Work

Significant production of ClNO 2 and possible source of Cl 2 from N 2 O 5 uptake at a suburban site in eastern China

Year: 2020

Type: article

Abstract: . ClNO2 and Cl2 can affect atmospheric oxidation and thereby the formation of ozone and secondary aerosols, yet their sources and production mechanisms are not well understood or quantified. In this study we present field observations of ClNO2 and Cl2 at a suburban site in eastern China during April 2018. Persistent high levels of ClNO2 (maximum ~ 3.7 ppbv; 1 min average) were frequently observed at night, due to the high ClNO2 yield (φ(ClNO2), 0.56 ± 0.20) inferred from the measurements. The φ(ClNO2) value showed a positive correlation with the [Cl−]/[H2O] ratio, and its parameterization was improved by the incorporation of [Cl−]/[H2O] and the suppression effect of aerosol organics. ClNO2 and Cl2 showed a significant correlation on most nights. We show that the Cl2 at our site was likely a co-product with ClNO2 from N2O5 uptake on aerosols that contain acidic chloride, rather than being produced by ClNO2 uptake, as previously suggested. The Cl2 yield (φ(Cl2)) derived from the N2O5 uptake hypothesis exhibited significant correlations with [Cl−] and [H+], based on which a parameterization of φ(Cl2) was developed. The derived parameterizations of φ(ClNO2) and φ(Cl2) can be used in models to quantify the nighttime production of ClNO2 and Cl2 and their impact on the next day’s photochemistry.

Source: Atmospheric chemistry and physics

DOI: 10.5194/acp-20-6147-2020