Satellite derived air pollution climatology over India and its neighboring regions: Spatio-temporal trends and insights

This study examines the spatial and temporal variations of key air pollutants, including Nitrogen Dioxide (NO2), Carbon Monoxide (CO), Tropospheric Ozone (O-3), Sulfur Dioxide (SO2), Aerosol Optical Depth (AOD), and Formaldehyde (HCHO) over India and neighboring regions, using satellite data from 2005 to 2022. Peak NO2 (similar to 11-13 x 10(15) molecules/cm(2)) occurs in pre-monsoon and winter, mainly over urban centers, thermal plants, and crop-burning areas, emphasizing anthropogenic emissions. High CO levels (2.0-2.3 x 10(18) molecules/cm(2)) during summer dominate in Indo-Gangetic Plains (IGP), Eastern India, and Northeastern region, linked to the incomplete combustion of organic matter (e.g., natural forest fires and biofuel-based household cooking). Stable CO trends reflect effective government policies promoting cleaner fuels. Tropospheric O-3 shows a spatial gradient, with higher values in northern and coastal regions influenced by sunlight, humidity, and precursor emissions. Seasonal peaks in summer are governed by solar intensity, while the December peak over the northern region is likely due to dynamical transport from O-3-rich areas. SO2 hotspots in IGP, central and eastern India, especially during winter (similar to 1.3-1.9 x 10(15)molecules/cm(2)), are attributed to local anthropogenic emissions and fossil fuel combustion such as coal. Long-term trends reveal rising SO2 levels. AOD hotspots occur over IGP, Central and Southern India, with particularly high values during the pre-monsoon (0.5-0.6) and winter seasons. HCHO shows hotspots in the IGP, west coast, eastern, and northeastern regions, peaking in summer (7.5-8.5 x 10(15)molecules/cm(2)) due to biogenic VOC emissions. This study underscores the need for integrated policies to mitigate emissions, improve air quality, and protect public health.