How Does Artificial Rain Reduce Pollution?

Scientists and governments are exploring the possibility of using artificial rain to alleviate the worst effects of pollution. In particular, the Indian government are considering deployment of artificial rain to improve the ever-worsening situation in New Delhi, which continues to suffer from increasingly high levels of nitrogen oxides (NOx) pollution.

Artificial rain works via a process called cloud seeding, during which chemicals are injected into the Earth’s atmosphere to mimic the composition of clouds. This then leads to precipitation in the form of rain or snow, thus cleansing the air and ridding it of excessive levels of contamination. It is also sometimes used in areas which suffer from extreme drought or to clear the fog near airports.

How does artificial rain work?

Cloud seeding is a specific form of geoengineering (or weather manipulation) which aims to replicate the effects of rainclouds in dry, polluted or smoggy regions. It is induced via a three-stage process, during which different chemicals are deployed to achieve different effects.

The first stage is called agitation and involves releasing chemicals into the air in order to stimulate air mass upwind of the location where the cloud is required. This air rises and gathers together to form rainclouds, which are then capable of absorbing moisture and water vapour from the surrounding atmosphere. This instigates the condensation process.

Next comes the building-up stage, during which chemicals such as ammonium nitrate or calcium chloride are injected to act as a catalyst for the process, enlarging the cloud’s size. Finally, the cloud is injected with chemicals like silver iodide or dry ice, which destabilise the cloud and lead to the formulation of water droplets. It is at this point that the ice crystals within the cloud either fall to the ground in the form of snowflakes or as rain, depending on ambient temperatures in and around the cloud.

Rain over New Delhi

Last month, the Indian Environment Minister announced that the government is considering using cloud seeding techniques to induce rainclouds over New Delhi, in a bid to rid the country’s capital of lingering pollution. The Air Quality Index (AQI) showed readings of up to 391 (out of a possible 500) towards the end of November, meaning its pollution rating was only nine points away from a “severe” classification.

A growing market for continuous emissions monitoring systems (CEMS) in the country has led to increased public awareness, which in turn has resulted in widespread protests and increased pressure on the government to take action on the subject of air pollution.

The idea of inducing artificial rain is an attempt to mitigate the worst effects of existing contamination, but the government has also been exploring ways in which it can be prevented in the first place. These include encouraging the use of public transport, halving the number of cars allowed on city streets during days of particularly poor air quality and even transitioning completely to electric vehicles (EVs).