Characterization of aerosol particles over the southern and South-Eastern Baltic Sea

Studies of aerosol particle number concentration (PNC) level over open sea in the southern and south-eastern Baltic Sea regions were performed during five cruises (2005-2006, 2008-2010) by RV Oceania and at the coastal Preila station (Lithuania). A comparative analysis was performed of aerosol PNC variation at open sea versus measurements taken at the coastal site under various conditions (breaking waves, fog events, NPF), considering transport of forest fire products and advection of different air mass types to the investigation sites. It was found that the average PNC over the open sea (3000-4000 cm− 3) was generally higher than at the coastal site (2000-3000 cm− 3). Breaking waves caused by the latitudinal or longitudinal long-lasting (3-4 days) constant-direction wind under stormy conditions had the strongest effect on the aerosol PNC over the Baltic Sea. The aerosol PNC in the marine boundary layer (MBL) of the south-eastern Baltic Sea during fog did not depend on the air mass type over open sea, in contrast to the coastal site, that is, the average PNC level (3000-4000 cm− 3) in the MBL, which could be constantly affected by specific environmental factors as a source of condensation nuclei for the fog formation. Short-term increases of aerosol PNC in the MBL (5000-10,000 cm− 3) were higher than in the same periods of the time scale at the coastal site (3000-6000 cm− 3) during NPF events, and therefore the open sea environment may facilitate a more favourable condition for the NPF, that is, exhaust and biogenic emissions from ships and the marine environment.