深圳市酸雨变化特征及形成原因分析

深圳市长年属于较重酸雨区，对城市生态带来重要影响，酸雨污染已经成为当前迫切需要解决的环境问题。为了了解近年来深圳市降水的变化特征及污染状况，利用2001—-2011年的降水监测数据，分析了降水酸化程度及化学组分特征，探讨了致酸原因，’为酸雨污染控制对策制定提供基础依据。研究结果表明，深圳市酸雨污染在2004--2006年达到较高水平（降水pH值4，49～4．59），2007年以来明显有所改善（降水pH值4．73～5．02），酸雨频率也显著降低。在时间变化上呈现夏季酸雨污染相对较严重，在空间变化上表现出宝安区和龙岗区酸雨污染相对较轻。相对于北京等城市，深圳市降水中离子浓度较低，同时大气中污染物浓度也较低，表明深圳市降水比较清洁，但由于大气中碱性物质含量较低，导致降水酸性较强。深圳市近年降水[SO42-]／[NO3-]的比值不断下降并低于2，硫酸硝酸混合型酸雨特征明显，表明机动车对降水酸性的影响不断增强。Cl-和Na＋对降水阴阳离子的贡献较高（分别达到24％和30％），反映降水受海洋的影响较大。深圳与广州、东莞、佛山等城市的降水酸度和酸雨频率变化趋势较为一致，区域传输对酸雨形成也有重要影响。

Variation characteristics and causes analysis of acid rain in Shenzhen city

Shenzhen city has been classified as heavy acid rain area for years. Due to the significant impact on urban ecology, controlling acid rain pollution has become an urgent issue need to address in Shenzhen. Based on the monitoring data from eight observation stations from year 2001 to 2011, this paper investigated the acidification feature, chemical composition of precipitation, and causes of acid rain in Shenzhen, which would provide fundamental basis for acid rain pollution control for the government. Results show that Shenzhen acid rain reached high pollution level during 2004 to 2006 （pH values of rainwater changed from 4.49 to 4.59）, and afterward the precipitation acidity and acid rain frequency reduced significantly since 2007 （pH values of rainwater changed from 4.73 to 5.02）. Acid rain occurrence was relatively more serious in summer for the seasonal variation, and showed relatively lighter pollution in Bao＇an and Longgang districts for the spatial distribution. The ions concentrations of rainwater, as well as air pollutants＇ concentrations, were both lower in Shenzhen compared to northern cities like Beijing, which indicated that precipitation in Shenzhen was much cleaner, and the determining factor leading to its strong acidity of precipitation was the low content of alkaline substances in atmosphere. [SO42-]/[NO3] ratio of rainwater has been declining and was less than 2 in recent years, reflecting sulfuric-nitrous mixed type of acid rain in Shenzhen, which also suggested the growing influence of vehicle emission on precipitation acidity. Besides, the contribution of CI＂ and Na＋ to rainwater chemical components was high （24% and 30% respectively）, implying the significant influence from marine environment nearby. Regional transportation also showed great impacts, as the annual trends of precipitation acidity and acid rain frequency in cities of Shenzhen, Guangzhou, Dongguan, Foshan were most consistent.