Potential controls of isoprene in the surface ocean

Isoprene surface ocean concentrations and vertical distribution, atmospheric mixing ratios, and calculated sea-to-air fluxes spanning approximately 125° of latitude (80°N–45°S) over the Arctic and Atlantic Oceans are reported. Oceanic isoprene concentrations were associated with a number of concurrently monitored biological variables including chlorophyll a (Chl a), photoprotective pigments, integrated primary production (intPP), and cyanobacterial cell counts, with higher isoprene concentrations relative to all respective variables found at sea surface temperatures greater than 20°C. The correlation between isoprene and the sum of photoprotective carotenoids, which is reported here for the first time, was the most consistent across all cruises. Parameterizations based on linear regression analyses of these relationships perform well for Arctic and Atlantic data, producing a better fit to observations than an existing Chl a-based parameterization. Global extrapolation of isoprene surface water concentrations using satellite-derived Chl a and intPP reproduced general trends in the in situ data and absolute values within a factor of 2 between 60% and 85%, depending on the data set and algorithm used

Microbial cycling of isoprene, the most abundantly produced biological volatile organic compound on Earth

Isoprene (2-methyl-1,3-butadiene), the most abundantly produced biogenic volatile organic compound (BVOC) on Earth, is highly reactive and can have diverse and often detrimental atmospheric effects, which impact on climate and health. Most isoprene is produced by terrestrial plants, but (micro)algal production is important in aquatic environments, and the relative bacterial contribution remains unknown. Soils are a sink for isoprene, and bacteria that can use isoprene as a carbon and energy source have been cultivated and also identified using cultivation-independent methods from soils, leaves and coastal/marine environments. Bacteria belonging to the Actinobacteria are most frequently isolated and identified, and Proteobacteria have also been shown to degrade isoprene. In the freshwater-sediment isolate, Rhodococcus strain AD45, initial oxidation of isoprene to 1,2-epoxy-isoprene is catalyzed by a multicomponent isoprene monooxygenase encoded by the genes isoABCDEF. The resultant epoxide is converted to a glutathione conjugate by a glutathione S-transferase encoded by isoI, and further degraded by enzymes encoded by isoGHJ. Genome sequence analysis of actinobacterial isolates belonging to the genera Rhodococcus, Mycobacterium and Gordonia has revealed that isoABCDEF and isoGHIJ are linked in an operon, either on a plasmid or the chromosome. In Rhodococcus strain AD45 both isoprene and epoxy-isoprene induce a high level of transcription of 22 contiguous genes, including isoABCDEF and isoGHIJ. Sequence analysis of the isoA gene, encoding the large subunit of the oxygenase component of isoprene monooxygenase, from isolates has facilitated the development of PCR primers that are proving valuable in investigating the ecology of uncultivated isoprene-degrading bacteria

Photosensitized reactions at the sea surface microlayer

International @ AIR+RCI:CGOInternational audienceThe sea surface microlayer is the organic-enriched layer present at the air-sea interface which has different physical and chemical properties than that of subsurface waters. The chemical analysis of this microlayer is of great interest for many reasons including its major influence to reduce airsea gas exchange by impeding molecular diffusion across the interface and by influencing the characteristics of water motion at the interface. Surface seawater contains a variety of substances which act as photosensitisers. They include components of the dissolved organic matter known also as humic acids. The sea surface microlayer is the primary recipient of the solar energy. Since the microlayer is enriched in chemicals and biota, it is probable that a number of processes are more effective here than in the rest of the water column. These include changes in the chemical composition of the living cells of phytoplankton and the photodegradati on of organic matter. The focus of this study is to quantify if the organic film acts as a hydrophobic barrier for the air-sea gas exchange and to identify and characterize the gaseous emissions from the surface due to the photochemical processing of the sea surface microlayer. Synthetic mixtures (aqueous solution containing NaCl, NaBr, NaI), photosensitizers (humic acids) containing an organic surfactant (hexanol, otanol, nonanoic acid) have been irradiated by a Xe lamp, the gaseous products being further identified and analyzed by a High Resolution Proton Transfer Reaction Time of Flight Mass Spectrometer and the particulate phase by a Condensation Particle Counter. It has been observed that the presence of a thick organic film on the salt solutions reduces the transfer from the aqueous solution to the gas phase. A net isoprene formation was observed under irradiation. The isoprene is formed only in the presence of the organic surfactant with the need for the photosensitizer. The dependence of the isoprene concentration with the photosensitizer is shown. A reaction mechanism of the isoprene formation is proposed. Furthermore, the oxidation products of isoprene and of the organic surfactant are identified

