2014年6月南京大气复合污染观测

Observational Study of Air Pollution Complex in Nanjing in June 2014

二次无机盐是PM_(2.5)的重要组成部分,厘清污染过程中二次无机盐的演变过程和影响因素,是提高对污染过程认识的关键.以2014年6月南京地区两次污染事件为例,研究了污染过程中二次无机盐的演变过程和影响因素.结果表明,两次污染过程均表现出显著的大气复合污染特征;污染初期,臭氧浓度较高,大气氧化性强,气态硝酸具有较高的生成潜势,为细颗粒物中NO-3的快速生成创造前提条件,后期相对湿度(RH)升高对NO-3的生成起决定性作用;当RH大于多组分的共同潮解相对湿度(DRH*)时,NH_4NO_3潮解平衡时NH_3和HNO_3的理论分压积显著降低,低于观测得到的分压积,有利于NO-3生成,同时,观测和理论的分压积差异能够很好地表征NO-3的浓度变化特征.

Studying the evolution of secondary inorganic aerosols,which are important components of PM2.5,is crucial to improving our understanding about the air pollution in big cities. This study investigates the evolution and factors of secondary inorganic aerosols based on two pollution incidences in Nanjing in June 2014. A significant characteristic of air pollution complex with the coexistence of higher concentrations of both PM2.5and ozone is observed. In the earlier stage of the pollution episode,ozone concentrations were high,which could exceed 250,triggering a stronger oxidation in the atmosphere and a higher production potential of nitric acid that leads to the quick production of nitrate. In the later period of the pollution episode,relative humidity played an essential role. An increase in relative humidity would result in a sharp decrease in the theoretical product of the partial pressures of NH3 and HNO3,especially when relative humidity exceeds the mutual deliquesce relative humidity that makes it easier to form nitrate. The difference in the theoretical and observational partial pressure product could characterize the evolution of nitrate perfectly.