A Switzerland-based air quality monitoring group has found Delhi to be the world's most polluted capital city by 2023.
After neighboring Bangladesh and Pakistan, India, whose capital is Delhi, is also ranked as the third most polluted country in the world, according to IQAir.
The country's air has worsened since 2022, making it the eighth most polluted country, it added.
Air pollution is a serious problem in many Indian cities.
Experts say rapid industrialization and weak enforcement of environmental laws have played a role in increasing pollution in the country.
India has seen a lot of growth in the last few decades, but industries have not followed pollution-control measures due to poor industrial regulation. Rapid construction has also contributed to increased levels of pollution.
According to a report by IQAir, India's average level of PM2.5 — fine particles that clog the lungs and cause many diseases — is 54.4 micrograms per cubic metre.
Globally, Air with 12 to 15 micrograms PM2.5 per cubic meter is considered safe to breathe, while air above 35 micrograms per cubic meter is considered unhealthy.
Delhi's air quality was worse than India's overall air quality, with the city having PM2.5 levels of 92.7 micrograms per cubic metre.
Delhi struggles with bad air throughout the year, but the air is especially toxic in winter.
This happens due to various factors including burning of crop residues by farmers in nearby states, emissions from factories and vehicles, low wind speed and bursting of firecrackers during festivals.
Last year, the government closed several days for schools and colleges due to toxic air.
Meanwhile, the northern Indian city of Begusarai and the northeastern city of Guwahati were ranked as the two most polluted cities in the world.
Only seven countries met the World Health Organization's (WHO) annual PM2.5 guideline, which is an annual average of 5 micrograms per cubic meter or less.
These include Australia, New Zealand, Iceland and Finland.
According to IQAir, this data is collected from more than 30,000 air quality monitoring stations deployed in 134 countries, regions and territories.