Diurnal variability and trends of air pollution in association with heat stress over five indian megacities.

Air pollutants play an important role in Earth's climatic processes and human health. Their association with meteorological parameters can have serious implications on heat stress. With the hot and humid climate in the Indian region, along with the fast-growing population, urbanization, and anthropogenic emissions, there could be a higher risk of mortality in the highly populated pockets of the country, i.e., the megacities. This study presents the diurnal variability and trends of air pollutants (PM, PM, ozone, SO, CO, NO, NO, NH) during 2016-23 over the five Indian megacities (Delhi, Mumbai, Chennai, Bengaluru, and Hyderabad). The corresponding behavior of heat stress in terms of WBGT is also reported. The diurnal variability of air pollutants and heat stress across the five cities across the four seasons reveals significant variations which could be influenced by local emissions and meteorology. A correlation analysis at a seasonal scale has been carried out between the air pollutants and the heat stress to observe the impact of one on another. Whereas decreasing trends for major pollutants like PM and PM could be observed for different seasons across the cities, there are instances of season- and city-specific increasing trends. Increasing trends of WBGT have also been observed. These insights underscore the urgency of adaptive, region-specific policies to mitigate air pollution and manage heat stress in India's urban centers.