To monitor the 15 days of the odd-even plan, the DPCC, that works closely with the Central Pollution Control Board (CPCB), added measures to its standard monitoring techniques.
As the Delhi's government fairly controversial experiment of reducing cars on the road according to their licence plates, known as the odd-even plan, came to an end, it remained difficult to determine the exact impact the pollution-reducing scheme had on New Delhi's air quality. Officials from the Delhi Pollution Control Committee (DPCC), said that there had definitely been an effect on the pollution levels, they said that it would take time for deeper analysis to show a more precise picture.
"Of course taking vehicles off the roads brings down pollution," said Ashwini Kumar, the Delhi government environment secretary. However, he added, the difference in pollution peak levels could only be seen after taking into account more "tricky" meteorological factors and atmospheric conditions that could differ from day to day.
To monitor the 15 days of the odd-even plan, the DPCC, that works closely with the Central Pollution Control Board (CPCB), added measures to its standard monitoring techniques. The norm is to take an average, either of a day or a year, explained Kumar. The DPCC already monitors air quality through the six continuous monitoring stations that give real time data of their locations, and via the manual air filter method that gives a 24 hours average. The DPCC expanded the manual monitoring to 20 more locations, though only keeping the filter out from 10 am to 8pm, to get the eight hour average and catch the evening peak time. It also deployed mobile van units in 200 locations to get 20 minute averages of the air quality.
The data from these units, measured via the light scattering principle used to count particles, said scientist with the DPCC, Dr MP George, could not be compared to averages, as it was more of a survey to give an indication of the current air quality. The fixed stations worked according to internationally accepted BAM method --Beta attenuation monitoring -- which differed from this principle.
Thus, these "instantaneous values" from these measurements were not, and could not be compared, to the averages that are usually used to measure air quality. They were used, Kumar said, to cover as much area as possible in these 15 days.
Nor should the real time figures from other stations, he added, be taken as a general rule for all of Delhi's, air, as many time parameters such as dust and particulate matter, shot up due to localised events.
"The Anand Vihar stations," said George, "is a hotspot because of the bus terminal, railway lines, the metro station, and the industrial activity happening just across the border in Uttar Pradesh. It cannot be compared to stations in more residential areas. It is more of a road curb station, that monitors vehicular movement and trans state movement of pollutants."
Similarly, he said, the Indira Gandhi International Airport station indicates emissions from air crafts.
George also elaborated on the meteorological conditions Kumar mentioned. December to January is one of the three peak periods of pollution in Delhi, caused by inversion conditions where due to lack of wind activity pollutants accumulate. Thus, many trends showed pollution going up because peak period dictated it had. To show the impact of odd-even, he said, on this period, one had to compare it to similar meteorological period, which couldn't be 2015 as its winter had rains.
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