氨与甲苯SOA形成含氮有机物的影响因素研究

摘要

Ozone was photolyzed to produce OH radicals, and photooxidation of toluene is initiated to generate secondary organic aerosol (SOA) particles in home-made smog chamber, nitrogen-containing organic compounds formed from toluene SOA reaction with ammonia were studied under different experimental conditions. The absorbance at 205 and 270nm of the reaction product solution measured by UV-visible spectrophotometer was used to study the influence of environmental factors such as irradiation time, the concentration of toluene, ammonia, ozone, and relative humidity on the formation of nitrogen-containing organic compounds. The experimental results demonstrated that the concentration of organic acid ammonium and imidazole products gradually increases with the increase of ultraviolet irradiation time and the concentrations of toluene, ammonia and ozone. However, when the concentration of ozone exceeds a certain value, the high concentration of OH radicals generated by photolysis of ozone can oxidize the photooxidation product of toluene into more volatile compounds, which is not conducive to the formation of nitrogen-containing organic compounds. Also, the increase of water molecules would reduce the concentration of OH radicals, resulting in the decrease of the concentration of organic acid ammonium and imidazole products as the relative humidity increases. These would provide the experimental basis for studying the formation of the nitrogen-containing organic brown carbon of anthropogenic SOA particles.%利用自制的烟雾腔系统使臭氧光解产生OH自由基,启动甲苯光氧化产生二次有机气溶胶(SOA)粒子,在不同的实验条件下研究甲苯SOA与氨反应形成的含氮有机物,并采用紫外-可见分光光度计测量反应产物溶液在205和270nm处的吸光度,探究光照时间、甲苯、氨、臭氧浓度和相对湿度等环境因素对含氮有机物形成的影响规律.结果表明,有机酸铵和咪唑类产物的生成浓度随着紫外光照时间的延长,甲苯、氨和臭氧的浓度的增加而逐渐增大.但是当臭氧浓度超过一定值后,光解生成的高浓度OH 自由基能够使甲苯光氧化产物变成更多的挥发性化合物,从而不利于含氮有机物的生成.水分子的增加会使臭氧光解产生的OH 自由基浓度减少,从而导致有机酸铵和咪唑类产物的生成浓度随着相对湿度的增大而降低.这为研究人为源SOA 颗粒中含氮有机物棕色碳的形成提供了实验依据.