What in the world: Anti-smog towers

2019 isn’t the first time we’ve considered anti-smog towers or outdoor air purifiers.

This is not the first time Delhi has experimented with this idea. Before the Commonwealth Games in 2010, an Italian company installed a $300,000-air-filter in Connaught Place, claiming it to be the cleanest spot in Delhi. There are no numbers to back this up, except for the 2.5 kg of dust collected during its one month of operation. Our estimate for Delhi’s particulate matter pollution is approximately 60,000 tons per year, not including seasonal dust storms and agricultural-clearing emissions. That is 5 million kg per month. Assuming that Connaught Place was the cleanest because of the filter’s operations, we would actually have needed at least 2 million of them to cover the city.

In an opinion piece at the time, Dr. Sarath Guttikunda noted that “installing an air filter in public is more like avoiding the problem and diverting attention away than solving it. Emissions should always be controlled at the source.”

In 2016, we started hearing about anti-smog towers or outdoor air purifiers again.

As pollution levels climbing up, attention was given to outdoor air purifiers and their possible role in controlling air pollution. NEERI and CPCB announced a plan to install outdoor air purifiers at traffic intersections.

Overall, there are widespread concerns in the scientific community about the effectiveness of such mitigation plans. In China, anti-smog towers were installed in at least two cities- Beijing and Xi’an but were not found to be successful and the idea has been considered to be a failure. However, an anti-smog tower has been proposed to control air pollution in Delhi (note that the anti-smog tower in Xi’an is referenced here!), and the Honorable Supreme Court has also suggested this as a solution to air pollution. Separately, Bengaluru has announced the plan to install 500 outdoor air purifiers and the Greater Hyderabad Municipal Corporation (GHMC) recently approved plans to install outdoor air purifiers across the city.

A range of experts agree on this: anti-smog towers are NOT the solution. Emissions need to be controlled at source.

It is costly and works for a limited area like 100 metres, and the pollutants can be easily transported to clean air (area) again. It is not practical to use these (smog-towers) to control air pollution

Dr. Hongliang Zhang, Fudan University

The outdoor purifiers are a distraction. We are saying, focus on the real action of cutting pollution at the source.

Ms. Anumita Roychowdhury, Centre for Science and Environment

It is like trying to air condition a room with the roof off. There is very little evidence they make a difference to concentrations of pollution.

Dr. Alistair Lewis, University of York

Here is an op-ed piece by Dr. Alistair Lewis on anti-smog towers and their inefficiency in controlling air pollution.

Across India, there has been consistent opposition to the idea to installing outdoor air purifiers or anti-smog towers.

In Bengaluru, members of the civil society responded to the plans for installation of outdoor air purifiers, and argued that the limited resources should be spent efficiently, and on measures that can demonstrably reduce air pollution. Most recently, Care for Air, a Delhi-based advocacy organized published an open letter against outdoor air purifiers to the Supreme Court of India.

Watch this space for new details in upcoming weeks.

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