Measurement of atmospheric aqueous phase OH radical and the elucidation of its toxic effects on higher plants

点击翻译按钮获取中文摘要

Chemistry of atmospheric aqueous phase hydroxyl radical (OH radical) and its toxic effects on the physiological status of higher plants have been investigated in this study. Analytical technique for automatic, rapid and sensitive measurement of aqueous phase OH radical was firstly developed and it was successively applied to the analysis of rain and dew samples. Identifications of sources of atmospheric aqueous phase OH radical indicated that nitrate, nitrite and Fenton reaction (involving hydrogen peroxide and dissolved iron species) are major sources of OH radical in rain, dew samples whereas unknown sources of OH (sometimes up to 50%) remain to be elucidated. The ppb level of nitrite existed in bubbling solution of the exhaust gas of diesel cars produced uM/h of OH whereas almost no OH generated in that of gasoline cars. From our studies, it can be concluded that atmospheric aqueous phase OH radical is originated from OH producing substances including nitric acid (nitrate), nitrous … More acid (nitrite), hydrogen peroxide with iron species occurring in the atmosphere and one of important anthropogenic sources of OH producing substances may be diesel exhausts. Decrease of photosynthetic activity and stomata conductance at leaf level and the decrease of biomass at individual level were observed when the OH radical generating solution (photo-Fenton reagent) that was fumigated on needles of red pine seedlings for 2-3 months. Interestingly, the influence of OH much diminished when mannitol (radical scavenger) was added into the fumigating solution in the exposure experiment and thus mannitol effectively controlled the toxic effect of OH to pine trees. Moreover, a growth model for pine trees showed that the decrease of photosynthetic production of pine needles with OH radical exposure would reduce biomass quantity and finally cause the death of tree after year-to-year exposure of OH producing substances. A numerical simulation examined emission trends of nitrogen oxides and sulfur dioxide from various anthropogenic sources in Hiroshima prefecture. In the prefecture, stationary sources such as iron and steel industry are major emitters of these pollutants. However, with the development of new technologies for saving the energy and cost, the emission of these pollutants will be lower by 20-30% from 1990 to 2010. This decrease of major air pollutant emissions would result in significant improvement of air pollution in the prefecture and thus further pine forest decline would be unlikely. Less