Vertical distribution of aerosol particles near the air-sea interface in coastal zone

Abstract Measurements of vertical aerosol concentration profiles in the Mediterranean coastal zone are presented in the size band 0.1 to 20 μm, with focus on aerosol particles smaller than 10 μm. The results show that the profile shape depends mainly on turbulent processes induced by the wind rather thanthe whitecap production of freshly generated aerosols from the wind-wave interaction. Therefore, the data recorded during weak and moderate wind speeds show the prevalence of turbulent mixing processes induced by the wind for profiles in the size range 0.1–1 μm. For the size range 1–10 μm, in addition to the effect of wind velocity and direction (i.e. the coastal influence), we also noted the importance of the relative humidity gradient (very close to the interface). Good agreement was found between vertical concentration profiles recorded for winds of marine origin and the marine mixed layer model (Davidson and Shutz, 1983). However, we show that the model cannot be used for winds of continental origin. For wind speeds above >9 ms −1 , a maximum occurs in the concentration profiles (near 2–3 m height) for all particles larger than 1 μm, which confirms the predominant influence of an eddy which appears in the lee of the crest, referred to as the “wave rotor” model (De Leeuw, 1986).

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