Insights into air pollution chemistry and sulphate formation from nitrous acid (HONO) measurements during haze events in Beijing

William J. Bloss*, Louisa Kramer, Leigh R. Crilley, Tuan Vu, Roy M. Harrison, Zongbo Shi, James D. Lee, Freya A. Squires, Lisa K. Whalley, Eloise Slater, Robert Woodward-Massey, Chunxiang Ye, Dwayne E. Heard, Shengrui Tong, Siqi Hou, Yele Sun, Jingsha Xu, Lianfang Wei, Pingqing Fu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Wintertime urban air pollution in many global megacities is characterised by episodic rapid increase in particulate matter concentrations associated with elevated relative humidity-so-called haze episodes, which have become characteristic of cities such as Beijing. Atmospheric chemistry within haze combines gas-and condensed-phase chemical processes, leading to the growth in secondary species such as sulphate aerosols. Here, we integrate observations of reactive gas phase species (HONO, OH, NOx) and time-resolved aerosol composition, to explore observational constraints on the mechanisms responsible for sulphate growth during the onset of haze events. We show that HONO abundance is dominated by established fast gas-phase photochemistry, but the consideration of the additional formation potentially associated with condensed-phase oxidation of S species by aqueous NO2 leading to NO2- production and hence HONO release, improves agreement between observed and calculated gas-phase HONO levels. This conclusion is highly dependent upon aerosol pH, ionic strength and particularly the parameterisation employed for S(iv) oxidation kinetics, for which an upper limit is derived. This journal is

Original languageEnglish
Pages (from-to)223-238
Number of pages16
Early online date21 Sept 2021
Publication statusE-pub ahead of print - 21 Sept 2021

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© The Royal Society of Chemistry.

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