January 18, 2016 5:45:51 pm
The odd even scheme has seen widespread debate over its impact on the quality of Delhi’s air. Some agencies have come out with data on dips in specific pollutants on certain dates, others have called such claims premature. So what makes it so difficult to arrive at a quantitative assessment of air quality that can be directly related to the restrictions imposed on vehicles during the fortnight January 1 to January 15?
There is a lot of disagreement between different agencies on the method of data assessment. While the Delhi government and some independent agencies like Centre for Science and Environment (CSE) have been going by daily peaks in measuring pollutants, others like the MoEF’s Central Pollution Control Board (CPCB) have been taking daily averages. The former claim that the purpose of the ’emergency’ policy was to arrest the peaks in the pollutants during the winter so only the peak levels should be analysed.
The latter say that by studying only the peaks can be misleading, and averages are a more scientific way of assessing any impact on air quality. A third set of experts swear by spot measuring of pollutants particularly at roadsides and traffic signals, rather than measuring the ambient air quality as done by the above agencies. Their argument is that reducing the number of vehicles will impact roadside pollution levels far more than ambient air quality.
Most experts use the PM 2.5 — the fine particles in the air of less than 2.5 microns– as the direct indicator of the scheme. The argument being that the particles are associated with combustion and hence are most likely to be affected by reduced fuel combustion when the number of cars on the road is reduced. Still others insist gaseous pollutants like NO2 and CO provide a better method of analysis since these particles have multiple components from several sources other than vehicles.
The burning of crops, and open garbage burning is for instance also strongly associated with PM 2.5.
The AQI which was developed by CPCB last year has emerged as the universally accepted index of measuring air quality since. It relies on the most prominent pollutant. The index has not given any strong evidence to indicate an improvement in the air quality after the introduction of the odd even scheme. While this has been used to argue the scheme’s apparent lack of efficacy, some experts say that when prominent pollutants are not associated with vehicular pollutants, the AQI can’t provide any direct evidence of the impact of the odd even scheme.
Scientists also say two weeks is too short a time to gauge the impact of the scheme with any certainty. Many experts told The Indian Express that to scientifically validate its impact on air quality, it needs to be extended for longer, possibly for an entire season. Experts also say that the exemptions and the 8 am – 8 pm time schedule of the scheme made assessment more difficult. People used their vehicles before and after the hours of the scheme, and many vehicles were still on the road. Experts said the scheme needed to be imposed in a more stringent form for its impact to be properly assessed. Public transport also needs to be strengthened to eliminate the extra taxis which were used during the scheme.
Finally, any impact discovered by any method of analysis, and on any pollutant this season, is still being attributed primarily to meteorological factors rather than to emissions. For instance, the drop in pollutants measured in the second week of the odd even scheme after an initial spike in the first week is largely being attributed to this year’s unique weather phenomenon. Experts say high temperatures, low humidity and a high boundary layer of the atmosphere phenomenon uncharacteristic of Delhi winters – helped disperse pollutants in the second week of January.
Agencies like ministry of earth sciences’ SAFAR, IMD, CPCB and even DPCC have said that whatever impact has been seen — including spikes and dips in pollutants — has a lot to do with meteorology.
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