Unravelling New Processes at Interfaces: Photochemical Isoprene Production at the Sea Surface

Isoprene is an important reactive gas that is produced mainly in terrestrial ecosystems but is also produced in marine ecosystems. In the marine environment, isoprene is produced in the seawater by various biological processes. Here, we show that photosensitized reactions involving the sea-surface microlayer lead to the production of significant amounts of isoprene. It is suggested that H-abstraction processes are initiated by photochemically excited dissolved organic matter which will the degrade fatty acids acting as surfactants. This chemical interfacial processing may represent a significant abiotic source of isoprene in the marine boundary layer

Photodegradation of methyl thioglycolate particles as a proxy for organosulphur containing droplets

Understanding the formation and transformation of sulphur-rich particles is of prime importance since they contribute to the global atmospheric sulphur budget. In this work, we performed a series of experiments on a photoactive organosulphur compound namely, methyl thioglycolate, as a model of an organosulphur species of marine origin. By investigating the photoproducts within levitated droplets, we showed that elemental sulphur (α-S8) and sulphate (SO4 2-) can be photochemically generated at the gas-liquid interface by heterogeneous interaction with gaseous O2 and H2O. These results demonstrate that the surface of levitated droplets facilitate the oxidation of methyl thioglycolate in the dark, while illumination is necessary to produce the oxidation in bulk experiments.Centro de Química Inorgánic

Photodegradation of methyl thioglycolate particles as a proxy for organosulphur containing droplets

Understanding the formation and transformation of sulphur-rich particles is of prime importance since they contribute to the global atmospheric sulphur budget. In this work, we performed a series of experiments on a photoactive organosulphur compound namely, methyl thioglycolate, as a model of an organosulphur species of marine origin. By investigating the photoproducts within levitated droplets, we showed that elemental sulphur (α-S8) and sulphate (SO4 2-) can be photochemically generated at the gas-liquid interface by heterogeneous interaction with gaseous O2 and H2O. These results demonstrate that the surface of levitated droplets facilitate the oxidation of methyl thioglycolate in the dark, while illumination is necessary to produce the oxidation in bulk experiments.Centro de Química Inorgánic

Photodegradation of methyl thioglycolate particles as a proxy for organosulphur containing droplets

Understanding the formation and transformation of sulphur-rich particles is of prime importance since they contribute to the global atmospheric sulphur budget. In this work, we performed a series of experiments on a photoactive organosulphur compound namely, methyl thioglycolate, as a model of an organosulphur species of marine origin. By investigating the photoproducts within levitated droplets, we showed that elemental sulphur (α-S8) and sulphate (SO4 2-) can be photochemically generated at the gas-liquid interface by heterogeneous interaction with gaseous O2 and H2O. These results demonstrate that the surface of levitated droplets facilitate the oxidation of methyl thioglycolate in the dark, while illumination is necessary to produce the oxidation in bulk experiments.Fil: Seng, Samantha. Universite Des Sciences Et Technologies de Lille;Fil: Picone, A. Lorena. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; ArgentinaFil: Bava, Yanina B.. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; ArgentinaFil: Juncal, Luciana C.. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; ArgentinaFil: Moreau, Myriam. Universite Des Sciences Et Technologies de Lille;Fil: Ciuraru, Raluca. Universite Des Sciences Et Technologies de Lille;Fil: George, Christian. Universite Claude Bernard Lyon 1;Fil: Romano, Rosana M.. Universite Claude Bernard Lyon 1;Fil: Sobanska, Sophie. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; ArgentinaFil: Tobon, Yeny A.. Universite Des Sciences Et Technologies de Lille

The heterogeneous reactivity of atomic chlorine with aerosol particles of atmospheric interest

L’atmosphère est un milieu oxydant au sein duquel les réactions en phase homogène, initiées par des espèces radicalaires (OH notamment), sont prépondérantes. Le chlore atomique peut être l'oxydant le plus important de la couche limite marine à l'aube lorsque la concentration en radicaux OH est faible. L’atmosphère est aussi chargée en particules d’aérosol où des collisions réactives peuvent se produire à l’interface gaz/solide ou gaz/liquide. Il est donc important de prendre en compte les mécanismes élémentaires de chimie hétérogène pour une meilleure description des processus physico-chimiques atmosphériques. L’objectif de cette thèse est d’étudier la réactivité entre le chlore atomique et des particules représentatives des sels marins (NaCl et sels marins synthétiques). Des mesures ont également été effectuées avec du sulfate et du nitrate d’ammonium, composés majoritaires dans les particules secondaires issues de la condensation d’espèces gazeuses d’origine anthropique. Le principe consiste à mettre une phase gazeuse en contact avec une phase solide au sein d’un réacteur à écoulement à parois recouvertes couplé à un spectromètre de masse. Nous cherchons à mesurer la vitesse de réaction et à déterminer le coefficient de capture de ces réactions ainsi que les produits formés. Nous avons fait varier un certain nombre de paramètres : concentration des réactifs, température, présence ou non de vapeurs d’eau. L’analyse de la surface solide après réaction a été réalisée par des techniques de microscopie avancée (XPS, TOF SIMS).The atmosphere is an oxidizing environment in which the homogeneous phase reactions initiated by radical species (OH in particular) are dominant. Atomic chlorine could be the most important oxidant in the marine boundary layer at dawn when the concentration of OH radicals is low. The atmosphere is loaded with aerosol particles, on the surface of which reactive collisions can occur at the gas / solid or gas / liquid interfaces. It is therefore important to take into account the basic mechanisms of heterogeneous chemistry for a better description of atmospheric chemical and physical processes. The objective of this thesis is to study the reactivity between chlorine atoms and particles representative of sea salts (NaCl and synthetic sea salts). Measurements have also been carried out with ammonium sulfate and nitrate particles, the major components in the secondary particles formed by the condensation of gaseous species of anthropogenic origin. The principle is to put a gas phase in contact with a solid surface in a coated wall flow tube reactor and microwave discharge coupled to a quadrupole mass spectrometer. The contact time between the two phases can be varied inside the reactor. In this work, we have measured the reaction rate and determined the uptake coefficient of these reactions and the possible products formed. Several parameters have been studied: the concentration, the temperature and the presence or absence of surface adsorbed water. The solid surface was analyzed after reaction by advanced microscopy techniques (XPS, TOF SIMS) during this study

