Strong winds help improve Delhi air quality

Forecasts, however, warned that the marginal improvement would be short-lived. The air quality is set to deteriorate to “very poor” by next week, with chances of touching a “severe”

New Delhi

Delhi was engulfed in smog early Friday. (Vipin Kumar/HT Photo)

Strong surface winds in the Capital improved the air quality to the upper echelons of the “poor” level — clocking an air quality index (AQI) of 270 — from a “very poor” AQI of 306 on Thursday, according to the 24-hour average data released by the Central Pollution Control Board (CPCB).

Forecasts, however, warned that the marginal improvement would be short-lived. The air quality is set to deteriorate to “very poor” by next week, with chances of touching a “severe” level as well.

“Delhi’s air quality is likely to be in ‘very poor’ category from Saturday till Monday. The outlook for subsequent six days shows the air quality is likely to be in ‘very poor’ to ‘severe’,” the Early Warning System for Delhi (EWS) said in its daily forecast bulletin. The EWS is a forecasting system under the ministry of earth sciences (MoES).

The Central Pollution Control Board (CPCB) classifies AQI between 0-50 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”.

Experts said that despite stubble burning’s increase in the contribution to Delhi’s PM 2.5 (particulate matter having a diameter of 2.5 microns or less) concentration, local strong surface winds are helping disperse pollutants.

According to the Decision Support System (DSS), another analysis model under MoES, the contribution of stubble burning to Delhi’s air was 14.5% on Thursday. It was a season-high 15.98% on Wednesday, it said.

“We saw wind speeds pick up locally, touching around 15 km/hr, especially through the day on Wednesday. On Thursday, this continued with winds of 5-10 km/hr being seen, which helped AQI improve further. The wind direction remains northwesterly, which transports stubble smoke towards Delhi, but as long as there is local dispersion through strong winds, Delhi will not be impacted too much,” said Mahesh Palawat, vice president at Skymet meteorology.

Delhi’s average AQI on Thursday was calculated based on data from 36 of 40 ambient air quality monitoring stations, with Anand Vihar recording the highest AQI, at 401. It was also the only station in the “severe” range, with five others clocking “very poor” AQIs. All other stations in Delhi were clocked “poor” AQIs, according to CPCB data.

PM 2.5 and PM 10 were prominent pollutants on the day, it said.

Delhi’s AQI touched “very poor” level for the first time this season on Monday. It remained in the category till Thursday, for four days in a row, before improving to “poor” on Thursday evening. Stage-2 measures under the Graded Response Action Plan (Grap) were invoked across NCR on Monday, following the deterioration in AQI.

DSS estimated the contribution of Delhi’s transport sector to air quality at 15.8% on Friday, predicting it will hover between 16% and 17% over the weekend. HT reported on Thursday that the DSS has stopped sharing forecasts related to stubble burning in the Capital, due to faults in accuracy.

Temperatures, meanwhile, continued to remain above normal for this time of the season. Delhi’s minimum temperature was 19.2°C on Friday, which was two degrees above normal, but down from 20.7°C recorded a day earlier.The maximum temperature was 34°C, which was two degrees above the normal and the same as Thursday’s.

The India Meteorological Department forecasted the maximum temperature to hover in the 32-33°C range over the weekend and the minimum temperature to remain around 19°C.