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Sunday, Nov 17, 2019

Make-or-break days ahead for Delhi’s anti-pollution battle

The study has also suggested that Delhi’s air quality is mainly dependent on pollution sources within a radius of 75km around the national capital.

delhi Updated: Oct 22, 2019 06:07 IST
Joydeep Thakur
Joydeep Thakur
Hindustan Times, New Delhi
Heavy smog in the national capital with a view of Humayun's Tomb at Nizamuddin in New Delhi.
Heavy smog in the national capital with a view of Humayun's Tomb at Nizamuddin in New Delhi.(Sanchit Khanna/HT PHOTO)

The period between October 29 and November 12 will be the most crucial for efforts to combat air pollution, scientists from the Indian Institute of Technology (IIT) Kanpur have said in a new analysis, calling for pre-emptive measures to be focussed on this period in order to avoid a crisis that has become routine for this time of the year in recent years.

It is in this period, the scientists said, that smoke from farm fires in nearby states drifts into the national capital region (NCR) while the air becomes still and heavy as the weather turns colder – creating a toxic mix in an environment already polluted by emissions from vehicles, road and construction dust, and industrial emissions.

“There is a sharp increase in PM2.5 concentration from October 29 and it begins to drop from November 12. This is the most critical window. We need to avoid this by bringing in pre-emptive measures because reacting after-the-fact will be nearly futile,” said Mukesh Sharma, a professor of civil engineering from IIT Kanpur.

The analysis, based on the last three years, has been sent to government agencies and pollution watchdogs for action and it comes at a time when satellite image analysis has shown a sharp rise in fires spotted in Punjab and Haryana.


According to data from National Aeronautics and Space Administration’s (Nasa) Visible Infrared Imaging Radiometer Suite (VIIRS), the number of incidents observed in the last two days was 177% higher than the average number over the seven days before that. In all, nearly 1,000 fires were spotted on Sunday alone.

The findings of the IIT Kanpur team are similar to a separate study done by researchers from IIT Delhi, University of California, University of Illinois, and other research organisations in 2018: They found pollution in Delhi at an all-time high between October 29 and November 4.

In the fortnight period identified by the IIT Kanpur team, pollution levels usually remain in the severe category with air quality index (AQI) varying between 400 and 500. The level of PM2.5 and PM10 particles reaches at least five to six times above the safe limits of 60μg/m3 and 100μg/m3.

PM2.5 are ultrafine particles which stick deep inside the lungs and take the heaviest toll on human health.

This year, the Delhi government has announced that the “odd-even” road rationing plan will be in force between November 4 and November 15, prohibiting the use of some private cars based on the date and the number in which their registrations end.

The study has also suggested that Delhi’s air quality is mainly dependent on pollution sources within a radius of 75km around the national capital.

“It can even be seen [from data of three previous years] that wind speed drops sharply during this period. The other factor is vertical mixing height, which also drops during this period,” the IIT Kanpur study said.

According to researchers from Indian Institute of Tropical Meteorology under the ministry of earth sciences, Delhi needs a minimum wind speed of 10km per hour for pollutants to be dispersed. According to the IIT Kanpur analysis, the wind speed on most days in the October 29-November 12 period remains less than 4 km per hour.

SAFAR, in its extended range outlook issued by on Monday, said high deterioration in Delhi’s AQI is expected by the first week of November. Till that time, the air quality will be helped by a chain of western disturbances that will bring strong winds and some squally conditions.

But a calm anti-cyclonic condition is expected to develop in the first week of November and an associated sinking motion of air will make the atmosphere very stable with calm surface winds. Both will lead to stagnant weather conditions which would favour rapid fine particulate matter formation and accumulation of pollutants, the pollution forecasting agency said.

The problem in the October-November period is one of two pollution spikes observed in the national capital. “The 2018 study of IIT Delhi had indicated two peak pollution episodes in Delhi-NCR. The first occurs in the week of October 29-November 4. The second, milder one hits between December 30 and January 5,” said Sagnik Dey, associate professor at the Centre for Atmospheric Studies in IIT-Delhi.

“Delhi’s air quality depends primarily on two things – ground level activities and meteorology. We can’t control meteorology. But if we can control the ground level activities well in advance then we can bring down pollution to a large extent,” said D Saha, former head of the Central Pollution Control Board.

(With inputs from Abhishek Jha)