Delhi’s AQI back in ‘severe’ zone amid GRAP-4 restrictions

With an average 24-hour AQI reading of 409 recorded daily, Delhi's air quality clocked five days of “severe” air over six days.

The air quality in the Capital deteriorated to the “severe” zone again on Sunday, after the air quality index (AQI) over the past day provided a much-needed respite from a four-day streak of “severe” AQI from last Tuesday to Friday, according to the Central Pollution Control Board’s (CPCB’s) daily air bulletin.

A train track in Dwarka amid heavy fog early morning. (Vipin Kumar/HT Photo)

With an average 24-hour AQI reading of 409 recorded on the day, Delhi clocked five days of “severe” air in a six-day period, marking the highest such streak since six consecutive days of “severe” air were clocked in December 2021. Experts attributed the dropping air quality, observed since last Sunday, to a decrease in wind speed.

“The decrease in wind speed aided the already accumulating levels of pollution in Delhi, leading to ‘severe’ air days. When wind speed is slow, dispersion of pollutants becomes hard because pollutants keep moving in a circulatory motion. They heat up from the heat emitted by the earth’s surface, get lighter and move upwards, and then cool down and come down to the surface again. The cycle goes on,” said Mukesh Khare, an expert on air pollution from the Indian Institute of Technology (IIT).

CPCB classifies AQI between 0 and 50 as “good”, between 51 and 100 as “satisfactory”, between 101 and 200 as “moderate”, between 201 and 300 as “poor”, between 301 and 400 as “very poor”, and over 400 as “severe”.

The Capital’s 24-hour average AQI was 370 (“very poor”) at the same time on Saturday, which was an improvement from AQIs of 429 (“severe”) recorded on Friday, 451 (“severe plus”) on Thursday, 445 (“severe”) on Wednesday and 433 (“severe”) on Tuesday.

According to a forecast by the Air Quality Early Warning System (AQEWS) for Delhi, the air quality is likely to be back in “very poor” by Monday. “The air quality is likely to be in very poor category from Monday to Wednesday. The outlook for subsequent six days is that the air quality is likely to be in very poor to poor category,” the AQEWS issued bulletin on Sunday evening said.

Delhi is, however, expected to be impacted by an active western disturbance from December 27, which may further improve air quality, according to experts.

Mahesh Palawat, vice president at Skymet, said, “The western disturbance is expected to cause widespread light to moderate rain, along with thundershowers in some isolated places. It is likely to bring down the pollution levels as a result.”

However, Khare contended that rain would provide a very short-term relief, if not accompanied by wind of high speed.

“Rain will initially wash out the pollutants and we will likely see an immediate improvement in the AQI. However, if the wind speed does not pick up significantly, we will be back to degrading levels of pollution again,” Khare added.