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Optical properties of aerosols were measured from the GAW Puy de Dôme station (1465 m) over a seven year period (2006–2012). The impact of hygroscopicity on aerosol optical properties was calculated over a two year period (2010–2011). The analysis of the spatial and temporal variability of the optical properties showed that while no long term trend was found, a clear seasonal and diurnal variation was observed on the extensive parameters (scattering, absorption). Scattering and absorption coefficients were highest during the warm season and daytime, in concordance with the seasonality and diurnal variation of the PBL height reaching the site. Intensive parameters (single scattering albedo, asymmetry factor, refractive index) did not show such a strong diurnal variability, but still indicated different values depending on the season. Both extensive and intensive optical parameters were sensitive to the air mass origin. A strong impact of hygroscopicity on aerosol optical properties was calculated, mainly on aerosol scattering, with a dependence on the aerosol type. At 90% humidity, the scattering factor enhancement (fσsca) was more than 4.4 for oceanic aerosol that have mixed with a pollution plume. Consequently, the aerosol radiative forcing was estimated to be 2.8 times higher at RH = 90% and 1.75 times higher at ambient RH when hygroscopic growth of the aerosol was considered. The hygroscopicity enhancement factor of the scattering coefficient was parameterized as a function of humidity and air mass type.

Ice-nucleating particles (INPs) have a large impact on the climate-relevant properties of clouds over the oceans. Studies have shown that sea spray aerosols (SSAs), produced upon bursting of bubbles at the ocean surface, can be an important source of marine INPs, particularly during periods of enhanced biological productivity. Recent mesocosm experiments using natural seawater spiked with nutrients have revealed that marine INPs are derived from two separate classes of organic matter in SSAs. Despite this finding, existing parameterizations for marine INP abundance are based solely on single variables such as SSA organic carbon (OC) or SSA surface area, which may mask specific trends in the separate classes of INP. The goal of this paper is to improve the understanding of the connection between ocean biology and marine INP abundance by reporting results from a field study and proposing a new parameterization of marine INPs that accounts for the two associated classes of organic matter. The PEACETIME cruise took place from 10 May to 10 June 2017 in the Mediterranean Sea. Throughout the cruise, INP concentrations in the surface microlayer r (INPSML) and in SSAs (INPSSA) produced using a plunging aquarium apparatus were continuously monitored while surface seawater (SSW) and SML biological properties were measured in parallel. The organic content of artificially generated SSAs was also evaluated. INPSML concentrations were found to be lower than those reported in the literature, presumably due to the oligotrophic nature of the Mediter ranean Sea. A dust wet deposition event that occurred during the cruise increased the INP concentrations measured in the SML by an order of magnitude, in line with increases in iron in the SML and bacterial abundances. Increases in INPSSA were not observed until after a delay of 3 days compared to increases in the SML and are likely a result of a strong in fluence of bulk SSW INPs for the temperatures investigated (T =-18 °C for SSAs, T =-15 °C for SSW). Results con firmed that INPSSA are divided into two classes depending on their associated organic matter. Here we find that warm (T >=-22 °C) INPSSA concentrations are correlated with water soluble organic matter (WSOC) in the SSAs, but also with SSW parameters (particulate organic carbon, POCSSW and INPSSW,-16C) while cold INPSSA (T

Aerosols of biogenic and anthropogenic origin affect the total radiative forcing of global climate. Poor knowledge of the pre-industrial aerosol concentration and composition, in particular of particles formed directly in the atmosphere from gaseous precursors, constitutes a large uncertainty in the anthropogenic radiative forcing. Investigations of new particle formation at pre-industrial-like conditions can contribute to the reduction of this uncertainty. Here we present observations taken at the remote Nepal Climate Observatory Pyramid station at 5,079 m above sea level, a few kilometres from the summit of Everest. We show that up-valley winds funnel gaseous aerosol precursors to higher altitudes. During this transport, these are oxidized into compounds of very low volatility, which rapidly form a large number of aerosol particles. These are then transported into the free troposphere, which suggests that the whole Himalayan region may act as an 'aerosol factory' and contribute substantially to the free tropospheric aerosol population. Aerosol production in this region occurs mainly via organic precursors of biogenic origin with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to be essentially unchanged since the pre-industrial period, and may have been one of the major sources that contributes to the upper tropospheric aerosol population during that time. Newly formed biogenic particles in the Himalaya increase free-tropospheric background aerosol concentration by a factor of up to two.

