Why Delhi’s experiment to fix toxic smog with artificial rain failed

Authorities in Indian capital Delhi unsuccessfully carried out a cloud seeding trial, which is the science of altering clouds to make rains, to tackle the city’s worsening air pollution on Tuesday.Cloud seeding is done by firing small particles – usually silver iodide – into clouds to produce rain. The technique is used around the world, but experts doubt its efficacy as a long-term air pollution control measure.A team of the Indian Institute of Technology (IIT) Kanpur and the Delhi government carried out the trial over several neighbourhoods, as thick smog enveloped the city.But the attempt – the first in 50 years – was “not completely successful” due to the lack of moisture in the air.

Over the past two weeks, Delhi’s Air Quality Index (AQI) – which measures the level of PM 2.5 or fine particulate matter in the air that can clog lungs – has been hovering between 300 and 400, which is nearly 20 times the acceptable limit.On Tuesday, authorities used a Cessna aircraft to release fire flares containing silver iodide and sodium chloride into the atmosphere to trigger rainfall.In a statement, IIT Kanpur said that despite the lack of rain, there had been a measurable reduction in particulate matter because of Tuesday’s experiment, “indicating that even under limited moisture conditions, cloud seeding can contribute to improved air quality”.However, the institute’s directorManindra Agarwal told NDTV news channelthat the technique was an “SOS measure” and not a long-term fix for Delhi’s perennial pollution problem.The trial is likely to be repeated in the coming weeks after the moisture levels in the clouds increases again, Delhi’s Environment Minister Manjinder Sirsa told reporters.

Delhi’s first cloud-seeding experiment was carried out in 1957, followed by another attempt in 1972, according to theIndian Institute of Tropical Meteorology.The city had considered cloud seeding in2023as well, but the plan did not materialise due to pending court approvals.Back then, scientists had also highlighted how it was an expensive strategy with low success rates.Cloud seeding speeds up the condensation of moisture in clouds to create rain. The salt granules act as ice-nucleating particles, which enable ice crystals to form in the clouds.

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