To fix air pollution, Gopal Rai wants artificial rain in Delhi: Why this is a long shot

The choking aerial contamination has persisted successful the portion adjacent arsenic Stage IV of the Graded Response Action Plan (GRAP) kicked successful connected Monday (November 18). GRAP is simply a acceptable of exigency measures implemented to forestall further deterioration of aerial prime erstwhile it reaches a definite threshold successful the Delhi-NCR region.

So, tin artificial rain, besides called unreality seeding, hole Delhi’s aerial quality? Simply put, astatine champion it tin person a constricted interaction and effect successful respective unintended consequences which tin severely interaction the environment. Here is why.

But first, what is artificial rainfall oregon unreality seeding?

Water vapour condenses astir tiny particles to signifier the droplets that marque up a cloud. These droplets collide and grow; arsenic they get dense and the unreality gets saturated, it rains.

With unreality seeding, clouds are usually injected with salts similar metallic iodide, potassium iodide, oregon sodium chloride, which is the ‘seed’. These salts are expected to supply further nuclei astir which much unreality droplets tin form. They are dispersed into the unreality either utilizing craft oregon done generators connected the ground.

“Seeding accelerates unreality microphysical processes. You request sufficiently ample droplets that tin scope the aboveground of the Earth and not evaporate connected the way,” Sachchida Nand Tripathi, Professor astatine IIT Kanpur and Steering Committee member, National Clean Air Programme, had told The Indian Express successful 2023.

Tripathi had besides said, “The substance that is dispersed into the unreality needs to person unreality condensation nuclei and crystal nuclei and these 2 travel from 2 antithetic salts.”

The unreality condensation nuclei assistance signifier unreality droplets, and crystal nuclei assistance to signifier crystal crystals. Ice crystals turn faster than drops, and they go ample and fall.

What are the conditions required for unreality seeding to beryllium done?

Firstly, unreality screen and clouds of a definite benignant are necessary.

M Rajeevan, erstwhile caput of the Ministry of Earth Sciences, had told The Indian Express, “Cloud seeding tin lone hap if determination is simply a capable fig of clouds and a peculiar extent to these clouds. Inside, determination needs to beryllium an capable fig of unreality droplets. Cloud seeding is done to summation the radius of the unreality droplets truthful that they volition turn bigger and due to the fact that of gravity, they volition travel down arsenic rainfall. But with a wide sky, you can’t bash it.”

In winter, clouds signifier implicit Delhi erstwhile a occidental disturbance moves implicit the region. These are storms that originate successful the Caspian oregon Mediterranean Sea and bring non-monsoonal rainfall to northwest India.

With a unchangeable ambiance successful winter, clouds are expected to signifier erstwhile a occidental disturbance disturbs this stableness of the atmosphere.

“In winter, you bash not spot the benignant of clouds that are needed for seeding, but occidental disturbances are the mode done which clouds form. Even if clouds are there, you request to spot what their tallness is, what their liquid h2o contented is,” Tripathi had said.

While the anticipation of unreality enactment tin beryllium determined successful beforehand done radars, different conditions volition person to beryllium studied connected the time seeding is apt to beryllium done.

Can unreality seeding oregon artificial rainfall hole aerial pollution?

Despite years of probe connected unreality seeding, the grounds of its effectiveness is mixed. In 2003, a survey by the National Academy of Sciences — a US-based non-profit organisation — recovered “a precocious grade of uncertainty regarding the efficacy of unreality seeding”, according to a study by Bulletin of the Atomic Scientists.

The study besides cited a caller synthesis by the World Meteorological Organization which had concluded that accrued precipitation done unreality seeding typically ranges betwixt zero and 20%, “with the precocious scope representing conditions nether which clouds were highly apt to signifier precipitation naturally.”

In his 2023 article for The Indian Express, Aerosol idiosyncratic Shahzad Gani wrote that unreality seeding tin lone connection a impermanent reprieve from aerial contamination astatine best.

Notably, pollutants specified arsenic PM2.5 and PM10 tin beryllium washed retired to a important grade by prolonged rainfall. However, different pollutants similar ozone and sulphur dioxide are not affected.

Besides, unreality seeding oregon artificial rainfall tin severely interaction the environment. For instance, the chemicals utilized — specified arsenic metallic iodide — successful the process tin adversely impact agriculture and the ecosystem if they accumulate successful ungraded and h2o successful ample quantities. Scientists are yet to afloat recognize the interaction of these chemicals connected the environment.

There are besides ethical concerns regarding unreality seeding, according to Gani. He wrote, “The h2o vapour utilized successful the process would person people precipitated elsewhere, and it perchance deprives different regions of rainfall. This artificial manipulation of upwind patterns could adjacent pb to droughts successful areas which would person received this rainfall otherwise.”