摘要
基于北京市城区点位2022年观测数据,运用ISORROPIA-Ⅱ模型分析冬季霾、春季沙尘、夏季高臭氧与秋季PM_(2.5)与臭氧复合污染共4次典型污染过程PM_(2.5)的酸度特征,获得气溶胶pH值与硝酸盐快速增长的演变规律.结果表明,北京市气溶胶pH值为中度酸性,四次污染过程pH值范围分别为3.59~5.07,3.70~7.76,2.44~6.15和2.80~4.69.4次污染过程气溶胶pH值呈正态分布,pH值中位数分别为4.60、4.59、3.91和4.09.冬季霾污染过程气溶胶水含量最高,其气溶胶pH值最大.春季沙尘污染过程气溶胶pH值呈双峰分布,受到人为源与天然源共同影响.夏、秋两次污染过程PM_(2.5)酸性分别为最强和次强,可能与大气氧化性增强促进酸性气体被氧化有关.夏季气温高气溶胶pH值低,HNO_(3)倾向于向气相分配,硝酸盐占比最低(22%);秋季气溶胶pH值昼低夜高,有利于硝酸盐的夜间积累,硝酸盐占比与冬、春两次污染过程相当(27%~28%).北京大气气态NH_(3)充分富余,HNO_(3)与NH_(3)的中和(均相)反应为NO_(3)^(-)的主要生成机制,气溶胶中NH_(4)^(+)也相对富余,气溶胶中(NH_(4))_(2)SO_(4)、NH_(4)NO_(3)和NH_(4)Cl均可以充分耦合.研究显示,较高的气溶胶水含量和气溶胶pH值是污染期间硝酸盐快速增长的原因,针对气态前体物NH_(3)和NO_(x)的进一步减排是控制北京大气细颗粒的有效手段.
Based on the online monitoring data from urban sites in Beijing during 2022,the ISORROPIA-Ⅱ model was used to analyze the acidity of PM_(2.5) during four typical pollution episodes,namely haze pollution in winter,dust pollution in spring,high ozone pollution in summer,and PM_(2.5) and O_(3) combined pollution in autumn.The evolution of aerosol pH with the rapid formation of nitrate was obtained.The results show that the aerosol pH in Beijing was moderately acidic,in ranges of 3.59~5.07,3.70~7.76,2.44~6.15,and 2.80~4.69 for the four episodes,respectively.The aerosol pH exhibited normal distribution for the four pollution episodes with median values of 4.60,4.59,3.91 and 4.09,respectively.During winter haze pollution,aerosol water content and the aerosol pH were the highest.During spring dust pollution,the aerosol pH presented bimodal distribution,affected by both anthropogenic and natural sources.The acidity of PM_(2.5) in summer and autumn episodes was the strongest and the second strongest respectively,which might be related to the oxidation of acid gas enhanced by strong atmospheric oxidation conditions.During high ozone pollution in summer,with high temperature and low pH,HNO_(3) tended to be distributed in the gas phase,and the nitrate proportion in PM_(2.5) was the lowest(22%).For PM_(2.5) and O_(3) combined pollution in autumn,pH was low in the daytime and high in the nighttime,conducive to the nitrate accumulation at night after the gaseous HNO_(3) formation in the daytime.The nitrate proportion was comparable to that during pollution episodes in winter and spring,reaching 27%~28%.Gaseous NH_(3) was abundant,and the neutralization(homogenization)reaction between HNO_(3) and NH_(3) was the main formation mechanism of NO_(3)^(-).Abundant of NH_(4)^(+),(NH_(4))_(2)SO_(4),NH_(4)NO_(3) and NH_(4)Cl in aerosol could also be fully coupled.This research shows that high aerosol water content and aerosol pH were responsible for the rapid growth of nitrate during pollution.Further reduction of the precursors NH_(3)
作者
王友峰
景宽
沈秀娥
王琴
王陈婧
富佳明
张博韬
张健
曹阳
张珂
刘保献
WANG You-feng;JING Kuan;SHEN Xiu-e;WANG Qin;WANG Chen-jing;FU Jia-ming;ZHANG Bo-tao;ZHANG Jian;CAO Yang;ZHANG Ke;LIU Bao-xian(Beijing Municipal Ecological and Environmental Monitoring Center,Beijing 100048,China;Beijing Key Laboratory of Airborne Particulate Matter Monitoring Technology,Beijing 100048,China)
出处
《中国环境科学》
EI
CAS
CSCD
北大核心
2024年第8期4167-4178,共12页
China Environmental Science
基金
生态环境新型治理体系构建与示范应用项目(2021YFC1809004)。
