NEW DELHI: Having announced another round of odd-even driving in April, the Delhi government has to gird itself for a crucial test. Particulate matter (PM) levels are usually "moderate" to "poor" during the warm season, but ozone emissions, which are linked with respiratory problems, go up dramatically when vehicular and other emissions react in the warmth of the sun.
Volatile hydrocarbons and compounds emitted by vehicles react photochemically to create ozone, catalyzed by NOx which is largely emitted by vehicles, especially diesel-fuelled engines. In 2015, the ozone levels between April 15 and 30 ranged from 120 to 250 micrograms per cubic metres, higher than the safe limit of 100. High ozone presence is known to trigger inflammation of the airways and reduce lung function in sensitive groups.
"Curbing ozone, which is a dominant pollutant during summer, is the additional benefit of reducing vehicle numbers," said AnumitaRoychowdhury, head of the Centre for Science and Environment's (CSE) clean air campaign. She added that since ozone is a gas, natural dust will not increase its levels unlike particulate matter.
A CSE scientist, who declined to be named, explained that since the weather is likely to be more stable in the spring than in winter, checking the number of cars on the roads could give a more conclusive evidence of traffic's impact on air quality. However, Naresh Kumar, associate professor at the University of Miami, who found the January experiment did improve the air quality marginally, said the government should have reworked the modalities for the second round. "A regular even-odd drive may help reduce air pollution. But the government also needs to look at the root causes. Moreover, the satellite cities located around Delhi need to enforce the same trial in order to create a meaningful impact," he said.
CSE reiterated that the intensity of smog episodes during the 15-day experiment in January hadn't been as high as it was before the trial. It pointed out how on the first Monday that cars were allowed back on the roads, the gains of the fortnight were immediately lost. More importantly, DTC's ridership increased by 8% and its fleet utilization improved from 84% to 95%, while the Delhi Metro reported a 7% rise in ridership. The Petrol Dealers Association reported a drop in sales of petrol and diesel by 4.7% and 7.8%, respectively, between December 2015 and January 2016.
Exemptions given to various categories, including to women drivers and two-wheelers and which will be available even in April, have, however, been criticized. Experts said that though a reduction in people's exposure to toxic tailpipe emissions was noticed, the benefits would not be substantial because many vehicles are excused from the restrictions. "The government is limiting the possibilities of the scheme," rued Roychowdhury.
Amit Bhatt, head of urban transport at Embarq, too felt that the linkage between transport density and air quality could have been well established had there been no exemptions for anyone. He suggested that it would be useful to plan emergency measures like immediately restricting traffic whenever pollution levels breached a specified threshold.
