New smog tower in Delhi: technology, impact, evidence

Smog tower components

The structure is 24 meters high, roughly the size of an 8-storey building with an 18-meter concrete tower, topped by a 6-meter-high canopy. At its base are 40 fans, 10 on each side.

Each fan can emit 25 cubic meters per second of air, adding up to 1,000 cubic meters per second for the tower as a whole. Inside the tower in two layers are 5000 filters. Filters and fans are imported from the United States.

Image: Tata Projects

Smog Tower: How it works

The tower uses a ‘down air purification system’ developed by the University of Minnesota, said Anwar Ali Khan, senior environmental engineer at the Delhi Pollution Control Committee, who was responsible for the project.

IIT-Bombay has partnered with American University 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 m, and filtered air is released at the bottom of the tower, at a height of about 10 m from the ground. When the fans at the bottom of the tower operate, the negative pressure created sucks in air from above. The ‘macro’ layer in the filter captures particles 10 microns and larger, while the ‘micro’ layer filters smaller particles of about 0.3 microns.

The descent method is different from the system used in China, where a 60-meter smog tower in Xian city uses an air update system to suck air close to the ground and propel it upward by heating and convection. The filtered air is released at the top of the tower.

Potential impact

Modeling computational fluid dynamics by IIT-Bombay suggests that the tower may have an impact on air quality up to 1 km from the tower. The current impact will be assessed by IIT-Bombay and IIT-Delhi in a two-year pilot study that will also determine how the tower operates in different weather conditions and how PM2.5 levels change with air flow.

An automated Surveillance and Data Acquisition (SCADA) system in the tower will monitor air quality. The sheets of PM2.5 and PM10, in addition to temperature and humidity, will be continuously measured and displayed on a board at the top of the tower.

Monitors will soon be installed at different distances from the tower to determine its impact on these distances. The project aims to provide clean air in a localized area, officials said.

The “Smog Tower” was inaugurated by Delhi Prime Minister Arvind Kejriwal on Monday.

Order of the Supreme Court

In 2019, the Supreme Court instructed the Central Pollution Control Board (CPCB) and the Delhi government to come up with a plan to install smog towers to combat air pollution. The court was hearing a case related to air pollution in the national capital due to the burning of pastures in Punjab, Haryana and Uttar Pradesh. IIT-Bombay then submitted a proposal for the towers to the CPCB. In January 2020, the Supreme Court ordered the two towers to be installed by April as a pilot project.

The smog tower at Connaught Place is the first of these towers. The second tower, being built at Anand Vihar in East Delhi with the CPCB as the nodal agency, is nearing completion.

Since 2009, a 258% to 335% increase was observed in the PM10 concentration in Delhi, a 2016 report by the CPCB noted. But the most prominent polluter in Delhi and neighboring areas is PM2.5, the report said.

No evidence so far

This is the first experiment with a large-scale air purification system in India. Small smog towers have been erected in the Netherlands and South Korea; the largest have been set up in China.

Experts said there is not enough evidence that smog towers work.

We have not come across any clear data that has shown that fog towers have helped improve the outdoor air quality of a city, whether in India or other parts of the world. How do you filter air in a dynamic scenario when it is not a restricted area? Anumita Roychowdhury, executive director of research and advocacy at the Center for Science and the Environment, said.

Dipankar Saha, former additional director, CPCB, and former head of the air quality monitoring division in Delhi, also said there were no proven efficiency calculations in such installations. We will have to control emissions at ground level, not create emissions and then try to clean it up, he said.

Delhi has three smaller air purifiers (about 12 feet long) installed by the Gautam Gambhir Foundation in Krishna Nagar, Gandhi Nagar and Lajpat Nagar basically large versions of indoor air purifiers.

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