Pollution levels in the Northeast rose nearly 50% in a decade, study finds

Guwahati: Air pollution levels in Northeast India have risen by nearly 50 per cent over the past two decades, pushing much of the region from a “polluted” to a “highly polluted” category, according to a new study based on 25 years of satellite observations.

The study, published in the journal Atmospheric Environment, was led by Prof Abhijit Chatterjee and researcher Soumen Raul of the Bose Institute, Kolkata. It analysed particulate matter (PM) pollution trends across the Indo-Gangetic Plain (IGP), Northeast India and the Himalayan region between 2000 and 2024.

Among its most significant findings is the sharp increase in carbonaceous aerosols in Northeast India, driven largely by biomass burning associated with slash-and-burn agriculture and the widespread use of firewood, crop residue and other biomass fuels for cooking and heating.

According to the study, concentrations of organic carbon and sulphate components of particulate matter increased by nearly 50 per cent during 2010–2019 compared with the 2000–2009 baseline period.

Researchers found that pollution hotspots, once concentrated in parts of Assam, Meghalaya and Tripura, have expanded significantly over the past two decades. Most of Northeast India has now crossed the threshold from “polluted” to “highly polluted” for carbonaceous aerosols.

The study attributes the trend primarily to intensified biomass burning practices that remain deeply embedded in rural livelihoods across the region.

“NCAP is primarily designed as a city-focused initiative. But our data shows that air pollution in rural India is equally severe, and in some cases more so. Biomass burning for cooking, heating and agriculture is not being adequately addressed by the programme as it currently stands. The rural dimension needs to be explicitly built into the clean air mission,” said Prof Chatterjee.

The findings also highlight a separate and growing industrial pollution challenge in Assam.

Researchers reported that sulphate emissions in the state increased by more than 30 per cent following the implementation of the National Clean Air Programme (NCAP), driven by emissions from thermal power plants, oil refineries and cement industries concentrated in areas such as Bongaigaon, Guwahati, Dibrugarh, Digboi, Numaligarh and Bokajan.

While dust pollution showed signs of improvement in districts such as Kokrajhar, Dhubri and Bongaigaon, industrial sulphate emissions continued to rise.

The study further found that Northeast India plays a significant role in regional pollution transport patterns. Satellite data showed that the region, together with the eastern Indo-Gangetic Plain, is a major source of aerosol loading over the eastern Himalayas.

At the same time, pollution generated in the central and eastern Himalayan regions also affects air quality in Northeast India, making the region both a source and a recipient of long-range pollution transport.

“The eastern Indo-Gangetic Plain, and increasingly North-East India, are carrying a disproportionate pollution burden — and it is being driven almost entirely by biomass burning. That is the signal that stands out most clearly across 25 years of data,” Chatterjee said.

The researchers argue that India’s clean air strategy needs to expand beyond its current focus on 131 non-attainment cities and incorporate rural regions and ecologically sensitive landscapes.

The study specifically recommends including Northeast India’s biodiversity-rich ecosystems within future clean air planning frameworks, alongside the Sundarbans and Himalayan regions.

According to the researchers, without such an expansion, India’s clean air efforts will continue to overlook some of the country’s fastest-growing and most significant sources of particulate matter pollution.

The study recommends protecting ecologically sensitive areas, addressing biomass burning through targeted interventions, and incorporating rural air quality concerns into future versions of the National Clean Air Programme to prevent further deterioration of air quality across Northeast India.

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