A recent study assessing the effect of the odd-even vehicle rationing scheme — enforced in the capital during the first fortnight in January, 2016 — found that there was no desired reduction in pollution levels during the scheme when compared to days post the initiative. The study, in fact, found a higher concentration of 13 out of 16 gases measured — all of them vehicle emissions.
The scheme was implemented on a pilot basis by the Delhi government as a measure to combat rising pollution levels in the capital. Published recently in Current Science, the study was jointly carried out by the Indian Institute of Tropical Meteorology (IITM), Pune, Indian Institute of Science, Education and Research (IISER), Mohali, and India Meteorological Department (IMD).
It analysed vehicular traffic emissions comprising 13 volatile compounds such as sulphur dioxide, ozone, particulate matter, carbon monoxide, carbon dioxide and methane, among others. A total of 27 air samples were collected, both during and after the scheme, during three time slots — 7 am-8 am, 1.30 pm-2.30 pm and 7 pm-8 pm.
Internal roads that connect residential colonies of Dwarka, business hubs of Sadar Bazaar in central Delhi, residential areas near Palam airport were chosen for sample collection. The samples, all of them from emissions of at least 15 to 20 vehicles, were analysed at the Atmospheric Chemistry Laboratory at IISER.
“Despite the odd-even scheme, anticipated reduction in traffic emissions was not obtained,” the study highlighted.
Further, the study observed that the concentration levels of these harmful gases shot up during morning and afternoon hours.
For instance, at 11,000 µg/m3, the concentration of CO2 during morning hours was at its peak when the scheme was implemented, as against 920 µg/m3 during the same hours on regular days. Methane levels, measured at 950 µg/m3, too, were on the higher side in the morning hours when the scheme was in place, in comparison to regular days when levels were around 800 µg/m3.
Offering possible reasons for this trend, one of the scientists who was part of the study said, “Since the concentration in pollutants was found to peak during morning and afternoon hours, it is understood that four-wheeler commuters possibly preferred to travel prior to 8 am, when the scheme would commence. Also, with public transport vehicles exempted from this scheme, their contribution would have remained the same as regular days.”
On the contrary, the study found no significant change in gas concentration during evening hours, both during and after the scheme. On the significance on these gases, the scientist said, “Volatile compounds contribute significantly in generating aerosol particles that cause greater air pollution.”