The air in Bangladesh has again been ranked as the world's most polluted by IQAir, a Swiss company that makes air quality monitors and air purification technologies.
"Central and South Asia had some of the world's worst air quality and were home to 46 of the world's 50 most polluted cities," the newly released report states after analysing the pollution data of 6,475 cities collected in 2021.
The reading of small and hazardous airborne particles – known as PM2.5 – in Bangladesh averaged at 76.9 micrograms per cubic metre last year.
The figures were 97.1, 83.3, and 77.1 micrograms per cubic metre (μg/m³) back in 2018, 2019 and 2020 respectively.
These figures came to light on Tuesday in the 2021 World Air Quality Report.
The country was followed by Chad and Pakistan in terms of PM2.5 exposures in the list of the world's most polluted countries.
To put things into perspective, the WHO recommends that average annual readings of PM2.5 should be no more than 5 micrograms per cubic metre.
Also, Dhaka was ranked the second most polluted capital city in the world with a PM2.5 level of 78.1 while neighbouring India's New Delhi topped the list (PM2.5 level 85).
Meanwhile, Chad's N'Djamena was recognised as the third most polluted capital city in the world with pollution levels averaging at 77.6.
The WHO revised its air quality guidelines last year citing that even low concentrations caused significant health risks.
According to the findings of the survey, not a single country managed to meet the WHO set air quality standard in 2021.
A mere 3.4% of the surveyed cities met the standard in 2021 while as many as 93 cities saw PM2.5 levels at 10 times the recommended level.
According to the United Nations Environment Programme, 70% of global air quality-related deaths occur in Central and South Asia.
Only two cities from this region met the WHO air quality guideline for the annual average concentration of 5 μg/m³, Chu and Zhezqazghan, both in Kazakhstan.
Industrialisation and urbanisation bring added pressure to air pollution burdens in South Asia, observes IQAir, adding that burning biomass, a popular fuel for cooking in the rural areas, is a frequent source of pollutants in the air.
According to the latest data, India and Pakistan experience the worst air quality in this region, with 48% and 67% respectively of cities with PM2.5 concentrations greater than ten times the 2021 WHO air quality guideline level.
With the exception of Afghanistan, Bangladesh, and Sri Lanka, PM2.5 concentrations increased in Central and South Asian countries in 2021, wiping out nearly all quarantine-correlated air quality improvements, the IQAir report says.
Addressing the findings, IQAir Air Quality Science Manager Christi Schroeders said, "There are a lot of countries that are making big strides in reduction.
"China started with some very big numbers and they are continuing to decrease over time. But there are also places in the world where it is getting significantly worse."
China, which has been waging war on pollution since 2014, fell to 22nd in the PM2.5 rankings in 2021, down from 14th place a year earlier, with average readings improving slightly over the year to 32.6 micrograms, according to IQAir.
Hotan in the northwestern region of Xinjiang was China's worst-performing city, with average PM2.5 readings of more than 100 micrograms, largely caused by sandstorms.
As per the WHO, air pollution kills an estimated seven million people worldwide every year largely as a result of increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.