典型西南岩溶区工业城市降水酸化缓解原因探究——以柳州市为例

利用柳州市环境保护监测站2013—2017年大气降水监测数据,分析近年来柳州岩溶区工业城市降水酸化缓解原因,并对离子来源进行探究.结果表明:①统计柳州近5年的降水pH值发现研究区降水酸化问题有了明显的改善,同时具有季节性差异,春冬季降水酸化相对夏秋季较重.②通过分析降水中主要离子组成及变化特征、计算中和因子(NF)和相对酸度(FA)发现,降水中主要离子浓度出现减少趋势,酸化类型逐渐向硫-硝酸混合型过渡,且99.97%的酸性离子被NH~+_4、Ca~(2+)等离子所中和,所以得出酸性物质的减少和碱性离子的中和作用可能是降水酸化改善的重要因素.③采用Hysplit模型对研究区降水酸化较严重的2016年(共60场)的降水水汽来源进行后向轨迹追踪及聚类分析,显示降水离子组成与浓度不仅与当地污染源有关,还与来自大陆内部西北和西南远距离物质输送有关.上述结果指示由于喀斯特化学风化作用、柳州市严格执行环保规定、大环境改善导致远程传输污染减弱等原因使得柳州市降水酸化情况得到极大改善.此外值得注意的是柳州市酸雨类型逐渐向硫-硝酸混合型过渡,指示随着工业污染的控制得到减弱,日益增长的机动车尾气排放或许成为研究区下一步治理重点方向.

Mitigation of precipitation acidity in typical industrial areas of southwest Karst areas: A case study in Liuzhou

According to the monitoring data of atmospheric precipitation in Liuzhou from 2013 to 2017, the effects of acid precipitation and its mitigation in the typical industrial karst areas of Southwest China were analyzed to trace the source of ions for the history of acidic precipitation. Our findings revealed that, in the past five years, the pH values increased slowly and had the obvious seasonal variation (pH values were lower in winter and spring than those in summer and fall). In this respect, the main ionic composition and variation of precipitation, the neutralization factor (NF) and the fractional acidity (AF) indicated that the ionic concentration of precipitation was still sulfur type with a reducing trend to sulfuric-nitrous mixed type and the 99.97% acid ions were neutralized by NH₄⁺ and Ca²⁺ ions, suggesting that it might be the important factor to mitigating acid precipitation. Besides that, the Hysplit model was applied to trace and cluster the precipitation with 60 times in 2016. It was found that the compositions and concentrations of ions about Liuzhou precipitation were not only controlled by local pollution sources, but also were affected by the transmission distance of pollution sources from the northwest and southwest in the interior of continents. Talked together, our results revealed that the reduced acid precipitation in Liuzhou might be as a result of the combined action of karst chemical weathering, strict implementing environmental policy, and the reduction of long-term pollutant. It should be noted that the precipitation has a reducing trend to sulfuric-nitrous mixed type, suggesting that vehicle exhaust should be focused on the future.