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Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (m=n-ik) of Icelandic dust from five major emission hotspots were retrieved between 370–950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90–0.94 at 370 nm to 0.94–0.96 at 950 nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60–1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370 nm and 0.002–0.003 at 950 nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing towards the near-infrared. In Icelandic dust, k(λ) between 660–950 nm was 2–8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has not been accounted for in climate predictions.

International audience; Glycolaldehyde (GAld) is a C2 water-soluble aldehyde produced during the atmospheric oxidation of isoprene and many other species and is commonly found in cloudwater. Previous work has established that glycolaldehyde evaporates more readily from drying aerosol droplets containing ammonium sulfate (AS) than does glyoxal, methylglyoxal, or hydroxyacetone, which implies that it does not oligomerize as quickly as these other species. Here, we report NMR measurements of glycolaldehyde’s aqueous-phase reactions with AS, methylamine, and glycine. Reaction rate constants are smaller than those of respective glyoxal and methylglyoxal reactions in the pH range of 3–6. In follow-up cloud chamber experiments, deliquesced glycine and AS seed particles were found to take up glycolaldehyde and methylamine and form brown carbon. At very high relative humidity, these changes were more than 2 orders of magnitude faster than predicted by our bulk liquid NMR kinetics measurements, suggesting that reactions involving surface-active species at crowded air–water interfaces may play an important role. The high-resolution liquid chromatography–electrospray ionization–mass spectrometric analysis of filter extracts of unprocessed AS + GAld seed particles identified sugar-like C6 and C12 GAld oligomers, including proposed product 3-deoxyglucosone, with and without modification by reactions with ammonia to diimine and imidazole forms. Chamber exposure to methylamine gas, cloud processing, and simulated sunlight increased the incorporation of both ammonia and methylamine into oligomers. Many C4–C16 imidazole derivatives were detected in an extract of chamber-exposed aerosol along with a predominance of N-derivatized C6 and C12 glycolaldehyde oligomers, suggesting that GAld is capable of forming brown carbon SOA

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.

The mineralogy of dust aerosols (i.e. the abundance, relative proportions and state of mixing of the different minerals composing the aerosols, including mainly silicates in the form of clays, quartz, and feldspars, carbonates, sulfates, and iron and titanium oxides) is of key relevance in driving its climatic and environmental effects. Ground–based and airborne observations support the evidence that the dust mineralogy is heterogeneous in the atmosphere, varying from local to global scale due to changes in the mineralogical composition of the emitting source soils and atmospheric processing. However, the capability to get regional and global mapping of airborne dust mineralogy is still missing to date. This gap represents a fundamental limitation for properly developing and validating the representation of dust in Earth System Models and constraining its regional and global climate forcing.Because the different minerals composing the fine and coarse fractions of dust show different spectral absorption signatures, remote sensing spectral and hyperspectral observations can be used to fill this gap by detecting the presence of diverse minerals and reconstructing their relative proportions in the dust aerosols. Based on this idea, recent efforts move into this direction, including the EMIT mission (Earth Surface Mineral Dust Source Investigation) started in 2022.In this study we demonstrate, starting from exemplary data acquired in the CESAM simulation chamber on dust aerosols from global sources (Di Biagio et al., 2017), that the extinction signature of suspended dust aerosols in the 740−1475 cm−1 infrared spectral range (6.8−13.5 µm) can be used to derive dust mineralogy in terms of its infrared−active and coarse−sized minerals: quartz, clays, feldspars and calcite. We show that diverse spectral infrared signatures allow to distinguish dust aerosols from different sources worldwide with variable composition, and that following the changes of the dust extinction spectra with time informs on particles size−selective mineralogy changes during atmospheric transport. Results from the present study confirm the major advance that hyperspectral infrared remote sensing observations, as those by IASI (Infrared Atmospheric Sounding Interferometer) and the IASI−NG (Next Generation) instruments, can provide to dust science. Di Biagio, C., Formenti, P., Balkanski, Y., Caponi, L., Cazaunau, M., Pangui, E., Journet, E., Nowak, S., Caquineau, S., Andreae, M. O., Kandler, K., Saeed, T., Piketh, S., Seibert, D., Williams, E., and Doussin, J.-F.: Global scale variability of the mineral dust long-wave refractive index: a new dataset of in situ measurements for climate modeling and remote sensing, Atmos. Chem. Phys., 17, 1901–1929, https://doi.org/10.5194/acp-17-1901-2017, 2017.

