桂林市酸雨污染特征及防治对策研究

为促进桂林市酸雨污染防控，利用2013—2017年桂林市3个监测站点采集的共1 147个降雨样品，分析了降雨pH、电导率和水溶性离子成分，结合气态污染物的变化特征和气象因素影响分析，探讨了桂林市酸雨污染成因，并提出了桂林市酸雨污染防治对策建议.结果表明:①2013—2017年桂林市降雨的pH年均值范围为4.85~5.23.酸雨频率范围为42.5%~74.9%，2017年酸雨频率达74.9%.虽然近年来桂林市环境空气质量明显改善，但是酸雨污染却没有明显减轻，反而在2015年后出现恶化.降雨的离子组成中，SO₄2-和NO₃-是主要的阴离子成分，分别占总离子当量浓度的28.19%和10.82%；Ca2+和NH₄+是主要的阳离子成分，分别占总离子当量浓度的23.46%和17.64%.酸中和效应分析显示，Ca2+和NH₄+为降雨中主要的中和物质.②降雨中碱性离子当量浓度的降幅比酸性离子当量浓度的降幅大，这是导致桂林市近年酸雨恶化的重要因素；此外，来自西部和东南部方向的气流对应了较高的降雨酸度和总离子当量浓度，因此污染物的远距离传输对降雨酸度和离子当量浓度也有一定影响.研究显示，桂林市SO₂和NO_x排放的持续管控将有利于酸雨污染防治，但桂林市目前实施的削减大气粗颗粒物和NH₃排放的大气污染控制策略对于降雨酸度的影响还需要开展进一步评估. 

Pollution Characteristics and Control Countermeasures of Acid Rain in Guilin

In order to promote the prevention and control of the acid rain pollution in Guilin, China, the pH, conductivity and water-soluble ionic components of rainfall were obtained by measuring 1147 rainfall samples collected from three observation stations in Guilin from 2013 to 2017. Combining with the analyses of the variation characteristics of gaseous pollutants and the influence of meteorological factors on acid rain, the cause of acid rain pollution in Guilin was investigated and suggestions for acid rain pollution control were put forward. The results showed that: (1) The annual mean pH values ranged from 4.85 to 5.23 in Guilin from 2013 to 2017, and the frequency of acid rain was 42.5% to 74.9%, it reached 74.9% in 2017. Although the overall ambient air quality in Guilin improved in recent years, the acid rain pollution did show down a trend. On the contrary, it began to deteriorate after 2015. The anion composition of the rainfall was mainly SO₄^2- and NO₃^-, accounting for 28.19% and 10.82% of the total ion equivalent concentration, respectively; Whereas, cations composition of the rainfall was dominated by Ca²⁺ and NH₄⁺, accounting for 23.46% and 17.64% of the total ion equivalent concentration, respectively. Acid neutralization effect analyses showed that Ca²⁺ and NH₄⁺ were the main neutralizing factors. (2) The significant reduction in the equivalent concentration of alkaline ions in rainwater compared to acid ions, which is an important factor causing the deterioration of acid rain in Guilin in recent years. Moreover, the long-distance transmission of pollutants also had a certain impact on rainfall acidity and ion concentrations because the airflow trajectories from the west and southeast directions corresponded to relatively higher rainfall acidity and total ion concentration. The research showed that continuous control of SO₂ and NO_x emissions will be beneficial to the control of acid rain pollution in Guilin, but the impact of current implementation of air pollution control countermeasures to reduce the emission of atmospheric coarse particulate matter and NH₃ on rainfall acidity needs to be further evaluated.