Across India, the time around Diwali brings festive cheer but in Delhi, it also brings toxic air. Dense smog has once again engulfed the nation's capital, endangering millions of its residents and heightening the calls for policy responses. One such policy response is launching today: the odd-even scheme. But going by the data and the previous odd-even experiments, Delhi's residents should temper their expectations: odd-even may provide some relief but much more is needed.

The odd-even policy seeks to reduce pollution levels by halving vehicle usage on Delhi’s roads (by limiting odd-numbered vehicles to only travel on odd-numbered dates between November 4th and 15th).

The effects of this move could have important implications even beyond Delhi. Though the national focus has been on Delhi’s pollution, India’s other metros also breathe in toxic air. For instance, over the last month, only Bangalore has had a significant number of days (16 of 31 days) with breathable air (based on the World Health Organization’s standard of air with less than 25 mg of PM2.5 - the smallest, most deadly pollutant). Other cities regularly cross this threshold and all cities saw a sharp spike in PM2.5 levels following Diwali though the spike was not as dramatic as in the case of Delhi. Results from Delhi’s odd-even experiment could potentially influence similar policies in these cities.

Odd-even hopes to decrease pollution by clamping down on transport emissions. Cars and bikes spew out toxic particles which pollute the air but the extent of this pollution is widely debated. In Delhi itself, estimates of transport’s contribution to overall pollution have ranged from 18% to 39%, according to a review of pollution studies conducted by the Council on Energy, Environment and Water (CEEW).

The wide range reflects the complications involved in measuring the sources of air pollution. According to CEEW, estimates vary so much because of differences in methodologies and samples. But taken together, they suggest that road transport emissions are indeed the biggest contributor.

Odd-even, then, is targeting the right source - but is it doing this effectively? The results from the previous two odd-even experiments in Delhi (two fortnights in January 2016 and April 2016) have been fiercely contested. Some studies claim it has helped alleviate pollution. Others suggest that it had little effect. Here, too, conflicting results reflect the complications in isolating the effects of odd-even, amid several different factors, on overall pollution levels.

For instance, the Central Pollution Control Board’s study, based on an analysis of pollution levels before and after odd-even, was ambiguous. It suggested that pollution may have reduced but this could not be attributed to a single factor. Another study published in the journal Current Science was more definitive and claimed that odd-even may have actually been associated with an increase in pollution. The researchers argue that odd-even did not decrease emissions because more commuters travelled before odd-even hours kicked in or used other vehicles such as taxis and three-wheelers.

Two other studies, though, are more optimistic. One study published in the journal Environmental Science and Policy combined satellite data with air pollution station data to conclude that odd-even decreased PM2.5 levels by 4% to 5% across Delhi. Another study by the Energy Policy Institute at the University of Chicago (EPIC) for the NCAER 2017 India Policy Forum estimated an even bigger decrease. By comparing PM2.5 data from Delhi’s monitors with data from monitors in neighbouring cities (such as Gurgaon and Noida) where odd-even did not apply, the study found that the January 2016 odd-even pilot in the winter decreased air pollution during the day by 14% to 16% (but there was no impact during the April 2016 pilot). And these were the findings that Chief Minister Arvind Kejriwal cited in the latest odd-even policy announcement.

Though studies differ in their verdicts of odd-even, they are unanimous in their overall conclusion: Delhi needs a longer-term holistic approach to tackling air pollution.

For instance, Santhosh Harish, Fellow at the Center for Policy Research and one of the researchers in the EPIC study, suggests that each of the sources of air pollution, such as power plants, crop burning, transport emissions and construction dust, have to be tackled in parallel. These are recommendations applicable not just to Delhi but the entire Northern Indian Gangetic belt, which contributes to Delhi’s pollution, and parts of which suffer from even fouler air because of the unique topography of the land-locked region. Proximity to stubble burning only aggravates the problem.

Taming pollution in this belt is tough but not impossible. Long considered one of the most polluted cities in the world, Beijing is now not even one of the 100 most polluted cities in the world, according to one ranking by Greenpeace, an international NGO. A UN study on Beijing’s air pollution control efforts attributes this improvement to several different policies, such as vehicle emission controls and reducing coal dependence, that tackled the city’s different sources of pollution. But underpinning all these policies is an air quality management approach centred on legislation and enforcement mechanisms, systematic planning, powerful local standards, strong monitoring capacity, and high public environmental awareness. Delhi and India will need to do the same.

Close