Mineral dust aerosols, which account for about 40% of global annual aerosol emissions, contribute to the persistent and large uncertainties on the global radiative budget and the oxidative capacity of the atmosphere.Indeed, the uptake of atmospheric volatile organic compounds (VOCs) on mineral dust particles can contribute to the formation of secondary organic aerosols (SOA), with consequent modification of the chemical and optical properties of the dust.Glyoxal, one of the most important VOC in the atmosphere, is a precursor of SOA, capable of interacting with mineral dust and forming SOA as a consequence of the interaction.In this experimental study we investigate the formation of SOA by the uptake of glyoxal on mineral dust particles. We present the results of the heterogeneous interaction obtained in the CESAM atmospheric simulation chamber (Chambre Expérimentale de Simulation Atmosphérique Multiphasique), used to conduct aging experiments in various controlled conditions in terms of relative humidity, irradiation, and gas phase composition. Prior entering the chamber, particles from a real soil sample (Gobi Desert) are size-selected using an aerodynamic aerosol classifier (AAC) in order to obtain a monodispersed size distribution centered at 300 nm in mobility diameter, narrow enough to be able to appreciate a dimensional variation from glyoxal condensation.In experiments conducted in humid conditions (RH=80%), a rapid uptake of glyoxal was observed on sub micrometric dust particles. 15 minutes after the injection of 1 ppm of glyoxal into the chamber, the mass of the particles increased by about 10%, with a variation of the modal diameter of the size distribution. As a consequence of glyoxal uptake in humid conditions, an increase of the aerosol organic mass concentration occurred immediately after the interaction, which was not observed in dry conditions. At the same time, the aerosol chemical speciation monitor (ACSM) mass spectra of the organic fraction show the increase in intensity of the glyoxal marker signals at m/z 58 and m/z 29. It is interesting to note also the drop of O/C ratio of the dust organic fraction after the injection of the glyoxal from 1.5 (the one of the dust itself) to a value close to 1, that is the one of the glyoxal.Hence, the first results of the study suggest the presence of a fast glyoxal uptake on submicronic mineral dust particles in high relative humidity conditions. This process modifies the mass and the size distribution of the aerosol, as well as the chemical composition of its organic fraction.

The nitrate radical (NO3) is mainly formed in the atmosphere through the reaction of nitrogen dioxide (NO2) with ozone (O3). It accumulates at night because during the day its photolysis in sunlight and its rapid reaction with nitric oxide (NO) can rapidly consume it. NO3 radical is a major nighttime atmospheric oxidant of biogenic volatile organic compounds (BVOCs), which represent alone 75 to 90% of global non-methane VOC emissions.Nighttime chemistry between NO3 and BVOCs has received increased attention in the recent literature due to its potential influences on climate, air quality, health and visibility through the formation of many gaseous and particulate secondary pollutants such as organic nitrates, secondary organic aerosol (SOA), ozone and other functionalized products. In several studies conducted in clean forested environments, NO3 concentrations were found to be very low, mostly below the detection limits (2-6pptv), which can be explained by the low concentrations of precursors (NO2 and O3) and the high reactivity of NO3 with unsaturated BVOCs. However, significant contribution of NO3-BVOC reactions to the secondary pollutants formation in these clean areas have been found.Since NO3 radicals are formed more rapidly in polluted air masses, it is expected that reactions with BVOCs are even more important in mixed atmospheres, i.e. influenced by both biogenic and anthropogenic sources and characterized by relatively high concentrations of both VOCs and NO2. The ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) field campaign was carried out in June and July 2022 in Ile-de-France region and aims, among other objectives, to assess the potential impact of NO3-BVOC nocturnal processes on SOA formation. For this purpose, a newly developed field instrument, called "NOyBox", was deployed on top of a 40-meter tower, which is above the canopy, located at the Rambouillet Forest supersite southwest of Paris. The instrument allows the measurement of NO3 radicals, N2O5 and HONO (IBB-CEAS, Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy), NO2 (CAPS, Cavity Attenuated Phase Shift) and NOy (gold heated converter coupled with a NO chemiluminescence analyzer). Significant concentrations of NO3 and N2O5 were detected on several nights with situations characterized by air masses coming from the direction of Paris, high concentrations of ozone and NO2, and moderate relative humidity levels. Concentrations of these species as well as concentrations of species of interest for NO3 chemistry are presented and the resulting implications on nighttime chemistry are discussed.

Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. They can rapidly react with the nitrate radical (NO3) during the nighttime to form a number of functionalized products. Among them, organic nitrates (ONs) have been shown to behave as reservoirs of reactive nitrogen and consequently influence the ozone budget and secondary organic aerosols (SOAs), which are known to have a direct and indirect effect on the radiative balance and thus on climate. Nevertheless, BVOC + NO3 reactions remain poorly understood. Thus, the primary purpose of this study is to furnish new kinetic and mechanistic data for one monoterpene (C10H16), terpinolene, and one sesquiterpene (C15H24), β-caryophyllene, using simulation chamber experiments. These two compounds have been chosen in order to complete the few experimental data existing in the literature. Rate constants have been measured using both relative and absolute methods. They have been measured to be (6.0 ± 3.8) ×10-11 and (1.8 ± 1.4) ×10-11 cm3 molec.−1 s−1 for terpinolene and β-caryophyllene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrates and SOA yields have been determined. Both terpenes appear to be major ON precursors in both gas and particle phases with formation yields of 69 % for terpinolene and 79 % for β-caryophyllene respectively. They are also major SOA precursors, with maximum SOA yields of around 60 % for terpinolene and 90 % for β-caryophyllene. In order to support these observations, chemical analyses of the gas-phase products were performed at the molecular scale using a proton transfer reaction–time-of-flight–mass spectrometer (PTR-ToF-MS) and FTIR. Detected products allowed proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.

Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. During the night, they react very rapidly with the nitrate radical ( NO3 ), leading to the formation of a variety of functionalized products including organic nitrates and to large amounts of secondary organic aerosols (SOAs). Organic nitrates (ONs) have been shown not only to play a key role in the transport of reactive nitrogen and consequently in the ozone budget but also to be important components of the total organic-aerosol mass, while SOAs are known to play a direct and indirect role in the climate. However, the reactivity of BVOCs with NO3 remains poorly studied. The aim of this work is to provide new kinetic and mechanistic data for two monoterpenes ( C10H16 ), α - and γ -terpinene, through experiments in simulation chambers. These two compounds, which have very similar chemical structures, have been chosen in order not only to overcome the lack of experimental data but also to highlight the influence of the chemical structure on the reactivity. Rate constants have been measured using both relative and absolute methods. They were found to be ( 1.2 ± 0.5 ) × 10 - 10 and ( 2.9 ± 1.1 ) × 10 - 11 cm 3 molecule −1 s −1 for α - and γ -terpinene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrate and SOA yields have been determined. While organic nitrate formation yields appear to be similar, SOA yields exhibit large differences with γ -terpinene being a much more efficient precursor of aerosols. In order to provide explanations for this difference, chemical analysis of the gas-phase products was performed at the molecular scale. Detected products allowed for proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.

The role of relative humidity (RH) in secondary organic aerosol (SOA) formation from high-NOx photooxidation of long-chain alkanes was investigated by performing simulation chamber experiments on n...

Iceland is a highly active source of natural dust. Icelandic dust has the potential to directly affect the climate via dust–radiation interaction and indirectly via dust–cloud interaction, the snow/ice albedo effect and impacts on biogeochemical cycles. The impacts of Icelandic dust depend on its mineralogical and chemical composition. However, a lack of data has prevented an accurate assessment of the role of Icelandic dust in the Earth system. Here, we collected surface sediment samples from five major Icelandic dust hotspots. Dust aerosols were generated and suspended in atmospheric chambers, and PM10 and PM20 fractions were collected for further analysis. We found that the dust samples primarily consist of amorphous basaltic materials ranging from 8 wt % (from the Hagavatn hotspot) to 60 wt %–90 wt % (other hotspots). Samples had relatively high total Fe content (10 wt %–13 wt %). Sequential extraction of Fe to determine its chemical form shows that dithionite Fe (Fe oxides such as hematite and goethite) and ascorbate Fe (amorphous Fe) contribute respectively 1 %–6 % and 0.3 %–1.4 % to the total Fe in Icelandic dust. The magnetite fraction is 7 %–15 % of total Fe and 1 %–2 wt % of PM10, which is orders of magnitude higher than in mineral dust from northern Africa. Nevertheless, about 80 %–90% of the Fe is contained in pyroxene and amorphous glass. The initial Fe solubility (ammonium acetate extraction at pH 4.7) is from 0.08 % to 0.6 %, which is comparable to low-latitude dust such as that from northern Africa. The Fe solubility at low pH (i.e. pH 2) is significantly higher than typical low-latitude dust (up to 30 % at pH 2 after 72 h). Our results revealed the fundamental differences in composition and mineralogy of Icelandic dust from low-latitude dust. We attribute these differences to the low degree of chemical weathering, the basaltic composition of the parent sediments and glacial processes. Icelandic dust contributes to the atmospheric deposition of soluble Fe and can impact primary productivity in the North Atlantic Ocean. The distinct chemical and mineralogical composition, particularly the high magnetite content (1 wt %–2 wt %), indicates a potentially significant impact of Icelandic dust on the radiation balance in the subpolar and polar regions.

Mineral dust is a natural tracer of atmospheric composition and climate variability. Yet, there is still much to be known about the Southern Hemisphere dust cycle during the last Pleistocene. Major efforts have attempted to solve the ‘puzzle’ of the origin of the potential source areas that contribute dust to the Southern Ocean and East Antarctica (EA). Here we present a comprehensive geochemical characterization of an important potential source area, which role as a dust supplier to different environments of the SH has significantly been underestimated, that is, the Southern Africa (SAF) region. On the basis of Sr-Nd-Pb isotope ratios and rare earth element concentrations analyzed in sediments collected along the major dust-producing areas in the Namibian coast (Kuiseb, Omaruru and Huab riverbeds and the Namibian sand sea region), this study demonstrates for the first time that SAF emerges as the second most important dust source to EA during interglacial times.

Reaction rate constants for the reaction of n-dodecane with hydroxyl radicals were measured as a function of temperature between 283 and 303 K, using the relative rate method in the CESAM chamber (...

We report on applications of ultraviolet light emitted diode based incoherent broadband cavity enhanced absorption spectroscopy (UV-LED-IBBCEAS) technique for optical monitoring of HONO, NO2 and CH2O in a simulation chamber. Performance intercomparison of the UV-LED-IBBCEAS with a wet chemistry-based NitroMAC sensor and a FTIR spectrometer has been carried out on real time simultaneous measurement of HONO, NO2 and CH2O concentrations during the reaction of NO2 with H2O vapor in the CESAM atmospheric simulation chamber. 1-σ (SNR = 1) detection limits of 200 pptv for NO2, 100 pptv for HONO and 5 ppbv for CH2O over 120 s were found for the UV-LED-IBBCEAS measurement. On the contrary to many set-ups where cavities are installed outside the simulation chamber, we describe here an original in-situ permanent installation. The intercomparison results demonstrate that IBBCEAS is a very well suitable technique for in situ simultaneous measurements of multiple chemically reactive species with high sensitivity and high precision even if the absorption bands of these species are overlapped. It offers excellent capacity to non-invasive optical monitoring of chemical reaction without any perturbation. For the application to simulation chamber, it has the advantage to provide a spatially integrated measurement across the reactor and hence to avoid point sampling related artefact.

