The Research on The Dry Deposition of Sulfur Dioxide in The Loess Zone.

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During fiscal 2000-2002, we measured dry deposition velocity of sulfur dioxide and ozone in Beijing and Lanzhou City, Gansu in China with the overseas cooperative researchers belong to Sino-Japanese Friendship Center for Environmental Protection and Chinese Research Academy of Environmental Sciences. In the selection of sampling sites, the following items were considered; Convenience of the traffic, convenience. of the material supply, flatness of the ground, terrain information such as the area of the extent, earth surface condition including the vegetation, base line concentration of sulfur dioxide, representative wind velocity, mean temperature, humidity, etc. In both sites, measurement experiment of the deposition velocity was respectively carried out at two seasons using the meteorological gradient method and representative surface method using actual soil proposed by us. Still, both of Beijing and Lanzhou are yellow sand receptor region and air-polluted cities where the photochem … More ical smog was observed in China first. Thus, we can examine the dry deposition of the ozone to the loess with it of sulfur dioxide.The dry deposition velocity of sulfur dioxide and ozone was obtained by the meteorological gradient method. Still, the deposition velocity of sulfur dioxide was obtained with representative surface method. In comparison of dry deposition velocity for sulfur dioxide estimated the above two methods, generally, the gradient method gave higher velocity than the representative surface method In order to clarify control factor of the deposition velocity, laboratory exposure experiment of loess collected in Lanzhou to sulfur dioxide was carried out under single and coexistence condition of the ozone and humidity changed considering the consistency with the field measurement data. Though the sulfur dioxide deposition velocity did not change by the coexistence of the ozone, as a result of the analysis of depositing sulfur compound, the proportion that oxidation of [S(IV)→S(VI)] for deposited sulfur dioxide was done tended to increase, as the ozone concentration is higher, more. The deposition velocity of sulfur oxide increased, as the humidity is higher, and under the drying condition such as the actual observation, it became low deposition velocity further than the humidifying. Less