‘Levels of pollutants increased during odd-even’

Study says emissions from increased fleet of exempt vehicles may have offset any reduction from cars

Levels of volatile organic compounds were found to be 60% higher than average.

The fortnight-long odd even policy (OEP) to check pollution in Delhi may have been counterproductive and may have exposed people to elevated levels — as much as 60% — of volatile organic compounds (VOCs), a key component of emissions from vehicles said to aggravate respiratory ailments, according to a multi-authored research study forthcoming in the peer-reviewed journal Current Science .

Based on whether cars bore odd-or-even-numbered licence plates, the Delhi-government policy restricted passenger cars from plying between 8 a.m. and 8 p.m. between January 1 and January 15, 2016, on Delhi roads in a bid to cut down pollution from vehicles during winter. The policy, however, posed no limits on movement of public transport, two-wheelers, three-wheelers, trucks and CNG-operated vehicles.

The researchers measured the concentrations of 13 major chemicals, including toluene, benzene, methanol, acetone all of which are grouped under volatile organic compounds.

Spike in levels

The samples were taken in special glass jars, along the Indian Oil Corporation Limited arterial road near Dwarka. The report states that the stretch sees nearly 35,000 petrol and diesel vehicles ply at peak traffic hours.

Pollutant concentrations spiked in the morning and afternoon but didn’t show a significant change during the night, the authors note.

For instance, the average mass concentration in morning samples collected between 7 a.m. and 8 a.m. for all measured VOCs during the days of the OEP was 436.6 ± 161.5 microgram per cubic metre out of which aromatic compounds contributed 256.0 ± 32.2 microgram per cubic metre.

This was about 60% higher than the average of 269.2 ± 124.3 microgram per cubic metre, on days when odd even wasn’t implemented.

In the afternoon, during the period, the average total mass concentration of VOCs was 256.0 ± 32.2 microgram per cubic metre, while that of the total aromatic compounds was 153.9 ± 23.5 microgram per cubic metre, which is about 40% higher compared to pollution levels seen during days when the policy wasn’t in effect.

Exempt vehicles

“This suggests that a large number of personal vehicle users may have opted to commute before the traffic restrictions were put in place [odd-even rule enforcement timings were 8 a.m.– 8 p.m.],” say the authors in their report. “There was an overall increase reported in the number of vehicles that were exempt from the rule, such as motorised two-wheelers, three-wheelers, taxis and buses by 12%–138%. The emissions from the increased fleet of exempt vehicles therefore appear to have offset the reduction of emissions accomplished by controlling personal four-wheeler vehicles/cars.”

Statistics from the transport ministry shows that Delhi has the highest number of personal vehicles in India, with a total registered fleet of 2.9 million cars and 6.1 million two-wheeler motor vehicles, which alone contributed to 93% of total registered vehicles (about 9.7 million).

From 2011 onwards, every year on an average, around 1,50,000 cars and 3,00,000 two-wheelers are being registered. However, several studies that have studied the sources of pollution in Delhi have blamed road dust and the burning of biomass, with vehicular emissions said to be the third major source of pollution.