广州白云山风景区酸雨梯度分布

THE RECENT STATUS OF ACID RAIN AT BAIYUN MOUNTAIN

对1999年白云山风景区l-10月的降水pH值、化学成分以及1月、6月大气低层的气溶胶进行了监测。分析结果表明：(1)白云山3个测点降水的平均pH值最低为4．83，最高为5．29；酸雨频率最低58％，最高9l％；强酸雨频率最低19％，最高39％。降水酸度和酸雨频率呈梯度变化，pH值随高度增高而减小，酸雨和强酸雨频率增加。(2)冬季近地层大气中偏碱性气溶胶在白云山的组成比较稳定，山上和山下测点气溶胶水溶性离子成分基本一致；而夏季山上、山下的成分有所不同，山上的SO4^2-比例明显增大。另外，尽管气溶胶中NO3^-的含量极少，但降水中NO3^-明显的富集现象。(3)白云山降水离子成分中SO4^2-占阴离子的比例最大、NO3^-次之；Ca^2+占阳离子的比例最大、NHd4^+稍低。随高度上升SO4^2-和Ca^2+在降水中的比例有所下降，而NO3^-和NH4^+比例明显增加，NO3^-和NH4^+对山上降水酸度的影响是相对增大的。(4)受附近公路交通的直接影响，白云山降水中的NO3^-比例较大，NO3^-／SO4^2-当量浓度比值平均达到0.4；NO3^-对白云山降水酸度有较大的贡献，而且这一贡献随高度而增大。

This paper analyzes the samples of rainwater from Jan. to Oct. 1999 at three monitoring sites of Baiyun Mountain and of aerosol composition in near-surface layer in Jan. and Jun. 1999 at two sites. The results suggest that (1) The pH value of rainwater is between 3.13 and 7.18, and the frequency of acid rain is more than 58 %. With the ascent of the monitoring sites, the pH value of rainwater decreases, and the frequency of acid rain increases. (2) In Jan., the chemical compositions of aerosol at different altitudes are similar, but in Jun. the acidity of aerosol rises at the higher site because of the increase of SO42-. (3) In rainwater, the proportion of SO42- is the most significant anion and Ca2+ is the most important cation, but both of them decrease as the altitude ascends. The proportion of NO3- and NH4+ rise at the higher site, and have more contributions to the acidity of rainwater. (4) As the impact of automobile emissions around Baiyun Mountain, the ratio of NO3-/SO42-molecular concentration reaches 0.40, and NO3- is relatively more important to the rain acidity at the higher site.