Sectoral Contributions to Primary and Secondary PM_2.5 in Regional Airsheds of India

The exceedance of annual ambient fine particulate matter (PM_2.5) concentrations above the national air quality standard across a large region in India, extending beyond the urban centers, necessitates an airshed approach for effective air quality management. Using over two decades of satellite-derived PM_2.5 concentration data, seasonal wind patterns, and topography, we identified 9–11 major regional airsheds in India and further delineated the local airsheds of nonattainment cities. We separated sectoral contributions to primary and secondary PM_2.5 in each airshed using outputs from a chemical transport model for the National Clean Air Program (NCAP) baseline year. In most airsheds, secondary PM_2.5 constituted a larger share than primary PM_2.5 except for the monsoon season. The domestic sector contributed the most to primary PM_2.5 in most airsheds, while transboundary transport, industry, power, and other sources were the major contributors to secondary PM_2.5. Our results can be used as a reference to assess progress in reducing ambient PM_2.5 levels through the implementation of the NCAP action plan. Our study provides a comprehensive analysis of airsheds in India and underscores the need to control precursor gases, along with primary sources, for effective air pollution mitigation in the context of airsheds.