关键词: 西宁地区, 大气混合厚度, 逆温, 大气稳定度, pH值

Abstract: Xining is one of the most severe cities suffered from air pollution in China, where pollution is especially heavy in winter and spring time. The heaviest air pollution more than five grades will happen in Xining when super-severe dust storms occur in springtime. In this paper, the meteorological characteristics about air pollution such as inversion, mixing depth and atmospheric stability were analyzed based on routine meteorological data from Xining observational station during January 2000 to December 2002. The analyzed results are as follows: The annual variation phase of monthly occurrence days of inversion is opposite to that of monthly mean mixing depth in Xining. Usually the sum of monthly occurrence days of inversion ranges from 15 to 24 days in cold half of a year but only from 7 to 12 days in warm half of a year. Monthly mean mixing depth is high in warm half of a year but low in cold half of a year. The maximum of them is in summer and the minimum is in winter. So it is an important reason that air pollution is heavier in winter than in summer in Xining City. In addition, the pH value of precipitation in Xining is the highest in May and June. This phenomenon is relative with frequent occurrence of dust-storm there at that time, because the dust from dust-storm can depress the acidification of precipitation due to air pollution. Besides, the improvement of atmospheric diffusion condition in summer is also beneficial to reducing air pollution. This can decrease the acidification of rainfall.

Key words: Xining city, atmospheric mixing depth, temperature inversion, atmospheric stability, pH value of precipitation