AEROSOL DISTRIBUTIONS IN THE NORTH-ATLANTIC MARINE BOUNDARY-LAYER DURING ATLANTIC STRATOCUMULUS TRANSITION EXPERIMENT MARINE AEROSOL AND GAS-EXCHANGE

Marine boundary layer aerosol size distributions observed during June 1992 are described. Measurements were made from on board the National Oceanic and Atmospheric Administration ship Malcolm Baldrige in suppor t of the Atlantic Stratocumulus Transition Experiment/Marine Aerosol a nd Gas Exchange field experiment in the area surrounding 32 degrees N latitude and 25 degrees W longitude. Measurements obtained from three instruments: the differential mobility particle sizer, the active scat tering aerosol spectrometer probe, and the forward scattering spectrom eter probe, were used to investigate the contributions of the differen t aerosol modes to total number, surface area, and volume concentratio ns. It was observed that aerosol populations in air masses that appear to have originated from remote marine areas have a bimodal number dis tribution with total number concentrations ranging from 200 to 800 par ticles cm(-3). In air masses that have been affected by anthropogenic emissions, the aerosol size distributions become monomodal and total n umber concentrations increase to 500 to 1800 cm(-3) The data also sugg est that air mass boundaries can be very sharp and that there may be s ome mesoscale variability in the aerosol population within an air mass .