Oxidizing capacity of the rural atmosphere in Hong Kong, Southern China

Zeyuan Li; Likun Xue; Xue Yang; Qiaozhi Zha; Yee Jun Tham; Chao Yan; Peter K K Louie; Connie W Y Luk; Tao Wang; Wenxing Wang

doi:10.1016/j.scitotenv.2017.08.310

Oxidizing capacity of the rural atmosphere in Hong Kong, Southern China

Sci Total Environ. 2018 Jan 15:612:1114-1122. doi: 10.1016/j.scitotenv.2017.08.310. Epub 2017 Sep 8.

Authors

Zeyuan Li¹, Likun Xue², Xue Yang¹, Qiaozhi Zha³, Yee Jun Tham³, Chao Yan³, Peter K K Louie⁴, Connie W Y Luk⁴, Tao Wang³, Wenxing Wang¹

Affiliations

¹ Environment Research Institute, Shandong University, Ji'nan, Shandong, China.
² Environment Research Institute, Shandong University, Ji'nan, Shandong, China. Electronic address: xuelikun@sdu.edu.cn.
³ Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong, China.
⁴ Environmental Protection Department, the Government of the Hong Kong Special Administrative Region, Hong Kong, China.

PMID: 28892855
DOI: 10.1016/j.scitotenv.2017.08.310

Abstract

Atmospheric oxidizing capacity (AOC), dominated by the hydroxyl radical (OH), is an important index of the self-cleaning capacity of atmosphere and plays a vital role in the tropospheric chemistry. To better understand the key processes governing the chemistry of rural atmosphere of southern China, we analyzed the oxidation capacity and radical chemistry at a regional background site in Hong Kong from 23 August to 22 December 2012, which covered the summer, autumn and winter seasons. A chemical box model built on the latest Master Chemical Mechanism (v3.3) was used to elucidate the OH reactivity and sources of RO_X radicals (RO_X=OH+HO₂+RO₂). The AOC showed a clear seasonal pattern with stronger intensity in late summer compared to autumn and winter. Reactions with NO₂ (30%) and oxygenated volatile organic compounds (OVOCs) (31%) together dominated the OH loss in summer, while reactions with CO (38% in autumn and 39% in winter) and OVOCs (34% in autumn and 25% in winter) made larger contributions in autumn and winter. Photolysis of O₃ (36%-47%) presented the major RO_X source during all three seasons. The second largest ROx source was HONO photolysis (25%) in summer compared to HCHO photolysis in autumn (20%) and winter (21%). Besides, photolysis of other OVOCs was another important primary source of ROx radicals with average contributions of 14%, 13% and 20% for the summer, autumn and winter cases, respectively. Overall, the present study evaluates the oxidizing capacity of the rural atmosphere of South China and elucidates the varying characteristics of photochemical processes in different air masses.

Keywords: Atmospheric oxidizing capacity; OH reactivity; Observation-based model; Radical source; Southern China.