[Observational Study of Air Pollution Complex in Nanjing in June 2014]

Studying the evolution of secondary inorganic aerosols, which are important components of PM_2.5, 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 PM_2.5 and 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.