Measurements of atmospheric extinction at sea-viewing wide-field-of-view sensor wavelengths were carried out during the Lagrangian Experiment on the Baltic Sea within the Baltic Sea System Study project, July 2--15, 1997. The empirical orthogonal functions method was applied to the aerosol optical thickness spectra, allowing three air mass types, containing different aerosol types, to be distinguished: continental, continental-maritime, and maritime, corresponding to different residence times of air masses over the Baltic Sea. The amplitude of the aerosol optical thickness, describing the temporal variability, was found to be strongly affected by the atmospheric stability. The contribution of the aerosol radiance to the atmospheric radiance depends directly on the aerosol type, the wavelength λ, and the solar zenith angle &thgr;s. The most significant contribution of more than 30% was detected for the continental and continental-maritime aerosol types, for &thgr;s=30¿, and at λ=865 nm. ¿ 1999 American Geophysical Union