摘要
NO_(2)是大气中常见污染气体,影响大气二次有机气溶胶(Secondary organic aerosol,SOA)的形成.运用实验室烟雾箱模拟二甲苯大气光氧化反应过程,研究NO_(2)对二甲苯SOA生成量、光学特性和化学组成的影响.结果显示,NO_(2)促进二甲苯SOA的形成,NO_(2)浓度从0增长到900×10^(-9),二甲苯SOA的质量浓度增长2倍左右,并且邻二甲苯SOA质量浓度大于对二甲苯SOA.这是因为邻位取代基相比于对位取代基更倾向于形成醛,有利于聚合反应形成低聚物,促进SOA形成.此外,NO_(2)浓度增加显著提高所生成SOA的单位质量吸光度(Mass absorption coefficients,MAC),这是由于前体物邻二甲苯和对二甲苯化学结构不同,邻二甲苯所生成的含氮有机物具有更强吸光性,从而导致邻二甲苯SOA的MAC_(λ=365 nm)大于对二甲苯SOA的MAC_(λ=365 nm).在线气溶胶质谱仪分析结果进一步显示:二者光化学氧化所形成的SOA主要由有机酸所组成,邻二甲苯SOA比对二甲苯SOA具有更低H/C比,表明其产物氧化程度更高.但是随着NO_(2)浓度持续增加,邻二甲苯SOA和对二甲苯SOA在化学组成上的差异逐渐变小.
NO_(2) is an important pollutant in the urban atmosphere and significantly affect the formation of tropospheric secondary organic aerosol(SOA).In this work the reaction process of photooxidation of xylene was studied by using a laboratory smog chamber,focusing on the influence of NO_(2) on the mass concentration,optical properties and chemical composition of the SOA.The results showed that along with an increase in concentration of NO_(2) from 0 to 900×10^(-9),mass concentration of the xylene SOA increased by about twice,suggesting a promoting effect of NO_(2) on the SOA formation.We found that the mass concentration of o-xylene SOA was greater than that of p-xylene SOA,because the ortho substitution group tends to form aldehydes,which favors the oligomerization and thus promotes the SOA formation.Moreover,the increase in NO_(2) concentration can also enhance the SOA mass absorption coefficients(MAC).Due to the different chemical structures of the two precursors,nitrogen-containing organic compounds(NOC)produced from o-xylene is of stronger light absorption.The online aerosol mass spectrometer(AMS)results further showed that the dominant components of o-xylene SOA and p-xylene SOA are organic acids with a lower H/C ratio for the o-xylene SOA,suggesting that the ortho-substituents are easier to be oxidized.However,the differences in chemical compositions between o-xylene SOA and p-xylene SOA was gradually diminished along with an increase in NO_(2) concentration.
作者
王益倩
刘仕杰
赵宇
张思
李大鹏
王格慧
WANG Yiqian;LIU Shijie;ZHAO Yu;ZHANG Si;LI Dapeng;WANG Gehui(Key Laboratory of Geographic Information Science of the Ministry of Education,School of Geographic Sciences,East China Normal University,Shanghai 200241;Institute of Eco-Chongming,Shanghai 200262)
出处
《环境科学学报》
CAS
CSCD
北大核心
2022年第5期136-147,共12页
Acta Scientiae Circumstantiae
基金
国家自然科学基金项目(No.41773117,42005088)。