International audience; As part of the CHARMEX (Chemistry Aerosol Mediterranean Experiments) project, more than one hundred or-ganic and inorganic gaseous compounds were measured in the summer of 2013 at the Mediterranean remote siteof ERSA in Cape-Corsica. During this period, New Particle formation (NPF) events were identified from July31th to august 2nd when air masses originated from the North-eastern sector (Southern Europe). The results werecompared to a non-NPF event from July 21th to July 23rd for which the same wind sectors were identified. Theyshowed that the particles number [10-20 nm] measured by SMPS (Scanning Mobility Particle Sizer) were morecorrelated with carbon monoxide (CO) during non-NPF events indicating an influence of more polluted and moreaged air masses (residence time of CO of ∼60 days). Sulfuric acid (H2SO4) and sulfur dioxide do not show a sig-nificant influence in the formation of nucleation events. On the other hand, biogenic Volatile Organic Compounds(BVOCs) such as isoprene, and mono-terpenes as well as their oxidation products (e.g. MACR+MVK, MTOP)showed good correlation during NPF-events in the range of (r from 0.45 to 0.59) higher than the ones reportedduring non-NPF events (0.11-0.34) highlighting the importance of these BVOCs on NPF days. The comparisonof measured vs calculated reactivity (Zannoni et al, 2016) showed that during NPF-events, the missing part ofOH reactivity was higher. It indicates that unmeasured species like sesquiterpenes, organo-nitrates, or oxygenatedcompounds may play a significant role in such events.

In the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.

International audience; abstract simple

International audience; Observatories of the climate system are essential to assess future climate predictions that are central and fundamental requirements for determining future mitigation strategies. such observing platforms are very few ones in the tropical southern hemisphere. Cnrs, Université de la réunion, région réunion and the european FeDer program support together the construction of a high- altitude observatory which is operational since October 2012 in La Réunion (South West Indian Ocean, 2160 m asl, latitude 21°S, longitude 55°E). The Maïdo observatory takes over from its predecessor programs at sea level over the island who started long-term observation data of atmospheric chemical composition since 1994. the Maïdo observatory is an ideal platform to sample the atmosphere with different techniques (in-situ analysers, radiosounding, passive and active remote sensing) and to record surface measurements and vertical profiles from ground to the mesosphere over a subtropical latitude band poorly sampled by other international programs. The Maïdo observatory hosts lidars, one UV spectrometer, one radiosonding station, Ftir spectrometers, microwave radiometers, one lightning antenna, cameras, one Gnss station, microbarometers, etc. these devices sample many atmospheric parameters (e.g., meteorological parameters, reactive and greenhouse gases, aerosols, lightning and transient luminous events, infrasounds, etc). part of this very extensive range of instruments is approved and belongs to international networks like nDaCC (network for the Detection of atmospheric Composition Change), sHaDOZ (southern Hemisphere aDditional OZonesondes), tCCOn (total Carbon Column Observing network), and WWLLN (World Wide Lightning Location Network). in-situ analysers regroup measurements of reactive and greenhouse gases, and aerosols measurements approved by or applying to networks like GAW/WMO (Global Atmospheric Watching / World Meteorological Organization), iCOs (integrated Carbon Observing system). The Maïdo observatory is currently the only way to provide regular remote and in-situ atmospheric observations at subtropical latitudes and at high resolutions (seconds in time, few tenths of meters vertically) over a marine-remote region poorly sampled by other programs. it provides data for users in science and policy including air quality forecasting, verification of CO2 emissions and Kyoto monitoring, numerical weather prediction, and validation of global chemical transport model, global climate chemical model and satellite products. since its participation in on-going european projects (nOrs, aCtris-2, arise-2), and thanks to the start of delivery of data in near real time, the Maïdo observatory will largely contribute to the Copernicus atmosphere Monitoring services (CaMs). the Maïdo observatory is open to transnational access thanks to its participation in european programmes like aCtris-2 and enVriplus. this presentation will give an overview of results achieved so far and a number of highlights to illustrate the promise Maïdo observatory data hold for the future, allowing new applications and analysis for a broad community of users.

