Abstract
Abstract. A typical multi-day ozone (O3) pollution event was chosen to explore the atmospheric oxidation capacity (AOC), OH reactivity, radical chemistry, and O3 pollution mechanism in a coastal city of southeastern China, with an observation-based model coupled to the Master Chemical Mechanism (OBM-MCM). The hydroxyl radical (OH) was the predominant oxidant (90 ± 25 %) for daytime AOC, while the NO3 radical played an important role in AOC during the nighttime (72 ± 9 %). Oxygenated volatile organic compounds (OVOCs; 30 ± 8 %), NO2 (29 ± 8 %), and CO (25 ± 5 %) were the dominant contributors to OH reactivity, accelerating the production of O3 and recycling of ROx radicals (ROx = OH + HO2 + RO2). Photolysis of nitrous acid (HONO, 33 ± 14 %), O3 (25 ± 13 %), formaldehyde (HCHO, 20 ± 5 %), and other OVOCs (17 ± 2 %) was a major ROx source, which played an initiation role in atmospheric oxidation processes. Combined with regional transport analysis, the reasons for this O3 episode were the accumulation of local photochemical production and regional transport. The results of sensitivity analysis showed that volatile organic compounds (VOCs) were the limiting factor of radical recycling and O3 formation, and the 5 % reduction of O3 would be achieved by decreasing 20 % anthropogenic VOCs. Controlling emissions of aromatics, alkenes, and alkanes with ≥4 carbons was beneficial for ozone pollution mitigation. The findings of this study provide significant guidance for emission reduction and regional collaboration for future photochemical pollution control in the relatively clean coastal cities of China and similar countries.
Highlights
Tropospheric ozone (O3) is mainly produced by photochemical reactions of anthropogenic and natural emitted volatile organic compounds (VOCs) and nitrogen oxides (NOx) and is an important factor resulting in regional air pollution (Zhu et al, 2020; Lu et al, 2018)
The O3 pollution events frequently appeared in the coastal city Xiamen during autumn, related to the West Pacific Subtropical High (WPSH), carrying favorable photochemical reaction conditions and encouraging the formation and accumulation of O3 in the southeastern coastal area
The time series and descriptive statistics of air pollutants and meteorological parameters during this multi-day O3 pollution event are shown in Fig. 1 and Table 2
Summary
Tropospheric ozone (O3) is mainly produced by photochemical reactions of anthropogenic and natural emitted volatile organic compounds (VOCs) and nitrogen oxides (NOx) and is an important factor resulting in regional air pollution (Zhu et al, 2020; Lu et al, 2018). Elevated O3 concentrations enhance the atmospheric oxidation capacity (AOC) and have harmful effects on global climate change, ecosystems, and human health The formation mechanisms of O3 pollution are extremely difficult to figure out, due to the complex types and sources of its precursors (Simon et al, 2015). O3 formation is affected by multiple factors, such as O3 precursor speciation or level, atmospheric oxidation capacity, meteorological conditions, and regional transport (Gong and Liao, 2019; Chang et al, 2019). To effectively control tropospheric O3 pollution, exploration of the photochemical mechanism and judgment of the controlling factors of O3 formation have become extremely important for the scientific community (Chen et al, 2020; Li et al, 2018)
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