Photosensitized reactions at the sea surface microlayer

International @ AIR+RCI:CGOInternational audienceThe sea surface microlayer is the organic-enriched layer present at the air-sea interface which has different physical and chemical properties than that of subsurface waters. The chemical analysis of this microlayer is of great interest for many reasons including its major influence to reduce airsea gas exchange by impeding molecular diffusion across the interface and by influencing the characteristics of water motion at the interface. Surface seawater contains a variety of substances which act as photosensitisers. They include components of the dissolved organic matter known also as humic acids. The sea surface microlayer is the primary recipient of the solar energy. Since the microlayer is enriched in chemicals and biota, it is probable that a number of processes are more effective here than in the rest of the water column. These include changes in the chemical composition of the living cells of phytoplankton and the photodegradati on of organic matter. The focus of this study is to quantify if the organic film acts as a hydrophobic barrier for the air-sea gas exchange and to identify and characterize the gaseous emissions from the surface due to the photochemical processing of the sea surface microlayer. Synthetic mixtures (aqueous solution containing NaCl, NaBr, NaI), photosensitizers (humic acids) containing an organic surfactant (hexanol, otanol, nonanoic acid) have been irradiated by a Xe lamp, the gaseous products being further identified and analyzed by a High Resolution Proton Transfer Reaction Time of Flight Mass Spectrometer and the particulate phase by a Condensation Particle Counter. It has been observed that the presence of a thick organic film on the salt solutions reduces the transfer from the aqueous solution to the gas phase. A net isoprene formation was observed under irradiation. The isoprene is formed only in the presence of the organic surfactant with the need for the photosensitizer. The dependence of the isoprene concentration with the photosensitizer is shown. A reaction mechanism of the isoprene formation is proposed. Furthermore, the oxidation products of isoprene and of the organic surfactant are identified

Photosensitized reactions at the sea surface microlayer

National @ AIR+RCI:LFI:CGOInternational audienceThe sea surface microlayer is the organic-enriched layer present at the air-sea interface which has different physical and chemical properties than that of subsurface waters. The chemical analysis of this microlayer is of great interest for many reasons including its major influence to reduce airsea gas exchange by impeding molecular diffusion across the interface and by influencing the characteristics of water motion at the interface. Surface seawater contains a variety of substances which act as photosensitisers. They include components of the dissolved organic matter known also as humic acids. The sea surface microlayer is the primary recipient of the solar energy. Since the microlayer is enriched in chemicals and biota, it is probable that a number of processes are more effective here than in the rest of the water column. These include changes in the chemical composition of the living cells of phytoplankton and the photodegradati on of organic matter. The focus of this study is to quantify if the organic film acts as a hydrophobic barrier for the air-sea gas exchange and to identify and characterize the gaseous emissions from the surface due to the photochemical processing of the sea surface microlayer. Synthetic mixtures (aqueous solution containing NaCl, NaBr, NaI), photosensitizers (humic acids) containing an organic surfactant (hexanol, octanol, nonanoic acid) have been irradiated by a Xe lamp, the gaseous products being further identified and analyzed by a High Resolution Proton Transfer Reaction Time of Flight Mass Spectrometer and the particulate phase by a Condensation Particle Counter. It has been observed that the presence of a thick organic film on the salt solutions reduces the transfer from the aqueous solution to the gas phase. It has also been observed the formation of certain aldehydes (heptanal, octanal, nonanal, nonenal), alkenes and dienes (butene, 5-methyl-1, 4-hexadiene) in the gas phase. All these compounds were confirmed by GC/MS analysis. A formation of methylglyoxal and acetylacetone has also been detected. An isoprene formation was observed under irradiation. The isoprene is formed only in the presence of the organic surfactant with the need for the photosensitizer. The dependence of the isoprene concentration with the photosensitizer is shown. Furthermore, the oxidation products of isoprene and of the organic surfactant are identified

