Organic aerosols (OA) play a significant role in influencing both climate and human health. However, in source-receptor modelling, a large fraction of OA is typically attributed to highly aged, atmospherically processed species collectively referred to as oxygenated organic aerosol (OOA). Nevertheless, the formation pathways and evolution of OOA as well as their impacts on aerosol optical properties, remain poorly understood. To address this knowledge gap, an experiment was conducted in a suburban site in the Paris region to study the evolution of OOA and their optical properties. Our results show that in regionally transported air masses with mixed biogenic and anthropogenic emissions, the formation of OOA through photochemical processes explains most of the increase in submicron particle mass. Meteorological conditions played a critical role: under dry and strong solar radiation conditions, enhanced formation of more-oxidized OOA (MO-OOA) was observed. BrC absorption increased concurrently, with short-wavelength absorption rising by similar to 35 % over relatively similar to 24 h of photochemical aging. Conversely, under humid, low-radiation conditions, the OA composition shifted toward less-oxidized OOA (LO-OOA). Suppressed photochemistry limited MO-OOA production, resulting in a lower overall OA oxidation state. These findings highlight the role of photochemistry in shaping both the chemical evolution and resultant optical properties of OA, underscoring the need to consider meteorological dynamics when evaluating aerosol-climate interactions in suburban forest environments.

The complex refractive index (CRI; n−ik) and the single scattering albedo (SSA) are key parameters driving the aerosol direct radiative effect. Their spatial, temporal, and spectral variabilities in anthropogenic–biogenic mixed environments are poorly understood. In this study, we retrieve the spectral CRI and SSA (370–950 nm wavelength range) from in situ surface optical measurements and the number size distribution of submicron aerosols at three sites in the greater Paris area, representative of the urban city, as well as its peri-urban and forested rural environments. Measurements were taken as part of the ACROSS (Atmospheric Chemistry of the Suburban Forest) campaign in June–July 2022 under diversified conditions: (1) two heatwaves leading to high aerosol levels, (2) an intermediate period with low aerosol concentrations, and (3) an episode of long-range-transported fire emissions. The retrieved CRI and SSA exhibit an urban-to-rural gradient, whose intensity is modulated by the weather conditions. A full campaign average CRI of 1.41−0.037i (urban), 1.52−0.038i (peri-urban), and 1.50−0.025i (rural) is retrieved. The imaginary part of the CRI (k) increases and the SSA decreases at the peri-urban and forest sites when exposed to the influence of the Paris urban plume. Values of k > 0.1 and SSA < 0.6 at 520 nm are related to a black carbon mass fraction larger than 10 %. Organic aerosols are found to contribute to more than 50 % of the aerosol mass and up to 10 % (urban), 17 % (peri-urban), and 22 % (forest) of the aerosol absorption coefficient at 370 nm. A k value of 0.022 (370 nm) was measured at the urban site for the long-range-transported fire episode.

In order to study aerosols in environments influenced by anthropogenic and biogenic emissions to variable extents, PM1 samples were collected during summer 2022 in the greater Paris area (ACROSS campaign, Atmospheric Chemistry Of the Suburban Forest, 14 June to 25 July) at two locations that represent the urban Paris and the suburban forested areas. They were analyzed using high-resolution mass spectrometry (HRMS) together with total carbon (TC) with a thermo-optical method. Both sites are compared here to explore differences in aerosol composition from urban and forested environments. The TC analysis shows similar organic carbon (OC) concentrations at both sites (3.2 ± 1.8 µg m−3 for Paris and 2.9 ± 1.5 µg m−3 for Rambouillet) and higher elemental carbon (EC) values in the urban area. Both OC and EC concentrations did not show significant variations for daytime and nighttime conditions. This work highlights the influence of anthropogenic inputs on the chemical composition of urban and forested areas, derived from the presence of CHO and CHON compounds but also the detection of two sulfur-containing compounds (C5H12SO7 and C10H17NSO7), which could be tentatively assigned as organosulfates. A smaller number of aromatic compounds were observed for clean periods that better represent the local biogenic and anthropogenic contributions in Rambouillet and Paris, respectively.

