新加坡和胡志明城区降水离子组成及来源分析

Ion Composition and Source Analysis of Precipitation in Urban Areas of Singapore and Ho Chi Minh City

近年来工农业发展导致东南亚城市大气污染日趋严重,然而其大气沉降离子组成观测仍稀少,导致关键污染组分的通量特征和来源并不十分清楚。本研究于2019年5月至2020年4月观测新加坡和胡志明城区降水离子(SO_(4)^(2-)、NO_(3)^(-)、NO_(2)^(-)、F^(-)、Cl^(-)、NH_(4)^(+)、K^(+)、Na^(+)、Ca^(2+)、Mg^(2+))浓度,基于正矩阵分解模型(PMF)进行来源分析,并重点讨论了占比较高的SO_(4)^(2-)的沉降通量及其变化特征。结果表明,偏北的胡志明市降水年均pH为6.9±0.5,但新加坡降水年均pH为4.5±0.4,呈重酸雨特征,其降水SO_(4)^(2-)在总离子中的占比(34%)和沉降通量(28.8 kg S/(ha·a))也显著高于胡志明市(分别为15%和19.3 kg S/(ha·a)),二者硫沉降也高于东南亚和中国大部分地区当前的沉降水平。PMF模型解析结果表明,农业源对新加坡和胡志明市降水NH4+的贡献分别为62%和47%,生物质燃烧源对降水K^(+)的贡献均达到73%,海洋源对新加坡和胡志明市降水Na+的贡献分别达到50%和92%,对降水Cl^(-)的贡献分别达到54%和45%。本研究提供了疫情前夕研究城市降水化学的重要数据,为评估后期疫情人为活动变化对空气污染的影响提供了参考依据,同时丰富了东南亚地区的降水化学组成和来源认识,为该地区城市空气质量管理及其生态环境效应评估提供了关键科学证据。

The development of industry and agriculture has led to increasingly serious air pollution in Southeast Asian(SEA)cities in recent years.However,observations on the composition of atmospheric deposition ions are still rare,so the flux characteristics and sources of key pollution components are not very clear.In this study,the concentration of ions(SO_(4)^(2-),NO_(3)^(-),NO_(2)^(-),F^(-),Cl^(-),NH_(4)^(+),K^(+),Na^(+),Ca2+,Mg^(2+))in precipitation in Singapore(SG)and Ho Chi Minh(HCM)urban area was observed from May 2019 to April 2020.Source analysis was conducted based on the Positive Matrix Factorization model(PMF).The deposition flux of SO_(4)^(2-),which occupies a relatively high proportion,and its variation characteristics are emphatically discussed.The results showed that the average annual pH of precipitation in HCM was 6.9±0.5,while that in SG was 4.5±0.4,showing the characteristics of heavy acid rain.The proportion of precipitation SO_(4)^(2-) in total ions(34%)and deposition flux(28.8 kg S/(ha·a))in SG were significantly higher than those in Ho Chi Minh City(15% and 19.3 kg S/(ha·a),respectively),and the SO_(4)^(2-) deposition of both cities was higher than that in most parts of SEA and China.The results of the PMF model showed that the contribution of agricultural sources to precipitation NH_(4)^(+) was 62% and 47%,biomass burning accounted for 73% and 73% of K^(+)in precipitation,marine factor accounted for 50% and 92% of Na^(+) and 54% and 45% of Cl^(-)in precipitation,respectively.This study provides important data for the study of urban precipitation chemistry before the outbreak of the pandemic and provides references for the assessment of the impact of anthropogenic changes on air pollution in the later period.At the same time,it enriches the understanding of the chemical composition and source of precipitation in SEA and provides key scientific evidence for urban air quality management and ecological environmental effects assessment in this region.