ATMOSPHERIC HYDROGEN-PEROXIDE CONCENTRATION MEASURED AT OGASAWARA-HAHAJIMA-ISLAND IN THE SUBTROPICAL PACIFIC-OCEAN

Concentrations of gaseous H2O2 and O-3 have been measured at Ogasawara Hahajima Island located 1000 km south of Tokyo in April and July 1995 . In April, when the Ogasawara Islands was covered with the continenta l air mass, O-3 and H2O2 concentrations were high. Although O-3 concen tration in July was significantly lower than that in April: the mean H 2O2 concentration in July was higher than in April. This may be due to a difference in the solar radiation. Hydrogen peroxide concentration was usually higher in daytime than at night. However, the increases of H2O2 concentrations were somtimes observed in the nighttime when the relative humidity was low. The nocturnal decrease of H2O2 concentratio n was strongly dependent on the relative humidity; in other words, H2O 2 concentration is somewhat inversely proportional to the relative hum idity. The loss of H2O2 at night is caused by a heterogeneous process in the marine atmosphere. The heterogeneous loss rate was estimated at 0.3 to 6.5 x 10(-5) s(-1) and was greatly influenced by the relative humidity. This process may significantly affect HOX concentrations in the marine atmosphere.