The air quality in Delhi has deteriorated mid April at a time when the implementation of car rationing odd-even scheme in the national Capital is going on.
However, the pollution history of the month maintained by US Embassy revealed that pollutant values had been usually low. The value of primary pollutants have crossed their prescribed standards in April, the mass concentration of same pollutants were under the limit in previous years.
According to the US Embassy data, the values of PM 2.5 were oscillated between 27 µg/m3 and 141µg/m3 of this month in 2015.
However, this year, mass concentration of primary pollutants PM (Particulate Matter) 2.5 and PM 10 both were observed two to three folds higher than their prescribed limits of Indian Metrological standards.
On day one of car rationing scheme on Friday, value of PM 2.5 fluctuated between 173 and 191(µgm-3) in various locations of the city despite less numbers of vehicles observed.
Moreover, SAFAR (System of Air Quality and Weather Forecasting and Research), a unit of Ministry of Earth Science (MoES) showed their advisory status as "very poor" which was "moderate" a day before. Notably, two days before the odd- even scheme, output values of PM 2.5 on the real time air ambient quality Indexes of Delhi Pollution Control Committee (DPCC), US Embassy and SAFAR oscillated between 7 µgm-3 and 61µgm-3 while it is increasing significantly.
The highest value of PM 2.5 at 6 PM on DPCC meters in RK Puram and Civil lines were 173 and 191 which was three times higher than its prescribed limit which is 60 µgm-3. Mass concentration value of primary pollutant on SAFAR meter was 125.9 µgm-3. Interestingly, just a few days before odd-even scheme, the national Capital's air quality changed to "good" from "moderate" on the advisory status of the National Air quality Index (NAQI) but it was modified after the minimum value of Particulate Matter (PM) 2.5 was observed at 9 µg/m3 (micrograms per cubic) and maximum value of the same pollutant was recorded 54 µg/m3 on April 13.
Both the values are under the prescribed limit of the Indian Metrological Sensors. The pollution levels were remarkably low not only in Delhi but in the outskirts of the city. During the first phase of odd-even, Anand Vihar area was considered as red zone because of high pollutant levels while this time round, mass concentrations of both the pollutants around Anand Vihar has been found to be very low.
Taking into account the real time air data of the Delhi Pollution Control Committee (DPCC), value of PM 2.5 was 24 µg/m3 in Anand Vihar area owing to normal wind speed. However, RK Puram was an exception where the pollutants level was marginally high during mid days of this running month.
Environmentalists with the National Physical laboratory (NPl) said Delhi climatography and geography is different. "Apart from weather, wind activities like dust storm or burning of agricultural waste are the main factors while in April and March month, none of these activities take place," said a scientist.
Values of other pollutants that have adverse impact on humans have been recorded as "low" on the Ambient Air Quality Monitoring Systems just a few days before the car rationing scheme. Value of carcinogenic compound Benzene was 1.5 µg/m3 while other pollutants like CO, Nitrogen Oxide, Ozone and Sulphur Dioxide were also on the lower side.
Meters of the United States Embassy at Chanakyapuri also reflected moderate values of PM 2.5 and PM 10. In New Delhi, value of PM 2.5 was 57 µg/m3 at 5 PM which is relatively low whereas in December -January 2015-16, value of same pollutant fluctuated between 400 and 800 µgm-3. Moreover in October and November, the concentration hit the highest point which was 1000 µgm-3.
Meanwhile IMD official stated that wind speed also plays pivotal role in bringing down pollutant values low. According to IMD sensors, wind speed recorded during day time was 1.4 meter per second with 233 degree, however, wind speed has been recorded as relatively low. It was observed that during the pilot run of odd-even scheme, no significant changes had occurred in pollutant values. Moreover, the observations of Central Road Research Institute (CRRI) during the pilot run of the scheme also showed that the overall impact of the scheme was more on traffic congestion not on air pollution, said an environmentalist.
Pollution data just a few days before the implementation of the scheme.