Investigating the sources of atmospheric nitrous acid (HONO) in the megacity of Beijing, China

Rongrong Gu; Hengqing Shen; Likun Xue; Tao Wang; Jian Gao; Hong Li; Yutong Liang; Men Xia; Chuan Yu; Yiming Liu; Wenxing Wang

doi:10.1016/j.scitotenv.2021.152270

Investigating the sources of atmospheric nitrous acid (HONO) in the megacity of Beijing, China

Sci Total Environ. 2022 Mar 15:812:152270. doi: 10.1016/j.scitotenv.2021.152270. Epub 2021 Dec 10.

Authors

Rongrong Gu¹, Hengqing Shen², Likun Xue³, Tao Wang⁴, Jian Gao⁵, Hong Li⁵, Yutong Liang⁶, Men Xia⁶, Chuan Yu⁷, Yiming Liu⁸, Wenxing Wang⁹

Affiliations

¹ Environment Research Institute, Shandong University, Qingdao 266237, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong 99907, China.
² Environment Research Institute, Shandong University, Qingdao 266237, China. Electronic address: hqshen@sdu.edu.cn.
³ Environment Research Institute, Shandong University, Qingdao 266237, China. Electronic address: xuelikun@sdu.edu.cn.
⁴ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong 99907, China; Environment Research Institute, Shandong University, Qingdao 266237, China. Electronic address: tao.wang@polyu.edu.hk.
⁵ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
⁶ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong 99907, China.
⁷ Environment Research Institute, Shandong University, Qingdao 266237, China.
⁸ School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China.
⁹ Environment Research Institute, Shandong University, Qingdao 266237, China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.

PMID: 34902418
DOI: 10.1016/j.scitotenv.2021.152270

Abstract

Nitrous acid (HONO) can powerfully influence atmospheric photochemistry by producing hydroxyl radical (OH), which is a crucial oxidant that controls the fate of atmospheric trace species. To deduce HONO formation mechanisms in polluted regions, two field observations were conducted in urban Beijing during the early summer of 2017 and the winter of 2018. These two seasons bore distinguishing pollution characteristics with a higher degree of ageing and heavier aerosol loading in the early summer and more abundant NO_x (NO_x = NO + NO₂) in the winter. Elevated concentrations of HONO were observed during these two seasons, with the mean ± standard deviation (maximum) concentrations of 1.25 ± 0.94 (6.69) ppbv and 1.04 ± 1.27 (9.55) ppbv in early summer and winter, respectively. The observed daytime (08:00-17:00 h, local time) HONO production rate was several times higher in early summer than in winter (4.44 ± 1.93 ppbv h^-1 vs. 0.88 ± 0.49 ppbv h^-1). Budget analysis revealed distinct daytime HONO formation mechanisms during these two seasons. Photo-induced heterogeneous conversion of NO₂ on the ground surface dominated in early summer, and homogeneous reaction of NO + OH was dominant in winter. Photolysis of HONO was the major source of primary OH in both seasons, and thus, played a key role in the regulation of atmospheric oxidising capacity. This study demonstrates the significant seasonal variations in HONO budget and underlines the predominant role of HONO in primary OH production in Beijing. Our findings will be helpful to gain an understanding of the chemical mechanisms underlying the formation of secondary pollution in metropolitan areas.

Keywords: Atmospheric oxidation capacity; Budget analysis; Hydroxyl radical (OH); Nitrous acid (HONO); Seasonal variation.

MeSH terms

Aerosols
Beijing
China
Hydroxyl Radical*
Nitrous Acid* / analysis

Substances

Aerosols
Hydroxyl Radical
Nitrous Acid