北京市酸雨变化趋势及成因分析

1993-2002年中国气象局酸雨观测站网在北京地区有两个观测站,2003年增至3个。根据北京3个酸雨观测站的有关资料,研究了北京市酸雨变化的特征及成因。研究结果表明:第一,1993-2007年北京地区降水酸度呈现两个阶段,即1993-2002年降水酸度稳定在较弱水平,而2003-2008年呈逐年增强趋势。第二,与2003年以前相比,2003年以后硫酸根和硝酸根离子浓度均呈明显增加趋势,二者比值逐步下降并低于3,这表明北京乃至华北地区的酸雨已由硫酸型转为硫酸与硝酸并重型。第三,北京周边省、市二氧化硫年排放量的增加及钙离子和可吸入颗粒物浓度减少是近年来北京地区酸雨增强的人为原因。第四,气象条件是酸雨发生的主要动力因素。一般情况下,在地面风速较小的季节酸雨频率较高,850hPa高度为弱的偏南风或发生低层逆温时可促进酸雨的发生。此外降水量的大小也与酸雨有密切关系,24 h降水量达暴雨量级时酸雨频率最高。

Variation trend and cause analysis of acid rain in Beijing Municipality

The acid rain observation network operated by China Meteorological Administration(CMA) contains 2 stations in 1993 through 2002 in Beijing area,and it was increased to 3 in 2003.According to monitoring data from the three observation stations,this paper studies the characteristic and causes of acid rain variation trend in Beijing.Four conclusions are made from the study.First,the precipitation acidity between 1993 and 2008 in the distinct has two different stages: From 1993 to 2002,it remains at low level,but gradually increases after 2003.Second,compared to the period before 2003 in Beijing and even in north China,the annual mean concentration of sulfate radical ion(SO-24) and nitrate radical ion(NO-3) obviously increases after 2003,and the ratio of two gradually decreases until less than 3,which indicates that the acid rain components have changed from sulfate to sulfate combined with nitric acid.Third,the increase of sulfur dioxide(SO2) emission and the decrease of the calcium ion and concentration of(PM10) around Beijing are human reasons of the aggravation of the acid rain in Beijing area in recent years.Fourth,climatic condition is the main drive to the occurrence of acid rain.Generally,lower speed of ground wind,weak south wind at 850 hPa,and inverse temperature under low level facilitate the occurrence of the acid rain.In addition,acid rain is closely related with the precipitation,e.g.,its frequency reaches the peak when the 24-hour precipitation accumulates to rainstorm level.