NH3 对二甲苯光氧化形成二次有机气溶胶的影响

二甲苯是一种重要的人为源 VOC, 也是城市地区 SOA 的重要前体物。二甲苯光氧化形成的 SOA 受多种环 境因素影响, 而 NH3 对该反应形成的 SOA 生成产率及反应机制的影响尚不清楚。基于室内烟雾箱模拟系统, 探讨了 NH3 对二甲苯光氧化形成 SOA 质量浓度、物理特性及化学组成的影响。研究表明, 在低浓度条件下, NH3 对二甲苯 光氧化生成 SOA 具有明显的促进作用, 结合气溶胶质谱结果发现 NH3 促进醛酮类物质进入颗粒相以及含氮有机物的 生成是导致 SOA 质量浓度增加的主要原因。此外, NH3 能够提高邻二甲苯生成 SOA 的吸光度, 但是对对二甲苯无明 显影响。分析表明, 相较于对二甲苯, 邻二甲苯光氧化会生成大量醛类物质, NH3 与醛类发生美拉德反应是导致 SOA 吸光性增加的主要原因。

Effects of NH3 on the formation of SOA derived from xylene photochemical oxidation

Xylene is one of the most important anthropogenic volatile organic compounds (VOCs) for the secondary organic aerosol (SOA) formation. As the effect of NH3 on the yield and reaction mechanism of SOA formed by photooxidation of xylene is not clear, SOA formation from atmospheric photooxidation of xylene with different NH3 concentrations was studied in a laboratory smog chamber, focusing on the mass concentration, optical properties and chemical composition of SOA. The results show that NH3 can obviously promote the formation of SOA at low concentration. And according to aerosol mass spectra results, the promotion of carbonyl compounds into the particle-phase and the formation of nitrogen-containing organic in the presence of NH3 are the main reasons for the increase of SOA mass concentration. In addition, it is found that NH3 can increase the mass absorption coefficient (MAC) of o-xylene SOA, but has no significant effect on p-xylene SOA. The analysis shows that the formation of aldehydes through photooxidation of o-xylene is more efficient than that of p-xylene, and then Maillard reaction between NH3 and aldehydes leads to the increase of light absorption of SOA.