Some recent measurements of H2S oxidation rates and their implications to atmospheric chemistry1

The general belief that significant fractions of atmospheric sulfur are donated naturally from the earth’s surface in the form of hydrogen sulfide and/or its organic homologs implies that atmospheric breakdown of these materials must be a rather fast process. It has been expected that oxidation of these materials by atmospheric ozone should contribute significantly in accomplishing this breakdown; and experimental measurements have been published which do, indeed, indicate rapid ozone oxidation rates, corresponding to lifetimes of the order of hours under typical tropospheric conditions. This paper discusses some later experimental measurements on H₂S ozone reaction rates which disagree with former determinations, predicting typical H₂S lifetimes of the order of months—much too long for this reaction to be a significant mechanism of atmospheric removal. The results also indicate the H₂S ozone reaction should be expected to proceed homogeneously in the atmosphere, with catalytic effects being of little or no importance. The reaction proceeds thermally; light in the visible region does not affect its rate appreciably. These measurements indicate that some mechanism(s) other than ozonation must be responsible for atmospheric breakdown of reduced sulfur compounds. Final portions of the paper examine some possibilities for these mechanisms.