Enhanced PM2.5 pollution in China due to Aerosol–Cloud Interactions

Aerosol-cloud interactions (aerosol indirect effects) play an important role in regional radiative energy budget and meteorological variations, which could further induce feedback on regional air quality. While the impact of aerosol-cloud interactions on meteorology and climate has been extensively studied, their feedback on air quality remains unclear. Using the Weather Research and Forecasting (WRF) model coupled with Chemistry, we find that increased aerosol loading due to anthropogenic activities in China substantially increases column cloud droplet number concentration and liquid water path (LWP), which further leads to a reduction in the downward shortwave radiation at surface, surface air temperature and planetary boundary layer (PBL) height. The shallower PBL and accelerated cloud chemistry due to larger LWP in turn enhance the concentrations of particulate matter with diameter less than 2.5 mm (PM_2.5) by up to 33.2 mg m⁻³ (25.1%) and 11.0 mg m⁻³ (12.5%) in January and July, respectively. Such a positive feedback amplifies the changes in PM_2.5 concentrations, indicating an additional air quality benefit under effective pollution control policies but a penalty for a region with a deterioration in PM_2.5 pollution. Also, this feedback loop helps to explain the extremely high PM_2.5 concentrations during heavy pollution periods, which cannot be reproduced by most chemical transport models. Additionally, we show that the cloud processing of aerosols, including wet scavenging and cloud chemistry, could also have substantial effects on PM_2.5 concentrations.