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Delhi’s Odd-Even drive apt as emergency response in winters: US Universities’ study

A study done by the Energy Policy Institute of the University of Chicagoalong with Evidence for Policy Design at the Harvard University has shown that the Aam Aadmi party’s (AAP) pilot Odd-Even project in January last year lowered fine particle concentrations (PM 2.5 and PM 10) in Delhi by 14-16 per cent. In contrast, the second pilot conducted in the warmer month of April did not improve the capital’s air quality substantially.

The research concluded that the odd-even scheme is more appropriate for use as an emergency measure during winter months when car emissions play a more prominent role in affecting air quality. 

The researchers associated with the study -- Santosh HarishAnant Sudarshan and 
Michael Greenstone from University of Chicago and Rohini Pande at Havard University -- measured the impact of the Odd-Even exercise on PM 2.5 concentration using a ‘Difference-in-Differences (DiD)’ statistical approach. Under the DiD approach, researchers looked at and compared data before and after the implementation of the Odd-Even exercise.

When the level of particulate matter PM2.5 in the air peaked at 743 microgram per meter cube the authorities were forced to shut schools and doctors had to declare public health emergency. But the government in the capital though again wanted to re-impose the Odd-Even rule from November 13 to 17, decided to call-off the exercise as the National Green Tribunal (
) objected to exemptions given during the previous two exercises (January, April 2016).

According to the study, there was a statistically significant reduction in PM 2.5 concentrations during the days and hours that the odd-even exercise was implemented in Delhi in the January round. Also, the study states that the estimated reduction was in the range of 24 microgram per meter cube to 37 microgram per meter cube. 

“This reduction in concentrations could be attributed to three factors: one, reduction in PM from vehicular exhaust of the cars taken off the road; two, reduced congestion and consequently, reduced idling and emissions from all the vehicles (allowed cars as well as buses and other vehicles) on the road; three, reduced re-suspension of road-dust due to reduced vehicular volumes,” the study said.

It added that it is possible that despite similar compliance and similar reduction in emissions, concentrations may have been affected less in April pilot as compared to the January pilot. The study reasons that dispersion of particulate matter is faster in summers as compared to winters as the atmospheric mixing heights are greater.

“For this reason, modest increases and decreases in emission sources on-ground may disperse upwards and not translate into observable changes in pollution concentrations near the ground. On the other hand, in winter when dispersion is minimal, these changes are immediately noticeable. This suggests a limitation of the program itself: it is perhaps more appropriate as an emergency measure during the winters, than as a long-term pollution reduction measure, even if compliance rates are high,” the study stated.

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