Air

Can artificial rain provide relief to polluted Delhi?

Down To Earth speaks to experts about the Centre’s recent statement that artificial rain would be used to lessen the capital’s smog

 
By Rajat Ghai
Last Updated: Wednesday 21 November 2018
Delhi Smog
Smog hangs over the Red Fort in Delhi. Credit: Getty Images Smog hangs over the Red Fort in Delhi. Credit: Getty Images

The Union government will resort to cloud seeding to artificially induce rain if the smog situation in Delhi grows worse.

“If the situation worsens, then the option of cloud seeding to induce rainfall artificially, as an immediate step can be considered,” Mahesh Sharma, Union Minister of State for Environment told wire agency ANI on Tuesday.

But will it happen? And even if it happens, will it work?

Media reports have said that the aircraft that will seed the clouds for artificial rains in Delhi may take off from one of the three airports in the National Capital Region—Safdarjung, IGI or Hindon near Ghaziabad. It will do so only when meteorological conditions are suitable. Officials have not divulged any other information.

And therein lies the problem. When exactly will there be suitable meterological conditions over the capital?

“The clouds required for cloud seeding are of a typical type. They are called convective clouds and they grow vertically. Only these can be seeded, not the other type, which are called stratified and grow horizontally,” explains J R Kulkarni, retired scientist from the Indian Institute of Tropical Meteorology, Pune, an autonomous institute of the Union Ministry of Earth Sciences.

He adds: “For making rain, air containing water vapour has to enter clouds from below. Clouds usually have drops and particles of micron size. When the water vapour enters the cloud, it collides with the particles to produce bigger particles or droplets. These are of millimetre size. This process is called collision and coalescence. In artificial rain, hygroscopic material that has an affinity to water is sprinkled on convective clouds. This material helps in the collision and coalescence process and thus creates rain.”

But the conditions that lead to air pollution are very different, says Kulkarni. “Air pollution is due to concentration or accumulation of particles in the lower troposphere. The accumulation is due to stable atmospheric conditions. In such conditions, formation of vertical, convective clouds is not possible. Even if clouds are formed, they are of the horizontal, stratified type on which seeding will not have any effect,” he says.

The world’s first experiment in cloud seeding goes back to 1946, immediately after World War 2. While researching aircraft icing, General Electric's Vincent Schaefer discovered cloud seeding in July 1946 through a series of events. At least 56 countries have used some sort of cloud seeding, according to the World Meteorological Organization.

“India has a long history of cloud seeding. The first such experiment here was in 1952. We have continued to use it till today, a period of more than 60 years. But it has been used mostly for drought mitigation and increasing water levels in the dams. Nowhere in the world has this process been successful till now in alleviating air pollution,” says Kulkarni.

Even if conditions stabilise and become conducive for cloud seeding, the actual rain triggered by it should have little effect on cleaning up the air. “Cloud seeding can only be done if the meteorological conditions for this are suitable, and if the moisture content in the local atmosphere meets the requisite criteria. However, it can only provide immediate symptomatic relief in terms of suppressing the pollutants present in the air. Ultimately, if the sources of the pollutants, i.e. vehicles, industry and construction are allowed to emit unabated, artificial rains through cloud seeding will have only a limited and temporary impact,” says Polash Mukerjee, Senior Research Associate, Clean Air and Sustainable Mobility Unit, Centre for Science and Environment (CSE), New Delhi.  

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