Preprints
https://doi.org/10.5194/acp-2020-728
https://doi.org/10.5194/acp-2020-728

  21 Aug 2020

21 Aug 2020

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Observations and explicit modeling of isoprene chemical processing in polluted air masses in rural areas of the Yangtze River Delta region: radical cycling and formation of ozone and formaldehyde

Kun Zhang1,2, Li Li1,2, Ling Huang1,2, Juntao Huo3, Yusen Duan3, Yuhang Wang4, Yangjun Wang1,2, and Qingyan Fu3 Kun Zhang et al.
  • 1School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China
  • 2Key Laboratory of Organic Compound Pollution Control Engineering, Shanghai University, Shanghai, 200444, China
  • 3Shanghai Environmental Monitoring Center, Shanghai, 200235, China
  • 4School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

Abstract. Ozone pollution has become one of the most severe environmental problems in China in recent years. Our online observations showed that high level of O3 were observed in rural areas of the Yangtze River Delta (YRD) region even there was no obvious ozone transport from the urban regions. To better understand the formation mechanism of local O3 pollution and investigate the potential role of isoprene chemistry in the budgets of ROx (OH+HO2+RO2) radicals, synchronous observations of volatile organic compounds (VOCs), formaldehyde (HCHO) and meteorological parameters were conducted at a rural site of the YRD region in 2018. Five episodes with elevated O3 concentrations under stagnant meteorological conditions were first identified; an observation-based model (OBM) with the Master Chemical Mechanism was applied to analyze the photochemical processes in these high-O3 episodes. High levels of O3, nitrogen oxides (NOx), and VOCs facilitated strong production and recycling of ROx radicals with the photolysis of oxygenated VOCs (OVOCs) being the primary source. Our results suggest that local biogenic isoprene is important to local photochemical processes. Removing isoprene could drastically slow down the efficiency of ROx recycling and reduce the concentrations of ROx. The absence of isoprene chemistry could further lead to decrease in the daily average concentration of O3 and HCHO by 36 % and 15 %, respectively. This study underlines that the isoprene chemistry in rural atmosphere becomes important with the participation of anthropogenic NOx and also provides insights into the radical chemistry that essentially drives the formation of secondary pollutants (e.g. O3 and HCHO) in rural YRD region.

Kun Zhang et al.

 
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Kun Zhang et al.

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Short summary
Recently, high O3 concentration was frequently observed at the rural areas of Yangtze River Delta (YRD) region under stagnant condition. Using online measurement and observation-based model, we investigated the budget of ROx radicals and the influence of isoprene chemistry on O3 formation. Our results underline that isoprene chemistry in rural atmosphere becomes important with the participation of anthropogenic NOx.
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