MEASUREMENT, BEHAVIOR AND ROLE OF REACTIVE OXYGEN SPECIES IN ATMOSPHERIC WATER DROPLETS AND NATURAL WATER

We analyzed hydrogen peroxide and OH radical as one of reactive oxygen species in cloud, snow, dew and natural waters in Hiroshima prefecture and in the Seto Inland Sea, western Japan to elucidate distribution, behavior and their effects to plant growth. Hydrogen peroxide was measured by fluorometry and OH radical was measured by chemical trap method. Concentration levels of hydrogen peroxide and OH radical were in range of nM to mM and 10^-18 to 10^-15M, respectively, in atmospheric water droplets and natural waters. Major source of hydrogen peroxide was the photochemical production in gas-phase followed by transfer to aqueous phase or aqueous phase generation by photochemical reactions involving photosensitized organic matter like fluorescent organic matter, whereas nitrite, nitrate, fenton reactions (involving hydrogen peroxide and Fe(II)) and fluorescent organic matter were sources of OH radical. Fluorescent organic matter contributed to most of OH production in rain, river and seawaters studied, whereas nitrite, nitrate and fenton reactions were major contributors for the radical production in dew, and natural spring water. Open top chamber experiment was conducted to elucidate direct effect of these reactive oxygen species to physiological status of Japanese red pine tree (Pinus densiflora). One to three months fumigation (three times per week) of these compounds dissolved in mist solution to pine seedlings indicated that 10-20% decrease of photosynthesis and significant closing of stomata were found when OH radical producible solution (photo-fenton reagents composed of hydrogen peroxide,Fe(III)and oxalic acid) was fumigated, whereas there was no such physiological change when same amount of hydrogen peroxide was only fumigated. The concentration levels of fumigated chemical substance used in this study was almost same levels found in atmospheric water droplets such as dew formed on pine needles at pine forests in Hiroshima Prefecture, where significant decline of pine forest was found during last decades. We found that automobile exhaust gas can generate OH radicals up to 10mM/hr m³ in aqueous phase and thus recent increase of emission of automobile exhausts might contribute the pine tree damage and decline of pine forests.