DNA Explainer: How Delhi's new 'smog tower' will help reduce air pollution

To help combat air pollution in the coming smog season usually around the winters, Delhi on Monday got a 'smog tower' installed behind Shivaji Stadium Metro station. This was inaugurated by Chief Minister Arvind Kejriwal. The main aim behind this is to reduce the air pollution in the national capital which is leading to health hazards.

"Today is a big day for Delhi in its fight for clean air against pollution," Chief Minister Arvind Kejriwal said on Monday after the inauguration. 

The smog covers Delhi skies just after the festival season and lasts till the winter. During smog season, a grey banket is formed over the sky which leads to breathing difficulties and movement on roads becomes riskier as visibility diminishes.

Details of Smog tower 

The structure is 25-metre (82-foot) high, about as much as an 8-storey building and 18-metre width concrete tower.

The tower is topped by a 6-metre-high canopy. There are forty giant fans at its base, 10 on each side.

The giant fans will pump 1,000 cubic metres of air per second through filters that halve the number of harmful particulates.

According to the engineers, the number of harmful particulates will be halved in a radius of one square kilometre (0.4 square miles).

Each fan can discharge 25 cubic metres per second of air, adding up to 1,000 cubic metres per second for the tower as a whole.

Inside the tower in two layers are 5,000 filters. The filters and fans have been imported from the United States.

Delhi CM Arvind Kejriwal inaugurates smog tower at Connaught Place pic.twitter.com/MLK4RbBLg5

— ANI (@ANI) August 23, 2021

How it works

The Delhi smog tower uses a 'downdraft air cleaning system' developed by the University of Minnesota, said Anwar Ali Khan, in charge of the project.

IIT-Bombay has collaborated with the University of Minnesota to replicate the technology, which has been implemented by the commercial arm of Tata Projects Limited.

Polluted air is sucked in at a height of 24 metre and filtered air is released at the bottom of the tower, at a height of about 10 metre from the ground.

When the fans at the bottom of the tower operate, the negative pressure created sucks in air from the top.

The 'macro' layer in the filter traps particles of 10 microns and larger, while the 'micro' layer filters smaller particles of around 0.3 microns.

The downdraft method is different from the system used in China, where a 60-metre smog tower in Xian city uses an 'updraft' system.

Air is sucked in from near the ground and is propelled upwards by heating and convection. Filtered air is released at the top of the tower.

The actual impact of the smog tower will be assessed by IIT-Bombay and IIT-Delhi in a two-year pilot study.

It will also determine how the tower functions under different weather conditions and how levels of PM 2.5 vary with the flow of air.

Drawbacks

Just one 'smog tower' costs USD 2 million. Critics say by this standard to build a sufficient number of towers to clean the air substantially across the city would cost huge amounts of public money.

Critics say that instead, it would be better to invest such a huge sum of money in efforts to work towards getting rid of the sources of the smog.

From carbon emissions from vehicles, heavy and small-scale industry, construction activity, the combustion of waste and fuel and crops burning in neighbouring regions add to the smog.

India has 14 of the world's 15 most polluted cities, according to the World Health Organisation.

A 2020 study in The Lancet found there were 1.67 million deaths in the country attributable to air pollution in 2019, including almost 17,500 in Delhi.

In 2018, China built a much larger 60-metre smog tower in the polluted city of Xian, but the experiment has not spread to other cities so far.

Experts say there isn't enough evidence to prove that 'smog towers' really work to help clean up the air.

(With Agency Inputs)