Thirteen of the world’s 20 most polluted cities in 2024 were in India, with Byrnihat town in Meghalaya topping the list, according to the 2024 World Air Quality Report published on Tuesday by Swiss air quality technology company IQAir.

The report analysed PM2.5 air quality data collected from 8,954 cities in 138 countries, regions and territories.

PM2.5 refers to tiny airborne particulate matter that is about 30 times smaller than the width of a human hair and can easily be breathed into the lungs and the bloodstream.

Delhi was the most polluted capital city in the world in 2024, according to the report. India was the fifth most polluted country, down from third in 2023, and home to six of the nine most polluted global cities.

The Indian cities featured in the 20 most polluted places are: Byrnihat, Delhi, Punjab’s Mullanpur, Faridabad, Loni, Gurugram, Ganganagar, Greater Noida, Bhiwadi, Muzaffarnagar, Hanumangarh and Noida.

Byrnihat, situated on the Assam-Meghalaya border, saw an annual average PM2.5 concentration of 128.2 μg/m³. The World Health Organization’s Global Air Quality Guidelines prescribes a “safe” annual average PM2.5 concentration of 5 μg/m³.

The annual average concentration of PM2.5 in India stood at 50.6 μg/m³ in 2024, more than 10 times higher than the World Health Organization’s guidelines. The figure was 54.4 μg/m³ in 2023, according to IQAir’s analysis.

The report showed that Chad and Bangladesh were the world’s most polluted countries in 2024.

The annual average PM2.5 concentration in Chad was 91.8 μg/m³, more than 18 times higher than the WHO standard. It was 78.0 μg/m³ in Bangladesh.

Pakistan was ranked third with 73.7 μg/m³ average PM2.5 concentration, followed by the Democratic Republic of the Congo, where the concentration was 58.2 μg/m³.

A total of 126, or 91.3% out of 138 countries and regions, exceeded the WHO standard. Only seven countries met it.

The countries where the PM2.5 concentration was 5 μg/m³ on average were: Australia, New Zealand, the Bahamas, Barbados, Grenada, Estonia and Iceland.

The report said that in Africa, only one monitoring station was present for every 3.7 million people, making real-time and publicly-accessible data scarce.

PM2.5 is one of six common airborne pollutants that are monitored and regulated by environmental agencies across the world, including by India’s Central Pollution Control Board, due to its significant impacts on human health and the environment.

Common components of PM2.5 include sulfates, black carbon, nitrates and ammonium. Human-made sources of PM2.5 include combustion engines, industrial processes, power generation, burning of coal and wood, agricultural activities and construction.

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