How Stubble Burning Spreads Black Carbon Across North India

Crop-residue burning can become a dominant source of black carbon pollution in parts of North India during the post-monsoon season, according to a new study by researchers from IIT Delhi. Real-time measurements from an agricultural site in rural Punjab found that biomass burning contributed an average of around 48% of total black carbon, or soot, during the October-November burning season, with its contribution periodically exceeding 90% during active burning hours. The findings provide fresh quantitative evidence of how emissions from burning crop residues can worsen air quality across the Indo-Gangetic Plain and travel to downwind cities, including Delhi. 

Stubble burning can briefly become the biggest source of black carbon

The researchers conducted the study at an agricultural field site in Kheral village in rural Punjab, using a mobile monitoring laboratory equipped to measure black carbon, PM2.5 composition, and meteorological conditions such as wind speed and direction.

The average black carbon concentration recorded at the site was 12.6 micrograms per cubic metre (µg/m³). Researchers used two source-apportionment approaches, the Aethalometer model and Positive Matrix Factorisation, to identify where the pollution was coming from. Both methods pointed to crop-residue burning as a major contributor.

The Aethalometer analysis attributed 48.5% of black carbon to biomass burning and 51.5% to fossil-fuel burning. The more detailed Positive Matrix Factorisation analysis identified biomass burning as the largest single source at 48%, followed by power plant emissions at 24% and traffic emissions at 20.2%. Industrial sources and waste incineration accounted for smaller shares.

The findings underline that while stubble burning is not the only source of black carbon pollution, it can temporarily dominate local air pollution during periods of intense agricultural burning.

Pollution from Punjab can travel across the Indo-Gangetic Plain

The study also tracked how emissions move beyond the fields where crop residues are burned. Using the NOAA-developed HYSPLIT atmospheric transport model, researchers confirmed that pollutants released from the Punjab study area could travel across the Indo-Gangetic Plain, affecting nearby and downwind regions.

This transport of pollution is particularly significant during October and November, when crop-residue fires coincide with changing weather conditions that can allow pollutants to accumulate over northern India. Emissions generated in agricultural areas can therefore add to pollution from vehicles, industries, power plants and other sources in densely populated cities such as Delhi.

However, researchers caution against applying a single percentage to represent stubble burning’s contribution to black carbon across India. Its role varies considerably depending on location, season and the presence of other emission sources. Previous research cited in the report, for example, found different contributions from crop burning in Delhi and across the wider Indo-Gangetic Plain.

Black carbon links air pollution, health and climate change

Black carbon is particularly important because it is both an air pollutant and a climate-warming agent. Unlike some aerosol particles that primarily reflect sunlight, black carbon strongly absorbs solar radiation and converts it into heat, contributing to atmospheric warming. When deposited on snow and ice, black carbon can also reduce surface reflectivity and accelerate melting. At the same time, because it is a component of fine particulate pollution, it can penetrate deep into the respiratory system and has been associated with serious cardiovascular and respiratory health impacts.

The report also highlights significant geographical differences in black carbon exposure across India. High exposure levels have been identified in the Indo-Gangetic Plain, Assam and the industrial region around Mumbai, while the health burden associated with exposure can vary depending on pollution levels as well as underlying social and health vulnerabilities.

Study strengthens the case for targeted action during burning season

The findings could help policymakers design more targeted interventions during the post-harvest burning season. The study points to the importance of focusing action during periods when crop-residue fires are most active, while other research highlighted in the report suggests that enforcement alone may not be enough to permanently reduce burning.

Research suggests that a ban imposed by the National Green Tribunal worked where authorities enforced it seriously, but had little lasting impact when penalties were low and enforcement was weak. Researchers have argued that policies reducing the cost and difficulty of managing crop residues without burning could be more effective alongside enforcement measures.

The broader significance of reducing black carbon emissions extends beyond improving seasonal air quality. Because black carbon remains in the atmosphere for a relatively short period, cutting emissions can produce comparatively rapid benefits for air quality and public health while also contributing to near-term climate mitigation.

The new findings reinforce a familiar but increasingly urgent reality for northern India: crop-residue burning is only one part of the region’s complex pollution problem, but during the post-monsoon season, its contribution can become large enough to shape the air breathed far beyond the farms where the fires begin.

References:

https://pubmed.ncbi.nlm.nih.gov/42440023

https://link.springer.com/article/10.1007/s10661-026-15679-2

https://www.ccacoalition.org/short-lived-climate-pollutants/black-carbon

https://www.pib.gov.in/newsite/PrintRelease.aspx?relid=190615&reg=48&lang=2

Banner image: Photo by Fernando Strabuli on Unsplash 

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