International audience; Interfacial regions are unique chemical reaction environments that can promote chemistry not found elsewhere. The air–water interface is ubiquitous in the natural environment in the form of ocean surfaces and aqueous atmospheric aerosols. Here we investigate the chemistry and photochemistry of pyruvic acid (PA), a common environmental species, at the air–water interface and compare it to its aqueous bulk chemistry using two different experimental setups: (1) a Langmuir–Blodgett trough, which models natural water surfaces and provides a direct comparison between the two reaction environments, and (2) an atmospheric simulation chamber (CESAM) to monitor the chemical processing of nebulized aqueous PA droplets. The results show that surface chemistry leads to substantial oligomer formation. The sequence begins with the condensation of lactic acid (LA), formed at the surface, with itself and with pyruvic acid, and LA + LA – H2O and LA + PA – H2O are prominent among the products in addition to a series of higher-molecular-weight oligomers of mixed units of PA and LA. In addition, we see zymonic acid at the surface. Actinic radiation enhances the production of the oligomers and produces additional surface-active molecules known from the established aqueous photochemical mechanisms. The presence and formation of complex organic molecules at the air–water interface from a simple precursor like PA in the natural environment is relevant to contemporary atmospheric science and is important in the context of prebiotic chemistry, where abiotic production of complex molecules is necessary for abiogenesis.

This work investigates the role of soot particles in the early steps of formation of condensation trails (contrails). Contrails are thin linear clouds that form behind cruising aircrafts and can evolve into persistent clouds, and therefore can contribute to the radiative forcing of the atmosphere. Mitigating their contribution is considered an efficient way for decreasing the radiative forcing. Condensation freezing is proposed as a major pathway leading to the heterogeneous nucleation of ice particles in the aircraft exhausts. Soot particles, freshly produced in the flames and not significantly oxidized in the post-flame, are hydrophobic. Therefore, many theoretical and experimental approaches that investigate contrails formation introduce prior activation by surface adsorption of sulfur compounds issued from kerosene combustion. Even though the role of sulfur content of the fuel is unclear, and may only weakly impacts contrails formation, many simulations still rely on this assumption. In this work, to elucidate the role of sulfur compounds on the activation of soot chemically aged with OH radicals, a comparative study is performed with soot sampled from a turbulent jet flame burning a sulfur-containing fuel (kerosene) and a sulfur-free fuel (diesel). Soot aging experiments are performed in the atmospheric simulation chamber CESAM, with controlled generation of OH radicals. Soot activation (ratio between the number of nucleated droplets and seeding particles) is measured in water supersaturation conditions. OH exposure significantly enhances soot activation regardless of the sulfur presence in the fuel. The possibility for soot oxidation by OH radicals formed in aeronautical engines to be sufficient to promote soot activation is explored. Large eddy simulation in the high pressure turbine is used to model the fluid particle and OH trajectories and their chemical evolution. Residence time in the turbine is found sufficient to activate soot particles, opening a new possible route to explain ice particles formation.

Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. During the night, they react very rapidly with the nitrate radical (NO3), leading to the formation of a variety of functionalized products including organic nitrates and to large amounts of secondary organic aerosols (SOAs). Organic nitrates (ONs) have been shown not only to play a key role in the transport of reactive nitrogen and consequently in the ozone budget but also to be important components of the total organic-aerosol mass, while SOAs are known to play a direct and indirect role in the climate. However, the reactivity of BVOCs with NO3 remains poorly studied. The aim of this work is to provide new kinetic and mechanistic data for two monoterpenes (C10H16), α- and γ-terpinene, through experiments in simulation chambers. These two compounds, which have very similar chemical structures, have been chosen in order not only to overcome the lack of experimental data but also to highlight the influence of the chemical structure on the reactivity. Rate constants have been measured using both relative and absolute methods. They were found to be (1.2±0.5)×10-10 and (2.9±1.1)×10-11 cm3 molecule−1 s−1 for α- and γ-terpinene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrate and SOA yields have been determined. While organic nitrate formation yields appear to be similar, SOA yields exhibit large differences with γ-terpinene being a much more efficient precursor of aerosols. In order to provide explanations for this difference, chemical analysis of the gas-phase products was performed at the molecular scale. Detected products allowed for proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.

Iceland is a highly active source of natural dust. Icelandic dust has the potential to affect directly the climate via dust-radiation interaction, and indirectly via dust-cloud interaction, snow/ice albedo effect and impacts on biogeochemical cycles. The impacts of Icelandic dust depend on its mineralogical and chemical composition. However, lack of data has prevented an accurate assessment of the role of Icelandic dust in the Earth system. Here, we collected surface sediment samples from five major Icelandic dust hotspots. Dust aerosols were generated and suspended in atmospheric chambers, and PM10 and PM20 fractions were collected for further analysis. We found that the dust samples primarily consist of amorphous basaltic material ranging from 8 wt% (from the Hagavatn hotspot) to 60–90 wt% (other hotspots). Samples had relatively high total Fe content (10–13 wt%). Sequential extraction of Fe to determine its chemical form shows that dithionite Fe (Fe oxides such as hematite and goethite) and ascorbate Fe (amorphous Fe) contribute respectively 1–6 %, and 0.3–1.4 % of the total Fe in Icelandic dust. The magnetite fraction is 7–15 % of total Fe and 1–2 wt% of PM10, which is orders of magnitude higher than in mineral dust from North Africa. Nevertheless, about 80–90 % of the Fe is contained in pyroxene and amorphous glass. The initial Fe solubility (ammonium acetate extraction at pH 4.7) is from 0.08–0.6 %, which is comparable to low latitude dust such as that from North Africa. The Fe solubility at low pH (i.e., 2) is significantly higher than typical low latitude dust (up to 30 % at pH 2 after 72 hrs). Our results revealed the fundamental differences in composition and mineralogy of Icelandic dust from low latitude dust. We attribute these differences to the low degree of chemical weathering, the basaltic composition of the parent sediments, and glacial processes. Icelandic dust contributes to the atmospheric deposition of soluble Fe and can impact primary productivity in the North Atlantic Ocean. The distinct chemical and mineralogical composition, particularly the high magnetite content (1–2 wt%), indicates a potentially significant impact of Icelandic dust on the radiation balance in the sub-polar and polar regions.

