March 13, 2025
BANGKOK – Nineteen out of the world’s 20 cities with the highest air pollution were in Asia, while only seven countries worldwide met World Health Organisation PM2.5 standards in 2024, according to IQAir’s annual air quality report.
PM2.5 are fine particles measuring 2.5 micrometres or less in diameter, which can penetrate deep into the lungs and bloodstream, causing premature death through respiratory and cardiovascular diseases.
Swiss air-monitoring organisation IQAir released the 2024 World Air Quality Report on Tuesday, with shocking findings for Asia.
Thirteen of the 19 Asian cities at the top of pollution rankings are in India.
Byrnihat in Assam was ranked as the most polluted city in the world. Four are in Pakistan, one in China, and one in Kazakhstan. The only city outside Asia on the list is Africa’s N’Djamena, capital of the Republic of Chad.
IQAir analysed data collected from over 40,000 air quality monitoring stations across 138 countries worldwide for its annual report, which revealed that the country with the highest pollution level last year was Chad, followed by Congo, Bangladesh, Pakistan, and India.
In a surprise to many in Thailand, the country did not make the list of the world’s 20 most polluted cities. The kingdom was ranked 29th, despite Thailand’s annual smog season pushing PM2.5 levels well beyond its own safe standard of 37.5 micrograms per cubic metre (µg/m³). Chiang Mai was listed as Thailand’s most polluted city, ranked 424th with an annual PM2.5 average of 91.
Only seven countries met the air quality standards set by WHO: Australia, the Bahamas, Barbados, Estonia, Grenada, Iceland, and New Zealand.
Only 17% of the 8,954 cities measured worldwide met the WHO standard for air quality – an annual average of no more than 5µg/m³.
Byrnihat topped the city rankings with an annual PM2.5 average of 128.2 µg/m³, while Chad recorded 91.8 µg/m³ – 18 times above the WHO standard.