Heterogeneous N 2O 5 uptake coefficient and production yield of ClNO 2 in polluted northern China: roles of aerosol water content and chemical composition

Tham, Yee Jun; Wang, Zhe; Li, Qinyi; Wang, Weihao; Wang, Xinfeng; Lu, Keding; Ma, Nan; Yan, Chao; Kecorius, Simonas; Wiedensohler, Alfred; Zhang, Yuanhang; Wang, Tao

Heterogeneous uptake of dinitrogen pentoxide (inline-formulaN2O5) and production of nitryl chloride (inline-formulaClNO2) are important nocturnal atmospheric processes that have significant implications for the production of secondary pollutants. However, the understanding of inline-formulaN2O5 uptake processes and inline-formulaClNO2 production remains limited, especially in China. This study presents a field investigation of the inline-formulaN2O5 heterogeneous uptake coefficient (inline-formulaγ(inline-formulaN2O5)) and inline-formulaClNO2 production yield (inline-formulaϕ) in a polluted area of northern China during the summer of 2014. The inline-formulaN2O5 uptake coefficient and inline-formulaClNO2 yield were estimated by using the simultaneously measured inline-formulaClNO2 and total nitrate in 10 selected cases, which have concurrent increases in the inline-formulaClNO2 and nitrate concentrations and relatively stable environmental conditions. The determined inline-formulaγ(inline-formulaN2O5) and inline-formulaϕ values varied greatly, with an average of 0.022 for inline-formulaγ(inline-formulaN2O5) (inline-formula±0.012, standard deviation) and 0.34 for inline-formulaϕ (inline-formula±0.28, standard deviation). The variations in inline-formulaγ(inline-formulaN2O5) could not be fully explained by the previously derived parameterizations of inline-formulaN2O5 uptake that consider nitrate, chloride, and the organic coating. Heterogeneous uptake of inline-formulaN2O5 was found to have a strong positive dependence on the relative humidity and aerosol water content. This result suggests that the heterogeneous uptake of inline-formulaN2O5 in Wangdu is governed mainly by the amount of water in the aerosol, and is strongly water limited, which is different from most of the field observations in the US and Europe. The inline-formulaClNO2 yield estimated from the parameterization was also overestimated comparing to that derived from the observation. The observation-derived inline-formulaϕ showed a decreasing trend with an increasing ratio of acetonitrile to carbon monoxide, an indicator of biomass burning emissions, which suggests a possible suppressive effect on the production yield of inline-formulaClNO2 in the plumes influenced by biomass burning in this region. The findings of this study illustrate the need to improve our understanding and to parameterize the key factors for inline-formulaγ(inline-formulaN2O5) and inline-formulaϕ to accurately assess photochemical and haze pollution.

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Tham, Yee Jun / Wang, Zhe / Li, Qinyi / et al: Heterogeneous N2O5 uptake coefficient and production yield of ClNO2 in polluted northern China: roles of aerosol water content and chemical composition. 2018. Copernicus Publications.

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