Étude de la réactivité du chlore atomique avec des particules d'aérosol d'intérêt atmosphérique

L atmosphère est un milieu oxydant au sein duquel les réactions en phase homogène, initiées par des espèces radicalaires (OH notamment), sont prépondérantes. Le chlore atomique peut être l'oxydant le plus important de la couche limite marine à l'aube lorsque la concentration en radicaux OH est faible. L atmosphère est aussi chargée en particules d aérosol où des collisions réactives peuvent se produire à l interface gaz/solide ou gaz/liquide. Il est donc important de prendre en compte les mécanismes élémentaires de chimie hétérogène pour une meilleure description des processus physico-chimiques atmosphériques. L objectif de cette thèse est d étudier la réactivité entre le chlore atomique et des particules représentatives des sels marins (NaCl et sels marins synthétiques). Des mesures ont également été effectuées avec du sulfate et du nitrate d ammonium, composés majoritaires dans les particules secondaires issues de la condensation d espèces gazeuses d origine anthropique. Le principe consiste à mettre une phase gazeuse en contact avec une phase solide au sein d un réacteur à écoulement à parois recouvertes couplé à un spectromètre de masse. Nous cherchons à mesurer la vitesse de réaction et à déterminer le coefficient de capture de ces réactions ainsi que les produits formés. Nous avons fait varier un certain nombre de paramètres : concentration des réactifs, température, présence ou non de vapeurs d eau. L analyse de la surface solide après réaction a été réalisée par des techniques de microscopie avancée (XPS, TOF SIMS).The atmosphere is an oxidizing environment in which the homogeneous phase reactions initiated by radical species (OH in particular) are dominant. Atomic chlorine could be the most important oxidant in the marine boundary layer at dawn when the concentration of OH radicals is low. The atmosphere is loaded with aerosol particles, on the surface of which reactive collisions can occur at the gas / solid or gas / liquid interfaces. It is therefore important to take into account the basic mechanisms of heterogeneous chemistry for a better description of atmospheric chemical and physical processes. The objective of this thesis is to study the reactivity between chlorine atoms and particles representative of sea salts (NaCl and synthetic sea salts). Measurements have also been carried out with ammonium sulfate and nitrate particles, the major components in the secondary particles formed by the condensation of gaseous species of anthropogenic origin. The principle is to put a gas phase in contact with a solid surface in a coated wall flow tube reactor and microwave discharge coupled to a quadrupole mass spectrometer. The contact time between the two phases can be varied inside the reactor. In this work, we have measured the reaction rate and determined the uptake coefficient of these reactions and the possible products formed. Several parameters have been studied: the concentration, the temperature and the presence or absence of surface adsorbed water. The solid surface was analyzed after reaction by advanced microscopy techniques (XPS, TOF SIMS) during this study.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Photosensitized formation of secondary organic aerosols above the air/water interface

