Abstract
Abstract. 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 µg 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 ± 3 W 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.
Highlights
The Mediterranean Basin is a crossroad for air masses bringing different types of aerosols, both from natural and anthropogenic origins (Lelieveld et al, 2012)
One of the ground-based instrumented sites was based in Ersa, Cap Corse and allowed the study of different aerosol types, the properties and relative impacts of primary marine aerosols (PMAs) compared to other aerosol types present in the western Mediterranean Basin
Using FLEXPART back-trajectory simulations and in situ optical, physical and chemical measurements, we show that www.atmos-chem-phys.net/17/7891/2017/
Summary
The Mediterranean Basin is a crossroad for air masses bringing different types of aerosols, both from natural and anthropogenic origins (Lelieveld et al, 2012) Of these aerosols, primary marine aerosols (PMAs; mainly composed of sea salt and to a lesser extent of organic matter) are important because they are always present over the Mediterranean Basin and compose the main part of background aerosols over the Mediterranean (Pace et al, 2006). This high variability in terms of PMA loading and optical, physical and chemical properties leads to significant uncertainties in the quantification of regional radiative impact, both for direct and indirect effects (Forster et al, 2007; Stevens and Feingold, 2009). It should be noted that most past studies have documented aerosol properties in the eastern part of the Mediterranean Basin (Crete Mihalopoulos et al, 1997; Bardouki et al, 2003; Sciare et al, 2003; Koulouri et al, 2008; Greece Chabas and Lefèvre, 2000), even though many studies took place in the central (Meloni et al, 2004; Di Iorio et al, 2009) and western (Sellegri et al, 2001; Cros et al, 2004; Pey et al, 2009; Guerrero-Rascado et al, 2009) Mediterranean Basin
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