Abstract
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 these cities in recent decades, 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. A total of 10 heavy air pollution events occurred during the research period and 8 of these took place while the region was affected by a dry low-pressure system at 700 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, 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 to 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 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 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.
Highlights
Air quality, especially the occurrence of heavy air pollution events, is strongly affected by excessive emission of air pollutants, but is closely associated with meteorological conditions, including atmospheric circulations, weather systems, structures of the atmospheric boundary layer, and the corresponding meteorological parameters (Deng et al, 2014; Gu and Yim, 2016; Li et al, 2015; Wei et al, 2011; Ye et al, 2016; Zhang et al, 2012)
Bei et al (2016) classified typical synoptic situations and evaluated their contributions to air quality in the Guanzhong Basin, China. They found that an inland high-pressure system at 850 hPa resulted in temperature inversion, low horizontal wind speed, and a shallow atmospheric boundary layer, which favor the formation of heavy air pollution
To quantitatively evaluate the horizontal dispersion of air pollutants in Sichuan Basin, the Mean wind speed (MWS) in the lower troposphere was constructed based on the concept of the ventilation coefficient (VC is a product of the mixing layer height multiplied by average wind speed through the mixing height)
Summary
Especially the occurrence of heavy air pollution events, is strongly affected by excessive emission of air pollutants, but is closely associated with meteorological conditions, including atmospheric circulations, weather systems, structures of the atmospheric boundary layer, and the corresponding meteorological parameters (Deng et al, 2014; Gu and Yim, 2016; Li et al, 2015; Wei et al, 2011; Ye et al, 2016; Zhang et al, 2012). Bei et al (2016) classified typical synoptic situations and evaluated their contributions to air quality in the Guanzhong Basin, China They found that an inland high-pressure system at 850 hPa resulted in temperature inversion, low horizontal wind speed, and a shallow atmospheric boundary layer, which favor the formation of heavy air pollution. This urban agglomeration lies close to the eastern slopes of Tibetan Plateau, and is affected by low-pressure systems moving east from the plateau (Feng et al, 2016). The main purpose of this study was to statistically analyze the relationships between lowpressure systems and winter heavy air pollution events in this urban agglomeration, and to explore the physical mechanisms involved in the formation of winter heavy air pollution.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
