Impact of open-field biomass burning on regional air quality in Northern India

Over the past decade, biomass burning has emerged as one of the main polluting events in northern India. It is one of the major sources of brown carbon (BrC), the light-absorbing organic carbon component of PM_2.5. Most studies on the impact of biomass burning in India are based on source locations or urban areas; very little is known about its effects on a regional background location. We examine the effect of biomass burning on regional air quality and co-occurring meteorological factors. Year-long PM_2.5 levels and light absorption by carbonaceous aerosols at 880 nm and 370 nm were measured at Rohtak, a regional background location. Results showed that post-harvest biomass burning in the Punjab-Haryana region affects the regional air quality with a lead of one to two days. A comparison of dispersion-normalized concentrations showed that open-field biomass burning not only affects regional air quality in the post-monsoon season (kharif crops) but is also a dominant source of PM_2.5 in the post-harvest summer season (rabi crop). A significant (p < 0.05) difference is observed in PM_2.5, b_abs-880, and b_abs-370 between biomass burning days and non-biomass burning days during the kharif and rabi harvest seasons. Regression analyses confirm that in summer, regional PM_2.5 and light absorption by aerosols are influenced more strongly by post-harvest burning of rabi crops. However, adverse meteorology plays a more dominant role in the post-monsoon season than biomass burning. These findings underscore the need for better policy interventions to curb biomass burning and improve air quality during both harvest seasons.