By HONG KONG — Six out the world’s 10 most polluted cities are in India, while California has the worst air pollution in North America, a new report shows.
New Delhi was the most polluted capital city globally, followed by N’Djamena, capital of Chad, a country in central Africa with the world’s worst air pollution, according to the 2024 World Air Quality Report published Tuesday by IQAir, a Swiss air monitoring company.
Ten out of the 15 most polluted cities in North America, including Ontario and Bloomington, are located in California as the United States reclaimed the top spot as the most polluted country in the region in 2024, the report said.
India, the world’s most populous country with more than 1.4 billion people, saw a 7% decline in PM2.5 concentration in 2024, but air pollution remains a “significant health burden” that reduces life expectancy in the South Asian nation by an estimated 5.2 years, the report said. The country’s major pollution sources include industrial discharge, construction dust and the burning of crop residues.
PM2.5 refers to tiny particles with a diameter of 2.5 micrometers or less that can go deep into lungs and even enter the bloodstream. Deriving from emission sources such as the combustion of gasoline and oil, it is linked to premature death, heart attacks and breathing difficulties.Though the World Health Organization (WHO) recommends that average annual concentrations of PM2.5 should not exceed 5 micrograms per cubic meter, only 17% of global cities meet its air quality standard, the report said.
Chad’s PM2.5 levels were more than 18 times higher than the WHO guideline, with mineral dust in the Sahara Desert as the primary source of air pollutants. Oceania, which includes Australia, New Zealand and Pacific island nations, is the world’s cleanest region, with 57% of cities meeting the WHO standard.
Smoke rising from chimneys at a steel production facility in Jiangsu Province, China, in January. Costfoto / NurPhoto via Getty Images
Bangladesh and Pakistan, both of which neighbor India, ranked as the second and third most polluted countries. Last November, air quality in Pakistan reached “hazardous” levels due to a combination of festival celebrations, brick kiln emissions and adverse weather.China, the world’s biggest emitter of greenhouse gases, recorded lower air pollution levels in more than 300 cities in 2024, the report said.
While noting Chinese authorities’ “ambitious” goal to reduce the country’s annual average PM2.5 concentration levels to below 25 micrograms per cubic meter, the report said that is still “significantly” above the WHO guideline of 5 micrograms.
A senior Chinese environmental official said last month that China aimed to effectively eliminate severe air pollution by the end of this year. China announced its “war against pollution” in 2014.
The report also noted the “considerable” gaps in air quality that still exist in many parts of the world. Currently, only 21% of the world population has access to hyper-local, real-time air quality information, according to IQAir estimates.
People crossing railway tracks in Kolkata, India, in January.Sudipta Das / NurPhoto via Getty Images
Cambodia had no official government monitoring, while many critical regions in Africa and West Asia lack sufficient monitoring. In comparison, North America has a “robust” air quality monitoring infrastructure that accounts for 56% of ground-based stations.“Air pollution remains a critical threat to both human health and environmental stability, yet vast populations remain unaware of their exposure levels,” Frank Hammes, global chief executive of IQAir, said in a statement.
“Air quality data saves lives,” Hammes said. “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.”
Last week, U.S. embassies and consulates said they had stopped monitoring air quality abroad, ending a program that had provided essential public health data for more than a decade.
Data the U.S. provided in dozens of countries had led to noticeable improvements in local air quality in China and elsewhere, reducing premature deaths and generating cost savings associated with lower mortality, studies found.
Air pollution accounted for 8.1 million deaths globally in 2021, according to the WHO. Children under the age of 5 are considered especially vulnerable, with health effects including premature birth, low birthweight, asthma and lung disease.
