Delhi air pollution: Why has India failed to clean up its toxic smog?

State authorities tout an experimental plan that involves stimulating clouds for rain, but scientists are sceptical.

Soaring air pollution in India’s capital, New Delhi, has reached “hazardous” levels this week, causing state officials to limit movement and revive plans to stimulate artificial rain to clear toxic smog.

Last week, authorities in the city ordered schools to shut down. Businesses and offices were also ordered to function at half-capacity from Monday.

Monitors earlier in the week recorded a “severe plus” reading (493) of the 24-hour air quality index (AQI), which is more than 30 times the World Health Organization’s (WHO’s) limit. This indicated extremely high levels of unsafe particulate matter called PM2.5 in the air, the highest reading this year.

The WHO guidelines state 24-hour average concentrations of PM2.5 should not exceed 15 microgrammes per cubic metre more than three or four days per year.

Delhi’s toxic smog season usually emerges every winter and contributes to the capital region of 33 million people being consistently ranked among the most polluted areas in the world.