SULFATE, NITRATE, METHANESULFONATE, CHLORIDE, AMMONIUM, AND SODIUM MEASUREMENTS FROM SHIP, ISLAND, AND AIRCRAFT DURING THE ATLANTIC STRATOCUMULUS TRANSITION EXPERIMENT MARINE AEROSOL GAS-EXCHANGE

We measured aerosol methanesulfonic acid (MSA), Cl-, NO3-, SO4=, Na+, and NH4+ concentrations and size distributions and gaseous ammonia and nitric acid concentrations from Santa Maria, Azores during the Atlant ic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) experiment in June 1992. We also sampled some of these s pecies in the free troposphere and marine boundary layer (MBL) from th e National Center for Atmospheric Research's (NCAR's) Electra aircraft and at the surface from the R/V Oceanus. In relatively clean Atlantic marine air masses the wean (and standard error of the mean) observed MSA concentrations (27 +/- 2 parts per trillion molar mixing ratio, pp t) were smaller than in continental polluted air masses (36 +/- 6 ppt) , reflecting either longer aerosol lifetimes in air with higher cloud condensation nuclei (CCN) concentrations or more active photochemical production in polluted air. Mean NH4+/non-sea-salt (nss) SO4+ molar ra tios in marine and continental air masses were 0.65 +/- 0.05 and 1.3 /- 0.2, respectively, indicating that continental sulfate was neutrali zed by ammonia to a greater extent than marine sulfate was. Most of th e NH4+ and nss SO4= was contained in submicrometer modes; Na+, Cl-, an d NO3- were in supermicron modes; and MSA showed bimodal behavior, wit h major and minor peaks at 0.3-0.4 mu m and 1.5 mu m, respectively. Th e molar ratio NH4+/nss SO4= relative to size confirms that most ammoni a vapor condensed on submicron nss SO4=. The average dry deposition fl uxes for aerosol nss SO4=, MSA, NH4+ and NO3- during ASTEX/MAGE were 1 .49, 0.09, 0.18, and 3.25 mu mol m(-2) d(-1), respectively.