The complex refractive index (CRI) is one of the key parameter driving aerosol spectral optical properties and direct radiative effects (DRE). Its value and spectral variation under different conditions, such as anthropogenic− and biogenic−dominated environments and anthropogenic−biogenic mixing situations, remains not fully understood. As a consequence, oversimplified representations of aerosol optical properties are generally used in climate models. Therefore, measurements of aerosol CRI in different environments and their inclusion in models are needed. The field observations from the ACROSS campaign, performed in June-July 2022 in the Ile de France region, are used in this study to deepen the knowledge of aerosol optical properties, aiming to improve the aerosol representation in the CHIMERE model and provide the best constraint for DRE simulations. Measurements obtained both at the Paris city center and the Rambouilllet rural forest sites during ACROSS are considered, in order to explore the CRI variability from anthropogenic−dominated to biogenic−dominated environments, including anthropogenic−biogenic mixing situations. The CRI retrievals at seven different wavelengths, performed by combining the Mie theory with optical and size distribution measurements, are representative of different atmospheric conditions, aerosol loadings as well as type and chemical compositions. In fact, the June-July 2022 period was characterized by highly diversified weather conditions: 1) two strong heatwaves, promoting SOA build-up and favoring the export of the Paris pollution plume towards the forest site; 2) Saharan dust events transported from the upper atmosphere to the ground; 3) biomass burning episode; 4) periods with reduced anthropogenic influence. The CRI retrievals under these different conditions and their link to particulate chemical composition is investigated. Hence, the CRI dataset presented here constitutes a unique dataset from which models can benefit to validate and constrain simulations and DRE estimations, under both urban and biogenic emissions influence. These data, in conjunction with those from the aircraft observations during ACROSS, are used to initialize and perform sensitivity studies on the aerosol DRE, using the CHIMERE−WRF coupled model, the OPTSIM model for the aerosol optical properties and the Rapid Radiative Transfer Model for GCMs (RRTMG).Keywords: Complex refractive index, direct radiative effect, aerosol mixing, urban, forest

Atmospheric aerosols make significant contributions to several atmospheric chemical and physical processes. Aerosols from anthropogenic emissions have negative impact on air quality and human health. In recent years, significant progress has been made in understanding the anthropogenic pollutants. However, it is still not clear how mixtures of anthropogenic and biogenic emissions impact the regional climate and human health. To better understand aerosol physicochemical properties within the Paris urban plume when mixed with biogenic emissions, a comprehensive airborne measurement platform was deployed in the Île-de-France region in summer 2022 as part of the ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) campaign. In this study, the vertical and spatial distributions of aerosol chemical composition, size distributions, and optical properties during urban plume aging are characterized based on couples of in-situ measurement techniques like aerosol mass spectrometer (c-ToF-AMS), Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) and AVIRAD staged onboard the Safire ATR 42 research aircraft. Gas phase components are also detailed characterized by Proton-transfer-reaction mass spectrometry (PTR-ToF-MS) to act as tracers of anthropogenic and biogenic emissions. Based on gas and particulate phase organic information provided by laser-induced fluorescence technique (TDLIF), the production rate of particulate organic nitrate (pON) can also be estimated. These detailed airborne measurements of aerosol properties provide data that can contribute to modelling studies of aerosol characteristics.

This study reports the only recent characterization of two contrasted wet deposition events collected during the PEACETIME (ProcEss studies at the Air–sEa Interface after dust deposition in the MEditerranean Sea) cruise in the open Mediterranean Sea (Med Sea) and their impact on trace metal (TM) marine stocks. Rain samples were analysed for Al, 12 TMs (Co, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Ti, V and Zn) and nutrient (N, P, dissolved organic carbon) concentrations. The first rain sample collected in the Ionian Sea (Rain ION) was a typical regional background wet deposition event, whereas the second rain sample collected in the Algerian Basin (Rain FAST) was a Saharan dust wet deposition event. Even in the remote Med Sea, all background TM inputs presented an anthropogenic signature, except for Fe, Mn and Ti. The concentrations of TMs in the two rain samples were significantly lower compared to concentrations in rains collected at coastal sites reported in the literature, due to the decrease in anthropogenic emissions during the preceding decades. The atmospheric TM inputs were mainly dissolved forms, even in dusty Rain FAST. The TM stocks in the mixed layer (ML, 0–20 m) at the FAST station before and after the event showed that the atmospheric inputs were a significant supply of particulate TMs and dissolved Fe and Co for surface seawater. Even if the wet deposition delivers TMs mainly in soluble form, the post-deposition aerosol dissolution could to be a key additional pathway in the supply of dissolved TMs. At the scale of the western and central Mediterranean, the atmospheric inputs were of the same order of magnitude as ML stocks for dissolved Fe, Co and Zn, highlighting the role of the atmosphere in their biogeochemical cycles in the stratified Med Sea. In case of intense dust-rich wet deposition events, the role of atmospheric inputs as an external source was extended to dissolved Co, Fe, Mn, Pb and Zn. Our results suggest that the wet deposition constitutes only a source of some of dissolved TMs for Med Sea surface waters. The contribution of dry deposition to the atmospheric TM inputs needs to be investigated.

