How do atmospheric pollutant changes driven by anthropogenic heat provide feedback on the urban thermal environment in Beijing?

Anthropogenic heat (AH) is crucial for understanding and responding to urban climate change. However, variations in atmospheric pollutants caused by AH and their feedback on the urban thermal environment remain unclear, hindering our comprehension of AH impacts and the urban climate system. Therefore, this study combined spatial-temporal heterogeneous AH modeling with an improved coupling method in the WRF-Chem model. Multiple sensitivity experiments were conducted in winter and summer to separate the physical and chemical effects of AH and further evaluate changes in outdoor thermal comfort (OTC). The results indicated a certain consistency and correlation in the spatial-temporal distribution of air pollutants. AH affected atmospheric convection and heat island circulation, promoting the mixing and diffusion of pollutants. It significantly reduced near-surface concentrations of primary pollutants in winter, with average reductions in urban center NO₂, SO₂, CO, and PM2.5 concentrations of 60 μg/m³, 8 μg/m³, 0.6 mg/m³, and 36 μg/m³, respectively. However, it exacerbated ozone pollution in summer, with urban O₃ concentrations increasing by an average of 40 μg/m³ at night, with vertical impacts reaching 800 meters. The indirect chemical effect of AH refers to the feedback of pollutant changes on near-surface climate. Compared to winter, this indirect chemical effect was more prominent in summer, significantly affecting temperature, humidity, and wind speed, with a maximum warming of over 0.4 °C. The effect enhanced afternoon shortwave radiation reaching the surface and weakened downward longwave radiation at night, playing a crucial role in the comprehensive impact of AH. In winter, AH affected OTC mainly through its direct physical effect, which positively impacted the mitigation of cold stress. In summer, the indirect chemical effect was not negligible; it mitigated heat stress at night but exacerbated the risk of heat stress at noon, with the OTC index rising by more than 1 °C. These findings underscore the importance of including atmospheric chemical mechanisms and air quality in studies of thermal environments. In the future, a comprehensive understanding of how AH affects urban climate systems will be crucial for improving urban quality of life and addressing climate change challenges.