成都市区降雨中主要低分子有机酸及来源分析

Study of Low-Molecular-Weight Carboxylic Acids and their Resources in Precipitation in Chengdu

为了解成都市区降水中有机酸的化学组成特征及来源,2011年3月至9月共采降水36次,用液相色谱法检测了降水中的无机阴离子及低分子有机酸,同时测定样品的pH、电导率。用SPSS软件统计得到:有机酸的含量占总阴离子量的20.19%,对自由酸度的平均贡献值分别为31.55%。相比安顺、贵阳等地,成都市区降水中单位有机酸的酸度贡献值较小,可能是降水中的大量碱性杂质削弱了有机酸对酸度的影响。甲、乙酸占有机酸含量的93.6%,表明最主要的低分子有机酸是乙酸、甲酸。相关分析显示有机酸与所有阴离子显著相关,表明有机酸来源较复杂,多样化。进一步分析得到:甲酸与乙酸的相关系数(0.900)和偏相关系数(0.822)都很高,表明甲酸与乙酸有相似的来源或者不同来源的相似源强;甲酸与NO3-始终显著相关表明主要来自人为活动;乙酸与nss-SO24-始终显著相关表明主要来自间接源;草酸与甲酸、乙酸的偏相关系数很大程度上小于相关系数表明主要来自与甲、乙酸来源相似的前体物的光化学反应。

In order to know the composition and resources of Low-Weight-Molecular Carboxylic Acid in rain of Chengdu area, 36 rainwater samples were collected at Chengdu from March to September 2011. Then analyzed major inorganic anions and soluble low-molecular-weight carboxylic acids using liquid chromatography, tested pH, conductivities as well. The results showed that Low-Weight-Molecular Carboxylic Acids in rain took up 20. 5 percents of anions and had an average contribution to free acidity of 31.55%, but contribution of unit carboxylic acids to free acidity was lower than Anshun and Guiyang which indicated the acidity of earboxylic acids in precipitation was declined by alkalie impurities Besides, formic acid and acetic acid accounted for 93.6% of carboxylic acid indicating they are the foremost carboxylic acids. On the other hand, the eorrelafion analysis and partial correlation analysis showed there was a high correlation （p = 0. 01 ） between formic acid and acetic acid which implied they had a same resource or similar power. The significant correlation between formic acid and nss-SO4^2- showed that formic acid came from human activities mainly. Followed this regular, acetic acid was produced by many steps, the major oxalic acid generated from photochemical reaction of precursor which has a similar resource with formic acid.