Critical review of air pollution contribution in Delhi due to paddy stubble burning in North Indian States

Abstract

The application of diverse methods/tools (satellite data, ground-based monitoring and dispersion modelling) for quantitative assessment of air pollution has created a critical challenge for policymakers, in understating the actual stubble burning contribution in North Indian states including Punjab, Haryana, Delhi and western Uttar Pradesh. Considering the variations in monitoring sites, quantified emissions, satellite data resolutions, parameterization schemes, meteorology and/or adopted models, huge differences in the source contribution are reported. Considering these ambiguities, the present study is an attempt to review the studies revealing actual paddy stubble burning contribution to air quality of Delhi conducted year 2015 onwards; one year before the severe episodic smog event of November 2016. A total of 114 articles were searched using different keywords for subsequent in-depth analysis. The biomass burning share was broadly studied for winter, summer and post-monsoon seasons. Further, to understand the season-specific nature of the paddy stubble burning activity, the analysis was restricted to post-monsoon months. A co-occurrence keyword network analysis was performed based on which biomass/stubble burning related studies were divided into three clusters based on i) source apportionment using receptor modeling, ii) satellite data (AOD values coupled with ground-based observation and wind back trajectory and, iii) regional scale chemical transport modeling approach. Some studies were generalized displaying correlation patterns, some used only fire count data and correlated with AOD while some used either satellite data or regional scale models. Learning from the gap analysis of the reviewed studies led to the development of an integrated assessment protocol to quantify the stubble-burning contribution in the region.