyoxal), with the degree of reduction increasing in the presence of OH radicals. This again suggests a radical-initiated redox mechanism where photolytically produced aqueous radical species trigger S(IV)–O2 auto-oxidation chain reactions, and glyoxal-S(IV) redox reactions especially if aerosol-phase O2 is depleted. This process may contribute to daytime BrC production and aqueous-phase sulfur oxidation in the atmosphere. The BrC produced, however, is about an order of magnitude less light-absorbing than wood smoke BrC at 365 nm

Glyoxal’s impact on dry ammonium salts: fast and reversible surface aerosol browning

Alpha-dicarbonyl compounds are believed to form brown carbon in the atmosphere via reactions with ammonium sulfate (AS) in cloud droplets and aqueous aerosol particles. In this work, brown carbon formation in AS and other aerosol particles was quantified as a function of relative humidity (RH) during exposure to gas-phase glyoxal (GX) in chamber experiments. Under dry conditions (RH \u3c 5%), solid AS, AS/glycine, and methylammonium sulfate aerosol particles brown within minutes upon exposure to GX, while sodium sulfate particles do not. When GX concentrations decline, browning goes away, demonstrating that this dry browning process is reversible. Declines in aerosol albedo are found to be a function of [GX]2, and are consistent between AS and AS/glycine aerosol. Dry methylammonium sulfate aerosol browns 4´ more than dry AS aerosol, but deliquesced AS aerosol browns much less than dry AS aerosol. Optical measurements at 405, 450, and 530 nm provide an estimated Ångstrom absorbance coefficient of -16 ±4. This coefficient and the empirical relationship between GX and albedo are used to estimate an upper limit to global radiative forcing by brown carbon formed by 70 ppt GX reacting with AS (+7.6 ´10-5 W/m2). This quantity is \u3c 1% of the total radiative forcing by secondary brown carbon, but occurs almost entirely in the ultraviolet range

Supplement of Wet deposition in the remote western and central Mediterranean as a source of trace metals to surface seawater [Dataset]

3 pages. -- Figure S1: Atmospheric conditions during rain ION period, the 29 May 2017. -- Figure S2: Atmopsheric conditions during rain FAST period, the 05 June 2017Peer reviewe

Kinetics, Products, and Brown Carbon Formation by Aqueous-Phase Reactions of Glycolaldehyde with Atmospheric Amines and Ammonium Sulfate

Glycolaldehyde (GAld) is a C2 water-soluble aldehyde produced during the atmospheric oxidation of isoprene and many other species and is commonly found in cloudwater. Previous work has established that glycolaldehyde evaporates more readily from drying aerosol droplets containing ammonium sulfate (AS) than does glyoxal, methylglyoxal, or hydroxyacetone, which implies that it does not oligomerize as quickly as these other species. Here, we report NMR measurements of glycolaldehyde’s aqueous-phase reactions with AS, methylamine, and glycine. Reaction rate constants are smaller than those of respective glyoxal and methylglyoxal reactions in the pH range of 3–6. In follow-up cloud chamber experiments, deliquesced glycine and AS seed particles were found to take up glycolaldehyde and methylamine and form brown carbon. At very high relative humidity, these changes were more than 2 orders of magnitude faster than predicted by our bulk liquid NMR kinetics measurements, suggesting that reactions involving surface-active species at crowded air–water interfaces may play an important role. The high-resolution liquid chromatography–electrospray ionization–mass spectrometric analysis of filter extracts of unprocessed AS + GAld seed particles identified sugar-like C6 and C12 GAld oligomers, including proposed product 3-deoxyglucosone, with and without modification by reactions with ammonia to diimine and imidazole forms. Chamber exposure to methylamine gas, cloud processing, and simulated sunlight increased the incorporation of both ammonia and methylamine into oligomers. Many C4–C16 imidazole derivatives were detected in an extract of chamber-exposed aerosol along with a predominance of N-derivatized C6 and C12 glycolaldehyde oligomers, suggesting that GAld is capable of forming brown carbon SOA

Glyoxal's impact on dry ammonium salts: fast and reversible surface aerosol browning

Alpha-dicarbonyl compounds are believed to form brown carbon in the atmosphere via reactions with ammonium sulfate (AS) in cloud droplets and aqueous aerosol particles. In this work, brown carbon formation in AS and other aerosol particles was quantified as a function of relative humidity (RH) during exposure to gas-phase glyoxal (GX) in chamber experiments. Under dry conditions (RH&thinsp;&lt;&thinsp;5&thinsp;%), solid AS, AS&ndash;glycine, and methylammonium sulfate (MeAS) aerosol particles brown within minutes upon exposure to GX, while sodium sulfate particles do not. When GX concentrations decline, browning goes away, demonstrating that this dry browning process is reversible. Declines in aerosol albedo are found to be a function of [GX]2 and are consistent between AS and AS&ndash;glycine aerosol. Dry methylammonium sulfate aerosol browns 4 times more than dry AS aerosol, but deliquesced AS aerosol browns much less than dry AS aerosol. Optical measurements at 405, 450, and 530&thinsp;nm provide an estimated &Aring;ngstrom absorbance coefficient of &minus;16&plusmn;4. This coefficient and the empirical relationship between GX and albedo are used to estimate an upper limit to global radiative forcing by brown carbon formed by 70&thinsp;ppt GX reacting with AS (+7.6&times;10&minus;5&thinsp;W&thinsp;m&minus;2). This quantity is &lt;&thinsp;1&thinsp;% of the total radiative forcing by secondary brown carbon but occurs almost entirely in the ultraviolet range.</p

Des chambres de simulation atmosphérique en réseau pour explorer ensemble la composition de l'atmosphère

International audienc

Composés organiques volatils : des mécanismes moléculaires intriqués au centre de la complexité de la chimie troposphérique

International audienceLa pollution de l'air demeure l'un des principaux fléaux des temps modernes. Outre la pollution atmosphérique dite « primaire » se développe aussi une pollution atmosphérique plus pernicieuse, appellée « secondaire », produite dans l'environnement atmosphérique. Elle est le fruit d'une chimie atmosphérique multiphasique, impliquant des composés organiques et radicalaires, rendue complexe à la fois par le grand nombre de composants de l'air et par la multiplicité de leurs voies d'évolution chimique. En mettant en perspective cette complexité, cet article se propose de donner quelques clefs pour l'appréhender et de présenter les stratégies de la recherche qui permettront de réduire cette pollution secondaire. Air pollution remains one of the main plagues of modern times. In addition to so-called "primary" air pollution, a more pernicious air pollution is also developing, termed "secondary", i.e. produced in the atmospheric environment. It is the result of an atmospheric multiphase chemistry involving organic and radical compounds, made complex both by the large number of components in the air and the multiplicity of their chemical pathways. Putting this complexity into perspective, this article provides some keys to understand it and to present research strategies that will reduce this secondary pollution