Less than one-fifth of the cities worldwide met the international criteria for clean air in 2024, a global study has found.
The IQAir World Air Quality Report, which analysed data from over 40,000 air quality monitoring stations across 8,954 locations in 138 countries, found that only 17 per cent of cities met the World Health Organisation’s (WHO) annual PM2.5 guideline of 5 micrograms per cubic metre (µg/m³).
The vast majority of the world’s population continues to breathe unsafe air, with pollution levels far exceeding recommended limits in most regions.
The study found that 126 of the 138 countries analysed – 91.3 per cent – exceeded the WHO guideline, with several recording pollution levels more than ten times the safe limit.
The most polluted country was Chad, which had an annual PM2.5 concentration of 91.8 µg/m³, 18 times higher than the WHO threshold. Bangladesh, Pakistan, the Democratic Republic of the Congo, and India also topped the list of countries with the worst air pollution.
India, in particular, saw extreme levels of pollution, with six of the world’s nine most polluted cities. The country’s capital, Delhi, remained the world’s most polluted capital, with an annual PM2.5 average of 91.8 µg/m³.
The most polluted metropolitan area globally was Byrnihat, India, which recorded an alarming PM2.5 level of 128.2 µg/m³ – more than 25 times the WHO guideline.
By contrast, just seven countries met the WHO’s air quality standard. Australia, Bahamas, Barbados, Estonia, Grenada, Iceland, and New Zealand all maintained average PM2.5 levels at or below 5 µg/m³, making them the cleanest places to live in 2024.
The least polluted metropolitan area in the study was Mayaguez, Puerto Rico, which had an annual PM2.5 concentration of just 1.1 µg/m³.
In the US, Los Angeles was the most polluted major city, while Seattle had the cleanest air among large American cities. Ontario, California recorded the highest pollution levels in the country.
In Europe, Bosnia and Herzegovina remained the most polluted nation, with PM2.5 levels averaging 25.3 µg/m³, five times the WHO limit.
The study also highlighted regional pollution trends, with some areas seeing slight improvements. In Southeast Asia, PM2.5 concentrations declined across all countries, though transboundary haze from wildfires and agricultural burning continues to affect air quality.
In Africa, where pollution levels are among the highest in the world, monitoring remains a major challenge. The report found that the continent has only one air quality monitoring station for every 3.7 million people, making it difficult to track pollution accurately or implement effective solutions.
“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.
“Air quality data saves lives. It creates much-needed awareness, informs policy decisions, guides public health interventions, and empowers communities to take action to reduce air pollution and protect future generations.”
In Latin America, wildfires in the Amazon rainforest had a severe impact on air quality. PM2.5 levels in some cities across Brazil’s Rondônia and Acre states quadrupled in September, driving pollution to hazardous levels. Oceania remained the cleanest region globally, with more than half of its cities meeting the WHO air quality guideline.
Health pollution is the second leading risk factor for deaths globally, responsible for 8.1 million deaths in 2021, a 2024 report by the Health Effects Institute (HEI) found.
Another study found that air pollution caused around 135 million premature deaths worldwide in the past four decades.
Apart from respiratory threats, a study published in Nature Communications also found that even brief exposure to air pollution can affect our brain’s ability to make decisions and focus on work.
Environmental groups are calling for stronger air quality regulations and urgent action to curb emissions.
“The World Air Quality Report, which compiles measurements of air pollution from around the globe, should be a rallying call for urgent and concerted international efforts to cut pollutant emissions,” said Aidan Farrow, Senior Air Quality Scientist at Greenpeace International.
“By highlighting the disproportionate risk posed to young people by air pollution, the report reminds us that a failure to act today will be felt by future generations, while frequent references to human activities like coal burning and deforestation are a reminder that air quality, climate change, and the world that will be inherited by our children are inextricably linked.”
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