大气环境中PAN污染现状及转化机理的研究进展

A Review on the Current Pollution Level and Transformation Mechanism of Atmospheric Peroxyacetyl Nitrate

过氧乙酰硝酸酯(PAN)是光化学烟雾中重要的二次有机污染物,跟细颗粒物和臭氧污染都有着相关联系,已逐渐引起国内外学者的广泛关注。基于近年来国内外对PAN进行的相关研究,总结了PAN的污染现状、监测技术和生成降解机制等方面的研究进展。目前监测到的PAN浓度的空间区域特征总体呈现出城区明显大于郊区,日浓度高峰值通常出现在12:00-16:00之间,一年中夏季平均浓度较低。PAN生成速率主要受过氧乙酰(PA)自由基的生成速率影响,大气中PA自由基主要由乙醛、丙酮、甲基乙二醛、丁烯酮和联乙酰等含氧挥发性有机物生成,多数情况下乙醛对PA自由基的贡献率最高。PAN热解反应路径O-N键断裂优于O-O键断裂以及协同的C-C键和O-O键断裂;水解反应路径C-O键断裂和无水分子参与的O-N键断裂优于水分子参与的O-N键断裂。

Peroxyacetyl nitrate(PAN)is an important secondary organic pollutant in photochemical smog,which is associated with fine particulate matter and ozone pollution,and it has gradually attracted extensive attention.Based on the recent research on PAN from the literatures,the pollution characteristics,monitoring technology,and generation and degradation mechanism were summarized.The results showed that the spatial regional concentration characteristics of PAN in urban areas were significantly higher than those in suburban areas.The peak daily concentration of PAN usually occurred between 12:00-16:00,and the average concentration was the lowest in summer.The formation rate of PAN is mainly affected by the formation rate of peroxyacetyl radical(PA radical).PA radicals are mainly generated by oxygenated volatile organic compounds(OVOCs)such as acetaldehyde,acetone,methylglyoxal(MGLY),butenone(MVK)and diacetyl.Also acetaldehyde has the highest contribution rate to PA radicals in most cases.The O-N bond cleavage was superior to the O-O bond cleavage and the C-C bond and O-O bond collaborative cleavage in PAN thermal decomposition reaction path.The C-O bond cleavage and O-N bond cleavage involving anhydrous molecules were better than the O-N bond cleavage involving water molecules in the hydrolysis reaction path.