Physicochemical characteristics of aerosols measured in the spring time in the Mediterranean coastal zone

Abstract

Aerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. This paper presents physicochemical characterization of aerosols observed during meteorological conditions characteristics of coastal areas. In particular, we study the influence of sea-breezes and land-breezes as well as the fetch variation, which superpose on larger synoptic conditions, on aerosol properties. This was achieved using a physical, chemical and optical analysis of the aerosol data acquired in May 2007 on the French Mediterranean coast. The aerosol distributions were measured using a TSI SMPS 3081 model and the chemical characterization was made using an Ion Chromatography analysis (IC) and a thermo-optical technique. In addition, aerosol optical characteristics were provided by aethalometer (absorption) and nephelometer (scattering) measurements. For low wind speeds, we detect high aerosol number concentrations as well as high NO3− and carbonaceous compounds contributions, which are observed even when the aerosol is sampled in pure maritime air masses. These results indicate that air masses are strongly impacted by pollution transported over the Mediterranean. In addition, the combination of low wind speeds and land/sea-breezes lead to the production of new ultrafine particle formation events that seem to take place over the sea before being transported back to the coast. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are significantly lowered due to the dispersion of anthropogenic pollutants. Optical measurements reveal that mean scattering and absorbing coefficients are about 15.2 Mm−1 and 3.6 Mm−1, respectively. Associated mean aerosol single scattering albedo is found to be about 0.87 and 0.94 (at 520 nm) for continental and maritime influences.