Mesophile, psychrophile bacteria and fungal colony-forming units (CFU) in air were investigated over the Gulf of Gdansk, Southern Baltic Sea and coastal locations from 1994 to 1998. The presence of viable mesophile and psychrophile bacteria and fungi in marine aerosols over the open sea and coastal locations was documented. The number of viable microbes over the coastal locations was significantly higher than over the open sea. Distinctly more mesophile bacteria (pollution related), compared to psychrophile (environment related) species, was found in aerosols over the open Baltic Sea. Evidence that oxygen supersaturation in the surface water may contribute to enhanced bubble-mediated sea-to-air bacteria transport was documented, in particular during the presence of summer plankton waterbloom in the Gulf of Gdansk, where Vistula River and sea waters are mixed. Several coastal investigations combined both field and laboratory experiments to estimate the enrichment factors of bacteria in sea-derived droplets. This part of the study was performed using an Air-Sea Exchange Simulator (A-SES) developed for this purpose. The A-SES produces streams of bubbles in the water and related jet and film droplets in the air. Laboratory experiments confirmed significant enrichment of the sea-to-air mesophile bacteria transfer. The estimated enrichment factor for mesophile bacteria may exceed that obtained for psychrophile bacteria ejected with droplets by a factor of 12. (C) 2001 Elsevier Science Ltd. All rights reserved.