Delhi’s new smog tower: the technology, the impact, the evidence

What is the news?

Ahead of its infamous smog season, Delhi has installed a ‘smog tower’, a technological aid to help combat air pollution.

Background

In 2019, the Supreme Court directed 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 matter related to air pollution in the national capital due to stubble-burning in Punjab, Haryana and Uttar Pradesh. IIT-Bombay then submitted a proposal for the towers to the CPCB.

Extent of Delhi’s pollution

• Delhi was the most polluted capital city in the world in 2020 for the third consecutive year, according to a report by a Swiss group (released in March 2021) that ranked cities based on their air quality measured in terms of the levels of ultrafine particulate matter (PM 2.5).
• Also, since 2009, an increase of 258% to 335% had been observed in the concentration of PM10 in Delhi, a 2016 report by the CPCB noted. But the most prominent pollutant in Delhi and neighboring areas is PM2.5

What is a smog tower?

• Smog towers are structures designed to work as large-scale air purifiers. They are fitted with multiple layers of air filters and fans at the base to suck the air.
• After the polluted air enters the smog tower, it is purified by the multiple layers before being re-circulated into the atmosphere.

How does a smog tower work?

The tower uses a ‘downdraft air cleaning system’ developed by the University of Minnesota. IIT-Bombay has collaborated with the American university to replicate the technology, which has been implemented by the commercial arm of Tata Projects Limited.

• Polluted air is sucked in at the top, 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 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.

Likely impact

Scientific modelling by IIT-Bombay suggests the tower could have an impact on the air quality up to 1 km from the tower. The actual impact will be assessed by IIT-Bombay and IIT-Delhi in a two-year pilot study.

Do smog tower actually work?

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

As per experts, there isn’t enough evidence that smog towers work.