Brief air respite triggers swift Grap 3 withdrawal

The Commission for Air Quality Management (CAQM) rolled back Stage 3 pollution restrictions on Friday, just hours after strong winds improved Delhi’s air quality, even as forecasts showed conditions would deteriorate to “very poor” again by Sunday and remain hazardous for at least the following week.

The decision marks the second time in 10 days that the commission has lifted emergency measures immediately after weather-driven improvements, despite predictions of worsening air quality within days. On December 25, the commission revoked Stage 4 curbs just hours after winds pushed the Air Quality Index (AQI) to “poor”, only for pollution to return to “very poor” levels as forecast.

Delhi’s 24-hour average AQI dropped from 380 at 4pm Thursday to 236 at the same time on Friday — a 144-point improvement driven by strong surface winds of 15-20km/h. By 7pm Friday, it further improved to 213.

The rollback of the third stage of the graded response action plan (Grap) allows private construction and demolition activities, mining and allied operations to resume immediately. Restrictions on older BS-3 petrol and BS-4 diesel vehicles operating in the region are also lifted, along with other vehicular curbs imposed under Stage 3.

However, the Air Quality Early Warning System (AQEWS) forecast shows air quality will remain in the “poor” category only through Friday and Saturday before returning to “very poor” from Sunday through Tuesday.

“The outlook for the subsequent six days is that the air quality is likely to be in the very poor category,” the AQEWS bulletin stated — meaning Delhi faces at least eight consecutive days of very poor air beginning Sunday.

“The entire concept of Grap should be focused on forecasting and if the forecasts show an improvement ahead — ideally, we can issue a notice that if conditionally the AQI reaches a certain threshold, we can revoke Grap,” said Sunil Dahiya, founder and lead analyst at environmental think tank Envirocatalysts. “However, we have seen multiple times the forecasts have failed and we have invoked Grap late.”

On the removal of Stage 3, Dahiya said CAQM should wait for sustained improvements. “We have seen this winter, due to meteorological conditions changing, that it does not take long for the AQI to slip again. If it stays clean for an extended period, ideally only then it should be removed,” he said.

Dipankar Saha, former head of the Central Pollution Control Board’s air laboratory, said while winter conditions have now firmly set in, authorities should wait longer before lifting restrictions.

“In the first half of winter, we see more extremities and uncertain weather. By January, winter has set in and forecasts are more accurate. Having said that, waiting longer to remove Grap is still a good decision than doing it based on a day’s change,” he said.

CAQM justified the rollback by citing the “prevailing trend of air quality” and the significant improvement from Thursday’s reading.

“The AQI of Delhi which was recorded as 380 yesterday has significantly improved and recorded 236 today at 4pm, exhibiting a declining trend,” the commission said in a statement on Friday evening, adding that restrictions under Stage 1 and Stage 2 will remain in place.

Under Stage 2, the entry of interstate buses from NCR states — other than electric, CNG or BS-6 diesel vehicles — remains prohibited in Delhi.

Delhi environment minister Manjinder Singh Sirsa attributed the improvement to “the government’s persistent ground level efforts under the chief minister’s leadership”.

The Central Pollution Control Board (CPCB) classifies air quality as “moderate” when AQI is between 101 and 200, “poor” between 201 and 300, and “very poor” between 301 and 400. Beyond 400, air quality is termed “severe”. Under Graded Response Action Plan (GRAP) protocols, Stage 3 measures are triggered when AQI crosses 400, while Stage 4 can be imposed if AQI is forecast to cross or exceeds 450.

The strong surface winds also dispersed fog on Friday, with visibility dropping to 800 metres in the early hours before bright sunshine emerged by afternoon. However, the India Meteorological Department (IMD) has issued a yellow alert for moderate to dense fog over the weekend.

Icy-cold northwesterly winds will lead to a sustained drop in minimum temperature, expected to dip by 2-3 degrees Celsius over the weekend. The minimum temperature on Friday stood at 9.1 degrees Celsius, two degrees above normal, but is forecast to hover between 6 and 8 degrees Celsius on Saturday and Sunday, IMD officials said.

The maximum on Friday was 17.4 degrees Celsius — two degrees below normal and marginally higher than Thursday’s 17.3 degrees Celsius. Wednesday had recorded 14.2 degrees Celsius, Delhi’s lowest maximum for December in six years.

“We are now seeing cold northwesterly winds blow and wind speed should remain consistent for another 1-2 days,” said Mahesh Palawat, vice president at Skymet Weather, adding that minimum temperatures will continue falling as no western disturbance is expected until the second week of January.

The sustained cold has pushed power demand above 5,500MW since Wednesday. Peak demand reached 5,595MW on Friday and 5,603MW on January 1 — the third-highest winter peak demand on record. Power distribution companies Tata Power DDL and BSES said they successfully met demand and are prepared for further increases, with peak demand forecast to touch 6,000MW this winter.

At Delhi airport, 66 flights were cancelled on Friday while over 500 were delayed, according to flight tracking website FlightRadar24. Airport officials said disruptions were predominantly due to impact at other airports, including several in northern India where visibility fell to zero.

IMD has forecast dense to very dense fog conditions to continue over Punjab, Haryana, Chandigarh, Uttar Pradesh, Bihar and Odisha for 5-7 days, while fog is likely in parts of Jammu, Himachal Pradesh, Uttarakhand, Rajasthan, northern Madhya Pradesh and northeast India over the next 4-5 days.