This study investigates the sources and oxidative potential (OP) of particulate matter (PM) in Northern India, focusing on five sites within and outside Delhi. The findings reveal that while PM concentrations are uniformly high across the region, local emission sources and formation processes dominate PM pollution. Inside Delhi, ammonium chloride and organic aerosols (OA) from traffic exhaust, residential heating, and oxidation of unsaturated vapors from fossil fuels are the primary PM sources. Outside Delhi, ammonium sulfate and nitrate, along with secondary OA from biomass burning vapors, are more prevalent. However, the OP is predominantly driven by OA from incomplete combustion of biomass and fossil fuels, including traffic emissions. These results suggest that addressing local inefficient combustion processes can effectively mitigate PM-related health exposure in northern India. The study also highlights the need for targeted local and regional control strategies to reduce PM pollution and improve air quality.This study investigates the sources and oxidative potential (OP) of particulate matter (PM) in Northern India, focusing on five sites within and outside Delhi. The findings reveal that while PM concentrations are uniformly high across the region, local emission sources and formation processes dominate PM pollution. Inside Delhi, ammonium chloride and organic aerosols (OA) from traffic exhaust, residential heating, and oxidation of unsaturated vapors from fossil fuels are the primary PM sources. Outside Delhi, ammonium sulfate and nitrate, along with secondary OA from biomass burning vapors, are more prevalent. However, the OP is predominantly driven by OA from incomplete combustion of biomass and fossil fuels, including traffic emissions. These results suggest that addressing local inefficient combustion processes can effectively mitigate PM-related health exposure in northern India. The study also highlights the need for targeted local and regional control strategies to reduce PM pollution and improve air quality.