Smog towers have no scientific basis as a policy measure - Part I

This is the first of a two-part analysis of the use of smog towers to tackle air pollution. The second part can be read here.

Smog towers have been in the news recently, with the Supreme Court objecting to the delay of a pilot project in Delhi to set up two 20-m-high towers. Despite there being no scientific evidence, smog towers and other outdoor air-purifying technologies keep distracting the air quality policy discourse in the country. Smog towers offer neither a scientific policy measure to tackle air pollution nor do they constitute an idea worth piloting.

This episode in the country’s air-quality narrative also offers a cautionary tale about over-relying on the judiciary to make policies on air pollution, and the role of reputed scientific institutions that are consulted in the process.

On January 13, 2020, based on the submissions of the Centre and the Delhi government, the Supreme Court ordered the installation of two smog towers on a pilot basis in Delhi within three months: in Connaught Place and in Anand Vihar (the latter is a lot more polluted). On July 29, Indian Express reported that the project was delayed as IIT Bombay, whose researchers were to lead the pilot, had backed out. The Supreme Court bench then hinted at contempt proceedings against IIT Bombay, and the matter was subsequently swiftly resolved.

As on August 4, an agreement had been signed and solicitor general Tushar Mehta reportedly told the bench that the centre had released Rs 18.58 crore to install the smog tower in Anand Vihar.

The patent for the tower’s design is owned by the University of Minnesota. While IIT Bombay will supervise the project, the tower will be built by Tata Projects Limited, with the consultation of the National Buildings Construction Corporation.

Smog towers and solutions like them are attractive to governments for multiple reasons. They are visible – a physical manifestation of the government’s promise to ‘do something’ in a way few air quality interventions are. Second, they don’t impose costs on polluters and therefore don’t antagonise any interest groups. Third, there is the enticing promise of a technological path to clean air without anybody having to change their polluting behaviours. And fourth, they seem plausible as an intervention to policymakers and the public alike – a giant vacuum cleaner sucking in dirty air and releasing clean air.

However, as the development economist Dean Spears argued in his 2019 book Air, such instances of “fake policymaking could crowd out demand for the genuine article” (p. 197). Such measures sow confusion among the people on what the most effective solutions to improve air quality could be instead of keeping the public demand focused firmly on long-term mitigation efforts.

Unfeasible from first principles

Expecting smog towers to provide the results that would justify their significant costs is unrealistic. Given the volume of the airshed that influences air quality where we breathe, filtering air outdoors can have very limited local impact. Filtering methods are useful when addressing emissions before they are released from industrial chimneys or to improve air quality indoors. But even used placed indoors, air purifiers are only effective if doors and windows are well-sealed.

Consider the experience with the WAYU roadside purifiers, developed by IIT Bombay and the National Environmental Engineering Research Institute (NEERI), and set up in traffic junctions in Mumbai and Delhi. There were operational challenges at both locations. In November 2019, the Union environment secretary even conceded that these purifiers and another pilot using a fleet of buses with roof-mounted filters had not been effective. Outdoor air purification just does not work.

On November 25, 2019, the Supreme Court had tasked the Delhi government and the Centre with setting up expert panels to assess the feasibility of smog towers and develop a plan to roll them out. Smog towers have only been piloted in China: there’s a 60-metre high tower in Xi’an – the only operational smog tower at the moment – and a demonstration and art project that converts the carbon in filtered particles into diamonds. In an affidavit dated December 5, 2019, filed by the special secretary (environment) of the government of the NCT of Delhi, the expert panel acknowledged that there is “no publication of the measured data to conclude the impact” of the Xi’an tower, and “no technical evidence available to critically evaluate the efficacy” of the demonstration.

Against this background, the panel could have chosen to reject the idea of smog towers and instead emphasise a focus on long-term mitigation measures. Instead, the panel recommended a pilot “to establish feasibility in Indian conditions”, and take a call on how many other towers would need to be deployed after assessing the impact. The affidavit also suggested that the Delhi government expert panel, and a separate committee under the Department of Science and Technology with representatives from IIT Delhi, NEERI, the Central Pollution Control Board and Delhi Pollution Control Committee, agreed with this recommendation.

Emissions at the source

With air pollution, efforts to reduce exposure – such as masks and air purifiers – are defensive measures: they don’t contend with the emission of pollutants itself but only with surviving them. But scientists have long stressed the need to cut emissions at their sources.

Even the use of public funds becomes more efficacious and sustainable when we implement permanent solutions like improving public transport and supporting related activities, making waste segregation, collection and management more effective, and promoting the use of cleaner fuels like LPG for cooking and heating.

Indeed, in its January 13 order that included the directions to install smog towers, the Supreme Court also addressed source-specific issues like waste and dust management in Delhi, and burning of crop-residue. This latter emphasis on mitigation measures is crucial and welcome, and admittedly, the judiciary has played an important part in nudging an inert executive along over the last two decades.

Originally published in the Wire Science on 6th August, 2020

Environmentality is a collection of ideas, perspectives, and commentary by researchers at the Initiative on Climate, Energy and Environment, Centre for Policy Research, New Delhi. Views and opinions expressed in this blog are solely those of the authors. They do not represent institutional views.

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