AEROSOL-SIZE DISTRIBUTION AND AEROSOL WATER-CONTENT MEASUREMENTS DURING ATLANTIC STRATOCUMULUS TRANSITION EXPERIMENT MARINE AEROSOL AND GAS-EXCHANGE

Aerosol size distribution data measured during the June 1992 Marine Ae rosol and Gas Exchange experiment are analyzed to investigate the char acteristics of fine marine aerosol particles measured over the North A tlantic near the Azores Islands. Measured aerosol size distribution da ta were corrected using the corrected size calibration data based on t he optical properties of particles being measured. The corrected size distribution data were then approximated with either one or two lognor mal size distributions, depending on air mass conditions. Under clean air mass conditions <3 mu m diameter aerosol size distributions typica lly exhibited two modes, consisting of an accumulation mode and the sm all end of the sea-salt particle mode. However, under the influence of continental polluted air masses, the aerosol size distribution was do minated by <1 mu m diameter particles in a single mode with an increas ed aerosol concentration. Aerosol water content of accumulation mode m arine aerosols was estimated from differences between several series o f ambient and dried aerosol size distributions. The average aerosol wa ter fraction was 0.31, which is in good agreement with an empirical ae rosol growth model estimate. The average rate of SO4= production in th e accumulation mode aerosol water by H2O2 oxidation was estimated to b e <7 x 10(-10) mol L(-1) s(-1), which is an insignificant contributor to the observed non-sea-salt SO4= in the accumulation mode.