This work presents the results of investigations of aerosol extinction and aerosol optical thickness in the coastal areas of the southern Baltic Sea. The investigations were carried out under various weather conditions and in various seasons in 1996-2000. Aerosols carried on winds from 300degrees-N-60degrees can be regarded as of marine origin. Their ensemble consisted of non-absorbing water droplets with the same light refractive index as sea water. The ensemble of aerosols carried on winds from 240degrees-S-120degrees consisted of a mixture of particles of both marine and continental origin, which have both absorbing and scattering properties. The values of the aerosol extinction and aerosol optical thickness in the atmosphere over the coastal zone of the southern Baltic Sea obtained from lidar measurements varied from 0.0038 to 0.0727 (km(-1)) and from 0.014 to 0.36, respectively, and they strongly depended on wind speed and direction. (C) 2002 Elsevier Science Ltd. All rights reserved.