Investigating air pollutant concentrations, impact factors, and emission control strategies in western China by using a regional climate-chemistry model

Abstract

In this study, in situ observations were conducted for six criteria air pollutants (PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃) at 23 sites in western China for 1 year. Subsequently, the detailed Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) results for the pollutants were determined. The WRF-Chem model provided a clear perspective on the spatiotemporal distribution of air pollutants. High pollutant concentrations were mainly observed over highly populated mega-city regions, such as Sichuan and Guanzhong basins, whereas low concentration levels were observed over the Tibetan Plateau (TP). The TP also showed an increased concentration of O₃. Seasonally, all six pollutants except O₃ exhibited high concentration values during winter and low values during summer. O₃ concentrations exhibited an opposite seasonal variation in low-altitude regions. Unlike other pollutants that exhibited gradually decreasing concentrations with an increase in altitude, O₃ concentrations revealed an increasing trend. Furthermore, NO₂ concentrations gradually increased in the upper atmosphere possibly due to lighting and stratospheric transmission. Atmospheric pollution is closely related to emissions and meteorological variations in western China. Meteorological conditions in the summer are conducive to pollutant dispersion and wet scavenging; however, unfavourable weather conditions (high pressure as well as a low planetary boundary layer height and precipitation level) in the winter can further worsen air pollution. Atmospheric pollutants from various emission sectors generally exhibited varying monthly profiles. In six typical cities, pollutants were positively correlated with multiple emission sources except for industrial emissions. Further sensitivity simulations indicated that eliminating residential emissions resulted in the largest decrease (up to 70%) in PM_2.5 and PM₁₀ concentrations. The most significant reductions in the concentrations of SO₂ and NO₂ were achieved by eliminating industrial and transportation emissions, respectively. The outcomes of this study could be helpful for future studies on pollution formation mechanisms as well as environmental and health risk assessments in western China.

Keywords: Emission control strategies; Impact factors; Pollutant distribution; WRF-Chem; Western China.