Optical Properties and Radiative Effects of Aerosols in a Coastal Zone.

Physical and optical properties of atmospheric aerosols were measured in the French Mediterranean coastal zone for over one year between October 2005 and 2006. BC mass concentration, absorption and scattering coefficients, number-size distributions of fine and coarse particles were continuously measured at ground level, along with the meteorological parameters. In addition to these surface based in situ measurements, a co-located Cimel Sun photometer continuously measured the columnar aerosol optical depth (AOD), Angstroms coefficient ( ) and the other microphysical parameters. Large surface BC concentrations and high values of scattering coefficients occurred during winter, followed by lower values during spring and summer season. However, the columnar aerosols showed different seasonal behaviour, with high AOD values occurring mostly during the summer months, and low to moderate values prevailed during the rest of the period. Monthly mean AOD at mid-visible wavelengths ranged between ~0.1 and 0.34. The Angstroms coefficient ( ) remained high (>1.2) during the entire study period, thereby indicating the relative dominance of fine particles. Monthly mean BC concentrations varied between 303 and 1026 ng m−3. The surface single scattering albedo at 525 nm was in the range from 0.7 to 0.8, thereby indicating the dominance of absorbing aerosols over this region. Mean reduction in the diurnally averaged solar flux (as estimated using discrete ordinate radiative transfer model GAME) was found to be 24.9 Wm−2 and 61.8 Wm−2 for pollution and dust event respectively in June 2006. Keywords Aerosol optical properties, radiative forcing, coastal zone [ABSTRACT FROM AUTHOR]