| Abstract: | There is an appreciable chemical interaction between SO2 and photochemical smog which depends on the concentration of SO2 and water vapor. The rate of decay of SO2 concentration is greatly increased in the presence of photochemical smog. With 0.75 ppm SO2, a light-scattering aerosol is produced in dry systems and systems at 22 and 55% relative humidity (RH). Aerosol is not observed until after the NO2 peak has been reached and the NO concentration has fallen to a very low value. The formation of aerosol corresponds in time to the region of most rapid decrease in the SO2 profile. In systems at 65% RH or with smaller amounts of SO2, no light scattering is observed, but the percentage of SO2 disappearing is greater. In relatively dry systems the presence of SO2 results in a general slowing down of the photochemical smog reactions. In systems containing water vapor concentrations comparable to those found in the atmosphere, the inhibiting influence of SO2 on the smog reaction is less pronounced. However, the maximum concentration of oxidant produced by the photochemical smog reactions is significantly lower when SO2 is present. |
