研究报告
王益倩,刘仕杰,赵宇,张思,李大鹏,王格慧.NO2对二甲苯光氧化生成SOA及其吸光度影响[J].环境科学学报,2022,42(5):136-147
NO2对二甲苯光氧化生成SOA及其吸光度影响
- Effects of NO2 on the formation and optical absorption of SOA derived from xylene photochemical oxidation
- 基金项目：国家自然科学基金项目（No．41773117， 42005088）
- 作者
- 单位
- 王益倩
- 华东师范大学地理科学学院，地理信息科学教育部重点实验室，上海 200241
- 刘仕杰
- 华东师范大学地理科学学院，地理信息科学教育部重点实验室，上海 200241
- 赵宇
- 华东师范大学地理科学学院，地理信息科学教育部重点实验室，上海 200241
- 张思
- 华东师范大学地理科学学院，地理信息科学教育部重点实验室，上海 200241
- 李大鹏
- 华东师范大学地理科学学院，地理信息科学教育部重点实验室，上海 200241
- 王格慧
- 华东师范大学地理科学学院，地理信息科学教育部重点实验室，上海 200241;崇明生态研究院，上海200262
- 摘要：NO2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NO2对二甲苯SOA生成量、光学特性和化学组成的影响.结果显示，NO2促进二甲苯SOA的形成，NO2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，NO2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MACλ=365 nm大于对二甲苯SOA的MACλ=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NO2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.
- Abstract：NO2 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 NO2 on the mass concentration， optical properties and chemical composition of the SOA. The results showed that along with an increase in concentration of NO2 from 0 to 900×10-9， mass concentration of the xylene SOA increased by about twice， suggesting a promoting effect of NO2 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 NO2 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 NO2 concentration.
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