dissolved S02 concentration is given by [S02 ]aq = Hso 2Pso2>

where H is the Henry's law constant based on physical solubility (Table 8.1) and P is the gas-phase pressure of S02. The total concentration of S(IV) in solution, taking into account the acid-base equilibria reactions (11)—(13), is then given by where k is the solution-phase rate constant (L mol~1 s~'), [X] and [S(IV)] are the aqueous-phase concentrations of the oxidant and S(tV), respectively, in units of moles per liter of solution, and V is the volume (L) of liquid water, that is, of aqueous solution available, per cubic meter of air. The rate of S(Vt) formation is then expressed in moles per cubic meter of air per second.

To express this rate of oxidation in % h"1, consistent with the units in which the results of field studies are often reported, one needs to divide this rate by the total number of moles of S(IV) per cubic meter of air, convert the unit time from s_1 to h-1, and multiply by 100 to convert the fraction to percent. The gas-phase moles of S02 in a cubic meter of air is given, according to the ideal gas law, by

where 17 is the ratio of the total dissolved S(1V) to that of dissolved S02. If there are V liters of liquid water per cubic meter of air, then the total number of moles of S(tV) contained in the atmospheric water droplets found in f m3 of air becomes

The total number of moles of S(IV) in a cubic meter of air, including both gas and aqueous phases, is thus given by

Total S(IV) per m3 of air fooo/v

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