Processus photochimiques à linterface air-mer : formation des composés organiques volatils et des particules

AIR+RCI:CGOLa microcouche de surface (SML) correspond à linterface entre leau et lair et représente un environnement chimique et biologique unique. Elle est opérationnellement définie comme le premier millimètre de la colonne deau. La SML reçoit des substances gazeuses, liquides (pluies) et solides (aérosols) qui proviennent de latmosphère et des apports continentaux. Due à l'enrichissement des produits chimiques et du biota dans cette région, la SML pourrait agir comme un microréacteur hautement efficace et sélectif où se concentrent et se transforment les matériaux apportés par latmosphère et par les océans. D'une part, cette microcouche a une influence majeure sur la fraction organique des aérosols marins, d'autre part elle contrôle le dépôt de gaz traces dans l'océan et joue un rôle important dans la formation des aérosols organiques secondaires dans latmosphère marine. La SML est directement exposée à l'énergie solaire. Cette couche étant plus riche en composés chimiques et microorganismes, plusieurs processus sont susceptibles d'être plus efficaces ici que dans le reste de la colonne d'eau comme, par exemple, la photodégradation de la matière organique. Beaucoup de ces substances sont des tensio-actifs et contribuent à une augmentation des concentrations des espèces dans la microcouche de surface. Les recherches effectuées à IRCELYON sinscrivent dans ce cadre, par létude des processus photochimiques à l'interface air-mer. Le but de ces études est de caractériser les réactions photochimiques, ou plus précisément photo-sensibilisées, se produisant dans la microcouche de surface et qui sont essentielles pour les échanges air-mer en termes de formation d'aérosols, de radicaux et de composés organiques volatils (COV). Lirradiation de la microcouche de surface conduit à lémission dune série de COV fonctionnalisés qui sont des candidats idéaux pour former des particules et donc augmenter la charge en aérosols organiques secondaires dans la couche limite marine. Les résultats de ces travaux ont mis en évidence, pour la première fois, une formation disoprène due aux processus photochimiques. De manière générale, cette chimie ouvre de nombreux chemins réactionnels très complexes pouvant engendrer de nouveaux processus aux interfaces

Investigating the pathway for the photochemical formation of VOCs in presence of an organic monolayer at the air/water interface.

