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

Investigation of the reaction of ozone with isoprene, methacrolein and methyl vinyl ketone using the HELIOS chamber

International audienceThe rate constants for the ozonolysis of isoprene (ISO), methacrolein (MACR) and methyl vinyl ketone (MVK) have been measured using the newly built large volume atmospheric simulation chamber at CNRS-Orleans (France), HELIOS (Chambre de simulation atmospherique a irradiation naturelle d'Orleans). The OH radical yields from the ozonolysis of isoprene, MACR and MVK have also been determined, as well as the gas phase stable products and their yields. The secondary organic aerosol yield for the ozonolysis of isoprene has been tentatively measured in the presence and absence of an OH radical scavenger. The measurements were performed under different experimental conditions with and without adding cyclohexane (cHX) as an OH radical scavenger. All experiments have been conducted at 760 torr of purified dry air (RH < 1%) and ambient temperature (T = 281-295 K). The data obtained are discussed and compared with those from the literature. The use of the HELIOS facility and its associated analytical equipment enables the derivation of kinetic parameters as well as mechanistic information under near realistic atmospheric conditions

Kinetic and product studies of Cl atoms reactions with a series of branched Ketones

International audienceThe rate constants for the Cl atom reaction with three branched ketones have been measured at 298 ± 2 K and 760 Torr using the relative rate method in the absence of NO. The rate constants values obtained (in units of 10− 10 cm3/(molecule·sec)) are: k(2-methyl-3-pentanone) = 1.07 ± 0.26, k(3-methyl-2-pentanone) = 1.21 ± 0.26, and k(4-methyl-2-pentanone) = 1.35 ± 0.27. Combining the chemical kinetic data obtained by this study with those reported for other ketones, a revised Structure Activity Relationship (SAR) parameter and R group reactivity (kR) of R(O)R′ and CHx (x = 1, 2, 3) group reactivity (kCHx) toward Cl atoms were proposed. In addition, the products from the three reactions in the presence of NO were also identified and quantified by using PTR-ToF-MS and GC-FID, and the yields of the identified products are: acetone (39% ± 8%) + ethanal (78% ± 12%), 2-butanone (22% ± 2%) + ethanal (75% ± 10%) + propanal (14% ± 1%) and acetone (26% ± 3%) + 2-methylpropanal (24% ± 2%), for Cl atoms reaction with 2-methyl-3-pentanone, 3-methyl-2-pentanone and 4-methyl-2-pentanone, respectively. Based on the obtained results, the reaction mechanisms of Cl atoms with these three ketones are proposed

Reactive uptake of NO2 on volcanic particles: A possible source of HONO in the atmosphere

International audienceThe heterogeneous degradation of nitrogen dioxide (NO2) on five samples of natural Icelandic volcanic particles has been investigated. Laboratory experiments were carried out under simulated atmospheric conditions using a coated wall flow tube (CWFT). The CWFT reactor was coupled to a blue light nitrogen oxides analyzer (NOx analyzer), and a long path absorption photometer (LOPAP) to monitor in real time the concentrations of NO2, NO and HONO, respectively. Under dark and ambient relative humidity conditions, the steady state uptake coefficients of NO2 varied significantly between the volcanic samples probably due to differences in magma composition and morphological variation related with the density of surface OH groups. The irradiation of the surface with simulated sunlight enhanced the uptake coefficients by a factor of three indicating that photo-induced processes on the surface of the dust occur. Furthermore, the product yields of NO and HONO were determined under both dark and simulated sunlight conditions. The relative humidity was found to influence the distribution of gaseous products, promoting the formation of gaseous HONO. A detailed reaction mechanism is proposed that supports our experimental observations. Regarding the atmospheric implications, our results suggest that the NO2 degradation on volcanic particles and the corresponding formation of HONO is expected to be significant during volcanic dust storms or after a volcanic eruption

Report on selected measurements in the canopy of a Rambouillet forest site during the ACROSS field campaign

International audienceIn this contribution we report on a subset of ground-based measurements performed by LPC2E and ICARE at a forest site of Rambouillet during June-July of 2022 in the frame of the project ACROSS (Atmospheric ChemistRy Of the Suburban foreSt). In particular, we present the following time-concentration profiles:- OH and sum of peroxy radicals (CIMS , LPC2E);- gaseous H2SO4 (CIMS, LPC2E);- large number of volatile organic compounds (VOCs) and their oxidation products, including N-containing oxygenated organic molecules (OOMs) (Orbitrap High Resolution CIMS, LPC2E);- directly emitted VOCs and their oxidation products measured by GC-MS/FID (ICARE)- HONO (LOPAP, ICARE)- NO and NO2 (ICARE)Based on a first analysis of this reduced data-set some preliminary conclusions are made about an influence of VOCs emissions and NOx variability on the composition of OOMs oxidation products, HONO formation and oxidation capacity in the forest canopy

Role of the dew water on the ground surface in HONO distribution: a case measurement in Melpitz

