THE AQUEOUS OXIDATION OF ELEMENTAL MERCURY BY OZONE

Relative consumptions of aqueous Hg0 and S(IV) due to reactions with O3 have been used to estimate the rate constant for the reaction of Hg0 and O3. Ratios [GRAPHICS] ranging from < 0.1 to > 10 were measured in the pH range 4.5-9.5. The results were interpreted in terms of a second-order reaction of Hg0 and O3 with a rate constant k = (4.7 +/- 2.2) x 10(7)M-1 s-1 which is independent of pH and temperature. Steady-state concentrations of dissolved inorganic mercury in atmospheric waters (rain and clouds) have been estimated using the rate constant determined in this work and previously reported rate constants for the reduction of Hg2+ by S(IV). At gas-phase concentrations of SO2 > 0.5 ppb, concentrations of dissolved inorganic mercury in the range 1-25 pM (0.2-5 ng l-1) are predicted at different pH and gas-phase concentrations of O3, which agrees reasonably well with measured concentrations. At lower SO2 concentration, the calculated values are unreasonably high, which indicates that other reducing processes may be of importance under these conditions.