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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 H 2 S ozone reaction rates which disagree with former determinations, predicting typical H 2 S 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 H 2 S 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. DOI: 10.1111/j.2153-3490.1974.tb01978.x

Observations are presented of the mean annual concentration and deposition of H + , SO 4 NO - 4 and NH + ions in precipitation in North America during 1980, the first year that a reasonably compatible merger of US and Canadian federal network data was possible. The maximum concentration and wet deposition of H + , SO = 4 and NO - 3 occurred in-and south of-the great lakes region near maximum anthropogenic emissions of sulphur and nitrogen oxides. The NH + 4 maximum, however, was located in the north central US where American livestock feedlots are concentrated. Peak H* concentrations were 60-80 μmole l -1 . In the region of maximum emissions, 1980 observations of H + , SO = 4 and NO - 3 wet deposition are within 25% of the 5-year mean for 1977-1981. The respective fraction of anthropogenic sulphur and nitrogen oxides released in eastern North America that are wet deposited in the same area is 24 ± 6 and 25 ± 6%. On a smaller scale, in the high sulphur and nitrogen oxide emissions area of the northeastern US. the deposition was 13 and 18% of emissions, respectively. Trends in emissions as well as in SO = 4 and NO - 3 concentrations in precipitation support the conclusion that a real increase in acidity of precipitation of 30-37 μmol l -1 has occurred in the southeastern US since 1955/56 DOI: 10.1111/j.1600-0889.1984.tb00253.x