Abstract：
Rainwater chemistry was investigated at a semi-rural site in Ya\'an, Sichuan basin with rain samples collected from May 2013 to July 2014. The rainwater pH values ranged from 3.25 to 6.86, with an annual volume-weighted mean (VWM) of 4.38, and the acid rain frequency was 74 %. Such severe acidification, 15 % of the total events showed a pH below 4.0, attributed to the deficiency of Ca(2+), significant anthropogenic pollution contribution, and rainy pattern to this area. The annual VWM of total ions concentration was 477.19 μeq/L. NH4 (+) was the most abundant ionic species, followed by SO4 (2-), NO3 (-), Ca(2+), Cl(-), Na(+), K(+), Mg(2+), and F(-) in a descending order. The total ionic concentrations presented a seasonal trend of lower values in autumn and summer but higher ones in winter and spring. Based on enrichment factor, correlation analysis and principle component analysis, three factors were identified: factor 1 (NH4 (+), SO4 (2-), NO3 (-), K(+), and Cl(-), 47.45 % of the total variance) related to anthropogenic sources (coal/fuel combustion, biomass burning and agriculture), factor 2 (Ca(2+), Mg(2+), Na(+), and Cl(-), 34.01 % of the total variance) associated with natural sources, and factor 3 (H(+), 11.78 % of the total variance) related to free acidity. Back trajectory analysis indicates that the rainwater chemistry in Ya\'an was mainly affected by regional air masses from Sichuan basin. Long-range transported air masses from southwest with heavy anthropogenic pollution increased the total ion concentration and acidity of rainwater. Considering its special topography, anthropogenic emissions from regional and long-range transport (especially from southwest) must be controlled effectively to improve the acid rain condition of non-urban areas in Sichuan basin.
摘要：
在雅安的半农村地区调查了雨水化学，2013年5月至2014年7月采集的四川盆地雨样。雨水pH值范围为3.25至6.86，年体积加权平均值（VWM）为4.38，酸雨频率为74％。如此严重的酸化，总事件的15％显示pH低于4.0，归因于Ca（2）的缺乏，显著的人为污染贡献，和这个地区的多雨模式。总离子浓度的年VWM为477.19μeq/L。NH4(+)是最丰富的离子种类,其次是SO4(2-)，NO3(-),Ca(2+),Cl(-),Na(+),K(+),Mg(2+),和F(-)按降序排列。总离子浓度呈现季节性趋势，秋季和夏季较低，而冬季和春季较高。基于富集因子，相关分析和主成分分析，确定了三个因素：因素1(NH4(+)，SO4(2-),NO3(-),K(+),和Cl（-），总方差的47.45%)与人为源(煤/燃料燃烧，生物质燃烧和农业)，因子2(Ca(2+)，Mg(2+),Na(+),和Cl（-），总方差的34.01%)与天然来源相关，和因子3(H(+)，总方差的11.78%)与游离酸度相关。反轨迹分析表明，雅安雨水化学主要受四川盆地区域气团的影响。来自西南的远距离运输气团人为污染严重，增加了雨水的总离子浓度和酸度。考虑到其特殊的地形,必须有效控制区域和远距离运输（尤其是西南）的人为排放，以改善四川盆地非城市地区的酸雨状况。
