南京三级分档雾水有机酸和无机组分化学特征

Characteristics of organic acids and inorganic components in three-stage fog water in Nanjing.

本研究于2017年11月~2018年1月在南京北郊开展为期45d的雾外场综合观测试验,并在2017年12月30~31日一次浓雾过程中,利用主动式分档雾水采集器采集三级分档雾水样品(三级切割直径:S1,>22μm;S2,16~22μm;S3,4~16μm),测定了样品的有机酸和无机离子浓度以及pH值和电导率,以探讨南京三级粒径雾水的有机酸和无机离子组分化学特征.结果表明,南京三级粒径雾水呈碱性,Ca^2+,NH^4+,SO4^2-和NO3-为三级分档雾水的主要离子组分.甲酸根(HCOO)、甲基磺酸根(CH3SO3-)、草酸根(C2O4^2-)和乙酸根(CH3COO)为主要有机酸组分.总离子浓度和各种离子浓度的体积加权平均随粒径变化呈“U”型分布,且在4~16μm小雾滴中富集.4种主要有机酸离子浓度间均存在显著相关性.雾水中Ca^2+和NH^4+是导致雾水呈碱性的主要原因.与2013年相比,2017年雾水酸度大幅降低,主要由于致酸成分的减少和中和反应的发生.

In this study,a systematic 45-day field observation of fog was conducted in the northern suburb of Nanjing during the winter of 2017.Eleven fog water samples were collected in a dense fog event occurring at December 30 and 31,2017,by using a Caltech Active Strand Cloud Collector(CASCC)with three cutting diameter ranges(S1:>22μm;S2:16~22μm;S3:4~16μm).In this observation,concentrations of organic acids and inorganic ions as well as the pH value and the electrical conductivity(EC)of the samples were measured,so that the chemical properties of the fog water were revealed.The results showed that the fog water samples were alkaline,and the dominant ionic compositions were Ca^2+,NH^4+,SO4^2-and NO3.The major organic acid compositions were found as formate(HCOO-),methanesulfonate(CH3SO^3-),oxalate(C2O4^2-),and acetate(CH3COO).Moreover,it was shown that the weighted mean volume concentrations of each type of the ions as well as the total ions were size-dependent,“U”-shaped,and concentrate in small fog droplets with a size range of 4~16μm.The concentrations of the four major organic acid compositions were also found strongly correlated with each other.The observational data showed that Ca^2+and NH^4+in the fog water were the key factors leading to the alkalinity of the water.In addition,we found that compared to the fog water collected in the year 2013,the acidity of the fog water collected in 2017 was lower,which was attributed to the reduction of acid-causing components and the occurrence of neutralization reactions.