All but one of the world’s top 20 most polluted cities last year were in Asia, a new study shows.

The majority of these cities – 13 – are in the world’s most populous country, India, where booming economic growth is fired largely by coal and where hundreds of millions live in traffic-clogged and congested megacities.

Another four are in neighboring Pakistan, with one in China and Kazakhstan respectively.

The only city outside of Asia featured on the list is N’Djamena, the capital of Chad in central Africa – which was named the country with the worst air pollution.

Meanwhile the cities with the worst pollution in North America were all in California.

The report by IQAir, a Swiss company that tracks global air quality, looked specifically at fine particulate matter, or PM2.5, one of the smallest but most dangerous pollutants.

PM2.5 comes from sources like the combustion of fossil fuels, dust storms and wildfires. It is so tiny – 1/20th of a width of a human hair – that it can travel past your body’s usual defenses into your lungs or bloodstream.

The particles cause irritation and inflammation and have been linked to respiratory problems and chronic kidney disease. Exposure can cause cancer, stroke or heart attacks and has been associated with a higher risk of depression and anxiety.

The World Health Organization (WHO) says average annual levels of PM2.5 should not exceed 5 micrograms per cubic meter.

Byrnihat, an industrial town in northeast India recorded a PM2.5 concentration of 128.2 last year – more than 25 times the WHO’s standard.

She blamed factories around the town and a booming construction industry and trees being felled as contributing to the toxic air.

“The pollution is particularly bad right now, visibility is not great, there is dust everywhere, my eyes also burn,” she said.

“I do not leave home without a mask.”

Twelve other cities in the top 20 are in India.

Its capital New Delhi featured as the world’s most polluted capital for the sixth consecutive year, with a PM2.5 concentration of 91.8. The report also listed six satellite cities – Faridabad, Loni, Delhi, Gurugram, Noida and Greater Noida – making the list.

Just last November, a throat-searing blanket of smog settled over Delhi, disrupting flights, blocking buildings from view and prompting the city’s chief minister to declare a “medical emergency.”

But overall, India – the world’s most populous nation with 1.4 billion people dropped from third to fifth place from the previous year, according to the report.

But the report said air pollution “remains a significant health burden… reducing life expectancy by an estimated 5.2 years.”

India’s neighbors Bangladesh and Pakistan – together home to some 400 million people – were second and third-most polluted countries globally in terms of PM2.5 molecules, according to the report.

China – which used to dominate global rankings of the world’s worst air – noted a small improvement, the report said.

Its national annual average PM2.5 concentration decreased from 32.5 micrograms per cubic meter to 31, with air quality improving in megacities like Beijing, Shanghai, Chengdu, Guangzhou and Shenzhen, the report said.

China is the world’s largest carbon dioxide emitter but in recent years has waged a campaign against air pollution, particularly in the cities that have fuelled its economic growth, and has pushed a massive expansion in solar and wind power.

But last month two clean-energy groups raised alarm over what they said were plans by China’s power industry to build nearly 100 gigawatts of new coal plant capacity last year, the most in nearly a decade.

All 20 of the world’s most polluted cities last year exceeded WHO PM2.5 guidelines by over 10 times, the IQ Air report showed.

Data gaps

“Air pollution remains a critical threat to both human health and environmental stability, yet vast populations remain unaware of their exposure levels,” said Frank Hammes, Global CEO of IQAir.

Iran and Afghanistan did not feature in this year’s report due to a lack of data availability.

Air quality monitoring in Southeast Asia is also a problem, with nearly all countries having “significant gaps in government-led initiatives,” the report found.

In 2024, 173 out of 392 cities in the region lacked government monitoring stations, while Cambodia had none, it said.

Those problems are likely to be exacerbated after the US announced earlier this month that it would stop sharing air quality data gathered from its embassies and consulates worldwide due to “funding constraints” the Associated Press reported.

“Air quality data saves lives,” said Hammes.

“It creates much needed awareness, informs policy decisions, guiding public health interventions, and empowers communities to take action to reduce air pollution and protect future generations.”

Worst cities in North America

Only 17% of 8,954 cities analyzed globally by IQAir recorded air quality which met WHO pollution guidelines, the report said.

The cities with the worst air pollution in North America were Ontario, Bloomington and Huntington Park – all in California, the report said.

Overall the United States saw a significant reduction in PM2.5 levels last year, with the annual average dropping 22% from 2023.

Northern America has long boasted vigorous air quality monitoring systems, contributing 56% of the total number of ground-based air quality monitoring stations included in the IQ Air report – helping scientists with their continued research on air quality and aiding policymakers to make decisions about public health.

Only 12 countries, regions, and territories recorded PM2.5 concentrations below the WHO guidelines, most of which were in the Latin America and Caribbean or Oceania region.

The report called on governments to dedicate funding for renewable energy projects and “strengthen emission limits for vehicles and industrial activities.”

Advice Suman wishes authorities in Byrnihat would take to save her city from appearing at the top of the most polluted list again next year.

“This is my birthplace. I am a local. I do not want to leave this area. We want the governments to do more, come together and work for us.”

Elections in Greenland, an island home to about 57,000 people, are usually a local affair.

There is little opinion polling, with only two newspapers in the Danish autonomous territory. Greenlanders mull over politics in private Facebook groups, with key issues in the past centering on the economy, mining, fishing law and of course, its relationship and history with Denmark.

But as Greenlanders head to the polls on Tuesday, US President Donald Trump’s idea to annex the nation has thrown this year’s elections into the international spotlight.

Speaking about Greenland in his speech to Congress last week, Trump said, “I think we’re going to get it one way or the other” – reigniting fears of the United States attempting to take the island by force or economic coercion.

