Effects of wintertime haze on regional thermal environment and urban heat island in the Yangtze River Delta, China

Urban heat island (UHI) is an important issue of regional thermal environment in urban climate, which is affected by airborne particulates. However, the influences of various aerosol compositions on the UHI have been rarely reported. This study investigates the radiative effects of particulates on regional thermal environment and the UHI intensity (UHII) in the YRD during January 2018 using the WRF-Chem model. The model performs reasonably in reproducing the observed evolutions of the key meteorological fields and air pollutants. Our results show that the UHI effect is prevalent over megacities of the YRD, with markedly higher surface UHII compared to the canopy one. The UHI effect generally gets more significant during nighttime and reaches the maximum in the late afternoon. Fine particulates nonlinearly reduce the surface and air temperature, which lowers the UHII throughout the day, but significant differences exist among different UHI indices. We highlight that these influences are predominantly attributed to the radiative effect of sulfate, nitrate, and ammonium aerosols. As a comparison, the effects of organic aerosols are much less and black carbon reduces the UHI almost negligibly. This study would contribute to a comprehensive understanding of radiative effects of aerosols on the UHI.

Automated summary

The urban heat island (UHI) is influenced by airborne particulates and this study investigates their radiative effects on the regional thermal environment and UHI intensity (UHII) in the Yangtze River Delta. The results show that UHI effect is prevalent in megacities of the region, with higher surface UHII than canopy UHII. The UHI effect is more significant during nighttime and reaches its maximum in the late afternoon. The study highlights the significant influence of sulfate, nitrate, and ammonium aerosols on UHI, while organic aerosols and black carbon have lesser effects.