Introduction: The ESA ExoMars rover mission mainly focuses on the search for potential life-relevant molecules (large, non-volatile organic or biological molecules that suggest current or ancient prebiotic activity) at the Mars surface and near-subsurface. The Mars Organic Molecule Analyzer (MOMA) aboard the Rosalind Franklin rover will be a key analytical tool to provide chemical (molecular) information from solid samples collected by the rover. The characterization of the organic content in the sample is the main purpose of the instrument. The MOMA instrument comprises a gas chromatograph coupled to a mass spectrometer (GC-MS) which offers the unique capability to analyze and identify a wide range of organic molecules, including species of interest for life and prebiotic chemistry. Here we present an evaluation of the performance of the instrument from the analysis of a full set of samples of interest for Mars, using the Engineering Test Unit of the GC and MS instruments. Method: The samples delivered to MOMA will be analyzed either by UV laser desorption/ionization ion trap mass spectrometry (LDI-ITMS) or pyrolysis gas chromatography ion trap mass spectrometry (pyr-GC-ITMS). Samples containing organic compounds previously detected by LDI-ITMS and/or pyr-GC-ITMS can undergo further analysis through reaction with chemical derivatization reagents before characterization. These reagents (MTBSTFA, DMF-DMA, or TMAH), stored inside sealed capsules, induce a chemical reaction with the sample (in particular with its organic compounds) enhancing the volatility of complex organic species. Due to the need to prevent organic contamination of the Flight Model (FM) and Spare Model (SM) of MOMA, it was not possible to perform extensive analytical tests on them. For that reason, a series of tests were performed by coupling the GC and the MS Engineering Test Units (ETU) which are very close replica of the FM on board the Exomars rover. The ETU GC (developed in France by LISA and LATMOS laboratories) was mated to the ETU ion trap mass spectrometer (developed in the USA by Goddard Space Flight Center) in a flight-like configuration (Fig. 1) for the coupling campaign. The MOMA GC ETU includes a tank filled with the carrier gas (helium), four separate analytical modules including columns and thermal conductivity detectors (TCDs) and two thermal injection traps. A homemade oven designed and built at LISA is used to mimic MOMA FM ovens. During the pyrolysis of the sample or after its chemical derivatization with one of the three reagents, the volatile compounds are injected and pre-concentrated in one of the traps. The trap is then flash-heated with a backflush carrier gas flow to release the trapped chemical species as quickly as possible into one of the GC columns. The GC column separates the different molecules. They are then ionized by the electron impact ionization source in the MS chamber and analyzed by the linear ion trap mass spectrometer. During the ETU campaign, the derivatization reagents (MTBSTFA, DMF-DMA, and TMAH) are added inside the oven by a syringe mimicking the release of reagent from the MOMA capsules. Figure 1: picture of the ETU gas chromatograph and the ETU MS ion trap. Samples: Several samples were studied during this campaign. Standard samples (standard gases, amino acids, carboxylic acids) were used to obtain the reference data. Then organic carbon-bearing natural and synthetic (mixing organic molecules and inorganic phases) Mars analog samples were analyzed, using both pyrolysis and derivatization as used in the MOMA instrument. These samples included JSC Mars-1, fragments of Murchison meteorite and synthetic samples composed of an organic-free mineral (vermiculite) doped with phenylalanine, phthalic acid and undecanoic acid. Also a synthetic “unknown” sample was used to run a blind analysis and to test the capability to identify a range of organic species under more realistic analytical conditions. This sample was used to simulate a day in the life of the instrument. Results and conclusion: The results described show the current state of end-to-end performance of the gas chromatography-mass spectrometry mode of operation. We show that from a technical point of view, the MOMA instrument works as expected. From a chemical perspective, we have shown that the four different types of MOMA analyses conducted here (pyrolysis and MTBSTFA, DMF-DMA, or TMAH derivatization) are efficient. Specific molecules have been detected (as expected) when using chemical standards. Analysis of the natural and synthetic samples reveals that a large number of molecules are released, and many species have been positively detected and identified (Fig. 2). Figure 2 : Total ion chromatogram (TIC) for vermiculite doped with phenylalanine, phthalic acid and undecanoic acid after online DMF-DMA derivatization.

Abstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for in situ monitoring of NO3 radicals at the ppt level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662 nm with a high finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82 cm allows for up to 3 km of effective absorption and a high sensitivity for NO3 detection (up to 6 ppt for an integration time of 10 seconds). This technique also allows NO2 monitoring (up to 9 ppb for an integration time of 10 seconds). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (FTIR) and the absolute rate determination for the reaction trans-2-butene + NO3 which is already well documented in the literature. The value of (4.13 ± 0.45) x 10-13 cm3 molecule-1 s-1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (with rate constants up to 10-10 cm3 molecule-1 s-1).

An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for the in situ monitoring of NO3 radicals at the parts per trillion level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662 nm with a high-finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82 cm allows for up to 3 km of effective absorption and a high sensitivity for NO3 detection (up to 6 ppt for an integration time of 10 s). This technique also allows for NO2 monitoring (up to 9 ppb for an integration time of 10 s). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (Fourier-transform infrared, FTIR) and the absolute rate determination for the reaction trans-2-butene + NO3, which is already well documented in the literature. The value of (4.13 ± 0.45) × 10−13 cm3 molecule−1 s−1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (VOCs; with rate constants up to 10−10 cm3 molecule−1 s−1).

An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for in situ monitoring of NO3 radicals at the ppt level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662 nm with a high finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82 cm allows for up to 3 km of effective absorption and a high sensitivity for NO3 detection (up to 6 ppt for an integration time of 10 seconds). This technique also allows NO2 monitoring (up to 9 ppb for an integration time of 10 seconds). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (FTIR) and the absolute rate determination for the reaction trans-2-butene + NO3 which is already well documented in the literature. The value of (4.13 ± 0.45) x 10-13 cm3 molecule-1 s-1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (with rate constants up to 10-10 cm3 molecule-1 s-1).

The NO3 radical is the main atmospheric oxidant at night. The night period is favorable to the formation and accumulation of NO3 radicals in the atmosphere. On the one hand, it is formed by the reaction of nitrogen dioxide with ozone while, on the other hand, NO3 being highly photosensitive, it cannot accumulate significantly during the day (S. S. Brown and J. Stutz, Chem. Soc. Rev. 2012). In addition, the reaction between NO and NO3 is very fast and so, urban environment is considered so far, being not favorable to the occurrence of NO3 radicals. However, atmospheric nitrogen chemistry near the earth surface is strongly linked to the dynamics of the boundary layer and in summer NO is rapidly depleted by ozone. A large variability of the mixing ratios for NO3 as a function of height above the ground is thus expected with non-negligible concentrations in altitude (Brown et al., Atmos. Chem. Phys., 2007). The contribution of NO3 radical to the atmospheric evolution of VOCs in urban and sub-urban areas may therefore also be influenced by this vertical distribution. To demonstrate the potential importance of NO3 radical even in urban environment, a field campaign was carried out at night during July 2018 inside Paris. A newly developed field instrument dedicated to the measurement of NO3 radical was deployed on a high payload touristic tethered balloon located in Paris 15th district that was used as vertical vector. The NO3 instrument is a compact, robust and easily deployable on field instrument based on the IBB-CEAS (Incoherent Broad band Cavity Enhanced Absorption Spectroscopy) technique. NO3 measurements were completed by ground and airborne measurements of NO (chemiluminescence analyzer), NO2 (CAPS cavity) and O3 (absorption analyzer) concentrations as well as particle number concentrations (OPC GrimmTM) and 355 nm lidar (Leosphere ALS300) measurement for mixing layer probing. Vertical profiles from 0 to up to 300 m were obtained at night characterized by high concentrations of ozone and moderate humidity. In this presentation, vertical profiles of the species measured and implications for VOC oxidation in urban environment will be discussed.

