Comment on acp-2021-541

doi:10.5194/acp-2021-541-rc1

Abstract

Nitryl chloride (ClNO2), an important precursor of Cl atoms, significantly affects atmospheric oxidation capacity and O3 formation. However, sources of ClNO2 in inland China have not been fully elucidated. In this work, laboratory experiments were conducted to investigate heterogeneous reaction of N2O5 with eight saline mineral dust samples collected from different regions in China, and substantial formation of ClNO2 was observed. ClNO2 yields, φ(ClNO2), showed large variations (ranging from < 0.05 to ~0.77) for different saline mineral dust samples, largely depending on mass fractions of particulate chloride. In addition, for different saline mineral dust samples, φ(ClNO2) could increase, decrease or show insignificant change as RH increased from 18 % to 75 %. We further found that current parameterizations significantly overestimated φ(ClNO2) for heterogeneous uptake of N2O5 onto saline mineral dust. Assuming a uniform φ(ClNO2) value of 0.10 for N2O5 uptake onto mineral dust, we used a 3-D chemical transport model to assess the impact of this reaction on tropospheric ClNO2 in China, and found that weekly mean nighttime maximum ClNO2 mixing ratios could be increased by up to 85 pptv during a severe dust event in May 2017. Overall, our work showed that heterogeneous reaction of N2O5 with saline mineral dust could be an important source of tropospheric ClNO2 in inland China.

Highlights

The formation of O3 and secondary aerosols, two major air pollutants, is closely related to atmospheric oxidation processes (Lu et al, 2019)
Rate constants for reactions of certain volatile organic compounds (VOCs) with Cl atoms can be a few orders of magnitude larger than those reacting with OH radicals (Atkinson and Arey, 2003; Atkinson et al, 2006); despite its lower concentrations in the troposphere, Cl can contribute significantly to atmospheric oxidation capacity in some regions (Saiz-Lopez and von Glasow, 2012; Simpson et al, 2015; Wang et al, 2019)
In order to check if initial N2O5 and ClNO2 concentrations were stable, during our experiments the mixed flow was switched back to pass through the blank filter from time to time

Summary

Introduction

The formation of O3 and secondary aerosols, two major air pollutants, is closely related to atmospheric oxidation processes (Lu et al, 2019). Primary pollutants emitted by natural and anthropogenic sources are oxidized by various oxidants to produce O3 and secondary aerosols, affecting air quality and climate. Lopez and von Glasow, 2012; Simpson et al, 2015; Wang et al, 2019). Rate constants for reactions of certain volatile organic compounds (VOCs) with Cl atoms can be a few orders of magnitude larger than those reacting with OH radicals (Atkinson and Arey, 2003; Atkinson et al, 2006); despite its lower concentrations in the troposphere, Cl can contribute significantly to atmospheric oxidation capacity in some regions (Saiz-Lopez and von Glasow, 2012; Simpson et al, 2015; Wang et al, 2019). One major source of tropospheric Cl atoms is daytime photolysis of ClNO2 (Thornton et al., 2010; Simpson et al, 2015), which is formed in heterogeneous reaction of N2O5 with chlorinecontaining particles (R1) at nighttime (Osthoff et al, 2008; Thornton et al, 2010): N2O5(g) + Cl-(aq) → φClNO2(g) + (2-φ)NO3-(aq)

Methods

Results

Discussion

Conclusion