International audienceTo characterize the role of dew water for the ground surface HONO distribution, nitrous acid (HONO) measurements with a Monitor for AeRosols and Gases in ambient Air (MARGA) and a LOng Path Absorption Photometer (LOPAP) instrument were performed at the Leibniz Institute for Tropospheric Research (TROPOS) research site in Melpitz, Germany, from 19 to 29 April 2018. The dew water was also collected and analyzed from 8 to 14 May 2019 using a glass sampler. The high time resolution of HONO measurements showed characteristic diurnal variations that revealed that (i) vehicle emissions are a minor source of HONO at Melpitz station; (ii) the heterogeneous conversion of NO2 to HONO on the ground surface dominates HONO production at night; (iii) there is significant nighttime loss of HONO with a sink strength of 0:16 +/- 0:12 ppbv h(-1); and (iv) dew water with mean NO2- of 7:91 +/- 2:14 mu gm(-2) could serve as a temporary HONO source in the morning when the dew droplets evaporate. The nocturnal observations of HONO and NO2 allowed the direct evaluation of the ground uptake coefficients for these species at night: gamma NO2 -> HONO = 2:4 x 10(-7) to 3.5 x 10(-6), gamma(HONO,ground) D 1.7 x 10(-5) to 2.8 x 10(-4). A chemical model demonstrated that HONO deposition to the ground surface at night was 90 %-100% of the calculated unknown HONO source in the morning. These results suggest that dew water on the ground surface was controlling the temporal HONO distribution rather than straightforward NO2-HONO conversion. This can strongly enhance the OH reactivity throughout the morning time or in other planted ar- eas that provide a large amount of ground surface based on the OH production rate calculation

Field measurements of organic and inorganic composition in the Rambouillet Forest during ACROSS campaign

International audienceRambouillet Forest is a large forested location, situated about 50km from central Paris. It covers some 200km2 and contains mainly a mix of oak and pine trees. Its size and proximity towards Paris makes it an interesting site to study the interaction between polluted air masses and biogenic emissions and the impact on air quality in areas surrounding polluted cities. The ACROSS (Atmospheric ChemistRy Of the Suburban forest) campaign represents a large international collaboration between various French, European and American institutes, which aims to further characterize these interactions. For our contribution, different instruments from ICARE and LPC2E CNRS Orléans performed in-situ measurements in this forest during June and July of 2022, including: VOCs/ BVOCs (GC-MS/FID); oxidants (OH radicals, CIMS); oxidant precursors (NOx, NOy, Ecophysics, CAPS, LOPAP); and highly oxidized products (orbitrap). In general, data coverage for all instrumentation was high throughout the campaign, furthermore this instrumentation was calibrated and characterized under field condition where possible. These observations represent a broad look at the composition of the forested environment, and contain information on organic emissions, their oxidized products, oxidants and oxidant precursors. We therefore anticipate that these measurements will contribute significantly to the understanding of the atmospheric chemistry operating during the ACROSS campaign

Ambient BTEX Concentrations during the COVID-19 Lockdown in a Peri-Urban Environment (Orléans, France)

International audienceDuring the period from 17 March to 10 May 2020, France saw dramatic shifts in domestic, industrial and transport activities as a national lockdown was introduced. So far, studies have generally focused on urban settings, by contrast, this work reports data for a peri-urban location. Air samples were collected and analyzed using a fully automated GC-MS-FID system in an air quality monitoring station situated in the suburbs of Orléans, France. Average concentrations of BTEX (benzene, toluene, ethylbenzene, and xylenes) before, during, and after lockdown, were 402 ± 143, 800 ± 378 and 851 ± 445 pptv, respectively. Diurnal variation in BTEX and correlations between each of its components were analyzed to determine its various sources. The toluene/benzene (T/B) and m,p-xylene/ethylbenzene (MP/E) ratios, photochemical ages were used to explore whether the BTEX were from local or more distant sources. Together with a host of complementary measurements including NOx, O3, black carbon, meteorological parameters, and anthropogenic activities, we were able to make some inferences on the sources of BTEX. The results suggest that although anomalous local anthropogenic activity can lead to significant changes in BTEX concentrations, pollution levels in Orléans are mostly dependent on meteorological conditions, specifically whether the winds are coming from the Paris region. It appears, based on these measurements, that the pollution in the Orléans area is very much tied to the nearby megacity of Paris, this may be true for other peri-urban sites with implications for city planning and pollution mitigation strategies

Atmospheric Chemistry of 1-Methoxy 2-Propyl Acetate: UV Absorption Cross Sections, Rate Coefficients, and Products of Its Reactions with OH Radicals and Cl Atoms

International audienceThe rate coefficients for the reactions of OH and Cl with 1-methoxy 2-propyl acetate (MPA) in the gas phase were measured using absolute and relative methods. The kinetic study on the OH reaction was conducted in the temperature (263-373) K and pressure (1-760) Torr ranges using the pulsed laser photolysis-laser-induced fluorescence technique, a low pressure fast flow tube reactor-quadrupole mass spectrometer, and an atmospheric simulation chamber/GC-FID. The derived Arrhenius expression is k(MPA+OH)(T) = (2.01 +/- 0.02) X 10(-12) exp[(588 +/- 123/T)] cm(3) molecule(-1) s(-1). The absolute and relative rate coefficients for the reaction of Cl with MPA were measured at room temperature in the flow reactor and the atmospheric simulation chamber, which led to k((Cl+MPA)) = (1.98 +/- 0.31) X 10(-10) cm(3) molecule(-1) s(-1). GC-FID, GC-MS, and FT-IR techniques were used to investigate the reaction mechanism in the presence of NO. The products formed from the reaction of MPA with OH and their yields were methyl formate (80 +/- 7.3%), acetic acid (50 +/- 4.8%), and acetic anhydride (22 +/- 2.4%), while for Cl reaction, the obtained yields were 60 +/- 5.4, 41 +/- 3.8, and 11 +/- 1.2%, respectively, for the same products. The UV absorption cross section spectrum of MPA was determined in the wavelength range 210-370 nm. The study has shown no photolysis of MPA under atmospheric conditions. The obtained results are used to derive the atmospheric implication