SummaryUsing CESAM, an atmospheric simulation chamber (cesam.cnrs.fr), we have developed a totally innovative platform for exposing mice to realistic atmospheric conditions. Here we present the first toxicological analyses of the organs of these mice after 48 hours to several days of exposure, carried out as part of feasibility experiments aimed at testing this experimental concept. This platform has received funding from the European Union’s Horizon 2020 research and innovation programme through the EUROCHAMP-2020 Infrastructure Activity under grant agreement N° 730997, and is now supporting the new REMEDIA H-2020 project (call H2020 “Exposome”) IntroductionThe World Health Organization (WHO) estimated that there were 3.7 million premature deaths due to air pollution in 2014, and confirmed that air pollution is the greatest environmental risk to health (responsible for a loss of more than 3% of productivity).The studies conducted so far show that the effects of air pollution on health depend not only on the quality of the surrounding air, but also on the subjects exposed and their individual vulnerability (asthma, obesity, period of life, etc.). Despite the evidence on the adverse health effects of exposure to air micro-pollutants, there are still uncertainties about the nature of these effects, and progress need to be made on their quantification. This limitation of knowledge is mainly attributed to the complexity of the polluted atmospheres, and to the great difficulty to model the impact of realistic situations of exposure. MethodologyThe innovative approach we set up is to realistically simulate, at the laboratory, the atmospheric mixture in all its complexity, thus keeping the ability to control, reproduce and carefully characterize the experimental conditions. We used the CESAM chamber (4.2 m3 stainless steel atmospheric simulation, evacuable down to a few 10-7 atm, temperature controlled between +15°C and +60°C) in order to study the myriad of products arising from the atmospheric oxidation of primary organic compounds.The experimental protocol consists in the continuous injection of relevant mixtures of primary pollutants (mainly nitrogen oxides, organic compounds from a representative mix of anthropogenic emissions, sulphur dioxide, soot, inorganic salts and potentially mineral dust particles if needed - e.g. to simulate Beijing’s atmosphere) at low concentrations (ppb levels) in air in the CESAM simulation chamber operated as a slow flow reactor. The residence time of simulated air parcels in the experimental volume is fixed to 4 hours, in order to represent air masses of regional scale. During this time the synthetic mixture is exposed to an artificial solar irradiation, allowing secondary pollutants such as ozone, nitric acid, formaldehyde, peroxyacetyl nitrate as well as complex polyfunctional organics including SOA to be produced and to reach their chemical steady state. Mice are exposed to constant flows of such a mixture during time scales of week to address their effects on health. ConclusionsHere we present the first toxicological analyses related to organs/tissue of these mice after exposure of 48h to several day, carried out with a representative atmosphere of Beijing or a representative atmosphere of Paris. ReferencesColl P. et al., 2018, WIT Transactions on Ecology and the Environment, 230.

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.

Reaction rate constants for the reaction of n-dodecane with hydroxyl radicals were measured as a function of temperature between 283 and 303 K, using the relative rate method in the CESAM chamber (French acronym for "Chamber for Atmospheric Multiphase Experimental Simulation"). The rate constants obtained at 283, 293 and 303 K are (1.27 ± 0.31)×10-11 , (1.33 ± 0.34)×10-11 , (1.27 ± 0.40)×10-11 cm 3 molecule-1 s-1 , respectively. Rate constants measured were in excellent agreement with the few available data in the literature over the studied temperature range (283-340K). Rate constants estimated by the structure-activity relationship and transition state theory methods agreed with our experimental data within 14 %. From these data combined with previous literature measurement, the following Arrhenius expression; + = (9.77 ± 6.19)10 −11 × exp [ −595 ±5580 ] 3 −1 −1 , was found valid over a temperature range (283-340 K) of the tropospheric interest.

Alpha-dicarbonyl compounds are believed to form brown carbon in the atmosphere via reactions with ammonium sulfate (AS) in cloud droplets and aqueous aerosol particles. In this work, brown carbon formation in AS and other aerosol particles was quantified as a function of relative humidity (RH) during exposure to gas-phase glyoxal (GX) in chamber experiments. Under dry conditions (RH 2 and are consistent between AS and AS–glycine aerosol. Dry methylammonium sulfate aerosol browns 4 times more than dry AS aerosol, but deliquesced AS aerosol browns much less than dry AS aerosol. Optical measurements at 405, 450, and 530 nm provide an estimated Ångstrom absorbance coefficient of -16±4. This coefficient and the empirical relationship between GX and albedo are used to estimate an upper limit to global radiative forcing by brown carbon formed by 70 ppt GX reacting with AS (+7.6×10-5 W m−2). This quantity is

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).

