CONTRIBUTION OF MARINE AEROSOLS IN THE PARTICLE-SIZE DISTRIBUTIONS OBSERVED IN MEDITERRANEAN COASTAL ZONE

Results from analysis of aerosol size distributions measured in a Medi terranean coastal zone are presented. This paper focuses on aerosol pa rticles smaller than 10 mu m because they specifically represent a mix ed contribution of aerosols in a coastal zone. The interpretation is f irst based on low wind speed periods to identify the background aeroso l in the study area. We can note the influence of wind direction on bo th aerosol concentrations and size distributions that have been measur ed. The contributions of the various particle sources, continental or marine, from anthropogenic or natural origin have been demonstrated re gardless of each aerosol size distribution. The influence of solar irr adiation has been observed for low wind speed periods. It induces a bi modal size distribution characterized by the classical fine particle p eak around 0.04 mu m and an accumulation mode at 0.1 mu m. Aerosol siz e distributions measured during high continental wind periods (which c orrespond to a 25 km fetch) show a strong concentration peak around 0. 02 mu m. The good correlation obtained between this particle concentra tion and wind speed shows that the smallest particles measured during high continental wind speed periods are probably of marine origin. The interpretation of this large contribution of very small particles has focused on two main hypotheses. The increase of gas transfers (probab ly the dimethyl sulfide) induced by the whitecap coverage upon the sea surface or a specific production of fine particles as previously sugg ested by Despiau et al. (Journal of Aerosol Science 1996, 27(3), 403-4 15). The specificities of the smallest particles are also observed if we compare background aerosol and concentrations recorded during high wind speed periods. In contrast with the sea-surface-generated aerosol s which decrease during an extended period of low wind speed (Smith et al., Atmospheric Environment 1991, 25A, 547-555), we have observed la rger concentrations of 0.1-0.3 mu m particles during the background co nditions. (C) 1997 Elsevier Science Ltd.