UPTAKE OF SO2(G) BY AQUEOUS SURFACES AS A FUNCTION OF PH - THE EFFECT OF CHEMICAL-REACTION AT THE INTERFACE

The uptake of SO2(g) by fast-moving water droplets was measured as a function of pH and surface-gas contact time in the range 0.5-10 ms. In the high pH range (>5) a parameter governing the uptake of SO2(g) by water is the rate for the reaction of SO2 with H2O to form HSO3-. The experimentally observed uptake is significantly greater than predicted by the rate measured for this reaction in bulk liquid water. Likewise at low pH, where uptake is limited by Henry's law solubility, the uptake is significantly greater than predicted. These observations together with the observation of uptake as a function of time suggest that at the gas-liquid interface the SO2-H2O reaction is facile, forming a HSO3--H+ surface complex which is in equilibrium with the gas-phase SO2. The species enters the bulk water as HSO3- via this complex. The equilibrium ratio of densities of the surface complex (cm-2) and gas-phase SO2 (cm-3) is 0.13 cm-1 at 10°C. Kinetic and thermodynamic parameters governing surface interactions are derived and discussed. © 1990 American Chemical Society.