International @ CARE+LTI:SRS:RCI:CGOInternational audienceInvestigating the pathway for the photochemical formation of VOCs in presence of an organic monolayer at the air/water interface.Liselotte Tinel, Stéphanie Rossignol, Raluca Ciuraru and Christian GeorgeUniversité de Lyon, Université Lyon 1, CNRS, UMR5256, IRCELYON, Institut de recherches sur la catalyse et l’environnement de Lyon, Villeurbanne, F-69626, FranceRecently the surface microlayer (SML) has received growing attention for its role in the deposition and emission of trace gases. This SML is presumably a highly efficient environment for photochemical reactions thanks to its physical and chemical properties, showing enrichment in chromophores [1]. Still, little is known about the possible photochemical processes that could influence the emission and deposition of volatile organic compounds (VOCs) in the SML. A recent study underlines the particularity of the presence of an organic microlayer, showing enhanced formation of peptide bonds at the air-water interface, although this reaction is thermodynamically disfavoured in bulk water [2]. Also, emissions of small gas phase carbonyl compounds formed photochemically by dissolved organic matter have been measured above natural water and glyoxal, for example, measured above the open ocean is thought to be photochemically produced [3, 4].This study presents the results of a set of laboratory studies set up in order to better understand the role of the SML in the photochemical production of VOCs. Recently, our group has shown the formation of VOCs by light driven reactions in a small quartz reactor (14mL) containing aqueous solutions of humic acids (HA) in the presence of an organic (artificial or natural) microlayer [5]. The main VOCs produced were oxidized species, such as aldehydes, ketones and alcohols, as classically can be expected by the oxidation of the organics present at the interface initiated by triplet excited chromophores present in the HA. But also alkenes, dienes, including isoprene and unsaturated aldehydes were detected and a reaction pathway, initiated by a H-abstraction of the surfactant by the excited HA*, has been proposed. This mechanism infers that the presence of the surface microlayer will enhance protonation and self-reactions, leading to the formation of dimers as suggested in [6]. These products could explain the formation of the unsaturated products observed.To confirm the hypothesis of an initiative step of H-abstraction, the system was simplified using OH radicals, generated by the photolysis of H2O2, in presence of an artificial organic layer of nonanoic acid. The VOCs produced, monitored by PTR/SRI-TOF-MS in NO+ and H3O+ ionization mode, were less abundant compared to the system with HA, but the same classes of products could be observed, including oxidation products such as aldehydes but also unsatured products like dienes. The underlying water was sampled before and after the experiment and analysed by HR-ESI-MS, showing mostly enrichment of oxidative products, such as hydroxy- and keto-acids immediately derived from the photochemical oxidation of the nonanoic acid layer. These products, showing lower volatility and higher polarity, partition preferentially to the bulk water. The results of this simplified system confirm the reaction mechanism proposed and the role an organic layer can play in the photochemical formation of VOCs, which could influence the marine boundary layer chemistry.1.Peter S. Liss, R.A.D., ed. Sea Surface and Global Change. 1997, Cambridge University Press: Cambridge. 509.2.Griffith, E.C. and V. Vaida, In situ observation of peptide bond formation at the water–air interface. Proceedings of the National Academy of Sciences, 2012. 109(39): p. 15697-15701.3.Sinreich, R., et al., Ship-based detection of glyoxal over the remote tropical Pacific Ocean. Atmospheric Chemistry and Physics, 2010. 10(23): p. 11359-11371.4.Kieber, R.J., X.L. Zhou, and K. Mopper, Formation of carbonyl-compounds from uv-induced photodegradation of humic substances in natural-waters - fate of riverine carbon in the sea. Limnology and Oceanography, 1990. 35(7): p. 1503-1515.5.R. Ciuraru, L. Fine, M. van Pinxteren, B. D'Anna, H. Herrmann, C. George, Unravelling new processes at interfaces: chemical isoprene production at the sea surface. submitted.6.Griffith, E.C., et al., Photoinitiated Synthesis of Self-Assembled Vesicles. Journal of the American Chemical Society, 2014. 136(10): p. 3784-3787

Volatile organic compounds emission from light-induced reactions at the sea surface microlayer

International @ ATARI+RCI:LFI:CGOInternational audienceVolatile organic compounds emission from light-induced reactions at the sea surface microlayerRaluca Ciuraru, François Bernard, Ludovic Fine, Christian GeorgeCNRS-IRCELYON, Université Lyon 1, 69629 Villeurbanne, FranceThe sea surface microlayer is the organic-enriched layer present at the air-sea interface which has different physical and chemical properties compared to subsurface waters1. The chemical analysis of this microlayer is of great interest for many reasons including its major influence to reduce air–sea gas exchange. Surface seawater contains a variety of substances which act as photosensitizers. They include components of the dissolved organic matter known also as humic acids. The sea surface microlayer is the primary recipient of the solar energy and since it is enriched in chemicals and biota, a number of processes are likely to be more effective here than in the water column2.The focus of this study is to determine if the organic film acts as a hydrophobic barrier for the air-sea gas exchange and to identify and characterize the volatile organic compounds emissions due to the photochemical processing of the sea surface microlayer. Synthetic salt solutions containing a photosensitizer (humic acids) and an organic surfactant (nonanoic acid) have been irradiated by a Xe lamp, the VOCs being further identified and analyzed by a High Resolution PTR-ToFMS.It has been observed that the presence of a thick organic film on the salt solutions reduces the transfer from the aqueous solution to the gas phase.The formation of certain saturated and unsaturated aldehydes, acids and a series of alkenes and dienes have been observed. All these compounds were confirmed by GC/MS analysis. An isoprene formation was also observed under irradiation. The isoprene is formed only in the presence of the organic surfactant with the need for the photosensitizer. The dependence of the isoprene concentration with the surfactant concentration and its surface tension is shown and discussed.1. Donaldson, D. J. & George, C., Environ. Sci. Technol. 46, 10385–10389, 2012.2. Liss, P. S. & Duce, R. A. Cambridge University Press, Cambridge, 1997

