Pollutants in the city's air dipped by around 10 per cent on average between 8 AM to 2 PM today compared to the last two days, "possibly" due to the odd-even restrictions, before rising sharply afterward with a fall in day time temperature.
As per initial observations of System of Air Quality and Weather Forecasting and Research (SAFAR), the gains of less vehicular emissions could have been more had there been less vehicular movement and no bursting of firecrackers on the night of January 31.
Although the average value of suspended particulate matter PM 2.5 rose to around 198 micrograms per cubic metre, an increase as compared to yesterday, a fall could be observed between 8 AM when the odd-even scheme kicked in and 2 PM, SAFAR's Project Director Gufran Beig said.
"Air quality remained very poor. But the reduction in PM 2.5, possibly around 15 per cent due to less emissions and vehicular dust reduction, that was observed for few hours could be seen as an impact of the odd-even measure as other factors like wind speed and temperature remained the same as last two days," Beig told PTI.
However, the jump that was seen afterward need to be examined scientifically and it was possibly due to a sudden dip in the day time temperature. Cooler temperature heightens pollution.
"It is still premature to conclude anything with just 10 hours available for comparison," he said in a statement.
(SAFAR) had yesterday said that air quality in Delhi was expected to deteriorate over the next few days with a possible rise in the level of particulate matter due to fall in minimum temperature and calm wind movement.
Officials said the air quality remained "very poor" today due to atmospheric conditions that did not allow pollutants to get dispersed.
While a section of the ruling AAP attributed the sharp drop in PM 2.5 figures between early morning hours and afternoon to the car rationing experiment, scientists said pollutants usually touch their peak in the dawn and then gradually fall.
SAFAR stations, located in various areas the city, displayed 'very poor' real-time Air Quality Index, which was in line with the forecast of the Union government body that was released yesterday.
In no marked change from yesterday, the average levels of PM 2.5 was around 180 microgrammes per cubic metre, three times above the safe limit of 60. The corresponding safe limit of PM 10 is 100.
Central Pollution Control Board's real time AQI for the Punjabi Bagh, R K Puram, NSIT Dwarka and Anand Vihar stations were 'severe' at 5 PM. Air quality is considered 'very poor' by Indian authorities when level of PM 2.5 ranges from 120 to 250 microgrammes per cubic metre.
"The boundary layer, beyond which pollutants cannot
escape, comes near the earth's surface during the early morning hours resulting in the accumulation of pollutants. So the spike that was observed around 5.30 AM and the subsequent fall is understandable," Project Director, SAFAR, Gufran Beig said.
Scientists also said that a straightforward comparison of today's pollution figures with last year's data would be "misleading" as weather was colder which had resulted in more pollution.
Tomorrow onwards, a sharp spike in the volume of PM 2.5 is expected due to possible fall in minimum temperature and calm wind movement, with it rising to 192 first and 201 by January 3. The corresponding figures for PM 10 are expected to be around 334 and 349.
