Modeling nitryl chloride and its source and effect on gaseous and aerosol chemistry

Nitryl chloride (ClNO2) has been reported as a critical species of chlorine chemistry. Its chemistry interrupts a nighttime sink of NOX and emits chlorine radical (Cl•) in the daytime, consequently altering gaseous and aerosol chemistry. Recent field studies have also measured considerable concentrations of ClNO2 in South Korea under the influences of natural and anthropogenic chlorine sources. However, the impacts of ClNO2 chemistry on air quality in South Korea have yet to be evaluated. We validate simulated ClNO2 and its chemistry in South Korea using observations and a 3-D chemical transport model (CTM) during the Korea-United States Air Quality field study. We implemented the latest Chinese and Korean anthropogenic chlorine emissions in the model. We found that the model reproduces the observed spatial and temporal variations of ClNO2, including its local and transboundary transport and precursors. We found that ClNO2 chemistry results in a more efficient conversion of NO to NO2 at night and daytime acceleration of the NOX-O3 cycle. It results in an increase of O3 (1.1%), NOX (3.1%), OH (2.0%), HO2 (0.8%), and Cl• (507.8%) and a decrease of TNO3(HNO3 + aerosol nitrate, 1.7%) on the campaign mean basis.