Greenland’s pro-independence Prime Minister Mute Egede responded: “We are not for sale and cannot simply be taken.”

“We don’t want to be Americans, nor Danes; We are Kalaallit (Greenlanders),” Egede said. “The Americans and their leader must understand that.”

In fact, all five parties in Greenland’s parliament have said they do not want the territory to become part of the United States. Their key divisions center more on economic, social and environmental policy than Trump’s pronouncements.

The dominant parties on Greenland’s political spectrum all agree on the desire for independence, with many parties, including Egede’s ruling democratic socialist party Inuit Ataqatigiit, viewing it as a long-term project, requiring years of negotiation with Denmark and further economic improvement.

Denmark ruled Greenland as a colony until 1953, when the island achieved greater powers of self-governance. Then, in 2009, it gained more powers pertaining to minerals, policing and courts of law. But Denmark still controls security, defense, foreign and monetary policy. Greenland also benefits from Denmark’s European Union and NATO memberships.

It is an open question what Greenland’s future security will look like if it votes to break away. Some politicians have floated establishing a post-independence defense treaty with Denmark, Canada, or even the United States, which already has a military base in the Arctic Circle in far northwest Greenland.

The island’s future security is especially important as Russia and China vie for greater influence in the Arctic.

Speeding up independence movement

In almost every election in recent years, politicians have promised to take steps to achieve autonomy. None of them have offered a concrete timeline, though.

But Trump’s aggressive stance has actually given the Arctic nation more bargaining power with Denmark, analysts say, and kicked the independence movement into high gear.

Independence isn’t on the ballot for Tuesday’s election, but the other partner in Greenland’s two-party government coalition, the Siumut party, has said it plans to hold a referendum on independence within the next election period. The main opposition party, Naleraq, has campaigned to sever ties with Denmark more quickly and wants to pursue a defense agreement with the US.

Greenland holds elections every four years, with 31 seats in parliament at stake.

Without reliable election polling, analysts hesitate to predict if Egede’s ruling left-wing coalition will win again.

“Whatever the outcome is going to be, there will be speed, there will be turbo on the issue of independence,” Noa Redington, an analyst and former adviser to previous Danish prime minister Helle Thorning-Schmidt, told Reuters news.

Greenlandic social media influencer and candidate for Naleraq, Qupanuk Olsen, told Reuters: “I strongly believe all this interest from Trump and the rest of the world is definitely speeding up our independence process times 100.”

Meanwhile, amid the influx of international attention, Greenland’s parliament last month outlawed political donations from foreign individuals and anonymous donors.

Danish intelligence services have announced they are actively monitoring attempts by foreign powers to interfere in the elections, citing China, Russia and the United States as potential tampering powers.

With multiple issues at play, “it has never been so important to mark a ballot,” wrote journalist Tôrtia Reimer-Johansen for the nation’s weekly newspaper Sermitsiaq.

‘Greenlanders have felt trapped’

A key issue is how full independence could be achieved and whether it’s economically viable, given that Greenland receives roughly 20% of its annual GDP from a Danish block grant every year – more than $500 million. That’s about half the island’s public budget.

Greenlanders also have Danish passports, healthcare and other Nordic welfare state benefits.

Analysts say any independence referendum would likely take years to implement and require lengthy exit-deal negotiations.

“Greenlanders have felt trapped, not just constitutionally, but also in terms of any kinds of relation, particularly economic relations,” said Ulrik Pram Gad, a senior researcher focused on Greenlandic-Danish relations at the Danish Institute for International Studies.

While Greenlandic politicians have repeatedly signaled that they’re uninterested in annexation, they are open to deals with the United States for rare earth mining, expanding tourism, stronger diplomatic connections and other investments.

Trump said in a social media post on Sunday: “We are ready to INVEST BILLIONS OF DOLLARS to create new jobs and MAKE YOU RICH,” he added, inviting Greenland to become “a part of” the United States.

Greenland is rich in oil and gas, as well as the rare earth metals in high demand for electric cars, wind turbines and manufacturing military equipment.

“They’re really eager to get someone digging, but they want to be sure to have a piece of the cake,” Gad added.

“Under the current Danish constitution and the self-government act, Greenland is in charge of minerals. They can dig up and export whatever that they want, but Denmark is in charge of security. That is kind of a stalemate, in the sense that, if you dig up something which is a security problem, who’s then to decide?” he said.

Security far from the only issue

Beyond security and foreign policy issues, Nuuk’s relationship with Copenhagen has also been fraught with allegations of historical misconduct and colonial oppression of the indigenous Inuit Greenlandic people.

The nation has been rocked in recent years by a birth control scandal, after it came to light that Denmark fitted many Greenlandic girls with an intrauterine device (IUD) in the 1960s and 70s without girls’ or their parents’ permission, as a means of population control. Prime Minister Egede recently called the birth control campaign “a genocide.”

And this election cycle has also exposed frustration over allegations that Denmark profited off a large cryolite mine on Greenland’s west coast from 1854 until 1987 – exploiting the area without benefiting locals.

A University of Greenland opinion survey conducted in spring 2024 – months before Trump floated ideas to control the island – found that more people saw the security threat as high compared to 2021. The survey also illuminated views on Greenland’s desire for greater international cooperation, with locals saying their preferred partners were Iceland, Canada and the Arctic Council.

Even still, people surveyed in 2024 said the biggest challenges for Greenland were the economic situation, cost of living and unemployment.

Those views have almost assuredly shifted in 2025, as Trump argues that controlling Greenland is vital for US national security and refuses to rule out using military force.

But the election is inherently unpredictable. The key issues on Greenlander’s minds may only become clear when results begin to trickle out of local polling stations in the early hours of Wednesday.