New Delhi emerged as the world’s most polluted capital city for the fourth straight year in 2021, according to a report released on Tuesday by Swiss organization IQAir.

The report studied across 6,475 cities in 117 countries, the levels of PM2.5 pollutants – tiny particles with a diameter of less than 2.5 micrometres, which can enter the lungs and the bloodstream.

According to the report, Delhi saw a 14.6% increase in concentration of PM2.5 in the atmosphere in 2021 with levels rising to 96.4 micrograms per cubic meter from 84 micrograms per cubic meter in 2020.

The PM2.5 concentration in Delhi’s air was nearly 20 times above the safety limit of 5 micrograms per cubic meter set by the World Health Organization, the report noted.

Apart from New Delhi, India was also home to 11 of the 15 most polluted cities in Central and South Asia in 2021, according to the report.

Source: IQAir 2021 World Air Quality Report

“India’s annual average PM2.5 levels reached 58.1 µg/m3 [micrograms per cubic meter] in 2021, ending a three-year trend of improving air quality,” the report said. “No cities in India met the WHO air quality guideline.”

Avinash Chanchal, campaign manager at non-government organisation Greenpeace India said the report was a wake-up call for governments and corporations.

“It [the report] once again highlights that people are breathing dangerously polluted air,” Chanchal said, according to PTI. “Vehicular emissions are one of the major contributors to urban PM2.5 concentrations. With annual vehicle sales in India expected to increase, it is certainly going to impact air quality if corrective measures are not taken in time.”