Identifying the provenance of mineral dust depositions in Antarctica is crucial to reconstruct Southern Hemisphere (SH) atmospheric circulation, validate numerical models, evaluate their contribution as micronutrients in the Southern Ocean and assess their control on the climate changes. For the last few decades, it has been demonstrated Southern South America (SSA) is the main precursor of dust reaching Antarctica during both ice ages and interglacial periods (e.g. Gili et al., 2017, 2016). However, the origin of modern dust depositions on the Antarctic continent is still poorly constrained. Back in the nineties, together with SSA, Australia, New Zealand, and Southern Africa were firstly identified as dust contributors to East Antarctica (EA) (e.g. Delmonte et al., 2004a). Since then, only SSA and Australian dust sources benefited from detailed studies. While some works identified the Makgadikgadi and Etosha Pans as southern Africa's major mineral dust sources in the SH, it was not until recently the Namib Desert coastal areas were described as another important regional dust sources. Within the Namib Desert and along the coast, the Kuiseb (K), Omaruru (O) and Huab (H) dry riverbeds are the three main areas identified as the dustiest ones with the higher frequency of dust emission events (Von Holdt et al., 2017). Here we use Sr, Nd and Pb isotopes (measured on HR-MC-ICP-MS) to characterize and evaluate the influence of this region in Southern Africa as a dust source to EA. Samples collected in K, O and H desertic areas were analyzed together with snow samples collected along a ~250 km N-S transect (defined from the coast to inland) at seven different sampling sites in the surroundings of Dronning Maud Land, EA. In addition, using the bulk of the Huab region, dust aerosols were generated into an atmospheric simulation chamber (CESAM) to reproduce, mechanically the saltation and sandblasting processes responsible for the release of mineral dust in natural conditions. Our isotopic results show Namibia’s coast emerged as another possible source end-member, together with some regions in SSA, that supply dust to EA during warmer periods.References:Delmonte, B., Basile-Doelsch, I., Petit, J.R., Maggi, V., Revel-Rolland, M., Michard, A., Jagoutz, E., Grousset, F., 2004. Comparing the EPICA and Vostok dust records during the last 220,000 years: stratigraphical correlation and provenance in glacial periods. Earth-Sci. Rev. 66, 63–87.Gili, S., Gaiero, D.M., Goldstein, S.L., Chemale, F. Jr., Koester, E., Jweda, J., Vallelonga, P., Kaplan, M.R., 2016. Provenance of dust to Antarctica: a lead isotopic perspective. Geophys. Res. Lett. 43. http://dx.doi.org/10.1002/2016GL068244.Gili, S., D.M. Gaiero, S.L. Goldstein, F. Chemale, J. Jweda, M.R. Kaplan, R.A. Becchio, and E. Koester (2017). Glacial/interglacial changes of Southern Hemisphere wind circulation from the geochemistry of South American dust. Earth Planet. Sci. Lett., 469, 98-109, doi: 10.1016/j.epsl.2017.04.007.Von Holdt, JR., Eckardt FD., and Wiggs GFS., 2017. Landsat identifies aeolian dust emission dynamics at the landform scale. Remote Sensing of Environment 198., 229–243.

The conformer-specific reactivity of gas-phase pyruvic acid following the S1(nπ*) ← S0 excitation at λmax = 350 nm (290-380 nm) and the effect of water are investigated for the two lowest energy conformers. Conformer-specific gas-phase pyruvic acid photolysis rate constants and their respective populations are measured by monitoring their distinct vibrational OH-stretching frequencies. The geometry, relative energies, fundamental vibrational frequencies, and electronic transitions of the pyruvic acid conformers and their monohydrated complexes are calculated with density functional theory and ab initio methods. Results from experiment and theory show that the more stable conformer with an intramolecular hydrogen bond dominates the gas-phase photolysis of pyruvic acid. Water greatly affects the gas-phase pyruvic acid conformer population and photochemistry through hydrogen bonding interactions. The addition of water decreases the gas-phase relative population of the more stable conformer and decreases the molecule's gas-phase photolysis rate constants. The theoretical results show that even a single water molecule interrupts the intramolecular hydrogen bond, which is essential for the efficient photodissociation of gas-phase pyruvic acid. Results of this study suggest that the aqueous-phase photochemistry of pyruvic acid proceeds through hydrogen-bonded conformers lacking an intramolecular hydrogen bond.

