A group of environmentalists have written an open letter to the Supreme Court, urging it not to direct the Centre or states to spend public money on "expensive" and "inefficient" smog towers which will only benefit the manufacturers and sellers. Earlier this week, the apex court asked the Centre to take concrete decision within 10 days on having smog towers in Delhi-National Capital Region to combat pollution which has shortened the lifespan of millions of citizens.
The direction had come after pollution levels in Delhi peaked to a three-year high notwithstanding claims of heightened checks and curbs by authorities.
"India's leading air pollution scientists and researchers unanimously say that outdoor air purifiers are inefficient to the point of being useless," Jyoti Pande Lavakare, co-founder of Care for Air India, a nonprofit advocacy group, wrote in the letter.
"We earnestly request you -- please don't direct any governments, local, state or central to spend public money to buy expensive smog towers. These are ineffective in bringing down PM2.5 levels and may even add to pollution when the dirty filters are disposed off in our already overflowing landfills and burnt," it said.
China had last year set up the world's largest air purification tower in the city of Xi’an. Co-director, UrbanEmissions.Info, and Care for Air India expert Dr Sarath Guttikunda said that at 100 per cent efficiency, a Xi'an-like smog tower can purify just 0.00007 per cent of Delhi's air.
"Delhi's airshed is around 80 km x 80 km. If you assume Delhi is a box (like a room), atmospheric height is at least 1 km (3 km in summer).
"At an average wind speed of 2 m/sec, the volume of air passing through the city is more than 5 trillion cubic metre per hour. The capacity of the smog tower in Xi'an is a fraction of that -- 4,16,000 cubic metre per hour," he said.
The reason indoor air purifiers work well and outdoor air purifiers don't, is that this ratio is more favourable indoors, the advocacy group said. "Like the odd-even scheme, the best one can expect from smog towers is increased public awareness and political mileage.
What is worse, in the case of smog towers, the only people who will profit will be the manufacturers and sellers," it said.
Lavkare said better results can be achieved if the Supreme Court could direct the power companies surrounding Delhi to add filters to their chimneys more quickly to catch emissions at source.
"This was supposed to be done by December 2017. Despite India's Environment Ministry directing them to do this by December 7, 2017, they have lobbied to get this pushed back to December 2019 to 2022, with staggered deadlines."
"China and other countries haven't brought their pollution down by using smog towers. Rather, they have strengthened industrial emissions standards, phased out small and polluting factories and outdated industrial capacities, upgraded industrial boilers, promoted clean fuels and strengthened vehicle emission standards," she said.