Box Model Applications for Secondary Inorganic Aerosol: A Review Focused on Nitrate Formation

More than a half of PM (2.5 )mass is composed of secondary inorganic aerosol (SIA) species in East Asia, with nitrate being the most abundant one, particularly during fine particulate matter pollution episodes. Although nitrate is produced from the oxidation of its precursor NO (x ), the reduction of NO x emissions does not always decrease the atmospheric nitrate concentration because of the non -linearity of the nitrate formation. Box models can be efficient tools to analyze the sensitivity of nitrate formation to the concentrations of its precursors and suggest appropriate policy directions to reduce SIA. This review article summarizes recent studies that developed and used various box models to investigate the principles and mechanisms of nitrate production in the air. Measurement of OH radical, ammonia, and trace species involved in the nitrate formation processes, sensitivity analyses of nitrate formation accounting for regional characteristics to deduce science -based policies, and integrated approach to manage ozone and SIA together are suggested as future directions for effective utilization of box models as a policy making tool.