International @ CARE+BDA; International audience; Marine emissions are among the largest source of both primary particles and do highly contribute secondary organic aerosols (SOA) at a global scale. Whereas physical processes control the primary production of marine aerosols, biological activity is responsible for most of the organic fraction released from marine sources, potentially transformed into SOA when exposed to atmospheric oxidants. The Mediterranean atmosphere displays important concentrations of SOA, especially in summer, when atmospheric oxidants and photochemical activity are at their maximum. The origin of these elevated concentrations of SOA remain unclear.Here we present the results from a mesocosms study in a remote location in Corsica and a chamber study (using fresh sea water from Western Mediterranean) as part of the Source of marine Aerosol particles in the Mediterranean atmosphere (SAM) project. The mesocosm study was conducted at the Oceanographic and Marine Station STARESO (Corsica) in May 2013. One mesocosm was used as a control (with no enrichment) and the other two were enriched with nitrate and phosphate respecting Redfield ratio (N:P = 16) in order to produce a bloom of biological activity. Physical and chemical properties of the enclosed water samples together with their surrounding atmosphere were monitored during 20 days by a multi-instrumental high-time resolution set-up. In parallel, numerous additional measurements were conducted including water temperature, incident light, pH, conductivity, chemical and biological analyses, fluorescence of chlorophyll, dissolved oxygen concentration. The chamber studies were performed in a Teflon chamber of 1. 5m3 that accommodates a pyrex-container for the fresh sea-water samples. After injection of sea-water in the pyrex-container, the system is allowed to stabilize to 20-30 minutes, then it was exposed to 60-100ppbv of ozone and/or UV-A irradiation. Aerosol concentrations and their physical characteristics were followed by means of Scanning Mobility Particle Sizers; clusters concentration was monitored using a Particle Size Magnifyer (PSM); the gas-phase composition of volatile organic compounds was determined by using Proton Transfer Reaction Time-of-Flight Mass Spectrometer and cartridges. Aerosol chemical composition was investigated using High Resolution Time-of-Flight Aerosol Mass Spectrometer, filters analysis and TEN-EDX microscopy. Results evidence a complex nature of the primary emitted aerosol which is not clearly associated to the biological bloom (ex. cholrophyll), VOCs emission was observed during high biological activity periods. Formation of new particles was observed in the chamber and seems to be related to iodine species (in the absence of any macroalgea population).

