India and China are leading the world with most polluted cities in the world. India has 46 most polluted cities, followed by 42 cities in China. Pakistan and Bangladesh have six and four cities which are amongst the 100 most polluted cities in the world.
Every year, a thick smog covers Indiaโs capital New Delhi. Last week, it got so bad for the 20 million residents that authoritiesย shut schools.
New Delhiโs concentration of PM2.5 particles, which damage peopleโs lungs, is 34 times the World Health Organizationโs (WHO) acceptable levels. The toxic haze is especially bad during the winter as farmers burn stubble left in their fields.
How is air quality measured?
Air quality is determined by the levels of air pollutants PM2.5, PM10, ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide.
Particulate matter (PM) comprises tiny particles that negatively impact health. PMs vary in size, most damaging are PM2.5 and PM10 โ with a diameter of less than 2.5 ฮผm and 10ฮผm respectively. A human hairโs diameter is 50-70 ฮผm.
PM2.5 levels lower than 12 are considered good, 55-150 unhealthy and 250 or above is hazardous.
The most polluted cities in the world
In 2020, India had 46 of the worldโs 100 most polluted cities, followed by China (42), Pakistan (6), Bangladesh (4), Indonesia (1), and Thailand (1), according to air quality tracker IQAir. All these cities had a PM2.5 air-quality rating of more than 50.
Nine out of the top 10 most polluted cities are in India. Hotan, in western Chinaโs Xinjiang, had the worst average air quality in 2020, with 110.2, according to Al-Jazeera.