International audience; The present work is an extensive laboratory study of organosulfate (OS) formation from the reaction of α-pinene oxidation products or proxies with acidified ammonium sulfate aerosols in three different acidity conditions (NH$_4$)$_2$SO$_4$ 0.06 M; (NH$_4$)$_2$SO$_4$/H$_2$SO$_4$ 0.06 M/0.005 M; (NH$_4$)$_2$SO$_4$/H$_2$SO$_4$ 0.03 M/0.05 M). The kinetics of the reactions of $\alpha$-pinene, $\alpha$-pinene oxide, isopinocampheol, pinanediol, and myrtenal with ammonium sulfate particles were studied using a quasi-static reactor. The reaction of $\alpha$-pinene oxide with the highly acidic ammonium sulfate particles was determined to be 7, 10, 21, and 24 times faster than for isopinocampheol, $\alpha$-pinene, pinanedial, and myrtenal, respectively, for an OS precursor concentration of 1 ppm and after 1 h reaction time. The effective rate coefficients for OS formation from $\alpha$-pinene oxide were determined to be 2 orders of magnitude higher in highly acidic conditions than for the two other acidity conditions. For $\alpha$-pinene oxide reactions with highly acidic ammonium sulfate particles, OS formation was observed to increase linearly with (i) the time of reaction up to 400 min ($r^2$= > 0.95) and (ii) α-pinene oxide gas-phase concentration. However, OS formation from $\alpha$-pinene oxide reactions with slightly acidic or pure ammonium sulfate particles was limited, with a plateau ([OS]max = 0.62 ± 0.03 $\mu$g) reached after around 15–20 min. Organosulfate dimers (m/z 401 and m/z 481) were detected not only with highly acidic particles but also with slightly acidic and pure ammonium sulfate particles, indicating that oligomerization processes do not require strong acidity conditions. Dehydration products of organosulfates ($m/z$ 231 and $m/z$ 383) were observed only under highly acidic conditions, indicating the key role of H$_2$SO$_4$ on the dehydration of organosulfates and the formation of olefins in the atmosphere. Finally, this kinetic study was completed with simulation chamber experiments in which the mass concentration of organosulfates was shown to depend on the available sulfate amount present in the particle phase ($r^2$ = 0.96). In conclusion, this relative comparison between five organosulfate precursors shows that epoxide was the most efficient reactant to form organosulfates via heterogeneous gas–particle reactions and illustrates how gas–particle reactions may play an important role in OS formation and hence in the atmospheric fate of organic carbon. The kinetic data presented in this work provide strong support to organosulfate formation mechanisms proposed in part 1 ( J. Phys. Chem. A 2016, 120, 7909−7923).

In order to predict the amount of secondary organic aerosol formed by heterogeneous processing of methylglyoxal, uptake coefficients (γ) and estimates of uptake reversibility are needed. Here, uptake coefficients are extracted from chamber studies involving ammonium sulfate and glycine seed aerosol at high relative humidity (RH ≥ 72%). Methylglyoxal uptake coefficients on prereacted glycine aerosol particles had a strong dependence on RH, increasing from γ = 0.4 × 10–3 to 5.7 × 10–3 between 72 and 99% RH. Continuous methylglyoxal losses were also observed in the presence of aqueous ammonium sulfate at 95% RH (γAS,wet = 3.7 ± 0.8 × 10–3). Methylglyoxal uptake coefficients measured at ≥95% RH are larger than those reported for glyoxal on nonacidified, aqueous aerosol surfaces at 90% RH. Slight curvature in first-order uptake plots suggests that methylglyoxal uptake onto aqueous aerosol surfaces is not entirely irreversible after 20 min. Methylglyoxal uptake by cloud droplets was rapid and largely reversible...

Pyruvic acid is an atmospherically abundant α-keto-acid that degrades efficiently from the troposphere via gas-phase photolysis. To explore conditions relevant to the environment, 2–12 ppm pyruvic acid is irradiated by a solar simulator in the environmental simulation chamber, CESAM. The combination of the long path length available in the chamber and its low surface area to volume ratio allows us to quantitatively examine the quantum yield and photochemical products of pyruvic acid. Such details are new to the literature for the low initial concentrations of pyruvic acid employed here. We determined photolysis quantum yields of ϕobsN2 = 0.84 ± 0.1 in nitrogen and ϕobsAir = 3.2 ± 0.5 in air, which are higher than those reported by previous studies that used higher partial pressures of pyruvic acid. The quantum yield greater than unity in air is due to secondary chemistry, driven by O2, that emerges under the conditions in these experiments. The low concentration of pyruvic acid and the resulting oxygen ef...

This paper presents new laboratory measurements of the mass absorption efficiency (MAE) between 375 and 850 nm for 12 individual samples of mineral dust from different source areas worldwide and in two size classes: PM10. 6 (mass fraction of particles of aerodynamic diameter lower than 10.6 µm) and PM2. 5 (mass fraction of particles of aerodynamic diameter lower than 2.5 µm). The experiments were performed in the CESAM simulation chamber using mineral dust generated from natural parent soils and included optical and gravimetric analyses. The results show that the MAE values are lower for the PM10. 6 mass fraction (range 37–135 × 10−3 m2 g−1 at 375 nm) than for the PM2. 5 (range 95–711 × 10−3 m2 g−1 at 375 nm) and decrease with increasing wavelength as λ−AAE, where the Ångström absorption exponent (AAE) averages between 3.3 and 3.5, regardless of size. The size independence of AAE suggests that, for a given size distribution, the dust composition did not vary with size for this set of samples. Because of its high atmospheric concentration, light absorption by mineral dust can be competitive with black and brown carbon even during atmospheric transport over heavy polluted regions, when dust concentrations are significantly lower than at emission. The AAE values of mineral dust are higher than for black carbon (∼ 1) but in the same range as light-absorbing organic (brown) carbon. As a result, depending on the environment, there can be some ambiguity in apportioning the aerosol absorption optical depth (AAOD) based on spectral dependence, which is relevant to the development of remote sensing of light-absorbing aerosols and their assimilation in climate models. We suggest that the sample-to-sample variability in our dataset of MAE values is related to regional differences in the mineralogical composition of the parent soils. Particularly in the PM2. 5 fraction, we found a strong linear correlation between the dust light-absorption properties and elemental iron rather than the iron oxide fraction, which could ease the application and the validation of climate models that now start to include the representation of the dust composition, as well as for remote sensing of dust absorption in the UV–vis spectral region.

