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 characterized. We modeled these processes under clean and polluted conditions. At pH 8, S((IV)) + O(3) in sea salt is the principal S-oxidation pathway. At pH 5.5, S((IV)) oxidation by HOCl dominates. Decreased SO(2) solubility at pH 3 slows S((VI)) production. The relative contribution of H(2)SO(4(g)) scavenging to S((VI)) in sea salt increases with decreasing pH. Significant sea-salt dehalogenation is limited to acidified aerosol. Volatilization rates of BrCl and Br(2) do not vary significantly between pH 5.5 and 3, whereas HCl production via acid displacement increases by a factor of 20. At pH 5.5 and 8, virtually all HNO(3), is scavenged by sea sail. Modeled HNO(3) increases at pH 3 but remains substantially lower than particulate NO(3)(-). Discrepancies between measurements and modeled results are assessed based on measurement artifacts, uncertainties in rate and equilibrium constants, organic reactants and surface films, and dynamics. (C) 1998 Elsevier Science Ltd. All rights reserved.