Clouds have an important role in Earth's radiative budget. Since the late 1970s, considerable instrumental developments have been made in order to quantify cloud microphysical and optical properties, for both airborne and ground-based applications. Intercomparison studies have been carried out in the past to assess the reliability of cloud microphysical properties inferred from various measurement techniques. However, observational uncertainties still exist, especially for droplet size distribution measurements and need to be reduced. In this work, we discuss results from an intercomparison campaign, performed at the Puy de Dôme in May 2013. During this campaign, a unique set of cloud instruments was operating simultaneously in ambient air conditions and in a wind tunnel. A Particle Volume Monitor (PVM-100), a Forward Scattering Spectrometer Probe (FSSP), a Fog Monitor (FM-100), and a Present Weather Detector (PWD) were sampling on the roof of the station. Within a wind tunnel located underneath the roof, two Cloud Droplet Probes (CDPs) and a modified FSSP (SPP-100) were operating. The main objectives of this paper are (1) to study the effects of wind direction and speed on ground-based cloud observations, (2) to quantify the cloud parameters discrepancies observed by the different instruments, and (3) to develop methods to improve the quantification of the measurements. The results revealed that all instruments showed a good agreement in their sizing abilities, both in terms of amplitude and variability. However, some of them, especially the FM-100, the FSSP and the SPP, displayed large discrepancies in their capability to assess the magnitude of the total number concentration of the cloud droplets. As a result, the total liquid water content can differ by up to a factor of 5 between the probes. The use of a standardization procedure, based on data of integrating probes (PVM-100 or visibilimeter) and extinction coefficient comparison substantially enhanced the instrumental agreement. During this experiment, the total concentration agreed in variations with the visibilimeter, except for the FSSP, so a corrective factor can be applied and it ranges from 0.44 to 2.2. This intercomparison study highlights the necessity to have an instrument which provides a bulk measurement of cloud microphysical or optical properties during cloud ground-based campaigns. Moreover, the FM and FSSP orientation was modified with an angle ranging from 30 to 90° angle with wind speeds from 3 to 7 m s−1. The results show that the induced number concentration loss is between 29 and 98 % for the FSSP and between 15 and 68 % for the FM-100. In particular, FSSP experiments showed strong discrepancies when the wind speed was lower than 3 m s−1 and/or when the angle between the wind direction and the orientation of the instruments is greater than 30°. An inadequate orientation of the FSSP towards the wind direction leads to an underestimation of the measured effective diameter.

International @ CARE+BDA; International audience; Nucleation and new particle formation in the marine atmosphere is usually associated to the presence of macroalgea emerged at low tides in coastal areas, while these processes were very rarely detected away from coastlines. In the present study, we evidence the formation of new particles from the 1 nm size above the seawater surface in the absence of any macroalgea population. Within the SAM project (Sources of marine Aerosol in the Mediterranean), coastal seawater mesocosmss experiments were deployed in May 2013 at the Oceanographic andSTARESO Marine Station STARESO in western Corsica, with the goal of investigating the relationship between marine aerosol emissions and the sea water biogeochemical properties. Three mesocosms imprisoned 3. ,3 m3 of seawater each and their emerged part was flushed with filtered natural air. One of these mesocosms was left unchanged as control and the two others were enriched by addition of nitrates and phosphates respecting Redfield ratio (N:P = 16) in order to create different levels of phytoplanctonic activities. We followed both water and air characteristics of three mesocosms during a period of three weeks with by using online water and atmospheric probes and as well as seawater daily sampling daily samples for chemical and biological analysis of the sea water. Secondary new particle formation was followed on-line in the emerged parts of the mesocosms, using a SMPS for the size distribution above 6 nm and a Particle Size Magnifyer (PSM) for the number of cluster particles between 1 and 6 nm. We will present howThe results indicated that the cluster formation rates and early growth rates were related to the gaz-phase emissions from the seawater and to its biogeochemical properties. In the present study, we evidence the formation of new particles from the 1 nm size above the seawater surface in the absence of any macroalgea population.

