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Claeys, M, Roberts G, Mallet M, Arndt J, Sellegri K, Sciare J, Wenger J, Sauvage B.  2017.  Optical, physical and chemical properties of aerosols transported to a coastal site in the western Mediterranean: a focus on primary marine aerosols. Atmospheric Chemistry and Physics. 17:7891-7915.   10.5194/acp-17-7891-2017   AbstractWebsite

As part of the ChArMEx-ADRIMED campaign (summer 2013), ground-based in situ observations were conducted at the Ersa site (northern tip of Corsica; 533 m a.s.l.) to characterise the optical, physical and chemical properties of aerosols. During the observation period, a major influence of primary marine aerosols was detected (22-26 June), with a mass concentration reaching up to 6.5 mu g m(-3) and representing more than 40% of the total PM10 mass concentration. Its relatively low ratio of chloride to sodium (average of 0.57) indicates a fairly aged sea salt aerosol at Ersa. In this work, an original data set, obtained from online real-time instruments (ATOFMS, PILS-IC) has been used to characterise the ageing of primary marine aerosols (PMAs). During this PMA period, the mixing of fresh and aged PMAs was found to originate from both local and regional (Gulf of Lion) emissions, according to local wind measurements and FLEXPART back trajectories. Two different aerosol regimes have been identified: a dust outbreak (dust) originating from Algeria/Tunisia, and a pollution period with aerosols originating from eastern Europe, which includes anthropogenic and biomass burning sources (BBP). The optical, physical and chemical properties of the observed aerosols, as well as their local shortwave (SW) direct radiative effect (DRE) in clear-sky conditions, are compared for these three periods in order to assess the importance of the direct radiative impact of PMAs compared to other sources above the western Mediterranean Basin. As expected, AERONET retrievals indicate a relatively low local SW DRF during the PMA period with mean values of -11 +/- 4 at the surface and -8 +/- 3W m(-2) at the top of the atmosphere (TOA). In comparison, our results indicate that the dust outbreak observed at our site during the campaign, although of moderate intensity (AOD of 0.3-0.4 at 440 nm and column-integrated SSA of 0.90-0.95), induced a local instantaneous SW DRF that is nearly 3 times the effect calculated during the PMA period, with maximum values up to -40 W m(-2) at the surface. A similar range of values were found for the BBP period to those during the dust period (SW DRF at the surface and TOA of -23 +/- 6 and -15 +/- 4 W m(-2) respectively). The multiple sources of measurements at Ersa allowed the detection of a PMA-dominant period and their characterisation in terms of ageing, origin, transport, optical and physical properties and direct climatic impact.

Stith, JL, Ramanathan V, Cooper WA, Roberts GC, DeMott PJ, Carmichael G, Hatch CD, Adhikary B, Twohy CH, Rogers DC, Baumgardner D, Prenni AJ, Campos T, Gao R, Anderson J, Feng Y.  2009.  An overview of aircraft observations from the Pacific Dust Experiment campaign. Journal of Geophysical Research-Atmospheres. 114   10.1029/2008jd010924   AbstractWebsite

Fourteen research flights were conducted in the Pacific Dust Experiment (PACDEX) during April and May 2007 to sample pollution and dust outbreaks from east Asia as they traveled across the northern Pacific Ocean into North America and interacted with maritime storms. Significant concentrations of black carbon (BC, consisting of soot and other light-absorbing particles measured with a soot photometer 2 instrument) and dust were observed both in the west and east Pacific Ocean from Asian plumes of dust and pollution. BC particles were observed through much of the troposphere, but the major finding is that the percentage of these particles compared with the total number of accumulation mode particles increased significantly (by a factor of 2-4) with increasing altitude, with peak values occurring between 5 and 10 km. Dust plumes had only a small impact on total cloud condensation nuclei at the sampling supersaturations but did exhibit high concentrations of ice nuclei (IN). IN concentrations in dust plumes exceeded typical tropospheric values by 4-20 times and were similar to previous studies in the Saharan aerosol layer when differences in the number concentrations of dust are accounted for. Enhanced IN concentrations were found in the upper troposphere off the coast of North America, providing a first direct validation of the transport of high-IN-containing dust layers near the tropopause entering the North American continent from distant sources. A source-specific chemical transport model was used to predict dust and other aerosols during PACDEX. The model was able to predict several features of the in situ observations, including the general altitudes where BC was found and a peak in the ratio of BC to sulfate between 5 and 10 km.