29-06-2025
Stubble burning behind nearly one-third of Delhi's post-monsoon pollution deaths: Study
Smoke from crop residue burning in Punjab and Haryana is responsible for nearly one-third of all PM2.5-related deaths in Delhi during the post-monsoon season, according to a new international study.
The research found that this smoke—transported over hundreds of kilometres—became the dominant share of organic aerosols, accounting for almost half of it during the worst post-monsoon haze episodes, even surpassing traffic or industrial pollution.
PM2.5 refers to particulate matter that has a diameter of 2.5 micrometres or smaller. These tiny particles are a major component of air pollution and can pose significant health risks because they can penetrate deep into the lungs and even enter the bloodstream.
The study, published earlier this month in the journal Environment International, is the first to use year-long, near-molecular-level data to identify specific sources of organic aerosols in Delhi and Kanpur.
Scientists from the Paul Scherrer Institute in Switzerland, IIT Delhi, and IIT Kanpur monitored pollution levels over 12 months in both cities and concluded that smoke from agricultural fires, primarily rice stubble, has a significant health impact. In Delhi, they found that during October and November, smoke from crop fires contributed to 32 per cent of premature deaths caused by PM2.5 exposure.
Overall, short-term exposure to PM2.5—tiny particles that can enter the lungs and bloodstream—was linked to about 6 per cent of all deaths annually in both cities. In Delhi, nearly half of this health burden came from organic aerosols. The study estimates that more than 1,000 premature deaths in Delhi during the post-monsoon period were tied to this transported smoke, referred to as AgrOA.
'Transported rural fire smokes remain a major detrimental factor threatening public health, despite intensive urban emissions,' the researchers noted.
The data also revealed that AgrOA was the largest single component of particulate matter during peak smog events, contributing up to 70 per cent of the organic aerosol load in Kanpur and nearly 50 per cent in Delhi.
While urban sources like traffic emissions, industrial waste, and biomass burning remain major contributors throughout the year, these were surpassed by crop-burning smoke during November's haze.
Interestingly, the study found that Kanpur—despite being located over 600 kilometres from the fire zones—experienced an even higher impact. Researchers said the smoke had more time to age chemically as it travelled east, making it even more toxic by the time it reached Kanpur. There, AgrOA was linked to 53 per cent of PM2.5-related deaths during the post-monsoon season.
The researchers also highlighted the increased health risks for vulnerable groups. Based on global data, the study estimates that women and the elderly face disproportionately higher mortality risks from exposure to crop-burning smoke. For women, AgrOA was estimated to be responsible for up to 67 per cent of pollution-related deaths in Kanpur and 46 per cent in Delhi during the post-monsoon period.
In addition to AgrOA, the researchers identified other key sources of pollution. In Delhi, a winter-specific industrial pollution signature was observed, linked to chemicals like melamine used in plastics and e-waste recycling. These emissions spike in colder months when pollutants remain trapped close to the ground. Traffic and cooking-related emissions also made up a significant share of organic aerosols in both cities.
However, the researchers emphasised that city-level pollution control will not be enough. 'Mitigation measures should extend beyond cities to regional scales, targeting regions particularly affected by stubble fires like Punjab and Haryana,' they wrote. The study recommends strengthening bans on open burning, promoting machines like the Happy Seeder for in-situ straw management, offering incentives for using straw as fertiliser or fuel and encouraging farmers to adopt low-residue or alternative crops.
The findings underline the urgent need for coordinated action across states and sectors. For Delhi, which has struggled for years with severe winter smog, the study confirms that efforts to clean the city's air must also include stopping crop fires outside its borders.
'These findings illustrate the urgent and critical need for regional cooperative air pollution mitigation strategies, accounting not only for urban emissions but also for stubble residue burning emissions,' the study noted.