International audienceIn this study, we evaluated photosensitized chemistry at the air−sea interface as a source of secondary organic aerosols (SOA). Our results show that, in addition to biogenic emissions, abiotic processes could also be important in the marine boundary layer. Photosensitized production of marine secondary organic aerosol was studied in a custom-built multiphase atmospheric simulation chamber. The experimental chamber contained water, humic acid (1−10 mg L −1) as a proxy for dissolved organic matter, and nonanoic acid (0.1−10 mM), a fatty acid proxy which formed an organic film at the air−water interface. Dark secondary reaction with ozone after illumination resulted in SOA particle concentrations in excess of 1000 cm −3 , illustrating the production of unsaturated compounds by chemical reactions at the air−water interface. SOA numbers via photosensitization alone and in the absence of ozone did not exceed background levels. From these results, we derived a dependence of SOA numbers on nonanoic acid surface coverage and dissolved organic matter concentration. We present a discussion on the potential role of the air−sea interface in the production of atmospheric organic aerosol from photosensitized origins. ■ INTRODUCTION Although the dominant mass fraction of sea-spray aerosol is inorganic sea salt, organic matter can also contribute to the overall mass of aerosols in the marine boundary layer (MBL). 1,2 Recent field measurements clearly documented the presence of organic matter in oceanic particles. 3,4 Cavalli et al. 5 and O'Dowd et al. 6 found a significant and dominating fraction of organic matter in the submicrometer size range, while the supermicrometer size range predominately consisted of inorganic sea salt. During high biological activity, the organic fraction ranges from 40 to 60% of the submicrometer aerosol mass, while during low biological activity periods, this fraction decreases to 10−15%. Concentrations of organic aerosol mass in air advected over regions of high biological activity were up to 4 μg m −3 and comparable to polluted air masses. 7 The concentration of organic aerosol formed by secondary processes has also been correlated with biological activity. 8 Volatile sulfur species greatly impact the formation of secondary marine aerosols 9−13 and are included in general circulation models predicting climate evolution. 13−15 Together, these findings potentially link ocean biota with marine derived organic aerosols. 16 As a result, the organic fraction of the marine aerosols as well as the trace gas composition over the ocean are controlled by the chemical and physical properties of the sea-surface microlayer (SML). 17−19 Indeed, recent studies reported the use of natural seawater to generate sea spray aerosol (SSA) in order to evaluate how SML composition drives the composition and associated properties of freshly emitted SSA. 20,21 Organic material present at the sea surface includes amphiphiles derived from oceanic biota (fatty acids, fatty alcohols, sterols, amines, etc.) and more complex colloids and aggregates exuded by phytoplankton, which mainly consist of lipopolysaccharides. 22−31 All of these compounds can be highly enriched in this microlayer. 32,33 The presence of complex and potentially photoactive compounds, such as a fatty acid film at the air−sea interface and therefore in the primary marine aerosol, was reported on the surface of continental and marine aerosols. 34−36 This could give rise to the assumption that new processes affect the chemistry in the MBL. Indeed, Reeser et al. 37,38 showed that photoexcited chlorophyll can oxidize halide anions at the salt water surface, producing atomic halogens. A similar chemistry is expected for nitrate and nitrite anions, suggesting a rich new source of oxidants in the MBL. These studies stress the need for a better understanding of the chemistry and potential photochemistry of the surface micro-layer. Indeed, the photochemistry at the air−sea interface has not been adequately considered over the past years. 39 Previous works from our group have shown that such photochemical processing of a surfactant in the presence of a photosensitizer led to the formation of unsaturated and highly functionalized volatile organic compounds (VOCs). 40,41 The use of humic acid as a photosensitizer initiates chemical transformation of surfactants, such as nonanoic acid 40 and octanol, 41 through multiple pathways. The initial step is H-abstraction on the alky

Formation of Atmospheric Molecular Clusters from Organic Waste Products and Sulfuric Acid Molecules: a DFT Study

International audienceThe interaction of one or two sulfuric acid molecules with the indole (C 8 H 7 N) molecule and with the skatole (C 9 H 9 N) molecule and two of its oxidation products (C 9 H 9 NO 2 and C 9 H 9 NO 3) has been investigated by means of computational methods at the quantum level. Gibbs free energies of formation have been calculated using the ωB97X-D exchange-correlation functional with three different basis sets to characterize the stability of the corresponding hetero-molecular clusters.The careful examination of the cluster geometries shows the key role of the hydrogen bonding in the stabilization of the critical nucleus that these organics can form with the sulfuric acid molecules. However, the thermodynamic results demonstrate that the interaction between indole/skatole and one or two sulfuric acid molecules remains quite weak in atmospheric conditions and may likely compete with the formation of sulfuric acid dimers. By contrast, the oxidized C 9 H 9 NO 3 and C 9 H 9 NO 2 species appear to be much better candidates for the formation of critical nuclei with sulfuric acid molecules than their parent compounds, indole or skatole. This supports the conclusions of recent experimental observations on the ability of molecules issued from organic waste products to form nuclei with sulfuric acid molecules and emphasizes the potential role of agricultural recycling of sewage sludge as an unaccounted source of nucleation precursors in the atmosphere

Photosensitized production of functionalized and unsaturated organic compounds at the air-sea interface

The sea-surface microlayer (SML) has different physical, chemical and biological properties compared to the subsurface water, with an enrichment of organic matter i.e., dissolved organic matter including UV absorbing humic substances, fatty acids and many others. Here we present experimental evidence that dissolved organic matter, such as humic acids, when exposed to sunlight, can photosensitize the chemical conversion of linear saturated fatty acids at the air-water interface into unsaturated functionalized gas phase products (i.e. saturated and unsaturated aldehydes and acids, alkenes and dienes,…) which are known precursors of secondary organic aerosols. These functionalized molecules have previously been thought to be of biological origin, but here we demonstrate that abiotic interfacial photochemistry has the potential to produce such molecules. As the ocean is widely covered by the SML, this new understanding will impact on our ability to describe atmospheric chemistry in the marine environment