Quantifying the Contribution of Stubble Burning to Glyoxal over Northwest India

Glyoxal (CHOCHO) is a short-lived oxygenated VOC formed by VOC oxidation and serves as a tracer of secondary photochemical pollution and a precursor to a secondary organic aerosol. We investigate the contribution of crop residue burning to CHOCHO concentrations over northwest India, particularly in the states of Punjab, Haryana, and Delhi, using observations from TROPOMI, VIIRS, and Sentinel-3 satellites. These data sets are used to study the temporal and spatial patterns of CHOCHO and the influence of crop residue burning on CHOCHO levels. HYSPLIT back-trajectory simulations revealed the potential transport of pollutants from stubble-burning areas to Delhi. Large seasonal variations in CHOCHO concentrations were observed, with the highest levels occurring during the postmonsoon months (October–November) as a result of agricultural stubble-burning activities. During peak crop residue burning months, the mean CHOCHO VCD over Punjab exceeded 6 × 1014 molecules cm–2, about 3 × 1014 molecules cm–2 higher than the nonburning baseline. Over Haryana, the mean CHOCHO VCDs reached >5 × 1014 molecules cm–2, about 2 × 1014 molecules cm–2 above baseline. Delhi consistently shows elevated CHOCHO levels across all seasons, but a clear signal of agricultural stubble burning is still observed. We estimate that CHOCHO emissions from agricultural stubble burning in Punjab and Haryana average 1.19 ± 0.91 Gg yr–1, with ≈96.6% of the regional total emitted from Punjab. The contribution of stubble burning to CHOCHO concentrations over Delhi was validated using ground-based AMS measurements at Delhi. This study highlights the role of agricultural stubble burning in regional CHOCHO emissions and the need for effective management policies and strategies to mitigate air pollution in northwest India.