Severe and persistent air pollution episodes across northern India arise from a complex interplay between emissions, meteorology, and cross-border transport. Present work synthesizes results from high-resolution WRF-Chem and WRF–CMAQ model simulations to quantify the contributions of local, regional, and transboundary sources to fine-particulate (PM2.5) pollution across the Delhi-NCR region and the Indo-Gangetic Plain. The analyses reveal that residential fuel combustion remains the largest contributor, accounting for 40–55% of PM2.5 concentrations, while episodic crop-residue burning in Punjab and Haryana causes short-lived spikes of 30–50%. Organic aerosols dominate the chemical composition, followed by black carbon and secondary inorganics. Meteorological variability alone modulates PM2.5 by ±25–35 µg m⁻³ through boundary-layer and ventilation effects, while cross-border inflows add ±8–11 µg m⁻³. Emission-control experiments show that reducing residential, transport, and industrial emissions by half, along with eliminating crop burning, can lower winter PM2.5 levels by up to 50% and significantly increase the number of satisfactory air-quality days. However, local mitigation in Delhi alone yields limited improvement because polluted inflows from adjacent states persist under prevailing wind conditions. These results demonstrate that India’s air pollution challenge is both meteorology- and transport-driven, highlighting the need for an integrated airshed-based management strategy that coordinates emission control, meteorological forecasting, and regional cooperation across the Indo-Gangetic Plain.