As Delhi continues to choke from air pollution, the Union environment ministry plans to create artificial rain through cloud seeding in the hope that it will wash away pollutants. This is the process of introducing chemical agents such as silver iodide, dry ice and common salt in certain types of clouds to induce rain. “The Centre has decided that if the air quality crosses the 500 [air quality index] mark then they will ask authorities to induce artificial rain or cloud seeding over the capital,” said Mahesh Sharma, Union Minister of State for Environment, Forest and Climate Change on November 20.

However, even as scientists are yet to pick a date for this experiment, experts point out that winter conditions do not usually permit the formation of clouds suitable for seeding. Others are not sure if this method is a feasible plan to improve Delhi’s worsening air quality. It is also expensive, costing approximately Rs 15 lakh a session.

The project is being conducted with the help of scientists from the Indian Institute of Technology, Kanpur. “Cloud seeding has been done in 53 countries and going by the experiments we conducted in May 2017, we saw a 50% success rate,” said S Tripathi, the scientist who is leading the project. “It costs Rs 10 to 15 lakh per session which goes on for five to six hours. We conducted six to seven trials in Kanpur with a small airborne vehicle. Sometimes there was rain and sometimes hail would form.”

Tripathi admitted that the clouds needed for seeding may not form over Delhi in the coming days. He also said that there were issues related to clearances as they had to acquire an aircraft from the Indian Space Research Organisation to carry out the experiment. They also needed other authorisations from the Directorate General of Civil Aviation, Ministry of Defence and Ministry of Home Affairs.

CK Mishra, secretary at Ministry of Environment, Forest and Climate Change, said as much. “IMD [Indian Meteorological Department] has not given a clearance for this,” said Mishra. “There are no clouds ideal for this now. Once that happens we will start the process. We have been preparing for this since a month.”

How it works

Seeding is done with the help of an aircraft that disperses the chemical agents into clouds. “If successfully done, these materials induce rain in that area,” said Tripathi. “Cloud seeding can be done either with aircrafts or ground-based rocket launchers.”

Thara Prabhakaran of the Indian Institute of Tropical Meteorology in Pune said that several factors contribute to the success of cloud seeding. “Background observations before seeding are mandatory,” she said. “It has to be done with proper selection of clouds that have enough liquid.” She added said that warmer weather was better suited for cloud seeding experiments. “In the winter, there is not much moisture in the atmosphere to form clouds,” she said. “If the atmosphere is dry then the rain droplets don’t fall, they instead evaporate.”

Prabhakaran has been studying cloud seeding and rain enhancement through the Cloud Aerosol Interaction and Precipitation Enhancement Experiment at the Pune institute since 2009. The purpose of this experiment is to observe the interaction between aerosol (suspension of fine solid particles or liquid droplets), clouds and precipitation, and gather data to make “protocols for rain enhancement” in India.

She said that an experiment was carried out between July and October to observe the changes in clouds after seeding. “Data gathered from this experiment is still being evaluated,” said Prabhakaran. “We need to gather more data to make a statistically more sound result about how effective this is. In some cases we see rain enhancement, while in some cases the cloud can dissipate completely.”

‘Temporary solution’

Scientist DS Pai from the Indian Meteorological Department said the effects of cloud seeding on curbing pollution would only last till it rains. “It is a very temporary solution,” said Pai. “It is difficult to carry out on a large scale and mostly limited only for academic purposes.”

Most times it is not possible to measure the success of such experiments, said Pai. “The success could also lie in the timing of seeding and where the precipitation happens,” Pai said. “Clouds that are seeded could end up moving elsewhere because of which it may not rain where we want it to.”

Prabhakaran also said that the effects of cloud seeding specifically on curbing pollution is not known. “Cloud seeding technology is not readily available in India and studies on several fronts and developments are still needed,” she said. “We have not yet tried this in the country and there still needs to be a systematic study. We have progressed in our study of cloud seeding but we still have a long way to go in terms of curbing pollution.”