Pollutants reduced by 18 pc on odd-even days, US-based study

The volume of respirable pollutants in the city's air reduced by 18 per cent during the odd-even scheme that regulated the plying of four-wheelers on Delhi roads for a fortnight, a new study has claimed.
While absolute pollution levels increased across the National Capital Region (NCR) in January as compared to the previous month, the levels in Delhi saw a "smaller increase" owing to the pilot license plate policy, the US-based study stated.
Jointly conducted by researchers at the Energy Policy Institute at the University of Chicago (EPIC) and Evidence for Policy Design group at Harvard University, the study found "stark reductions" in pollutants around the noon hours from January 1 to 15.

The impact was much "higher" during the hours when the scheme was in force as the gap between Delhi's pollution and the neighbouring regions widened steadily until at least midnight, the study said.
The study has based its findings on Central Pollution Control Board and private portal IndiaSpend data.
"Particulates (PM 2.5) declined by 10-13 per cent on an average (i.E overall 24 hours) and by 18 per cent on average during the period when the scheme was in force (i.E between 8 AM to 8 PM).

"After 8 PM there was (as expected) no effect, which is why the average for overall 24 hours is lower than the average of daytime," Anant Sudarshan, Director EPIC-India, told PTI.

PM 2.5, the tiniest and deadliest of all respirable pollutants, measures around 2.5 microns enabling it to embed deep into the lungs and subsequently enter the bloodstream. Its safe limit is 60 ug/m3 as per Indian standards.
The conclusion was arrived at by comparing Delhi's pollution figures to that of Faridabad, Gurgaon and Noida, where the scheme was not enforced, as the NCR region has very similar weather conditions and are "equally exposed" to external factors affecting such as crop burning in the nearby states.
An IIT-Kanpur study on Delhi's air quality had identified
vehicular emissions as the second largest source of pollution at 25 per cent. However, cars account for around 10 per cent of that figure, it added.

Researchers explained that reducing half the cars could make "so much difference" despite them accounting for a fraction of overall pollution chiefly in two key ways.
"Fewer cars on the road-thereby, directly removing some of the polluting sources and reduced congestion would reduce idling and slow moving traffic across the city, thereby reducing pollution for everybody," they said.
The researchers, Sudarshan, Santosh Harish and Michael Greenstone at Chicago University and Rohini Pande at Harvard University, measured the impact of the program on PM 2.5 concentrations using a 'Difference-in-Differences (DiD)' statistical approach.
In DiD approach, researchers look at and compare data before and after the implementation of a program, both in the area that comes under the regulations and suitable areas out of its ambit.

"In other words, we are assuming that pollution levels within and outside Delhi should change in a similar way due to external factors like weather. That way, any additional change that is seen can be attributed to dissimilar factors like the odd-even program being implemented only in Delhi," they said.
Sudarshan said that they are in the process of looking at other pollutants other than PM 2.5, although they chose it as it has has the highest levels in Delhi and "consequently the highest health effects".