Byrnihat looks like many other towns in India's picturesque northeastern states of Assam and Meghalaya. But while it is nestled among lush green hills and scenic river valleys, it holds the unwanted title of the world's most polluted city, according to Swiss air quality monitor IQAir's 2024 report.

Walking along the town's hilly roads on a rainy afternoon, the views and stillness are only broken by the rhythmic clanking from nearby factories.

This town of about 50,000 people is also home to about 80 industries, many of them focused on iron and steel. The serpentine roads are lined with long rows of trucks — some stalled, others hauling goods to and from factories.

The National Highway 40 (NH40) cuts through the town, which straddles the border between Assam and Meghalaya states.

According to IQAir's Armen Araradian, Byrnihat's air had an average PM2.5 concentration of 128.2 micrograms per cubic meter in 2024. That is more than 25 times higher than what the World Health Organization (WHO) considers safe to breathe.

Sharp rise in respiratory illnesses

Dr. Prasanta Kr Brahma has spent eight years treating patients in Byrnihat. He said he has seen an "increasing number of cases of respiratory tract infection and other issues related to pollution." 

According to government data analyzed by IQAir, the number of cases of respiratory infection in the region rose 76.77% between 2022 and 2024.

"Over the years, cancer has also become very common, especially head and neck cancer (HNC), which is related to air pollution," Dr. Brahma said.

Studies have shown that exposure to PM2.5, a term referring to air particles with a diameter smaller than 2.5 micrometers, is associated with an increased incidence of HNC, like oral, nasal and throat cancers.

The recommended safe level of PM2.5 is no more than 5 micrograms per cubic meter of air, according to the WHO. 

"Of the 359 days IQAir has data from Byrnihat, 356 did not meet the WHO's PM2.5 guidelines," Araradian told DW. 

What is causing the pollution?

Byrnihat developed into an industrial and transport hub in the late 1990s due to its access to coal in Meghalaya and its proximity to Guwahati, the largest city in India's northeast, about 30 kilometers (18.6 miles) away.

The major industries in the region are iron and steel plants, cement factories, wood manufacturing units and plants for industrial equipment like ferroalloy products.

With pollution levels soaring, a 2022 report by the Meghalaya Pollution Control Board recommended halting construction and limiting truck traffic to reduce harmful PM2.5 levels in Byrnihat.

Faced with Byrnihat's severe air quality, the Meghalaya government shut down a handful of factories that were thought to be the main drivers of pollution.

However, the Central Pollution Control Board (CPCB) found that there was a negligible change in the ambient air quality in Byrnihat after six ferroalloy and related units were ordered to shut down on January 29, 2025, for non-compliance with environmental regulations.

In fact, CPCB data showed the highest PM2.5 level of 385 was recorded on February 3, four days after the closures. 

Looking beyond industrial factors

The factories are not the only cause of pollution. Experts also point to other contributing factors, primarily the traffic that passes through the town.

"Some check on trucks is a must to reduce PM2.5," said Dr Sharad Gokhale, an environmental engineering professor at Indian Institute of Technology in Guwahati.

Byrnihat is on one of India's key transit routes, with the NH40 enabling a constant flow of old, heavy commercial vehicles, many of which use low-quality fuel and don't meet emissions standards.

Sunil Dahiya, founder of the environmental group EnviroCatalysts, said the trucks, whether idling for hours or just passing through, exacerbate local pollution levels.

Byrnihat also serves as a transit hub for coal transport to other regions. Dahiya told DW that the area's coal stockpiles and storage methods also contribute to air pollution. 

"A major concern is that much of the coal is stored in the open, uncovered, and across multiple sites. This leads to fugitive emissions, as coal dust becomes airborne and spreads, contributing further to air pollution," he said.

Geography and weather also play a role 

Dahiya pointed out that municipal and industrial waste management in the area must also be considered. Burning industrial waste, which raises pollution levels, is common in Byrnihat and other areas.

When DW visited some of Byrnihat's factories, some were engulfed in emitted smoke.

Wind direction and the proximity of the major city of Guwahati, as well as geography, also play significant roles in Byrnihat's pollution levels.

"Byrnihat's bowl-shaped topography also traps pollution. The city is surrounded by hills on nearly all sides, and its topography does not allow pollutants to easily disperse," IQAir's Araradian said.

Yet another factor behind Byrnihat's position at the top of the world's most polluted cities in 2024 was that last year, both Assam and Meghalaya saw below-normal rainfall. Less rain means more particles, including harmful PM2.5, in the air.

Smaller towns going unnoticed

Byrnihat's top ranking spotlighted a town many in India would not be able to locate on a map.

But the focus on air pollution is usually on New Delhi and the country's other major cities. In 2024, more than half of the world's 20 most polluted cities were in India.

Araradian said IQAir's global data often reveals extremely high — but largely unnoticed — air pollution levels in small or lesser-known towns that barely feature in national discussions. 

Many of these smaller urban centers weren't even monitored until recently, said Dahiya.

And while smaller metropolitan areas are slowly getting more attention, most of the policy and media focus remains concentrated on Delhi and other big cities.

"Ultimately, environmental planning should be a core part of urban development. Without that, we continue making poor policy decisions," Dahiya said.

"Even five years after the launch of the NCAP (National Clean Air Programme), the debate still centers on Delhi, while smaller towns remain on the sidelines. That needs to change," he added.

Improving air quality takes political will, experts say. If small towns keep slipping through the cracks of anti-pollution regulations, less visible communities like Byrnihat will keep paying the price. 

"This is our home," said Lucy Marak, a local resident. "Where are we supposed to go if our home becomes unlivable?"

Edited by: Karl Sexton