Discovering the Urban Heat and Pollution Island variability over Kolkata, India

Abstract

Urban environments are distinguished by elevated aerosol optical depth (AOD) and increased temperatures, primarily driven by the concentrated emissions of heat and pollutants originating from various anthropogenic activities. These processes lead to the development of Urban Pollution Islands (UPI) and Urban Heat Islands (UHI). The interaction between UHI and UPI is complex: turbulent air dispersion associated with UHI modifies the spatial distribution and intensity of aerosols within the UPI, while the UPI influences UHI through radiative forcing mechanisms by altering the balance of incoming and outgoing solar radiation between the atmosphere and the surface. In this study, multiple remote sensing datasets alongside in situ measurements are utilized to comprehensively characterize the spatial and temporal dynamics of heat and pollution islands across the Kolkata metropolitan area (KMA). Observations confirm the presence of distinct UHI and UPI phenomena in KMA, with land surface temperature (LST) and aerosol optical depth (AOD) exhibiting significantly higher magnitudes in urban cores relative to surrounding rural areas. Notably, LST and AOD show a negative correlation, which corresponds with a measurable reduction in direct solar radiation reaching the surface by approximately 22.64 W/m², accompanied by an increase in diffuse radiation of about 18.82 W/m² over urban zones. This study further investigates the bidirectional feedback mechanisms between UPI and UHI through their influence on radiative forcing components, specifically analyzing how changes in aerosol concentration impact both direct and diffuse solar radiation fluxes, and in turn, how these radiative alterations modulate surface temperatures and atmospheric stability within the urban environment.