Anne Monod

Based on a combination of ground-sites and aircraft observations, the ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) project seeks to better understand how the pollution from Paris affects air quality over large regional scales, particularly through interaction with biogenic species. A field campaign took place in June-July 2022 at three sites: a forested remote site (Rambouillet, 50 km southwest from downtown Paris) a peri-urban (SIRTA) and an urban ones (PRG). The extensive instrumentation deployed at those sites allows to gain insights into the transformation of gaseous and particulate species from local to regional scales. Besides, the Rambouillet site has not only served as a receptor site from Paris plume but also led to detailed observations of freshly emitted biogenic compounds and their role in local chemistry, reactivity, and aerosol properties.This work focuses on the real-time aerosol composition at the Rambouillet site. High resolution time-of-flight aerosol mass...

ABSTRACT The kinetics and mechanism of the reactions of OH radicals with IBr and HOI have been studied using the mass spectrometric discharge-flow method at 320K and at a total pressure of 1Torr of Helium. The rate constant of the reaction OH+IBr→products (1) was measured under pseudo-first order conditions either in excess of IBr or in excess of OH radicals: k1=(1.4±0.4)×10−10cm3molecule−1s−1. Both HOI and HOBr were detected as products of reaction (1) and the branching ratios 0.84±0.07 and 0.14±0.05, respectively, were found for the channels forming these species. For the reaction OH+HOI→products (2) the total rate constant was determined from the kinetics of HOI consumption in excess of OH radicals: k2=(5.0±1.2)×10−12cm3molecule−1s−1.

www.atmos-chem-phys-discuss.net/13/2913/2013/ doi:10.5194/acpd-13-2913-2013 © Author(s) 2013. CC Attribution 3.0 License. This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available.

<p>The vertical structure of the water vapor field in the lower troposphere is only sparsely documented in mountainous regions and particularly above Alpine lakes. This may in part due to the complexity of the system, being intimately linked to the orography surrounding the lakes and the forcing of the topography-induced winds. The question arises as to how the vertical extent of evaporation processes over the lakes and how these are influenced by larger scale forcing, in particularly with regard to the vertical dimension.</p><p>In order to gain understanding on the vertical structure of atmospheric water vapour above mountain lakes, the L-WAIVE (Lacustrine-Water vApor Isotope inVentory Experiment) field campaign was conducted in the Annecy valley in the French Alps in June 2019. This campaign was based on a synergy between ground-based lidar measurements and ship-borne as well as airborne observations. Two ultra-light aircraft (ULA) were equipped with remote sensing and in-situ instruments to characterize the vertical distribution of the main water vapour isotopes. One ULA embarked a backscatter lidar to monitor the horizontal evolution of the vertical structure of the lower troposphere above and around the lake, and the other one carried an L2130-i Picarro isotope analyser for the in-situ measurement of the H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>18</sup>O and HDO concentrations, an iMet probe for the measurement of thermodynamic properties (T, RH, p), as well as a pre-cleaned Caltech Active Strand Cloud Water Collector which was modified to efficiently collect cloud water at the speed of the ULA. Offset calibration of the Picarro analyser was carried out for each flight before take-off and after landing. Three-dimensional explorations of the lake environment up to 4 km above the mean sea level (~3.5 km above the ground level) were conducted with the ULAs. Simultaneous vertical profiles of water vapour, temperature, aerosols and winds were acquired from two co-located ground-based lidars installed on the shore of the southern part of the Annecy Lake named “petit lac”, in the commune of Lathuile (45°47' N, 6°12' E). Finally, ship-borne profile measurements of the lake water temperature, pH, conductivity and dissolved O<sub>2</sub> as well as water sampling for isotopic analyses were accrued out across the lake of Annecy.</p><p>The campaign period included several cases of weather events leading to variability between dry and humid conditions, cloudy and cloud-free conditions, and regimes dominated by weak and strong winds. Flight patterns have been repeated at several times in the day to capture the diurnal evolution as well as variation between different weather regimes. Additional flights have been conducted to map the spatial variability of the water vapour isotope composition with regard to the lake and topography. The scientific strategy of the experiment will be presented, and the first observational results will be described with emphasis on the vertical structure of the lower troposphere and its relationship to orography, including the characterisation of the water…

The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical propertie...