Measurements of aerosol composition and size distributions were taken during the summer of 2013 at the remote island of Lampedusa in the southern central Mediterranean Sea. These measurements were part of the ChArMEx/ADRIMED (Chemistry and Aerosol Mediterranean Experiment/Aerosol Direct Radiative Forcing on the Mediterranean Climate) framework and took place during Special Observation Period 1a (SOP-1a) from 11 June to 5 July 2013. From compact time-of-flight aerosol mass spectrometer (cToF-AMS) measurements in the size range below 1 µm in aerodynamic diameter (PM1), particles were predominately comprised of ammonium and sulfate. On average, ammonium sulfate contributed 63 % to the non-refractory PM1 mass, followed by organics (33 %). The organic aerosol was generally very highly oxidized (f44 values were typically between 0.25 and 0.26). The contribution of ammonium sulfate was generally higher than organic aerosol in comparison to measurements taken in the western Mediterranean but is consistent with studies undertaken in the eastern basin. Source apportionment of organics using a statistical (positive matrix factorization) model revealed four factors: a hydrocarbon-like organic aerosol (HOA), a methanesulfonic-acid-related oxygenated organic aerosol (MSA-OOA), a more oxidized oxygenated organic aerosol (MO-OOA) and a less oxidized oxygenated organic aerosol (LO-OOA). The MO-OOA was the dominant factor for most of the campaign (53 % of the PM1 OA mass). It was well correlated with SO42-, highly oxidized and generally more dominant during easterly air masses originating from the eastern Mediterranean and central Europe. The LO-OOA factor had a very similar composition to the MO-OOA factor but was more prevalent during westerly winds, with air masses originating from the Atlantic Ocean, the western Mediterranean and at high altitudes over France and Spain from mistral winds. The MSA-OOA factor contributed an average 12 % to the PM1 OA and was more dominant during the mistral winds. The HOA, representing observed primary organic aerosol, only contributed 8 % of the average PM1 OA during the campaign. Even though Lampedusa is one of the most remote sites in the Mediterranean, PM1 concentrations (10 ± 5 µg m−3) were comparable to those observed in coastal cities and sites closer to continental Europe. Cleaner conditions corresponded to higher wind speeds. Nucleation and growth of new aerosol particles was observed during periods of north-westerly winds. From a climatology analysis from 1999 to 2012, these periods were much more prevalent during the measurement campaign than during the preceding 13 years. These results support previous findings that highlight the importance of different large-scale synoptic conditions in determining the regional and local aerosol composition and oxidation and also suggest that a non-polluted surface atmosphere over the Mediterranean is rare.

An experimental chamber (CIME2) has been specially designed to simulate wet atmospheric deposition on limestones used in Paris cultural heritage. This instrument is a complementary tool to CIME, a previously developed chamber dedicated to the simulation of dry atmospheric deposition on monuments and artifacts. The aim of this paper is to describe CIME2 and characterize the wet deposits produced inside it. Mist (fog), drizzle, and rainfall are differentiated in order to document their ability to saturate the limestones most currently used in Paris monuments: The Saint-Maximin's limestone, the Liais of Saint-Maximin, and the Chauvigny's limestone are tested. The comparison between normalized and environmental petrophysical data shows that in the wet deposition simulations, limestones are not systematically water-saturated. Moreover, the realistic experimental conditions chosen favor a more rapid evaporation of the stone water. The quantification of the non-saturation state is a first step that has to be taken into account to improve the geochemical models used to predict the alteration.

For decades of space exploration, mass spectrometry has proven to be a reliable instrumentation for the characterisation of the nature and energy of ionic and neutral, atomic and molecular species in the interplanetary medium and upper planetary atmospheres. It has been used as well to analyse the chemical composition of planetary and small bodies environments. The chemical complexity of these environments calls for the need to develop a new generation of mass spectrometers with significantly increased mass resolving power. The recently developed OrbitrapTM mass analyser at ultra-high resolution shows promising adaptability to space instrumentation, offering improved performances for in situ measurements. In this article, we report on our project named “Cosmorbitrap” aiming at demonstrating the adaptability of the Orbitrap technology for in situ space exploration. We present the prototype that was developed in the laboratory for demonstration of both technical feasibility and analytical capabilities. A set of samples containing elements with masses ranging from 9 to 208 u has been used to evaluate the performance of the analyser, in terms of mass resolving power (reaching 474,000 at m/z 9) and ability to discriminate between isobaric interferences, accuracy of mass measurement (below 15 ppm) and determination of relative isotopic abundances (below 5%) of various samples. We observe a good agreement between the results obtained with the prototype and those of a commercial instrument. As the background pressure is a key parameter for in situ exploration of atmosphere planetary bodies, we study the effect of background gas on the performances of the Cosmorbitrap prototype, showing an upper limit for N2 in our set-up at 10−8 mbar. The results demonstrate the strong potential to adapt this technology to space exploration.

(1) CNRS/UPEC/UPD/IPSL, LISA, Creteil, France (paola.formenti@lisa.u-pec.fr), (2) Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany, (3) CNRS, DT-INSU, Meudon, France, (4) Laboratoire d’Optique Atmospherique (LOA), Lille, France, (5) CNRM, MeteoFrance, Toulouse, France, (6) Laboratoire de Meteorologie Physique (LaMP), Clermont-Ferrand, France , (7) Laboratoire d’Aerologie (LA), Toulouse, France , (8) University of Genoa, Department of Physics & INFN, Genoa, Italy