Pollution levels in Delhi have reached dangerous levels, prompting the Indian government to try cloud seeding as a radical approach to solving the problem.Photo: Prakash Singh/Bloomberg via Getty.
An ambitious attempt by the Indian government to combat dangerous air pollution in Delhi by producing artificial rain failed to produce any rainfall, prompting researchers to question why the experiment was allowed to continue.
The experiment was conducted in collaboration with Indian Institute of Technology (IIT) Kanpur on October 28. Two planes flew over several areas of Delhi and released plumes containing particles of silver iodide and sodium chloride into the atmosphere, aiming to cause condensation and cause rain.
The Delhi government and IIT Kanpur say the seeding experiment resulted in a slight reduction in pollution, but scientists believe the improvement had nothing to do with the intervention.
“The skies seem to have cleared, but that is because the weather conditions have changed. This is not due to the planting efforts,” says Shahzad Ghani, an aerosol scientist at IIT Delhi.
Toxic smog
Every winter for nearly a decade, Delhi and surrounding areas have battled dangerous levels of fine particulate matter in the air from industries, vehicular emissions and stubble burning in neighboring states. On some days, pollution levels are 20 times higher than World Health Organization recommended limits.
During October and November, the air in and around Delhi becomes cooler, drier and more stable, slowing down the spread of pollutants. The Delhi government has tried to take various measures to improve air quality, such as closing polluting industries and banning fireworks during Diwali celebrations. However, poor compliance has meant that most of these initiatives have had little impact. This year, when pollution levels turned dangerous on the night after Diwali, the government decided to take a different approach.
The technique of cloud seeding—the release of fine particles such as silver iodide and sodium chloride into existing clouds to help water vapor condense—has been around since the mid-twentieth century. But there is no reliable evidence that this process can produce precipitation on demand, and its ability to disperse pollution has not been tested, Ghani says.
Roxy Mathew Call, a climate scientist at the Indian Institute of Tropical Meteorology in Pune, says the atmospheric conditions were not right for the experiment to succeed. “Cloud seeding can only increase precipitation if there are already moist convective clouds with enough liquid water. In dry or stagnant air, there is simply nothing to seed,” Call says. During the experiment, “two storms—a depression in the Arabian Sea and a cyclone in the Bay of Bengal—carried moisture into these areas and made Delhi drier.”
Another trial scheduled for Wednesday was cancelled. Manindra Agrawal, director of IIT Kanpur, told Indian news agency ANI that the experiment will be postponed until the day when the cloud humidity is at least 40-50%.
Earlier this year, the Royal Rainmaking Project in Thailand tried to combat pollution by spraying cold water from airplanes, hoping it would disperse some of the particulate matter trapped in the layer of warm air in the atmosphere.
