The Central Pollution Control Board (CPCB) in its report on the odd-even restriction has made one thing clear – pollution concentration is heavily dependent on wind speed.
The CPCB analysis says the car rationing scheme did not bring down pollution during the 16-day restriction last month. But it pointed out that meteorological factors such as wind speed and temperature affected the concentration for particulate matter 2.5 the most.
“The decrease in vehicular emission was not a dominant enough factor to impact observed data. Further, since meteorological factors as well as emission from various sources outside Delhi in the airshed vary from time to time, data for different periods do not lend themselves to scientifically accurate comparison,” says the CPCB report submitted before the National Green Tribunal on Friday.
If injection of pollutants is high in an area, as it is in and around Delhi, it is the meteorological factors that matter more than restriction on the source of one pollutant.
This finding highlights the need for a comprehensive policy for the belt, north of the Vindhyas, in which lie India’s and some of the world’s most polluted cities, including Gwalior (number 2 on WHO’s list of most polluted cities/towns) and Allahabad (number 3 on the list).
According to CPCB’s report, the most direct relationship is between wind speed and particulate matter concentration.
As per data, which was collected between April 1 and April 30, on April 11, when the wind speed was the highest at 4.3 metres per second, the PM 2.5 concentration was the least at 76 micro grams per cubic metre.
Both values are averages from nine monitoring stations across the city.
The pollution concentration was highest at 179 micro grams per cubic metre on April 29 when the wind speed was 2.4 metres per second.
There were days when the wind speed was higher but the pollution concentration not as low as it should have been and this has been attributed to farm fires in Punjab and Haryana by the Delhi government and the Centre for Science and Environment based on satellite images by NASA.
The co-author of the IIT Kanpur study on air pollution, Mukesh Sharma identified biomass burning, which includes farm fires in Delhi’s neighbouring states, as the biggest threat to clean air in the area.
In Delhi for a lecture earlier this week, Sharma said it is not just Delhi that gets polluted by other cities because of pollution travelling from one to place to another.
“If pollutants come to Delhi from other states we must remember that they also travel to other places from Delhi. Our air is shared and there are no boundaries. We need to keep in mind regional backgrounds when we talk about pollution. We can’t only discuss air pollution in Delhi. It is a regional issue,” he said.