A comparative study to reveal the influence of typhoons on the transport, production and accumulation of O 3 in the Pearl River Delta, China

Qu, Kun; Wang, Xuesong; Yan, Yu; Shen, Jin; Xiao, Teng; Dong, Huabin; Zeng, Limin; Zhang, Yuanhang

The Pearl River Delta (PRD) region in South China is faced with severe ambient tropospheric ozone (Oinline-formula3) pollution in autumn and summer, which mostly coincides with the occurrence of typhoons above the Northwest Pacific. With increasingly severe Oinline-formula3 pollution in the PRD under the influence of typhoons, it is necessary to gain a comprehensive understanding of the impact of typhoons on Oinline-formula3 transport, production and accumulation for efficient Oinline-formula3 reduction. In this study, we analysed the general influence of typhoons on Oinline-formula3 pollution in the PRD via systematic comparisons of meteorological conditions, Oinline-formula3 processes and sources on Oinline-formula3 pollution days with and without typhoon occurrence (denoted as the typhoon-induced and no-typhoon scenarios, respectively) and also examined the differences in these influences in autumn and summer. The results show that the approach of typhoons was accompanied by higher wind speeds and strengthened downdraughts in autumn, as well as the inflows of more polluted air masses in summer, suggesting favourable Oinline-formula3 transport conditions in the typhoon-induced scenario in both seasons. However, the effect of typhoons on the production and accumulation of Oinline-formula3 were distinct. Typhoons led to reduced cloud cover, and thus stronger solar radiation in autumn, which accelerated Oinline-formula3 production, but the shorter residence time of local air masses was unfavourable for the accumulation of Oinline-formula3 within the PRD. In contrast, in summer, typhoons increased cloud cover, and weakened solar radiation, thus restraining Oinline-formula3 formation, but the growing residence time of local air masses favoured Oinline-formula3 accumulation. The modelling results using the Community Multiscale Air Quality (CMAQ) model for the typical Oinline-formula3 pollution days suggest increasing contributions from the transport processes and sources outside the PRD for Oinline-formula3 pollution, confirming enhanced Oinline-formula3 transport under typhoon influence in both seasons. The results of the process analysis in CMAQ suggest that the chemical process contributed more in autumn but less in summer in the PRD. Since Oinline-formula3 production and accumulation cannot be enhanced at the same time, the proportion of Oinline-formula3 contributed by emissions within the PRD was likely to decrease in both seasons. The difference in the typhoon influence on Oinline-formula3 processes in autumn and summer can be attributed to the seasonal variation of the East Asian monsoon. From the meteorology–process–source perspective, this study revealed the complex influence of typhoons on Oinline-formula3 pollution in the PRD and their seasonal differences. To alleviate Oinline-formula3 pollution under typhoon influence, emission control is needed on a larger scale, rather than only within the PRD.

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Qu, Kun / Wang, Xuesong / Yan, Yu / et al: A comparative study to reveal the influence of typhoons on the transport, production and accumulation of O3 in the Pearl River Delta, China. 2021. Copernicus Publications.

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