Measurement of hydroperoxides and ozone in Oku-Nikko area

Hydroperoxides were measured at the Oku-Nikko observation station, which is situated at the foot of mountains where severe forest decline was observed. Hydrogen peroxides (H2O2) showed a diurnal variation with the maximum mixing ratio of 1.6 ppbv. The concentration of H2O2 was high in the daytime and low at night. The diurnal variation is caused by photochemical processes. Methylhydroperoxide (CH3OOH, MHP) was observed with an average mixing ratio of 0.1 ppbv. A strong correlation was observed between H2O2 and O3. High concentrations of H2O2 and O3 were observed in the late afternoon, which is considered to be due to the transport of polluted air masses from urban areas. The total amount of H2O2 to which the forest around the observation station was exposed was estimated to be 275 ppbv h between 18 July and 14 August, 2000.