Oceanologia (Mar 2011)
Seasonal variability in the optical properties of Baltic aerosols
Abstract
A five-year dataset of spectral aerosol optical thickness was used to analyse the seasonal variability of aerosol optical properties (the aerosol opticalthickness (AOT) at wavelength λ=500 nm, AOT(500) and the Ångström exponent for the 440-870 nm spectral range,α(440, 870)) over the Baltic Sea and dependence of these optical properties on meteorological factors (wind direction, wind speed and relativehumidity). The data from the Gotland station of the global radiometric network AERONET (Aerosol Robotic Network, http://aeronet.gsfc.nasa.gov)were taken to be representative of the Baltic Sea conditions. Meteorological observations from Fårosund were also analysed. Analysis of the data from 1999 to 2003 revealed a strong seasonal cycle in AOT(500) and α(440, 870). Two maxima of monthly mean values of AOT(500)over the Baltic were observed. In April, an increase in the monthly mean aerosol optical thickness over Gotland most probably resulted from agricultural waste strawburning, mainly in northern Europe and Russia as well as in the Baltic states, Ukraine and Belarus. During July and August, the aerosol optical thickness wasaffected by uncontrolled fires (biomass burning). There was a local minimum of AOT(500) in June. Wind direction, a local meteorological parameter strongly related to air mass advection, is the main meteorological factor influencing the variabilityof aerosol optical properties in each season. The highest mean values of AOT(500) and α(440, 870) occurred with easterly winds in both spring and summer,but with southerly winds in autumn.
