上海大气冷凝水化学特性分析

Analyses on chemical characteristic of air condensation water in Shanghai

2011年3月8日至4月11日期间利用新研制的大气冷凝水采样器收集了上海大气冷凝水样品.从冷凝水的化学组成及常见大气湿沉降的比较、冷凝水离子间的相关性、冷凝水离子浓度随时间变化等方面,分析了上海大气冷凝水的化学特性.结果表明,上海大气冷凝水pH值介于6.1~7.2,加权均值为6.5,多呈弱酸性;NH4+和SO42-是含量最高的2种离子,浓度分别为139.7μeq/L和125.7μeq/L,SO42-是主要致酸离子;NO2-含量为9.9μeq/L,比NO3-(9.5μeq/L)略高,且所有冷凝水样品中NO2-检出率为100%;4种低分子量有机酸MSA-(6.0μeq/L)、CH3COO-(5.9μeq/L)、C2O42-(3.9μeq/L)和HCOO-(3.7μeq/L)占阴离子总量的8.5%,含量远高于上海雨水;Ca2+(19.2μeq/L,4.0%)、Mg2+(4.9μeq/L,1.0%)含量比同期雾水低2~3个数量级;冷凝水离子浓度随时间变化较大,这与光化学反应、春季逆温等有关.

The air condensation water（ACW） was collected using an in-situ self-assembled collector on 8 March^11 April,2011,in Shanghai.The chemical characteristics of the samples were studied in detail,and the results were compared to those of other wet deposition in terms of inter-ion correlativity,ion concentration in relation to temporal variations.The pH values of the samples ranged from 6.1~7.2 with a volume-weighted mean pH value of 6.5,mostly exhibiting weak acidity.Both NH4＋ and SO42-were the most abundant components and volume-weighted means were 139.7μeq/L and 125.7μeq/L,respectively.SO42-was the predominant acid anion.The NO2-（9.9 μeq/L） concentration was somewhat higher than that of NO3-（9.5μeq/L） and the detection rate of NO2-was 100% in all samples.The low-volatility organic acids of MSA-（6.0μeq/L）,CH3COO-（5.9μeq/L）,C2O42-（3.9μeq/L） and HCOO-（3.7μeq/L） accounted for 8.5% of total anions,much higher than those in Shanghai rainwaters.Ca2＋（19.2μeq/L,4.0%） and Mg2＋（4.9μeq/L,1.0%） were two or three orders of magnitude lower than those detected in fogwaters.The ion concentration changed more appreciably as a function of time,in close association with photochemical reaction,inversion layer in spring,and so forth.