Concentrations of gaseous peroxides and other trace gases (O3, SO2) have beenmeasured near the summit ofmt. Norikura (altitude, 2770m) in central Japan, during summer and early autumn. Hydrogen peroxide (H2O2) and O3 reached themaximum concentrations atmidnight and theminimum atmidday. Themaximum concentrations of H2O2 and 03 appearing atmidnight are likely to be caused by subsidence from a higher atmospheric level. This tendency is quite opposite to that appearing in the low-altitude flat

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... . The ratio of [H2O2]/[SO2], which is a useful indicator of the oxidizing capacity from SO2(S(IV)) to H2SO4(S(VI)), was almost larger than 1 during summer. Thismeans that oxidant of SO2 is plentiful in the summer season and is likely to accelerate the heterogeneous oxidation in atmospheric water droplets.