Delhi’s Odd-Even Scheme Led to Hike in Emissions, Not Drop: Study

By Sunderarajan Padmanabhan

New Delhi: There seems to be no early end to the debate on whether the odd-even scheme implemented by the Delhi government in January 2016 was a success.

The conclusions of a new research study, published in the journal Current Science on March 25, suggest that the rule led to a rise in vehicular emissions, not drop. Specifically, the study found that there was a significant increase in the median concentration of gases measured from air samples as chemical tracers for emissions.

The study was conducted by researchers from the Ministry of Earth Sciences, the India Meteorological Department, the Indian Institute of Tropical Meteorology and the Indian Institute of Science Education and Research (IISER), Mohali.

The median concentration of 13 of the 16 gases measured were higher in the mornings (7 am to 8 am) and afternoons (1.30 pm to 2.30 pm) on days when the scheme was in effect when compared to three random reference days before and after the fortnight-long implementation period.

Vinayak Sinha, a member of the research team from IISER, explained to India Science Wire that the higher concentration of gases was likely due to a drop in the number of cars causing other vehicles take to the road. This included public transport buses, trucks, two-wheelers, three-wheelers and CNG-operated cars (which were exempted from the scheme).

A study by the Council on Energy, Environment and Water (CEEW) had found that the daily average number of vehicles increased by 10% during the odd-even period in January 2016 compared to the last week of December 2015. The increase was attributed primarily to a 17% increase in two-wheelers, 12% increase in three-wheelers, 22% rise in taxis and 138% rise in the number of private buses.

Additionally, a large number of personal vehicle owners seemed to have simply commuted earlier in the morning and later in the evening, before and after the hours in which the odd-even rule was enforced – 8 am to 8 pm – to avoid penalties.

The study’s paper said, “The odd-even rule may have resulted in traffic decongestion during peak hours, which may certainly have benefitted commuters. However, it must also be kept in mind that enhanced traffic emissions during times of the day when the dilution effect due to the atmospheric boundary layer is low (early morning before 8 am and at night after sunset) could lead to higher peak concentration exposure for several health-relevant carcinogenic volatile organic compounds such as benzene”.

The atmospheric boundary layer refers to the part of the atmosphere in contact with the planet’s surface.

Sinha said that the study examined the concentration of chemical tracers that were specific to vehicle emissions and biomass emissions. This is unlike other studies that investigated the scheme’s impact on the ambient concentration of nitrogen oxides, sulphur dioxides, ozone and particulate matter (PM10 and PM2.5), which are driven by multiple sources of emission.

The report suggested that in future, the government would be better off measuring the levels of volatile organic compounds at multiple strategic sites as well as installing webcams at sampling locations to get a better idea of the number and types of vehicles passing by. According to the report’s authors, this will help address prevailing uncertainties about what proportion of air pollutants different sources emit.

Sunderarajan Padmanabhan writes for India Science Wire and tweets at @ndpsr.

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