中文摘要：

降雨化学成份的变化间接反映大气污染特征,是研究大气环境及沉降物影响的重要途径.本文比较了2013与2014年雨季北京市区到郊县延庆4个样点上降雨成份的时空差异,并结合PMF模型分析了各主要离子的可能来源.结果表明,4个样点降雨pH中值分别为6.52、6.57、6.60、6.52,从市区到远郊略有增加.各离子浓度都是春秋季高,夏季低.降雨中各离子的雨量加权平均浓度（VWM）表现为：Ca2＋、NH_4＋、SO_42-较高,分别在100-400μeq·L^-1、100-350μeq·L^-1、150-500μeq·L~--1之间,Mg2＋、Na＋和NO_3-分别在0-150μeq·L^-1、0-250μeq·L^-1、0-150μeq·L^-1之间,K＋和Cl-较低,分别在0-45μeq·L^-1、0-90μeq·L^-1之间.NH_4＋、Mg2＋的VWM从市区到郊区递减,K＋、SO_42--S、Na＋、NO_3呈近郊区略有增大,远郊区全部减小的趋势.SO_42-是主要的致酸离子,Ca2＋、NH_4＋和Mg2＋对雨水中酸根离子的中和因子平均值分别为0.5、0.4和0.1.市区BNU点SO_42--S（以S计）与Ca2＋的沉降量分别为55.66 kg·hm-2·a-1和24.10 kg·hm-2·a-1,在远郊YQ点为26.03 kg·hm（-2）·a-1和10.84kg·hm-2·a-1.NH_4-＋-N与NO_3-N的沉降量在4点的变化范围为7.27-14.05 kg·hm-2·a-1及2.50-5.07 kg·hm-2·a-1.Mg2＋和Cl^-从市区到远郊分别在1.32-4.48 kg·hm-2·a-1及3.67-6.10 kg·hm-2·a-1之间变化.所有离子以湿沉降为主,沉降量与相应的降雨量变化较为一致.根据PMF模拟结果,4点的地面扬尘和建筑源污染均较高,市中心尾气污染最严重,近市区二次源污染严重,近郊区氮污染严重,远郊区受养殖场、垃圾源等的NH_3排放影响较大.

英文摘要：

Changes of chemical composition of rainfall can indirectly reflect the characteristics of atmospheric pollution. This study explores the spatial and temporal variations of chemical composition in rainfall from four sites along an urban-to-rural transect in Beijing during rainy season in 2013--2014. Meanwhile, possible sources for major ions are identified by PMF model. Results show that the pH values of rainfall at four sites are 6.52, 6.57, 6.60 and 6.52, with slight increases from urban to rural site. Ion concentrations are high in spring and fall but low in summer. VWM of main ions can be separated into three groups. Higher concentration group includes Ca2＋ , NH＋ and SO2-4 with VWM between 100-400 μeq.L-1 , 100-350 μeq.L-1 , and 350-500 μeq.L-1 , respectively. Middle concentration group includes Mg2＋, Na＋ and NO-3 with VWM in the range of 0-150 μeq-L-1 , 0-250 μeq.L-1 , and 0- 150 μeq. L-1 , respectively. K＋, CI- are in lower concentration group, with VWM in the range of 0 - 45 μeq. L-1 and 0 - 90 μeq.L-1, respectively. VWM of NH＋ and Mg2＋ decreases from urban to rural area. SO2-4 is the major acid ion while Ca2＋, NH＋ and Mg2＋ are major neutralizing ions with average neutralization indices of 0.5, 0.4 and 0.1, respectively. Deposition fluxes of S024- and Ca2＋are 55.66 kg.hm-2.a-1 and 24.10 kg.hm-2.a-1 at BNU and 26.03 kg-hm-La-1 and 10.84 kg.hm-2.a-1 at YQ, respectively. Deposition flux of nitrogen in ammonium and nitrate at four sites change from 7.27 to 14.05 kg-hm-2.a-1 and from 2.50 to 5.07 kg.hm.La-1, respectively. Flux of Mg2＋ and C1- change between 1.32-4.48 kg.hm-2, a-1 and 3.67-6.10 kg .hm-2.a-1 at four sites, respectively. Wet deposition is the major form of ion settlement, and co-varies seasonally with rainfall. PMF simulations show that dust and construction associated pollutants are high at the four sites. Vehicle emissions are serious in the downtown area. Secondary pollution is serious at urban site. The suburban site is greatly influenced by NH3 emission from far