19 of the world’s 20 most polluted cities are in Asia: IQAir

[misskit]

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.

19 of the world’s 20 most polluted cities are in Asia: IQAir

[Salsa dancer]

Byrnihat in Assam was ranked as the most polluted city in the world.

Why Byrnihat on Assam-Meghalaya border has ‘world’s worst air’

The annual average PM2.5 concentration in Byrnihat was 128.2 micrograms per cubic m (µg/m3), many times the World Health Organization’s annual air quality guideline of 5 µg/m3.

According to the World Air Quality Report for 2024 published by IQAir, a Swiss company that tracks global air quality, Byrnihat on the Meghalaya-Assam border is the “most polluted city in the world”.
The annual average PM2.5 concentration in Byrnihat was 128.2 micrograms per cubic m (µg/m3), many times the World Health Organization’s annual air quality guideline of 5 µg/m3.
In January this year, the Helsinki-based Centre for Research on Energy and Clean Air ranked Byrnihat the most polluted city in India, based on monthly average PM2.5 levels.


Byrnihat is located around 20 km from Guwahati and 65 km from Shillong, in Meghalaya’s Ri-Bhoi district, where the hills of Meghalaya descend into Guwahati.
Over the years, Byrnihat has developed into a regional industrial hub. The residential town is in Meghalaya, and the industrial units surrounding it are in both Meghalaya and Assam.
In Meghalaya, the industries are in the Byrnihat Export Promotion Industrial Park (EPIP); in Assam, they are in Tamulikuchi in the Kamrup Metropolitan district, along the national highway that runs through the town.



The industries include those involved in the production of coke (fuel), cement, ferro alloys, and steel, and in distillation and brickmaking. They mushroomed in the area because of the proximity to coal reserves in Meghalaya and the large urban centre of Guwahati, as well as the supply of water from the Umtru river.
The Meghalaya state Action Plan for Prevention and Control of Air Pollution was released in December 2024. It records 39 industrial units in Assam and 41 in Meghalaya in Byrnihat.
Twenty units in Assam and five in Meghalaya are “red category” industries — identified by the Union Ministry of Environment and Forests as “heavily polluting” (including cement, distillery and fermentation, iron and steel, coke production).
Fifteen units in Assam and 22 in Meghalaya are in the “orange category” (brick manufacturing, cement clinker grinding units), according to the Action Plan.


“This is an important transit point for vehicles. Material is loaded and unloaded from heavy diesel vehicles, many of which do not comply with tailpipe emission norms. Vehicles idle in congestion on the road. Besides PM2.5 and PM10, sulphur dioxide levels are also high in the area,” he said.
A CSIR-NEERI team that surveyed the area in 2022-23 found that unpaved roads in the area aggravated road dust.
Experts have also pointed to the area’s “bowl-like” topography. The surrounding hills inhibit the dispersal of pollutants in the air.

“It is like a basin. While there are hills and high elevation on either side, the area itself has an altitude of only about 60 metres. It experiences a valley-and-basin effect, because of which wind speed is reduced. This may be impacting the transport of air out of here,” Dr Rajesh Bajpai, who teaches environmental studies at North-Eastern Hill University, said.

[cyrille]

'It is like a basin. While there are hills and high elevation on either side, the area itself has an altitude of only about 60 metres. It experiences a valley-and-basin effect, because of which wind speed is reduced. This may be impacting the transport of air out of here"

This is similar to Chiang Mai.

[Salsa dancer]

Taipei is like this too...in a river delta and almost completely surrounded by mountains