Hydroperoxides and aldehydes are considered as atmospheric reservoirs of OH, HO_2 and RO_2 radicals and can reflect the oxidizing levels of the atmosphere. They are considered as important gas phase photo-oxidants present in the atmosphere. However, the atmospheric role of these compounds can vary from one species to another, therefore it is essential to investigate their measurement and speciation in the atmosphere. Atmospheric measurements were realized during two different field campaigns in the Marseilles area (France). Hydroperoxides were trapped in aqueous phase, with a glass coil and analyzed by HPLC/fluorescence detector with post column derivatization. Aldehydes were trapped in a liquid phase containing 2-4 DNPH, with a mist chamber and analyzed by HPLC/UV. The analytical techniques provided individual separation and quantification of seven hydroperoxides (hydrogen peroxide, hydroxymethyl hydroperoxide, bis(hydroxymethyl) peroxide, 1-hydroxyethyl hydroperoxide, methyl hydro...

This study investigated the oligomer formation from the photo-oxidation of acetic acid in the aqueous phase. Using results from these and methylglyoxal+OH radical experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. Increasing attention has been paid to the oligomers and SOA produced by oxygenated small molecule organic compounds through aqueous reaction. However, currently it is difficult to directly get the information about the structure of oligomers because of unavailable standards. It is significant for one to propose reasonable structures and formation of oligomers based on available experimental observations. The results reported by the authors are interesting and may have important consequences on oligomers formation in the wet aerosols. I

Submitted for the MAR14 Meeting of The American Physical Society Effects of Aqueous Solvation on the Photochemistry of Pyruvic Acid ALLISON REED-HARRIS, University of Colorado at Boulder, BARBARA ERVENS, Cooperative Institute for Research in Environmental Sciences (CIRES) / National Oceanic & Atmospheric Administration (NOAA), RICHARD SHOEMAKER, REBECCA RAPF, JAY KROLL, ELIZABETH GRIFFITH, University of Colorado at Boulder, ANNE MONOD, Aix Marseille Universite, VERONICA VAIDA, University of Colorado at Boulder — The role of organic compounds in atmospheric chemistry leading to aerosol formation is under investigation due to the necessity to understand the effects of aerosols on global climate change. It has recently been shown that important pathways in formation of organic aerosols are in aqueous environments where high molecular weight products are formed and can potentially contribute to atmospheric aerosol mass. This presentation describes the photochemistry of pyruvic acid in a...

Aerosol and molecular processing in the atmosphere occurs in a complex and variable environment consisting of multiple phases and interfacial regions. To explore the effects of such conditions on the reactivity of chemical systems, we employ an environmental simulation chamber to investigate the multiphase photolysis of pyruvic acid, which photoreacts in the troposphere in aqueous particles and in the gas phase. Upon irradiation of nebulized pyruvic acid, acetic acid and carbon dioxide are rapidly generated, which is consistent with previous literature on the bulk phase photolysis reactions. Additionally, we identify a new C6 product, zymonic acid, a species that has not previously been reported from pyruvic acid photolysis under any conditions. Its observation here, and corresponding spectroscopic signatures, indicates it could be formed by heterogeneous reactions at the droplet surface. Prior studies of the aqueous photolysis of pyruvic acid have shown that high-molecular-weight c...

Organic compounds of both anthropogenic and natural origin are ubiquitous in the multiphasic atmospheric medium. Their transformation in the atmosphere affects air quality and the global climate. Modelling provides a useful tool to investigate the chemistry of organic compounds in the tropospheric multiphase system. While several comprehensive explicit mechanisms exist in the gas phase, explicit mechanisms are much more limited in the aqueous phase.<br><br> Recently, new empirical methods have been developed to estimate HO<sup>•</sup> reaction rates in the aqueous phase: structure-activity relationships (SARs) provide global rate constants and branching ratios for HO<sup>•</sup> abstraction from and addition to atmospheric organic compounds. Based on these SARs, a new detailed aqueous-phase mechanism, named the cloud explicit physico-chemical scheme (CLEPS), to describe the oxidation of hydrosoluble organic compounds resulting from isoprene oxidat...

Flash photolysis (FP) coupled to resonance fluorescence (RF) was used to measure the absolute rate coefficients (k(1)) for the reaction of OH(X(2)Π) radicals with diiodomethane (CH(2)I(2)) over the temperature range 295-374 K. The experiments involved time-resolved RF detection of the OH (A(2)Σ(+)→X(2)Π transition at λ = 308 nm) following FP of the H(2)O/CH(2)I(2)/He mixtures. The OH(X(2)Π) radicals were produced by FP of H(2)O in the vacuum-UV at wavelengths λ > 120 nm. Decays of OH radicals in the presence of CH(2)I(2) are observed to be exponential, and the decay rates are found to be linearly dependent on the CH(2)I(2) concentration. The results are described by the Arrhenius expression k(1)(T) = (4.2 ± 0.5) × 10(-11) exp[-(670 ± 20)K/T] cm(3) molecule(-1) s(-1). The implications of the reported kinetic results for understanding the atmospheric chemistry of CH(2)I(2) are discussed.

