乌鲁木齐市酸雨变化特征及其与气象因子的关系

利用1992-2018年乌鲁木齐国家基本气象站酸雨监测资料共1316个采集样品，统计分析降水样品中pH值和K值变化特征及其与气象因子的关系。结果表明：近27 a乌鲁木齐市年平均pH值为6.64，酸雨发生频率仅为4.56%，大气降水主要以中性和碱性降水为主，年平均pH值呈微弱的上升趋势，且pH值在1998年发生突变，在四季中从大到小顺序为：夏季>秋季>春季>冬季；采样期间，年平均K值为90.40 μs·cm^-1，且呈下降趋势，2001年发生突变，在四季中由高到低的顺序与pH值相反，即：冬季>春季>秋季>夏季；乌鲁木齐市出现酸雨时地面和高空风向以偏北风为主，pH值与风速呈正相关，K值与降水量呈负相关；由于近年来乌鲁木齐市在采暖季实行"煤改气"，大大减少煤炭的用量，使大气所含SO₂等含硫化合物明显减少，其次是近年来市政府加大了对环境污染治理，酸雨出现频率较2007年以前有明显减少。

Variation characteristics of acid rain and its relationship with meteorological factors in Urumqi

Using the acid rain monitoring data of 1316 samples from the national basic meteorological stations in Urumqi from 1992 to 2018, the variation characteristics of the pH and K values in precipitation samples and their relationship with meteorological factors were analyzed.The results showed that in recent 27 years, the average annual pH value is 6.64.The acid rain frequency is only 4.56% and the precipitation in Urumqi is mainly neutral and alkaline.The average annual pH values show a slightly increasing trend and change abruptly in 1998.During the sampling period, the average annual K value is 90.40 μs·cm^-1 and shows a decreasing trend.The mutation occurs in 2001.The sequence of K values from high to low in the four seasons are opposite to the pH value, namely, winter, spring, autumn, and summer.When acid rain occurs in Urumqi, the northerly wind direction on the ground and at the upper layer is dominant.The pH value is positively correlated with wind speed, while the K value is negatively correlated with precipitation.In recent years, the implementation of "replacing coal with gas" in the heating season in Urumqi has greatly reduced the consumption of coal, resulting in a significant reduction of sulfur compounds such as SO₂ in the atmosphere.Besides, the municipal government has intensified its control of environmental pollution in recent years, and the frequency of acid rain has been significantly reduced compared with that before 2007.