乌鲁木齐市米东区大气降水的化学特征及来源分析

Chemical characteristics and source apportionment of atmospheric precipitation in Urumqi City

为研究乌鲁木齐市米东区大气降水中的化学组分特征及来源,对2017—2019年降水中主要离子浓度及来源进行了分析。研究结果显示,米东区2017—2019年降水的雨量加权pH年均值为7.95,雨量加权平均电导率年均值为16.15 mS·m^(-1),雨量加权平均总离子浓度为72.75—95.89µeq·L^(-1),年均浓度为81.93µeq·L^(-1)。降水中各离子的雨量加权平均浓度顺序为SO_(4)^(2-)>Ca^(2+)>C^(l-)>Na+>NO_(3)^(-)>NH_(4)^(+)>K^(+)>Mg^(2+)>F^(-),浓度最高的阴、阳离子分别为SO_(4)^(2-)(29.01µeq·L^(-1))、Ca2+(21.91µeq·L^(-1)),二者对总离子浓度的贡献分别为35.41%、26.74%。总离子浓度按季节排序为冬季>夏季>秋季>春季。[SO_(4)^(2-)/NO_(3)^(-)]平均值为7.51,SO_(4)^(2-)对雨水酸度的贡献率逐渐减弱,NO_(3)^(-)的贡献率逐年增加,降雨的酸化类型为硫酸型,但具有逐步向硝酸型转变的趋势。中和降水中酸性组分的主要碱性离子为连续3年占比最高且稳中有升的Ca^(2+)离子。Ca^(2+)、Mg^(2+)、Na^(+)、Cl^(-)、SO_(4)^(2-)、NO_(3)^(-)之间存在着较为显著的相关性,说明上述离子有相似的来源并形成化合物共同存在。Ca^(2+)在大气中优先与SO_(4)^(2-)、NO_(3)^(-)结合,且Ca^(2+)对雨水酸性的中和贡献率大于NH_(4)^(+),表明乌鲁木齐市米东区大气降水中可能存在以CaSO_(4)和Ca(NO_(3))_(2)为主的化学物质。

To investigate the characteristics and sources of chemical compositions of precipitation in the Midong district of Urumqi,the concentration and sources of major ions in the precipitation collected during the period from 2017 to 2019 were analyzed.The results showed that the annual weighted mean pH of precipitation was 7.95,and the annual weighted mean conductivity of precipitation was 16.15 mS·m^(-1).The variation range of total ion concentrations in precipitation was 72.75—95.89µeq·L^(-1),with the annual weighted average concentrations of 81.93µeq·L^(-1).The weighted mean concentration of precipitation components followed the order SO_(4)^(2-)>Ca^(2+)>Cl^(-)>Na^(+)>NO_(3)^(-)>NH_(4)^(+)>K^(+)>Mg^(2+)>F^(-),the highest contents of anion and cation was SO_(4)^(2-)(29.01µeq·L^(-1))and Ca^(2+)(21.91µeq·L^(-1)),the contribution of total ion concentration was 35.41%and 26.74%,respectively.The order of concentration of total ions was winter>summer>autumn>spring.The mean ratio of theSO_(4)^(2-)/NO_(3)^(-)was 7.51,and the ratio of NO_(3)^(-)had increased year by year,which indicated that precipitation of Urumqi City belonged to sulfuric acid,and might gradually evolve from a sulfuric acid to nitric acid type.The significant correlation among Ca^(2+)、Mg^(2+)、Na^(+)、Cl^(-)、SO_(4)^(2-)and NO_(3)^(-)indicated their similar sources or the formation of compounds with them.Ca^(2+)was preferentially combined with SO_(4)^(2-)、NO_(3)^(-)in the atmosphere,and the contribution of Ca^(2+)to the acid neutralization of rainwater was greater than NH_(4)^(+),indicated that the chemical compositions of precipitation were mainly existed in the form of CaSO_(4) and Ca(NO_(3))_(2).