Shining light on the air-sea interface: investigating the photochemical production of functionalized VOC

SSCI-VIDE+CARE+LTI:SRS:CGOInternational audienceThis study presents the results of a set of laboratory experiments aiming at a better understanding of the role of the sea surface microlayer in the photochemical production of VOCs. Recently, we have shown that light driven reactions, in aqueous solutions containing a photosensitizer (P) in the presence of a surface organic microlayer, leads to the formation of various gaseous VOCs.. The main VOCs produced, analysed by PTR/SRI-ToF-MS, were oxidized species, such as aldehydes, ketones and alcohols, as expected by the photo-oxidation of the organics at the air/water interface. However also alkenes, dienes and unsaturated aldehydes were detected and a reaction pathway, initiated by an H-abstraction of the surfactant by the excited P*, has been proposed. This mechanism infers that the presence of the surface microlayer will enhance protonation and self-reactions, leading to the formation of dimers, as confirmed by UPLC-HR-ESI-MS analysis. As most of these compounds were thought to be solely produced by biological activities, the existence of such interfacial photochemistry opensnew directions that will discussed

Particle formation through photosensitized reactions at the air-sea interface

International @ ATARI+RCI:LFI:CGOInternational audienceThe sea surface microlayer (SML) represents more than 70% of the Earth’s surface and constitutes the boundary layer interface between the ocean and the atmosphere. The sea surface is characterized by an organic enriched microlayer originating from marine chemical and biological activities. Exposed to solar radiation, it has been demonstrated that the surface is a source of volatile organic compounds (VOC) as well as of highly functionalized VOCs.Consequently, the question arises as to whether photo-induced chemical processes under relevant atmospheric conditions lead to the secondary organic aerosol (SOA) loading in the marine boundary layer. Previous works have shown that photochemical processing lead to the formation of highly functionalized VOCs which may be potential candidates to the SOA loading. In order to bring further comprehension, a multiphase atmospheric simulation chamber has been used in order to study the chemical processes occurring at the air-sea interface. Experiments have been performed in a 2 m3 chamber made of FEP film in which a glass container for liquids is inserted. Light processing was initiated using VUV lamps (centred at 365 nm) in order to irradiate the liquid mixture containing humic acid used as photosensitizer and nonanoic acid used as a surfactant. Particle formation was monitored using an ultrafine condensation particle counter (d50 > 2.5 nm) and particle growth was followed by a SMPS. VOCs formed have been identified and analysed by Proton Transfer Reaction – Time of Flight Mass Spectrometer and GC/MS. The chamber is also equipped with trace gas analyzers continuously measuring NO-NOX and ozone.The liquid mixture was exposed to VUV irradiation for 14 hours at least. When the light was turned off, ozone was added in the gas phase. Light-induced processes showed a low increase of particle concentration while secondary reaction implying ozone showed a significant contribution in SOA formation. These observations indicate the presence of SOA precursors among the VOCs formed during irradiation. Atmospheric implication of photosensitized reactions as a source of SOA loading in the marine boundary layer will be discussed