长江源区大气降水化学特征及离子来源

Chemical Characteristics and Ionic Sources of Precipitation in the Source Region of the Yangtze River

基于长江源区冬克玛底流域2013年6~9月采集的64个降水样品,分析了降水的pH值、电导率及离子浓度特征,并应用因子分析、相关分析、富集因子及后向轨迹法,讨论了降水离子主要来源及其与大气环流的联系.结果表明,长江源区冬克玛底流域降水pH值变化范围为5. 26~9. 25,加权平均值为6. 70;电导率变化范围为0. 23~28. 70μS·cm-1,加权平均值为3. 45μS·cm-1,低于瓦里关全球大气本底站降水电导率;总离子浓度变化范围为7. 0~376. 9μeq·L-1,平均总浓度仅为40. 8μeq·L-1;各离子加权平均浓度大小顺序为:HCO3-> NH4+> Ca2+> NO3-> SO42-> Na+> Cl-> K+> Mg2+;HCO3-、NH4+、Ca2+和NO3-是降水中的主要离子,占总离子浓度的74. 75%;相对酸度(FA)分析表明,有97. 8%的降水酸度被碱性物质中和,同时中和因子(NF)分析表明NH4+和Ca2+对降水酸性的中和起主导作用;研究区降水离子主要来自陆源的贡献,而来自海源的输入则相对较少;结合气团的后向轨迹分析发现,不同来源的总离子浓度差异明显,其加权平均浓度大小顺序为:局地源>西风源>季风源,表明不同的大气环流背景和气团来源对降水化学组成具有重要影响.长江源区大气降水受人类活动影响较小,其降水化学特征一定程度上可以代表偏远地区的大气质量状况和本底值.研究结果能够为长江源区水质的保护以及为评估人类活动对该区域大气环境的影响提供科学依据.

Using 64 precipitation samples collected from June to September 2013 in the Dongkemadi Basin in the source region of the Yangtze River,the pH,conductivity,and main ionic concentration characteristics of precipitation were analyzed.The main ionic sources of precipitation and their relationships with atmospheric circulation were examined using factor analysis,correlation analysis,enrichment factor analysis,and backward trajectory analysis.The results showed that the range of precipitation pH values varied from5.26 to 9.25 with a weighted average of 6.70,and conductivity ranged from 0.23 to 28.70μS·cm-1 with a weighted average of 3.45μS·cm-1.The conductivity of precipitation was lower than for the Mt.Waliguan basin(China Global Atmosphere Watch baseline observatory).The total ionic concentrations in the precipitation ranged from 7.0 to 376.9μeq·L-1 with a weighted average of 40.8μeq·L-1.The ranked order of ionic concentrations was HCO3->NH4+>Ca2+>NO3->SO24->Na+>Cl->K+>Mg2+.HCO3-,NH4+,Ca2+,and NO3-were the dominant ions,which accounted for 74.75%of the total ionic concentration.Fractional acidity(FA)analysis showed that 97.8%of the precipitation acidity was neutralized by alkaline constituents.Neutral factor(NF)analysis indicated that NH4+and Ca2+were the dominant neutralization constituents in the precipitation.The precipitation ions in this study area were mainly derived from terrestrial material,while input from marine sources was relatively low.Backward trajectory analysis revealed that the total ionic concentrations varied significantly between the different sources,which followed the order of local sources>westerly sources>monsoon sources.This indicates that different atmospheric circulation conditions and air mass sources have a significant influence on the chemical composition of precipitation in this area.To some extent,the chemical characteristics of precipitation could reflect the air quality and background values for remote areas due to the limited effect of human activities.The results of this study provide a scientific basis for the protection of water quality and the assessment of the impact of human activities on the atmospheric environment in the source region of the Yangtze River.