OXIDANT LIMITATION TO THE FORMATION OF H2SO4 NEAR A SO2 SOURCE REGION

The question of whether the aqueous-phase formation of H2SO4 is limited by the availability of oxidant is examined using concurrently measured concentrations of H2O2 and SO2 from the mid-western U.S. in a summer month. Between the surface, and an altitude of 850 mb, [SO2] > [H2O2] on most days. The reverse is true above 850 mb. Oxidant limitations-defined here simply as situations in which [SO2] > [H2O2]-thereby depend upon the altitude at which a cloud ingests air. Even allowing for complete mixing between SO2 rich boundary layer air and H2O2 rich trospospheric air (up to 600 mb), oxidant limited conditions existed on 9 out of 12 experimental days. Measurements were made in a area with high SO2 emission rates. According to previous SO2 monitoring data similar SO2 concentrations exist over a large area in the eastern U.S.