Decadal shifts in aerosol hotspots and source attribution over IGP, north-east India and Himalayas: A 25-year (2000–2024) study

Abstract

To examine decadal changes in aerosol pollution, trends, hotspots, and aerosol types across the Indo-Gangetic Plain (IGP), north-east India (NEI), and the Himalayas, a 25-year (2000–2024) analysis was conducted using MODIS and MERRA-2 datasets. The highest aerosol loading and trend (MODIS AOD) occurred over the lower IGP (0.71 ± 0.09; 0.016 yr⁻¹), followed by the middle IGP (0.65 ± 0.10; 0.009 yr⁻¹), upper IGP (0.51 ± 0.10; 0.003 yr⁻¹), and NEI (0.40 ± 0.10; 0.008 yr⁻¹). Within the Himalayas, the central region showed the highest AOD (0.24 ± 0.09) with low trends (0.001–0.003 yr⁻¹). Significant rising trends were observed in SO₄²⁻_AOD over the lower IGP (0.006 yr⁻¹) and OC_AOD over NEI (0.004 yr⁻¹). AOD across the entire IGP and NEI increased by more than 20 % in the 2010s relative to the 2000s. Notably, SO₄²⁻_AOD increased by ∼30–40 % over the lower IGP, while OC_AOD rose by over 50 % in NEI and the eastern Himalayas, with an additional 30–40 % rise during 2020–2024. Bangladesh, the lower IGP, and NEI consistently emerged as hotspots of carbonaceous and sulphate aerosols, shifting into highly polluted zones after 2020. The upper and middle IGP for the western and central Himalayas and NEI and the lower IGP acted as major source regions. Clean-continental and biomass/urban aerosols dominated the Himalayas, whereas anthropogenic aerosols prevailed over the IGP and NEI, with notable increases across the Himalayas after 2020. These insights can guide targeted mitigation strategies for the IGP and vulnerable Himalayan regions.