As cooler temperatures in Delhi bring back steadily worsening pollution, the Central Pollution Control Board under the Union Ministry of Environment has started installing outdoor air purifiers across the city. The project was announced in August. In all, 54 such machines will be placed in areas with heavy traffic flow and high pollution levels by the end of October, the board’s officials said.

However, environmental experts doubt if these machines will significantly improve air quality in these areas while the authorities installing them also have no idea of their effectiveness. This despite the Delhi government, in partnership with the National Environmental Engineering Research Institute and the Indian Institute of Technology-Bombay, having experimented with outdoor air purifiers in 2016. Delhi government officials say they have not yet received a report detailing the outcome of that project.

The experts had been sceptical then too, saying the machines did not curb pollution at the source. They had also pointed to the difficulty in assessing the air purifiers’ effectiveness outdoors. The same concerns are being raised again.

WAYU to the rescue

The Central Pollution Control Board is installing the air purifiers as part of a six-month pilot project and at a cost of Rs 2.6 crore, reported The Indian Express.

Called Wind Augmentation and Air Purifying Units or WAYU, these machines were developed by the Indian Institute of Technology, Bombay, and the National Environmental Engineering Research Institute. The 54 machines will come up in areas such as Anand Vihar, ITO, Wazirpur and Bhikaji Cama.

Environment minister Harsh Vardhan inaugurates a WAYU unit at ITO in New Delhi on September 25. (Credit: Press Information Bureau)

In addition, 30 smaller air filters developed by the Faridabad-based Manav Rachna International Institute of Research and Studies will be placed on the roofs of city buses and some atop rickshaws and two-wheelers.

“Since they [the WAYU machines] are being installed in areas where there is heavy traffic and pollution, they will ensure clean air in the vicinity,” said Dr VK Shukla of the Central Pollution Control Board. He, however, said he was “not aware” of how the clean air thus produced will be quantified. “NEERI [National Environmental Engineering Research Institute] will measure it and give us a report,” he said.

Dr Sunil Gulia, a scientist at the National Environmental Engineering Research Institute, said the machines are specifically designed to function in areas with high pollution levels. He explained that the machines have filters made of activated charcoal and non-woven fabric such as porous sheets of plastic film. “This helps trap particulate matter 2.5 and 10,” he added.

The World Health Organisation defines particulate matter as “a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air”. Particles with a diameter of 10 microns or less can penetrate and lodge deep inside the lungs while those with a diameter of 2.5 microns or less can enter the blood system. Chronic exposure to both is said to raise the risk of cardiovascular and respiratory diseases as well as lung cancer.

Gulia said the machine’s effectiveness will be measured by checking the quality of air seeping in and out. “We will check the air inlets as well as the dust collected by the machine twice every week,” he explained. “If the pollution levels are high, then we will check the machine every two days.”

Both Shukla and Gulia denied any knowledge of a similar project with outdoor air purifiers in 2016.

‘Not effective outdoors’

While the Central Pollution Control Board insists the air purifiers will improve air quality, experts are not convinced.

Dr Sarath Guttikunda of Urban Emissions, an independent research group on air pollution, said there is no way to quantify how much air is being purified if the machine is installed outdoors. “It is simple logic,” he said. “You can quantify something if it is in an enclosed space because you know the measurements. But you cannot do so outdoors.”

In 2016, Guttikunda wrote in The Wire that installing air purifiers at traffic intersections did not curb harmful emissions at its source. “If we could suck up pollution on the roads, then why worry about emission and fuel standards?” he wrote. “What difference does it make if the vehicle is one year old or 10 years old, if the vehicle is running on diesel, petrol or CNG [compressed natural gas]? What difference does it make if the waste is burnt or packed at the landfills?”

Over the years, some of the steps taken to clean Delhi’s air have included a ban on all diesel vehicles older than 10 years, restrictions on the registration of new diesel vehicles, and a ban on the burning of trash.

Guttikunda added that the Delhi government had used outdoor air purifiers to combat pollution not only in 2016 but also when the city hosted the Commonwealth Games in 2010.

Polash Mukherjee, research associate at the Centre for Science and Environment, pointed out that there is little evidence to prove that air purifiers make a difference. “Cities like Beijing and Shanghai also tried this,” he said. “But they did this with a bunch of other measures like controlling the number of cars on the road and reducing industrial emissions. There is no way to verify how effective air purifiers outdoors are.”

Mukherjee said that if the air purifiers are installed next to ambient air monitoring stations, it could even lead to “manipulation of data”. But if located at the source of pollution, they could provide some relief, he added.

Mukherjee said governments tend to use technology-based solutions rather than work towards cutting down sources of pollution. “There are a lot of initiatives that are being taken but they are arguably restricted to paper,” he said. “We need to make standards and ensure they are being strictly enforced in and around Delhi.”