Assessing Urban Pollution and Heat Island Feedback in a Northern Megacity Using the Fully Coupled COSMO-ART Model

The interaction between the urban heat island (UHI) and urban air pollution (UAP) is widely studied in temperate climates, but it remains underexplored in high latitudes. Using the COSMO-ART atmospheric model with the TERRA_URB urban parameterization, we analyzed feedback during winter and summer pollution episodes in Saint Petersburg, the world’s northernmost megacity. We show that UHI-induced enhancement of turbulent mixing and boundary layer height significantly reduces near-surface primary pollutants (NO, CO, PM10): by 15–54% on average in the winter case and by 5–33% in the summer case, with peak PM10 reduction exceeding 44%. In contrast, ozone concentrations increase. In turn, the UAP effect on UHI, i.e., urban aerosol radiative feedback, is weak (hundredths of °C on average, peak magnitudes < 0.3 °C), and it exhibits a seasonal asymmetry. In the summer case, aerosols attenuate incoming shortwave radiation, producing weak cooling, while in the winter case, high snow albedo reverses the sign, causing a weak warming. Overall, this aerosol feedback is substantially weaker than urban canopy forcing, amounting to less than a fifth of the average UHI intensity. Our findings underscore the importance of considering urban canopy effects and their influence on the boundary layer in air pollution modeling in cold-climate cities.