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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-61
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Feb 2018

Research article | 26 Feb 2018

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Impact of low-pressure systems on winter heavy air pollution in the northwest Sichuan Basin, China

Guicai Ning1, Shigong Wang1,2, Steve H. L. Yim3,4, Jixiang Li1, Yuling Hu1, Ziwei Shang1, Jinyan Wang1, and Jiaxin Wang2 Guicai Ning et al.
  • 1The Gansu Key Laboratory of Arid Climate Change and Reducing Disaster, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China
  • 2Key Laboratory of Education Bureau of Sichuan Province for Mountain Environmental Meteorology and Public Health, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225, China
  • 3Department of Geography and Resource Management, The Chinese University of Hong Kong, Hong Kong, China
  • 4The Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kon g, Hong Kong, China

Abstract. The cities of Chengdu, Deyang, and Mianyang in the northwest Sichuan Basin are part of a rapidly developing urban agglomeration adjoining the eastern slopes of the Tibetan Plateau. Heavy air pollution events have frequently occurred over the cities in recent decade, but the effects of meteorological conditions on these pollution events are unclear. We explored the effects of weather systems on winter heavy air pollution from 1 January 2006 to 31 December 2012 and from 1 January 2014 to 28 February 2017. Ten heavy air pollution events occurred during the research period and eight of these took place while the region was affected by a dry low-pressure system at 700hPa. When the urban agglomeration was in front of the low-pressure system and the weather conditions were controlled by a warm southerly air flow, and a strong temperature inversion appeared above the atmospheric boundary layer acting as a lid. Forced by this strong inversion layer, the local secondary circulation was confined within the atmospheric boundary layer and the horizontal wind speed in the lower troposphere was low. As a result, vertical mixing and horizontal dispersion in the atmosphere were poor, favoring the formation of heavy air pollution events. After the low-pressure system had transited over the region, the weather conditions in the urban agglomeration were controlled by a dry and cold air flow from the northwest at 700hPa. The strong inversion layer gradually dissipated, the secondary circulation enhanced and uplifted, and the horizontal wind speed in the lower troposphere also increased, resulting in a sharp decrease in the concentration of air pollutants. The strong inversion layer above the atmospheric boundary layer induced by the low-pressure system at 700hPa thus played a key role in the formation of heavy air pollution during the winter months in this urban agglomeration. This study provides scientific insights for forecasting heavy air pollution in this region of China.

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Under the effects of the Tibetan Plateau, dry low-pressure systems are often formed at 700 hPa in Sichuan Basin, China during winter. Here, we found that the activities of these dry low-pressure systems has significant influence on most winter heavy air pollution events in Sichuan Basin and the influencing mechanism had been summarized. The strong inversion layer above the atmospheric boundary layer induced by the low-pressure system played a key role in the formation of heavy air pollution.
Under the effects of the Tibetan Plateau, dry low-pressure systems are often formed at 700 hPa...
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