Sur la présence de chlore « gazeux » d'origine marine dans l'atmosphère

International audienc

Mise en évidence dans l'atmosphère marine d'aérosols enrichis en potassium et calcium ayant la surface de la mer pour origine.

International audienc

Sur la distribution d'aérosols d'origine marine dans la basse troposphère.

International audienc

Variations in Ionic Ratios between Reference Sea Water and Marine Aerosols

International audienceAtmospheric particles were collected over the open sea (western Mediterranean, North Atlantic, and Norwegian Sea) by air filtration and cascade impactor sampling. The observed K/Na concentration ratios exhibited marked variation and were greater than the reference ratio in bulk sea water. These concentration ratios can be related to the existence of

Particulate content of savanna fire emissions

International audienc

Source terms and source strengths of the carbonaceous aerosol in the tropics

International audienc

Flux verticaux de diméthylsulfoniumpropionate particulaire (DMSPp) dans l'Océan Atlantique tropical

International audienceWe report results from free-drifting sediment trap deployments at 200 rn depth which enable measurement of the diel variations in the downward flux of detrital particulate dimethylsulphoniopropionate (DMSPp) over periods of 24-72 hours in three contrasting trophic regimes of the tropical northeastern Atlantic Ocean off Mauritania. The source of DMSPp was the phytoplankton living in surficial water Iayers. The three regimes exhibited sirnilar strong diel cycles, the nocturnal fluxes being up to 100-fold lower than the daytime fluxes. High (or low) detrital DMSPp fluxes were associated with high (or low) numbers ofpteropods trapped inside the sampling cups. Thus, contamination of sinking material is likely to have occurred, promoting an overestimate of the daytime fluxes. It is concluded that the transport of DMSPp at depths deeper than 200 rn is strongly influenced by the downward migration of pteropods during the daylight hours. This mode of transport is shown to be a general process in tropical waters for accelerating DMSPp sedimentation. Under these oceanic and experimental conditions the daily DMSPp flux at 200 rn accounted for only about 0.1 % of the DMSPp standing stock. Renee, the DMSPp downward flux is likely to have a minor influence in the upper ocean budget of DMSPp.La variabilité journalière du flux vertical de diméthylsulfoniumpropionate particulaire (DMSPp) a été étudiée avec un pas de temps de 4 heures à l'aide d'une trappe à sédiment dérivante multi-godets de type PPS5/2. Le déploiement s'est effectué en trois sites de richesse biologique contrastée au large de l'upwelling de Mauritanie, à une profondeur de 200 m. Le phytoplancton des eaux superficielles constitue le principal réservoir du DMSPp. Les flux mesurés en chacun des sites présentent des variations nycthémérales très marquées et synchronisées. L'intensité des flux diurnes est jusqu'à 100 fois supérieure à celle des flux nocturnes. Dans la plupart des cas, les flux de forte intensité ont été mesurés à l'occasion de fortes accumulations d'organismes mésozooplanctoniques (ptéropodes du genre Clio et Limacina) dans les godets, et réciproquement. Ces organismes, qui effectuent des migrations verticales nycthémérales, sont interceptés par la trappe au cours de leur descente vers les profondeurs où ils séjournent pendant la journée. Il y a donc eu certainement intégration de leurs pelotes fécales et, par conséquent, surestimation des flux journaliers de DMSPp à 200 rn de profondeur. Ceux-ci ne représentent cependant qu'au plus 0,15 % du réservoir phytoplanctonique de DMSPp. Le transport actif de DMSPp par le zooplancton accélère donc les échanges de DMSPp entre les eaux superficielles et les eaux profondes, mais n'est pas suffisamment important sur le plan quantitatif pour justifier une prise en compte par les futurs modèles du cycle biogéochimique marin des composés DMSP et DM

Atmospheric input of trace metals to the western Mediterranean: uncertainties in modelling dry deposition from cascade impactor data

International audienceThe mass-particle size distributions (MSDs) of Na, Al, Cd, and Pb were determined from 17, 1-5 day, high-volume cascade impactor samples collected throughout the Western Mediterranean atmosphere between 1980 and 1983. As expected, the mass median diameter (MMD) was the largest for Na, representative of sea-salt aerosol, with a median value of 5.9 pm. The median value for the MMD for Al, representative of mineral aerosol, was 2.8 pm. The smallest values of the MMD were found for pollution-derived elements, Cd and Pb: 0.7 pm. In most cases, the MSDs, for each of the elements, were log-normal. Total dry deposition velocities were calculated from the two-layer deposition model of Slinn and Slinn (1980) using three approaches: (i) by characterizing the distribution as a MMD, (ii) by considering the size distribution as directly given by the cascade impactor, (iii) by fitting the assumed log-normal distribution and dividing it into 100 successive intervals. The first approach appeared to give underestimates. The two other approaches yielded similar results for Cd and Pb, of the order of 0.05 cm S K I , For these elements, however, more than 20% of the total dry deposition flux was due to particles with diameters of 7.2 pm or greater (collected by impactor stage 1). For Na and Al, the third approach yielded values at least one order of magnitude higher than when using the two others. This clearly underlines the major role played by large particles in controlling the dry deposition of sea-salt and mineral aerosol particles. Direct measurements of Al dry deposition, made in 1985-1986 on the northwestern coast of Corsica, agree best with the values predicted by the third approach (mean calculated and measured values of 1.8 and 3.0 cm s-I respectively). Scanning electron microscopy examinations of samples confirm that mineral aerosol particles with diameters of 10 pm or greater dominate the dry deposition flux. Preliminary data indicate that for mineral aerosol particles, this flux is, on a yearly basis, about half of the wet deposition flux. However cascade impactor data are not adequate to retrieve true mass-particle size distribution in the size range which controls dry deposition (D > 7 pm), and this is shown to be the source for one order of magnitude uncertainties in dry deposition calculations

Seasonal variability of the elemental composition of atmospheric aerosol particles over the northwestern Mediterranean

International audienceBeginning in 1985, a continuous aerosol sampling program has been undertaken at a coastal location in northwestern Corsica. This site is 300 m above sea-level and at least 20 km from local pollution sources. It is exposed during 80% or more of the time to maritime air masses which have travelled over the western Mediterranean from southern, western and northern directions. Daily 24-h aerosol samples were collected on 0.4 pm pore size nuclepore filters from a 10 m high tower and analysed for Al, Si, P, S, K, Ca, Ti, Mn, Fe and Zn by X-ray fluorescence, and for Na, Cu and Pb by flameless atomic absorption. The data obtained up to now, from April 1985 to April 1986, show that the temporal variability of the concentrations displays 2 distinctive patterns. First, a seasonal pattern is observed for the elements of continental origin, either natural (e.g.. Al, Si) or anthropogenic (e.g., S, Pb). This pattern is inversely related to the frequency and amount of rainfall such that the highest concentrations are observed between May and October. Estimates based on these data indicate an average time of 2 days to reload that atmospheric environment with aerosol particles from continental sources. This seasonal pattern is not observed for locally produced sea-salt aerosol particles (index Na), whose concentration is related to local wind speed. Elements associated with mineral aerosol particles exhibit sporadic but intense concentration peaks that are superimposed on this general pattern. 20 of these events were recorded for the sampling period considered with their frequency being maximal in spring and summer. 3-D air-mass trajectories show that all these events are associated with transport of soil dust from Africa

Rapid removal of Chernobyl fallout from Mediterranean surface waters by biological activity

International audienc