Presence of high nitryl chloride in Asian coastal environment and its impact on atmospheric photochemistry

Abstract

Nitryl chloride (ClNO2) is a product of nocturnal halogen activation of nitrogen oxides and has potential to impact atmospheric photochemistry. Here we report the first observation result of ClNO2 in an Asian environment. The measurements were made with a thermal decomposition chemical ionization mass spectrometer at a coastal site in southern China during late summer of 2012. A clear diurnal pattern of ClNO2 was observed with nighttime 1-min average mixing ratio up to 1997 pptv, which is among the highest values ever reported in the world. The elevated ClNO2 mixing ratios were observed in plumes from Hong Kong and the Pearl River Delta region compared to the lower levels in maritime air. Calculations suggest that the production of chlorine atom from photolysis of ClNO2 in the early morning exceeds the production of hydroxyl radical via ozone photolysis by several factors. Therefore, ClNO2 plays an important role in jump-starting the atmospheric photochemistry in polluted marine boundary layer of southern China.