Contribution of Regional PM 2.5 Transport to Air Pollution Enhanced by Sub-Basin Topography - A Modeling Case over Central China

Aug 27, 2026

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The Twain-Hu basin (THB) in central China has faced severe PM2.5 pollution, while the role of sub-basin topography in shaping air quality remains insufficiently understood. During a heavy PM2.5 episode from 4–10 January 2019, observations and WRF-Chem simulations with sensitivity experiments were used to identify mechanisms. Results show stronger western urban pollution (189.8 µg m−3 vs 106.3 µg m−3) and an overall inverse contribution of terrain effects through regional transport enhancement and boundary-layer ventilation changes.

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CategoryResearch & Report

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atmosphere Article Contribution of Regional PM 2.5 Transport to Air Pollution Enhanced by Sub-Basin Topography: A Modeling Case over Central China Weiyang Hu 1, Tianliang Zhao 1, *, Yongqing Bai 2,*, Lijuan Shen 1, Xiaoyun Sun 1 and Yao Gu 1 1 Climate and Weather Disasters Collaborative Innovation Center, Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, PREMIC, Nanjing University of Information Science&Technology, Nanjing 210044, China; [wyhu_aca@126.com](wyhu_aca@126.com) (W.H.); [20181103046@nuist.edu.cn](20181103046@nuist.edu.cn) (L.S.); [sunxy6362@126.com](sunxy6362@126.com) (X.S.); [guyao@nuist.edu.cn](guyao@nuist.edu.cn) (Y.G.) 2 Institute of Heavy Rain, China Meteorological Administration, Wuhan 430205, China * Correspondence: [tlzhao@nuist.edu.cn](tlzhao@nuist.edu.cn) (T.Z.); [baiyq2007@126.com](baiyq2007@126.com) (Y.B.) Received: 29 October 2020; Accepted: 20 November 2020; Published: 22 November 2020 􀀁􀀂􀀃􀀁􀀄 􀀆􀀇􀀈 􀀁􀀂􀀃􀀄􀀅􀀆􀀇 Abstract: The Twain-Hu basin (THB), covering the lower plain of Hubei and Hunan provinces in Central China, has experienced severe air pollution in recent years. However, the terrain effects of such sub-basin on air quality over the THBhave been incomprehensibly understood. A heavy PM2.5 pollution event occurred over the THB during 4–10 January 2019. By using the observations and WRF-Chem simulations, we investigated the underlying mechanisms of sub-basin effects on the air pollution with several sensitivity experiments. Observationally, air pollution in the western THB urban area with an average PM2.5 concentration of 189.8 􀀖g m􀀀3, which was more serious than the eastern urban area with the average PM2.5 concentration of 106.3 􀀖g m􀀀3, reflecting a different influence of topography on air pollution over the THB. Simulation results revealed that the terrain effect can contribute 12.0% to increasing the PM2.5 concentrations in the western THB, but slightly mitigate the pollution extent in the eastern THB with the contribution of 􀀀4.6% to PM2.5 during the heavy pollution episode. In particular, the sub-basin terrain was conducive to the accumulation of PM2.5 by regional transport with the contribution of 39.1 %, and contrarily lowered its local pollution by 􀀀57.0% via the enhanced atmospheric boundary layer height and ventilation coefficients. Given a heavy air pollution episode occurring over the THB, such inverse contribution of terrain effects reflected a unique importance of sub-basin topography in regional transport of air pollutants for air pollution in central China. Keywords: sub-basin e􀀋ect; PM2.5 pollution; Twain-Hu basin; regional transport; WRF-Chem 1. Introduction For the high PM 2.5 concentrations (i.e., the atmospheric particles with aerodynamic diameters equal to or less than 2.5 􀀖m) in ambient atmosphere [1,2] and its negative e􀀋ects on human health [3,4], PM2.5 variations [5,6], causes [7,8], and the impacts on environment and climate [9,10] have been intensively studied in recent years. Anthropogenic emissions of air pollutants are the primary driver for the increase in PM 2.5 concentrations [11,12], and unfavorable meteorological conditions are the major driver to exacerbate air pollution [13–15] . Four regions are closely associated with heavy air pollution on account of their high emission intensity—the North China Plain (NCP) [16,17], the Yangtze River Delta (YRD) [18,19] in East China, the Pearl River Delta (PRD) [20,21] in South China, and Sichuan Basin (SCB) [22–24] in Southwest China. Adverse meteorological conditions, including weak surface winds, temperature inversion layer, Atmosphere 2020, 11, 1258; [doi:10.3390](doi:10.3390/atmos11111258 www.mdpi.com/journal/atmosphere)[/](doi:10.3390/atmos11111258 www.mdpi.com/journal/atmosphere)[atmos11111258 www.mdpi.com](doi:10.3390/atmos11111258 www.mdpi.com/journal/atmosphere)[/](doi:10.3390/atmos11111258 www.mdpi.com/journal/atmosphere)[journal](doi:10.3390/atmos1111

FAQs

What is the main research question of the study?

How sub-basin topography affects air pollution in the Twain-Hu basin, especially by enhancing PM2.5 regional transport during a heavy pollution episode.

Which tools and data are used to investigate the mechanisms?

The study combines observations with WRF-Chem simulations and applies sensitivity experiments to isolate terrain-related effects.

How does sub-basin terrain influence PM2.5 in different parts of the Twain-Hu basin?

Terrain increases PM2.5 concentrations in the western urban area (contribution 12.0%), while it slightly mitigates pollution extent in the eastern area (contribution −4.6%) during the heavy episode.

Aug 27, 2026

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