AEROSOL PH IN THE MARINE BOUNDARY-LAYER - A REVIEW AND MODEL EVALUATION

Impacts of sea-salt-aerosol pH on oxidation processes, sulfur cycling, and surface-ocean fertilization are uncertain; estimates vary from pH <1 to > 9 and the pH-dependence of some transformations is poorly cha racterized. We modeled these processes under clean and polluted condit ions. At pH 8, S-(IV) + O-3 in sea salt is the principal S-oxidation p athway. At pH 5.5, S-(IV) oxidation by HOCl dominates. Decreased SO2 s olubility at pH 3 slows S-(VI) production. The relative contribution o f H2SO4(g) scavenging to S-(VI) in sea salt increases with decreasing pH. Significant sea-salt dehalogenation is limited to acidified aeroso l. Volatilization rates of BrCl and Br-2 do not vary significantly bet ween pH 5.5 and 3, whereas HCl production via acid displacement increa ses by a factor of 20. At pH 5.5 and 8, virtually all HNO3, is scaveng ed by sea sail. Modeled HNO3 increases at pH 3 but remains substantial ly lower than particulate NO3-. Discrepancies between measurements and modeled results are assessed based on measurement artifacts, uncertai nties in rate and equilibrium constants, organic reactants and surface films, and dynamics. (C) 1998 Elsevier Science Ltd. All rights reserv ed.