Modeling PM_2.5 and O₃ with aerosol feedbacks using WRF/Chem over the Sichuan Basin, southwestern China

With a large population and fast economic growth, the Sichuan Basin (SCB) has been suffering from air pollution in recent years. However, limited studies have estimated air pollution levels in consideration of the feedbacks of aerosols on meteorology in the SCB. In this study, simulation of fine particulate matter (PM_2.5) and ozone (O₃) over the SCB with a horizontal resolution of 36 km over China and 12 km was conducted for summer (July) and winter (January) in 2015 using the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem). The model well captured the variations of PM_2.5 and daily maximum 8 h average (MDA8) O₃ in the 18 cities, especially O₃ in July and PM_2.5 in January. From rim to center, averaged PM_2.5 increased from 40 μg/m³ to 100 μg/m³ in January while averaged O₃ ranged from 60 to 90 ppb in July. Aerosol radiation decreased surface temperature by 1-2 °C, wind speed (WS) by ∼ 0.3 m/s, planetary boundary layer (PBL) height by 10-20%, solar radiation (SR) by ∼30%, and precipitation by 0.02-0.2 mm, while increased relative humidity (RH) by up to 2-4% in January, which resulted in up to 10 μg/m³ increase of PM_2.5 in January and 2 ppb decrease of O₃ in July. The effect increased as the increase of PM_2.5 concentration and can be up to 18% in January and 25% in July. This study highlights the importance of considering meteorology feedbacks in understanding and controlling air pollution in the SCB.