4 min readNew DelhiMay 25, 2026 03:45 PM IST
Particulate matter pollution across the Indo-Gangetic Plain (IGP) increased by more than 20 per cent during 2010-2019 compared to the previous decade, with pollution plumes from Punjab, Haryana, and Bihar now reaching deep into the Himalayan ranges, according to a new study published in the Atmospheric Environment journal.
The study, conducted by researchers at the Bose Institute in Kolkata, analysed aerosol data from 2000 to 2024 across the IGP, Northeast India, and the Himalayas using Nasa’s MODIS and MERRA-2 satellite datasets. The study was led by Prof Abhijit Chatterjee, with Soumen Raul as the primary researcher.
Persistent aerosol hotspot
The highest pollution levels over the entire study period were recorded in the eastern IGP – particularly Bihar, southern West Bengal, and large parts of Bangladesh – which the study identifies as a persistent and worsening aerosol hotspot. The lower IGP recorded the highest aerosol optical depth of 0.71, a measure of how much sunlight is blocked by particles suspended in the atmosphere.
Particulate matter pollution is a major health hazard as it enters the respiratory organs and bloodstream, causing respiratory ailments and chronic diseases.
Biomass burning emerged as the dominant and growing driver of pollution, with carbonaceous aerosols, which are particles produced by burning crop residue, wood, and other organic material, showing sharp increases across the eastern IGP and Northeast India.
Northeast India
In Northeast India, organic carbon and sulphate components of particulate matter rose by nearly 50 per cent in the 2010s compared to the 2000s, driven largely by slash-and-burn agriculture and widespread use of biomass for household energy. As a result, most of Northeast India has shifted from a “polluted” to a “highly polluted” aerosol classification over the past two decades.
Dust pollution, concentrated over the western IGP, showed an overall declining trend in contrast to the surge in biomass burning-led aerosol elsewhere.
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The study used backward trajectory modelling to trace the movement of pollution plumes from their sources to the Himalayan range. It found that emissions from the upper and middle IGP – Punjab, Haryana, Delhi, and western Uttar Pradesh – are significantly affecting aerosol loading over the western and central Himalayas. The lower IGP and Northeast India are the primary sources influencing the eastern Himalayas. The research also found strong inter-Himalayan transport, with emissions from the central and western Himalayas flowing into the eastern ranges.
“The Himalayas are not insulated from IGP pollution. Our trajectory analysis shows that what is emitted in Punjab or Bihar does not stay there – it travels into the mountains. These are ecologically and climatically sensitive zones, and they are currently outside the scope of any structured clean air intervention in India,” said Raul.
The study also assessed the impact of India’s National Clean Air Programme (NCAP), launched in 2019. States including Bihar, West Bengal, and Assam showed measurable improvements in overall particulate levels in the post-NCAP period.
Biomass burning
However, biomass burning pollution has not declined significantly in any of these states. Assam presents a particular concern: sulphate emissions there rose by more than 30 per cent after NCAP implementation, driven by thermal power plants and oil refineries concentrated in industrial hubs such as Guwahati and Dibrugarh.
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The researchers argue that NCAP’s successor programme must expand beyond its current focus on 131 non-attainment cities. The study specifically calls for rural regions and ecologically sensitive areas, including the Sundarbans mangrove ecosystem, Northeast India’s biosphere reserves, and the Himalayan ranges, to be brought within the ambit of India’s clean air mission.
