Anthropogenic heat island motivated by coal-burning plants and its dispersion on the air pollutants

The anthropogenic activities are playing an increasingly important role in regulating the atmospheric environment and local climate, therefore, it is of great significance to explore the effects of large anthropogenic heat sources on the structure of the atmospheric boundary layer (ABL), as well as their dispersion on the air pollutants. In this study, high spatio-temporal resolution observations of the ABL structure within a large coal-burning steel plant were performed in Yuncheng city (Shanxi province) in July of 2021. Results revealed that the strong anthropogenic heats disturbed the thermodynamic and material structure of the ABL, resulting in vertically homogeneous air pollutants in the daytime and high concentration pollutants stored within the nighttime residual layer (RL). Moreover, a dry heat island was formed above the coal-burning plant at night due to the horizontally spatial thermal contrast with the surrounding fields and villages. The dry heat-island was generally generated after sunset and disappeared within 1-2 hours beyond sunrise, with 3-10°C higher and 30-60% drier than the neighboring areas. Large-eddy simulations constrained by the in-situ measurements show that the heat-island circulation can diffuse the plant-discharged pollutants to penetrate through the stable boundary layer and enter into the RL, horizontally spreading below the upper boundary of the RL and eventually forming a "mushroom cloud". The formation, size, and pollutant concentration of the “mushroom cloud” are significantly influenced by the dynamic wind speed and anthropogenic heat intensity. As the increase of the solar irradiance in the next day, the pollutants retained within the RL can be downward transported to the ground, leading to the morning peaks of various pollutants at the surface level, which were statistically found to be common phenomenons not only in the areas adjacent to the plant, but also in the major urban clusters across China.