The air quality of the national capital improved on Wednesday to "very poor" category.
On Tuesday, 16 out of 17 active pollution monitoring stations saw Delhi air coming out of the "severe" category.
The average PM2.5, or particles with diameter less than 2.5mm, in Delhi was 351 units -- still 14 times the safe limit -- at 6.00 p.m.
Expecting normalcy in breathing to return with a favourable wind speed as well as direction, the movement of trucks, which was stopped at the Delhi border for the past few days as a precautionary measure, may resume.
According to officials, the Supreme Court-appointed Environment Pollution Control Authority (EPCA) may ask the officials concerned to revoke the restrictions imposed under the "severe-plus" or "emergency" category of Graded Response Action Plan (GRAP) and replace them with those under the "very poor" category.
"EPCA may write a letter by tomorrow (Thursday) morning to the state governments concerned, asking them to revoke severe-plus GRAP and implement the very-poor category GRAP," said an official.
"This may allow entry of trucks which have been waiting at the border," Usman Naseem, researcher at the Centre for Science and Environment (CSE) and member of the EPCA, told IANS.
The severe-plus category comes into force when the PM2.5 levels cross 300 units (microgrammes per cubic meters) or PM10 levels cross 500 units (which is five times above the standard limit) and persist for 48 hours or more.
Under severe-plus, truck movement in Delhi is stopped, construction work is banned, odd-even scheme for vehicles is imposed and schools are shut.
However, since November 7, while all other restrictions were in place following the National Green Tribunal's (NGT) intervention, the odd-even scheme could not be implemented due to a difference in views of the green court and the Delhi government which is the implementing agency for the vehicular restriction scheme.
The very-poor GRAP comes in force when PM2.5 levels are between 121-250 units or PM10 levels are between 351-430 units. Under very-poor, diesel generator sets are also banned and the motor parking fee is enhanced by three-four times to discourage private cars on roads.
On Wednesday, the Central Pollution Control Board (CPCB) recorded the average Air Quality Index (AQI) of Delhi-NCR at 6 p.m. at 353 as compared to 398 on Tuesday. The major pollutant PM2.5 or particles with diameter less than 2.5mm recorded 353 units as compared to 397 units on Tuesday -- considered very poor.
With an average AQI of 419, Ghaziabad was still under severe category and the most polluted city in NCR while Delhi Technical University in North Delhi was the most polluted within the national capital with an AQI of 444.
According to weather analysts, at present Delhi is receiving south-easterly winds coming from the Bay of Bengal at a speed of 15 kmph. However, this is expected to change into the cold north-westerly in next two to three days, which may pull down the temperature and increase humidity.
"Due to the fog and humidity, while the air entering Delhi will be good, the pollution levels may still increase. However, they will not be even close to what we experienced recently," Mahesh Palwat, Director of private weather forecast agency Skymet told IANS.
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