Cloud water sulfate production rates

The low amount of liquid water associated with particles (volume fraction 10-10, compared to clouds, for which the volume fraction is on the order of 10-7) precludes significant aqueous-phase conversion of S02 in such droplets. These particles can contribute to sulfate formation only for very high relative humidities (90% or higher) and in areas close to emissions of NH3 or alkaline dust. Seasalt particles can also serve as the sites of limited sulfate production (Sievering et al. 1992), as they are buffered by the alkalinity of seawater. The rate of such a reaction as a result of the high pH of fresh seasalt particles is quite rapid, 60 pM min-1, corresponding to 8% h 1 for the remote oceans (S02 = 0.05 ppb). Despite this initial high rate of the reaction, the extent of such production may be quite limited. For a seasalt concentration of 100 nmol m 3, the alkalinity of seasalt... 

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