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

Guicai Ning, Shigong Wang, Steve H. L. Yim, Jixiang Li, Yuling Hu, Ziwei Shang, Jinyan Wang, Jiaxin Wang
2018 Atmospheric Chemistry and Physics Discussions  
<p><strong>Abstract.</strong> 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
more » ... 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 700<span class="thinspace"></span>hPa. 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 700<span class="thinspace"></span>hPa. 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 700<span class="thinspace"></span>hPa 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.</p>
doi:10.5194/acp-2018-61 fatcat:wq4bvk5sz5fjlifonuuayn2ciy