Photochemical formation of OH radicals in dew formed on the pine needles at Mt. Gokurakuji

Photochemical formation rates and sources of the hydroxyl (OH) radical were determined in dew water formed on the surface of Japanese red pine (Pinus densiflora) needles of declining (NO₂ polluted area) and healthy pine stands at Mt. Gokurakuji located west of Hiroshima city in western Japan. The measured OH radical photoformation rates in dew water (n=10), which were normalized to the rate at midday on May 1 at 34° N, ranged from 0.67 to 5.18 μM h^-1 (1M=1mol L^-1). The mean value (2.69 μM h^-1) was higher than that in dew water collected on a Teflon board and higher than the mean value in rain water published previously. Of the total OH radical formation rate observed in dew water on the pine needles, 16.4% was estimated to originate from N (III) (NO₂^- and HNO₂) and 24.6% was estimated to originate from NO₃^-. There were other sources of OH radical photochemical formation in dew water on the pine needles besides photolysis of NO₂^- and NO₃^-.