Weak coupling of observed surface PM2.5 in Delhi-NCR with rice crop residue burning in Punjab and Haryana

Air pollution impacts on human health are of serious concern in northern India, and over the Delhi National Capital Region (NCR) in particular. The Kharif crop residue burning (CRB) is often blamed for degradation of Delhi-NCR’s seasonal air quality. However, the concentration of fine particulate matter (PM2.5) remained stable in Delhi, while the fire detection counts (FDCs) from satellites over Punjab and Haryana declined by 50% or more during 2015-2023. We further analysed measurements of PM2.5, carbon monoxide (CO) and related parameters in Delhi-NCR, Haryana and Punjab from a network of 30 low-cost sensors (CUPI-Gs) in a selected period (September–November) of 2022 and 2023. Measured PM2.5 showed lower concentration in 2023 compared to 2022 at Punjab and Haryana sites, in compliance with FDC reductions. We have conducted airmass trajectories, particle dispersion and chemistry-transport model simulations to depict the formation of air pollution events from CRB emissions. Using model sensitivity simulations, we estimated meagerly ~14% of PM2.5 in Delhi-NCR was contributed directly by the emissions from CRB in Punjab during October-November 2022. Model-observation comparisons of PM2.5, and day-night variations of PM2.5 and CO suggest emissions from incomplete combustion dominate in Delhi-NCR, which explains the effectiveness of the Graded Response Action Plan (GRAP).