Marine organic matter in the remote environment of the Cape Verde islands-an introduction and overview to the MarParCloud campaign

The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September-October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation-and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean-atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecularweight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited. © Author(s) 2020

Marine organic matter in the remote environment of the Cape Verde islands – an introduction and overview to the MarParCloud campaign

The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September–October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation- and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean–atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited

Reactions of acetone oxide stabilized Criegee intermediate with SO2, NO2, H2O and O3

International audienceAtmospheric aerosol particles represent a critical component of the atmosphere, impacting global climate, regionalair pollution, and human health. The formation of new atmospheric particles and their subsequent growth to largersizes are the key processes for understanding of the aerosol effects. Sulphuric acid, H2SO4, has been identified toplay the major role in formation of new atmospheric particles and in subsequent particle growth. Until recently thereaction of OH with SO2 has been considered as the only important source of H2SO4 in the atmosphere. However,recently it has been suggested that the oxidation of SO2 by Criegee biradicals can be a significant additionalatmospheric source of H2SO4 comparable with the reaction of SO2 with OH.Here we present some results about the reactions of the acetone oxide stabilized Criegee intermediate, (CH3)2=OO,produced in the reaction of 2,3-dimethyl-butene (TME) with O3.The formation of the H2SO4 in the reaction of acetone oxide with SO2 was investigated in the speciallyconstructed atmospheric pressure laminar flow reactor. The Criegee intermediate was generated by ozonolysisof TME. The H2SO4, generated by addition of SO2, was directly monitored with Chemical Ionization MassSpectrometer (SAMU, LPC2E). Relative rates of reactions of acetone oxide with SO2, NO2, H2O and ozone weredetermined from the dependencies of the H2SO4 yield at different concentrations of the reactants.Atmospheric applications of the obtained results are discussed in relation to the importance of this additionalH2SO4 formation pathway compared to the reaction of OH with SO2

Atmospheric chamber measurements of H2SO4: characterization of formation and loss rates during the ozonolysis and aerosol formation studies

International audienceSulphuric acid, H2SO4, has been identified to play major role in atmospheric new particle formation and in subsequent particle growth. The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) initiated by the reaction with the hydroxyl radicals (OH) is assumed to be the dominant formation pathway of sulfuric acid (H2SO4) in the troposphere. It has been suggested in the recent years that the reactions of Criegee Intermediates (CIs) with SO2 may also contribute to the H2SO4 formation, although the significance of this pathway compared to the reaction of OH with SO2 is still under discussion. As the ozonolysis of anthropogenic and biogenic terpenes emitted into the atmosphere may represent an important source of OH and CIs a better understanding of the ozonolysis mechanism in relation to the H2SO4 formation is required. In this study, we present the results obtained during the investigation of the ozonolysis of several unsaturated volatile organic compounds, including tetramethylethylene, α-pinene and limonene, using a newly constructed large atmospheric simulation chamber, HELIOS (ICARE-CNRS, Orléans, France). The HELIOS facility consists of a large outdoor simulation chamber (volume of 90 m3) equipped with a wide range of in-situ on-line and off-line analytical instrumentation (FTIR, PTR-TOF-MS, GC-MS, CIMS (OH and H2SO4), SMPS, Figaero-API-TOF-CIMS, HCHO monitor and others). The results of kinetic and mechanistic studies of the reactions of different CIs with SO2 induced by the ozonolysis of the studied VOCs under different conditions will be presented. The H2SO4 loss on the Teflon chamber wall and by the aerosol uptake were characterized using direct H2SO4 and particle measurements. Keywords: ozonolysis, Criegee Intermediate, sulfur dioxide, sulfuric acid, HELIO

Atmospheric chamber measurements of H2SO4: characterization of formation and loss rates during the ozonolysis and aerosol formation studies

International audienceSulphuric acid, H2SO4, has been identified to play major role in atmospheric new particle formation and in subsequent particle growth. The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) initiated by the reaction with the hydroxyl radicals (OH) is assumed to be the dominant formation pathway of sulfuric acid (H2SO4) in the troposphere. It has been suggested in the recent years that the reactions of Criegee Intermediates (CIs) with SO2 may also contribute to the H2SO4 formation, although the significance of this pathway compared to the reaction of OH with SO2 is still under discussion. As the ozonolysis of anthropogenic and biogenic terpenes emitted into the atmosphere may represent an important source of OH and CIs a better understanding of the ozonolysis mechanism in relation to the H2SO4 formation is required. In this study, we present the results obtained during the investigation of the ozonolysis of several unsaturated volatile organic compounds, including tetramethylethylene, α-pinene and limonene, using a newly constructed large atmospheric simulation chamber, HELIOS (ICARE-CNRS, Orléans, France). The HELIOS facility consists of a large outdoor simulation chamber (volume of 90 m3) equipped with a wide range of in-situ on-line and off-line analytical instrumentation (FTIR, PTR-TOF-MS, GC-MS, CIMS (OH and H2SO4), SMPS, Figaero-API-TOF-CIMS, HCHO monitor and others). The results of kinetic and mechanistic studies of the reactions of different CIs with SO2 induced by the ozonolysis of the studied VOCs under different conditions will be presented. The H2SO4 loss on the Teflon chamber wall and by the aerosol uptake were characterized using direct H2SO4 and particle measurements. Keywords: ozonolysis, Criegee Intermediate, sulfur dioxide, sulfuric acid, HELIO