Secondary Organic Aerosol (SOA) were generated from the ozonolysis of α-pinene in the CESAM simulation chamber. The formation and ageing of the SOA were studied by following their optical, hygroscopic and chemical properties. The optical properties investigated by determining the particle Complex Refractive Index (CRI). The hygroscopicity was quantified by measuring the effect of RH on particle size (Growth Factor, GF) and scattering coefficient (<i>f</i>(RH)). The oxygen to carbon (O : C) atomic ratio of the particle surface and bulk were used as a sensitive parameter to correlate the changes in hygroscopic and optical properties of the SOA composition in CESAM. <br><br> The real CRI at 525 nm wavelength decreased from 1.43–1.60 (±0.02) to 1.32–1.38 (±0.02) during the SOA formation. The decrease in real CRI correlates with a decrease in the O : C ratio of SOA from 0.68 (±0.20) to 0.55 (±0.16). In contrast, the GF stayed roughly constant over the reaction tim...

First- and higher-generation products from the oxidation of isoprene and methacrolein with OH radicals in the presence of NO<sub>x</sub> have been studied in a simulation chamber: (1) significant oxidation rates have been maintained for up to 7 h allowing the study of highly oxidized products, (2) gas-phase products distribution and yields are provided, and show good agreement with previous studies. Secondary organic aerosol (SOA) formation resulting from these experiments has also been investigated. Among the general dispersion exhibited by SOA mass yields from previous studies, the mass yields obtained here were consistent with the lowest values found in the literature, and more specifically in agreement with studies carried out with natural light or artificial lamps with emission spectrum similar to the solar one. An effect of light source is hence proposed to explain, at least in part, the discrepancies observed between different studies in the literature for both is...

... Design of an environmental chamber for the study of atmospheric chemistry : New developments in the analytical device. ... Une chambre de simulation atmosphérique a été conçue et réalisée au Laboratoire interuniversitaire des systèmes atmosphériques (Lisa), afin de mener à ...

Secondary organic aerosol (SOA) represents a substantial part of organic aerosol, which affects climate and human health. It is now accepted that one of the important pathways of SOA formation occurs via aqueous phase chemistry in the atmosphere. Recently, we have shown in a previous study (Renard et al., 2013) the mechanism of oligomerization of MVK (methyl vinyl ketone), and suggested that unsaturated water soluble organic compounds (UWSOC) might efficiently form SOA in wet aerosol particles, even for weakly soluble ones like MVK. The atmospheric relevance of these processes is explored by means of process model studies (in a companion paper). In the present study we investigate the aging of these aqueous phase MVK-oligomers (Part 1). <br><br> We compared aqueous phase composition and SOA composition after nebulization, mainly by means of UPLC-ESI-MS and AMS, respectively. Both instruments match and show similar trend of oligomer formation and aging. The SMPS analysis ...

Pyruvic acid in the atmosphere is found in both the gas and aqueous phases, and its behavior gives insight into that of other α-keto acids. Photolysis is a significant degradation pathway for this molecule in the environment, and in aqueous solution the major photoproducts are higher-molecular-weight compounds that may contribute to secondary organic aerosol mass. The kinetics of the aqueous-phase photolysis of pyruvic acid under aerobic and anaerobic conditions was investigated in order to calculate the first-order rate constant, Jaq, in solution. Analysis of the exponential decay of pyruvic acid was performed by monitoring both pyruvic acid and its photolytic products over the course of the reaction by (1)H NMR spectroscopy. Detection of major and minor products in the 0.1, 0.05, and 0.02 M pyruvic acid photolyses clearly demonstrates that the primary reaction pathways are highly dependent on the initial pyruvic acid concentration and the presence of dissolved oxygen. The Jaq values were calculated with approximations based on the dominant pathways for limiting cases of the mechanism. Finally, a model study using the calculated rate constants demonstrates the importance of aqueous-phase photolysis as a sink for pyruvic acid in the atmosphere, compared with gas-phase photolysis and OH oxidation.