time t and t = 0, respectively. The percentage change per hour in the ambient S02 concentration is thus given by

Substituting into Eq. (E) from (D), one obtains

where the time t is 1 h, expressed in the same time units used for the rate constant k4. Given similar assumptions, the same type of relationship, of course, holds true for other oxidizing species as well.

d. Computing Oxidation Rates in the Atmosphere

The S02 oxidation rates in the units of % h"1 expected from the gas-phase reactions of S02 with OH and the Criegee intermediate can be computed as shown in Box 8.1 for comparison to rates of oxidation observed in field studies (see Section C.l), if the rate constants and the concentrations of OH and Criegee intermediates are known.

3. Oxidation in the Aqueous Phase a. S(IV) Aqueous Equilibria

Sulfur dioxide gas dissolves in water to set up equilibria similar to those of C02:

S02(g) + H20 « S02 • H20(aq) Hi, = 1.242 M atm"1,

0 0

Post a comment