Long-term variability and drivers of aerosol loading across India's major atmospheric regimes

Aerosol pollution in India is a severe environmental and climate challenge. The current air quality mitigation strategies focus on uniform national mandates, without considering a region's physiographic diversity. This study aims to investigate the evolution of aerosols and their influence on the physiographically distinct atmospheric regimes. The analyses incorporate 23-year dataset (2000-2023) covering the five physiographic regions of India - Himalayan, arid, industrial, valley and coastal environments - using reanalyzed satellite products. A multi-method framework was adopted, including Mann-Kendall trend detection, change-point analysis, and Principal Component Analysis, with Random Forest and HYSPLIT trajectory modeling used to provide process-based transport diagnostics and environmental consistency support for the identified aerosol regimes. The results indicated that the coastal regime exhibited higher Aerosol Optical Depth (AOD) values (τ = 0.357, p < 0.0001), yielding an absolute increase of ∼0.21 (representing a 70.9% relative increase) over 23 years, while cloud albedo decreased significantly over the same period. Contrastingly, at higher altitudes, relative humidity showed a strong upward trend (τ = 0.255, p < 0.0001; +0.767% annually). Whereas the industrial and arid regimes demonstrated major accumulation of sulfur-based species and black carbon. The highest predictability was observed for Sonitpur (out-of-bag coefficient of determination, R²_OOB = 0.80), while the lowest was observed in Kanpur (R²_OOB = 0.52), reflecting higher spatial and temporal variability in emissions and atmospheric processes. The influence of westerly continental transport in the northern regimes and continuous marine inflow in coastal systems confirm the region-specific source attribution. The aerosols in India are driven by emissions, moisture, and terrain, providing a new framework for regime-specific climate and air-quality interventions.