The temperature and concentration dependence of secondary organic aerosol (SOA) yields has been investigated for the first time for the photooxidation of n-dodecane (C12H26) in the presence of NOx in the CESAM chamber (French acronym for “Chamber for Atmospheric Multiphase Experimental Simulation”). Experiments were performed with and without seed aerosol between 283 and 304.5 K. In order to quantify the SOA yields, a new parametrization is proposed to account for organic vapor loss to the chamber walls. Deposition processes were found to impact the aerosol yields by a factor from 1.3 to 1.8 between the lowest and the highest value. As with other photooxidation systems, experiments performed without seed and at low concentration of oxidant showed a lower SOA yield than other seeded experiments. Temperature did not significantly influence SOA formation in this study. This unforeseen behavior indicates that the SOA is dominated by sufficiently low volatility products for which a change in their partitioning...

Reaction rate constants for the reaction of

The optical properties of airborne mineral dust depend on its mineralogy, size distribution, shape, and might vary between different source regions. To date, large differences in refractive index values found in the literature have not been fully explained. In this paper we present a new dataset of complex refractive indices (m=n‒ik) and single scattering albedos (SSA) for 19 mineral dust aerosols over the 370–950 nm range in dry conditions. Dust aerosols were generated from natural parent soils from eight source regions (Northern Africa, Sahel, Middle East, Eastern Asia, North and South America, Southern Africa, and Australia). These were selected to represent the global scale variability of the dust mineralogy. Dust was re‒suspended into a 4.2 m3 smog chamber where its spectral shortwave scattering (βsca) and absorption (βabs) coefficients, number size distribution, and bulk composition were measured. The complex refractive index was estimated by Mie calculations combining optical and size data, while the spectral SSA was directly retrieved from βsca and βabs measurements. Our results show that the imaginary part of the refractive index (k) and the SSA largely vary from sample to sample, with values for k in the range 0.001 to 0.009 at 370 nm and 0.0003 to 0.002 at 950 nm, and values for SSA in the range 0.70 to 0.96 at 370 nm and 0.95 to 0.99 at 950 nm. In contrast, the real part of the refractive index (n) is mostly source (and wavelength) independent, with an average value between 1.48 and 1.55. The sample‒to‒sample variability in our dataset of k and SSA is mostly related to differences in the dust’s iron content. In particular, a wavelength‒dependent linear relationship is found between the magnitude of k and SSA and the mass concentrations of both iron oxide and total elemental iron. As an intrinsic property of matter, k is independent of size. When the iron oxide content exceeds > 3 %, the SSA linearly decreases with increasing fraction of coarse particles at short wavelengths ( We recommend that source‒dependent values of the SW spectral refractive index and SSA are used in models and remote sensing retrievals instead of generic values. In particular, the close relationships found between k/SSA and the iron content in dust enable establishing predictive rules for spectrally‒resolved SW absorption based on particle composition.

Methylamine, a common atmospheric amine species, is found in the gas, particle, and aqueous phases. It has been shown to form light-absorbing, oligomeric species in reactions with methylglyoxal and other aldehyde species in bulk aqueous-phase experiments and when mixed into seed aerosol as a sulfate salt. Here, we explore the influence of multiphase methylamine chemistry on aerosol production, properties, and molecular composition. When methylglyoxal aerosol particles were exposed to ∼2 ppm methylamine gas in a humid chamber, rapid browning was observed, but not growth. Aerosol bounce measurements indicated that particles became slightly more viscous and hydrophobic upon methylamine exposure. Subsequent cloud processing increased both viscosity and hygroscopicity but had little effect on browning, consistent with high-resolution mass spectrometry results showing that aerosol oligomer dicarbonyl functional groups were transformed into cationic imidazole rings. Photolytic cloud processing triggered the inco...

We report laboratory measurements of H2O-broadening coefficients of O2 absorption lines in the A-band near 13,000 cm−1. For this, four spectra of oxygen gas mixed with water vapor were recorded with a high resolution Fourier transform spectrometer for total pressures ranging from 125 to 175 Torr at 323 K, and a fifth at 175 Torr and 365 K. Broadening coefficients of 39 transitions (up to J ″ = 21 ) were retrieved from the measured spectra through fits using Galatry line profiles. Values at room temperature (296 K) were then extrapolated and compared with previous determinations in the A-band and millimeter waves region. This enables to resolve some controversial issues related to the inconsistencies between these studies. Finally, comparing our results with the line broadening coefficients by dry air confirms that H2O-broadenings of oxygen lines are, on average, 10% larger than those by dry air.

Transmission spectra of CO 2 highly diluted in water vapor have been recorded at 50 and 95 °C for four pressures between 0.02 and 0.1 atm using a high resolution Fourier Transform spectrometer. The collisional (Lorentz) widths of many lines of the ν 3 band (and of some of the ν 3 + ν 2 − ν 2 hot band) have been retrieved from each spectrum through fits using Voigt line shapes. Our result are about 4% lower than the values recommended in a previous study but they confirm the relative variations of the line broadening on the rotational quantum numbers. We also provide the first determination of H 2 O-induced line shifts of CO 2 lines.

Reflection spectra of pure CO2 gas have been recorded in the 4.3 μ m region by using a high resolution Fourier transform spectrometer, providing measured values of the refractive index. Comparisons with the results of calculations using available spectroscopic data, and free of any adjusted line parameter, show a very good agreement. This confirms that this experimental technique provides an alternative approach for the test or determination of spectroscopic parameters. Its advantages for studies of extremely strongly absorbing species and investigations of spatially (tightly) confined molecular gases are discussed.