N₂O₅ uptake onto saline mineral dust: a potential missing source of tropospheric ClNO₂ in inland China

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 reactions of N₂O₅ with eight saline mineral dust samples collected from different regions in China, and substantial formation of ClNO₂ was observed in these reactions. ClNO₂ yields, φ(ClNO₂), showed large variations (ranging from < 0.05 to ∼ 0.77) for different saline mineral dust samples, depending on mass fractions of particulate chloride. In addition, φ(ClNO₂) could increase, decrease or show insignificant change for different saline mineral dust samples when relative humidity (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. In addition, 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 have been 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. © Author(s) 2022.