Post-monsoon air quality degradation across Northern India: assessing the impact of policy-related shifts in timing and amount of crop residue burnt

H Sembhi,T Zhang,S Agarwal,M Wooster,S Sharma,N Singh,H Boesch,S N Tripathi,S Mor,S Gupta,A Misra,R Khaiwal

doi:10.1088/1748-9326/aba714

Abstract

The past decade has seen episodes of increasingly severe air pollution across much of the highly populated Indo-Gangetic Plain (IGP), particularly during the post-monsoon season when crop residue burning (CRB) is most prevalent. Recent studies have suggested that a major, possibly dominant contributor to this air quality decline is that northwest (NW) Indian rice residue burning has shifted later into the post-monsoon season, as an unintended consequence of a 2009 groundwater preservation policy that delayed the sowing of irrigated rice paddy. Here we combine air quality modelling of fine particulate matter (PM2.5) over IGP cities, with meteorology, fire and smoke emissions data to directly test this hypothesis. Our analysis of satellite-derived agricultural fires shows that an approximate 10 d shift in the timing of NW India post-monsoon residue burning occurred since the introduction of the 2009 groundwater preservation policy. For the air quality crisis of 2016, we found that NW Indian CRB timing shifts made a small contribution to worsening air quality (3% over Delhi) during the post-monsoon season. However, if the same agricultural fires were further delayed, air quality in the CRB source region (i.e. Ludhiana) and for Delhi could have deteriorated by 30% and 4.4%, respectively. Simulations for other years highlight strong inter-annual variabilities in the impact of these timing shifts, with the magnitude and even direction of PM2.5 concentration changes strongly dependent on specific meteorological conditions. Overall we find post-monsoon IGP air quality to be far more sensitive to meteorology and the amount of residue burned in the fields of NW India than to the timing shifts in residue burning. Our study calls for immediate actions to provide farmers affordable and sustainable alternatives to residue burning to hasten its effective prohibition, which is paramount to reducing the intensity of post-monsoon IGP air pollution episodes.

Highlights

Outdoor air pollution is the world’s greatest environmental health risk (WHO 2020), and fine particulate matter (PM2.5) is its most harmful component and a leading cause of morbidity and premature death across much of South Asia (Landrigan et al 2018)
Similar findings are observed for the scenarios based on the 2017 meteorology and changed crop residue burning (CRB) emissions with PM2.5 always larger when CRB emissions are higher. These results suggest that significant increases in CRB magnitude over the past 15 years, which is corroborated by increased crop production (Jethva et al 2019), are likely to be responsible for the increasing severity of post-monsoon air pollution episodes
Focusing on episodes of post-monsoon air pollution across the Indo-Gangetic Plain (IGP), our results demonstrate how a combination of satellite data and atmospheric modelling can greatly aid the understanding of how drivers of agricultural productivity and poor air quality are coupled to changes in state government legislation

Summary

Introduction

Outdoor air pollution is the world’s greatest environmental health risk (WHO 2020), and fine particulate matter (PM2.5) is its most harmful component and a leading cause of morbidity and premature death across much of South Asia (Landrigan et al 2018). Seasonal crop residue burning (CRB) in the northwest (NW) agricultural states of Punjab and Haryana is a major source of PM2.5 air pollution in north India (Kaskaoutis et al 2014, Lohan et al 2018) Transport of these emissions along the Indo-Gangetic Plain (IGP), can cause impacts on hundreds of millions of citizens (Vadrevu et al 2015), including in the National Capital Territory (NCT) of Delhi (population 20 million). During the post-monsoon months of 2016 for example, CRB in Punjab and Haryana has been implicated in the severely amplified ‘smog’ episode that was experienced across the IGP (Jethva et al 2018) At this time, when rice residue burning is most prevalent, PM2.5 concentrations at locations in Delhi NCT can reach 500 μg m-3 (Chowdhury et al 2019). The US Environmental Protection Agency considers any concentration above 300 μg m-3 to be ‘hazardous’ for everyone, and high enough to sometimes prompt emergency condition alerts

Methods

Results

Discussion

Conclusion