People brave “severe plus” smog shrouding New Delhi, India, on November 15 when the National Capital Region’s Air Quality Index hit 424, according to the Central Pollution Control Board. A below-50 reading means air quality is good. Anything over 300 is hazardous to health. File photo by Rajat Gupta/EPA-EFE
Fewer than one in five global cities met World Health Organization air pollution standards in 2024 with Central and South Asia accounting for the nine most polluted metropolitan areas on Earth, six of which were in India, a new report out Tuesday shows.
Byrnihat, straddling the border between the Meghalaya and Assam states of northeastern India was the most polluted city with an annual average concentration of tiny, breathable so-called PM2.5 particulates of 128.2 micrograms suspended in each cubic meter of air, Swiss environmental technology company IQAir said in its annual World Air Quality Report. Advertisement
The city’s PM2.5 level was more than 25 times the WHO’s 5 µg/m3 annual limit. India-wide, the level was 10 times the limit at 50.6 µg/m3.
Bangladesh recorded 78.0 µg/m3, more than 15 times WHO’s PM2.5 annual limit, while Pakistan’s level exceeded the limit by than 14 times. Advertisement
The two other worst offenders were the African nations of the Democratic Republic of the Congo and Chad, where particulate levels were 11 and 18 times the WHO-required standard, with IQAir lamenting an extreme shortage of air quality monitoring data due to the fact there was just one monitoring station for every 3.7 million people on the continent.
In all, 126 of 138 countries and regions, or 91%, exceeded the 5 µg/m3 limit, with only Australia, Bahamas, Barbados, Estonia, Grenada, Iceland and New Zealand meeting the standard, according to the Steinach, Switzerland-headquartered manufacturer of air purification products and air quality measuring instruments.
PM2.5 is defined as fine particulate matter of 2.5 micrometers or less in diameter — so small it can only be seen through an electron microscope — but because it is so small bypasses filters in the nose and lungs when breathed in, passing directly into the bloodstream.
The World Health Organization ranks air pollution as the second leading mortality risk factor overall after ischemic heart disease or, in the case of children, malnutrition.
Elevated PM2.5 levels contribute to and worsen asthma, cancer, stroke and lung diseases. Exposure during pregnancy and early childhood is linked to congenital heart defects, eczema and allergic disease, cognitive impairments and delays, and neurodevelopmental and mental health disorders. Advertisement
However, IQAir sounded a note of optimism due to a jump in the proportion of cities that recorded levels below the PM2.5 limit in 2024 to 17%, up from 9% the previous year.
“While this marks some progress, much more work needs to be done to protect human health, especially that of children. It is our shared responsibility to safeguard the health and well-being of the world’s children, who will one day become the leaders of tomorrow,” it said.
“By equipping them with the knowledge and resources they need, we empower them to tackle the global challenges of the future.”
Two Californian cities were the most polluted U.S. cities with Los Angeles the having the dirtiest air among major metro areas while Ontario, in San Bernardino county, east of Los Angeles, was the most polluted city overall.
However, the report found Mayaguez in the U.S. Commonwealth of Puerto Rico had the cleanest air of any metro area around the world with a PM2.5 level of just 1.1 µg/m3.
IQAir said man-made activities such as fossil fuel burning for transportation, generating electricity and domestic heating, industrial processes, fireworks and smoking were the largest sources of pollutant PM2.5, but that natural sources including wildfires, dust, pollen and dirt also contributed to particulate loads in the air. Advertisement