International @ AIR+BDA:AMM:BRM:CGO; International audience; The Mediterranean Sea is a special marine environment characterized by low biological activity and high anthropogenic pressure. It is often difficult to discriminate the contribution of Primary Sea Salt Aerosol formed at the sea-air interface from background level of the aerosol. An alternative tool to study the sea-air exchanges in a controlled environment is provided by the mesocosms, which represent an important link between field studies and laboratory experiments. The sea-air transfer of particles and gases was investigated in relation to water chemical composition and biological activity during a mesocosm experiment within the SAM project (Sources of marine Aerosol in the Mediterranean) at the Oceanographic and Marine Station STARESO in Western Corsica (May 2013). Three 2 m mesocosms were filled with screened (

International @ AIR+BDA:AMM:BRM; International audience; Marine aerorols are an important component of the atmosphere. Different factors influence the way they are produced from the sea water and injected in the atmosphere. The sea state (whitecap coverage) and sea temperature influence the size and concentration of primarily produced particles but also biogeochimecal caracteristics of the sea water may influence both the physical and chemical fluxes. In order to study marine emissions, one approach is to use semicontrolled environments such as mesocosms. Within the SAM project (Sources of marine Aerosol in the Mediterranean), we characterize the primary Sea Salt Aerosol (SSA) and Secondary aerosol formation by nucleation during mesocosms experiments performed in May 2013 at the Oceanographic and Marine Station STARESO in Western Corsica. We followed both water and air characteristics of three mesocosms containing an immerged part filled with 3,3 m3 of sea water and an emerged part filled with filtered natural air. Mesocosms were equipped with a pack of optical and physicochemical sensors and received different treatements: one was left unchanged as control and two were enriched by addition of nitrates and phosphates respecting Redfield ratio (N:P = 16) in order to create different levels of phytoplanctonic activities. The experiment lasted 20 days during which a phytoplanctonic bloom were observed with different intensities in the different mesocosms. The set of sensors in each mesocosm was allowed to monitor the water temperature, conductivity, pH, incident light, fluorescence of chlorophyll a and dissolved oxygen concentration. The mesocosms waters were daily sampled for chemical (colored dissolved organic matter, particulate matter and related polar compounds, transparent polysaccharides and nutrients concentration) and biological (chlorophyll a, virus, phytoplankton and zooplankton concentration) analyses. Secondary new particle formation was followed on-line in the emerged parts of the mesocosms, while a primary production by bubble bursting was simulated from a sample of sea water in a dedicated set-up every day. The size segregated aerosol number fluxes, cloud condensation nuclei (CCN) fluxes, and biological and organic contents were determined as a function of the sea water characteristics.

International @ AIR+BDA:CGO:AMM:BRM; International audience; The Mediterranean Sea is a special marine environment characterized by low biological activity and high anthropogenic pressure. It is often difficult to discriminate the contribution of Primary Sea Salt Aerosol (SSA) formed at the sea-air interface from background level of the aerosol. An alternative tool to study the sea-air exchanges in a controlled environment is provided by the mesocosms, which represent an important link between field studies and laboratory experiments. A mesocosms experiment was performed in May 2013 at the Oceanographic and Marine Station STARESO in Western Corsica. Three mesocosms were simultaneously filled with pooled and screened (

International audience; Long-term monitoring of the chemical composition of clouds (73 cloud events representing 199 individual samples) sampled at the puy de Dôme (pdD) station (France) was performed between 2001 and 2011. Physicochemical parameters, as well as the concentrations of the major organic and inorganic constituents, were measured and analyzed by multicomponent statistical analysis. Along with the corresponding back-trajectory plots, this allowed for distinguishing four different categories of air masses reaching the summit of the pdD: polluted, continental, marine and highly marine. The statistical analysis led to the determination of criteria (concentrations of inorganic compounds, pH) that differentiate each category of air masses. Highly marine clouds exhibited high concentrations of Na+ and Cl−; the marine category presented lower concentration of ions but more elevated pH. Finally, the two remaining clusters were classified as "continental" and "polluted"; these clusters had the second-highest and highest levels of NH4+, NO3−, and SO24−, respectively. This unique data set of cloud chemical composition is then discussed as a function of this classification. Total organic carbon (TOC) is significantly higher in polluted air masses than in the other categories, which suggests additional anthropogenic sources. Concentrations of carboxylic acids and carbonyls represent around 10% of the organic matter in all categories of air masses and are studied for their relative importance. Iron concentrations are significantly higher for polluted air masses and iron is mainly present in its oxidation state (+II) in all categories of air masses. Finally, H2O2 concentrations are much more varied in marine and highly marine clouds than in polluted clouds, which are characterized by the lowest average concentration of H2O2. This data set provides concentration ranges of main inorganic and organic compounds for modeling purposes on multiphase cloud chemistry.

