中国典型城市大气降水离子特性、来源及其对环境的影响

Ionic characteristics and sources of atmospheric precipitation and its impacts on environment at typical cities in China

基于采样数据和东亚酸沉降监测网数据,对2019年华北、西北、西南、华东和华南地区典型代表城市的大气降水化学组分、酸度及其成因、湿沉降量和污染来源进行了研究,评估了降水对环境的生态效应.结果表明,离子总浓度在季节上表现为旱季明显大于雨季,空间分布特征为:北京(706.87μeq/L)>西安(369.26μeq/L)>重庆(265.17μeq/L)>厦门(244.54μeq/L)>珠海(134.31μeq/L)>五指山(81.88μeq/L).NH_(4)^(+)、Ca^(2+)、SO_(4)^(2-)和NO_(3)^(-)是内陆城市降水中最主要的离子成分,而Cl^(-)和Na^(+)在沿海城市中占比较大.华北城市降水主要呈中性,酸雨事件仅占全年降水事件的2.3%;西北城市降水呈弱碱性,没有出现酸雨事件;而西南城市酸雨问题严重,城区站点和乡郊站点酸雨频率分别为30.3%和80.3%,且季节变化明显;华东城市城区站点降水主要呈中性,偏远地区站点酸雨问题严重,全年酸雨率高达99%;华南城市夏季降水主要呈中性,其余季节均为酸性,全年酸雨事件占总降水的62.2%.中和能力分析表明酸雨问题严重的地区,主要是由降水中碱性成分不足导致的.受降雨量影响,各城市氮和硫湿沉降量在季节上表现为雨季大于旱季,并且在雨季对生态环境有重要的促进作用.中国氮和硫湿沉降量均呈现出从东部向西部、沿海向内陆递减的空间分布特征.不同城市降水离子来源及贡献差异较显著,尤其是酸雨问题严重的城市,其以Ca^(2+)和Mg^(2+)为主的扬尘源贡献小于以SO_(4)^(2-)和NO_(3)^(-)为主的二次源贡献.

Based on the observation data from sampling and the data from the Acid Deposition Monitoring Network in East Asia,the chemical composition,acidity and its causes,wet deposition fluxes,and pollution sources of atmospheric precipitation at typical cities in North,Northwest,Southwest,South and East China in 2019 were studied,and the ecological effects of the precipitation on the environment were evaluated.The results showed that the total ion concentrations in the precipitations showed an obvious seasonal variation with the order of dry season>rainy season,and also presented a significant spatial distribution with the order of Beijing(706.87μeq/L)>Xi'an(369.26μeq/L)>Chongqing(265.17μeq/L)>Xiamen(244.54μeq/L)>Zhuhai(134.31μeq/L)>Wuzhishan(81.88μeq/L).NH_(4)^(+),Ca^(2+),SO_(4)^(2-)and NO_(3)^(-)were the main ions of precipitation in the inland cities,while Cl^(-)and Na^(+)had a higher fraction in the coastal cities.The precipitation at the city in North China was mainly neutral,with acid rain events only accounting for 2.3%of the annual precipitation.The precipitation at the city in Northwest China was weakly alkaline,without any acid rain events occurring.The acid rain problem at the city in Southwestern China was severe,with acid rain frequencies reaching 30.3%and 80.3%at the urban and suburban stations,respectively,and presenting significant seasonal changes.The precipitation at the urban station in the city of East China was mainly neutral,however the acid rain problem at the station in remote area was extremely severe,with an annual acid rain rate of 99%.The summer precipitation at the city in Southern China was mainly neutral,while the other seasons were all acidic,and acid rain events accounted for 62.2%of the total precipitation events throughout the entire year.The neutralization capacity indicated that the areas with severe acid rain problems were mainly due to insufficient alkaline components in precipitation.Influenced by precipitation,the wet deposition fluxes of nitrogen and sulfur in each city were larger in the rainy season than those in the dry season,and played an important role in promoting the ecological environment in the rainy season.The wet deposition fluxes of nitrogen and sulfur in China showed a spatial distribution pattern decreasing from the east to the west and from the coastal areas to the inland areas.There were significant differences in the sources and contributions of precipitation ions in different cities,especially in cities with severe acid rain problems.The contribution of dust sources mainly composed of Ca^(2+)and Mg^(2+)to precipitation was smaller than that of secondary sources mainly composed of SO_(4)^(2-)and NO_(3)^(-).