International @ AIR+BDA:AMM:CGO:BRM; International audience; The Mediterranean Sea is a special marine environment characterized by low biological activity and high anthropogenic pressure. It is often difficult to discriminated the contribution of Primary Sea Salt Aerosol (SSA) formed at the sea-air interface from background level of the aerosol. An alternative tool to study the sea-air exchanges in a controlled environment is provided by the mesocosms, which represent an important link between field studies and laboratory experiments. A mesocosms experiment was performed in May 2013 at the Oceanographic and Marine Station STARESO in Western Corsica. Three mesocosms were simultaneously filled with pooled and screened (

Atmospheric aerosol impact on climate is one of the most uncertain aspects of the climate change. The need for a better knowledge of its physical, chemical and optical properties, as well as there seasonal and inter-annual variations, was clearly expressed by the scientific community. In particular, long term measurements series available for the free troposphere are scarce, although it is crucial to better understand the origin, the different properties, and the role of aerosol particles on climate processes in the Troposphere. The site of the puy de Dôme (Central France, 1465 m.a.s.l.) lies in the free troposphere most of the time. Continuous measurements of aerosols properties (number size distribution, optical properties and chemical composition), combined with in-situ meteorological instrumentation and continuous measurements of reactive gaseous species (O3, NOx, NOy, HCHO, CO and SO2) have been performed over the past years. We will present the evolution over a 3-year period of aerosol chemical, optical and physical properties at this site. The puy de Dôme site is dominantly under the influence of westerly winds although advection of air masses from Northern and Eastern Europe as well as episodes of Saharan dust occurs frequently. Weekly filter samples have been collected and analyzed for their inorganic and organic contents. The variations of both carbonaceous matter (Elemental and Organic Carbon, (EC and OC), divided into water soluble and insoluble organic carbon (WSOC and WISOC and organic acids)) and inorganic species show significant seasonal variability The variations of the chemical properties are analyzed as a function of the air mass trajectory and linked to the optical (black carbon concentrations and diffusion coefficient) and physical (Number concentration and, for some periods, size distribution) properties. This analysis permits a classification of aerosol properties associated to the different air masses encountered at the puy de Dôme. This data set will be of interest model validation in an area (free troposphere, Western Europe) that is still poorly documented.

International audience; The EMEP network aims at providing scientific supporton atmospheric monitoring and modelling, emissioninventories and projections, and integrated assessmentmodelling. To reach these objectives, it has encouragedlong- and short-term measurement periods in order toimprove the scientific knowledge on PM levels, sourcesand formation processes at the European scale.Within this framework and in coordination withthe existing ChArMEx French program and ACTRIS EUproject, two intensive periods have been held betweenJune 8 and July 12, 2012 for summer and January 11 toFebruary 8, 2013 for winter. Five locations in France (cf.Figure 1) were equipped with various on-line and offlineinstruments (cf. Table 1) aiming at measuring PMchemical and physical properties, as well as precursorgases (both organic and inorganic).The main objectives of these two campaigns wereto (i) provide a large quality controlled database of PMlevels and chemical composition for sites under rural,mid-altitude, urban or marine influences during twocontrasted seasons; (ii) measure simultaneously PMcompounds and their precursors to better understandprocesses such as secondary organic aerosols (SOA)formation or condensation of semi-volatile species; (iii)assess the importance of vertical exchanges in thevariability of PM ground levels, especially in case ofdust events; (iv) determine PM sources and their relativecontributions.Preliminary results will be presented anddiscussed.