Fog, PM2.5 spike push Delhi air into ‘very poor’ category

AQI jumped over 60 points in 24 hours, with pollution expected to ease as stronger surface winds set in later this week.

A combination of fog and high particulate matter (PM) 2.5 build-up led the Capital’s air quality to deteriorate several points into the “very poor” category on Wednesday, ending a three-day streak of “poor” air. However, forecasts say pollution levels are expected to improve, even up to the “moderate” category, in the coming days on the back of increasing wind speeds.

CPCB data showed AQI crossing 300 by Wednesday afternoon; early warning system predicts improvement to moderate levels. (Vipin Kumar/HT)

aqi trends_dc

On Wednesday, the 24-hour average air quality index (AQI) was recorded at 339 (very poor) at 4pm, according to data from the Central Pollution Control Board (CPCB). The AQI was 272 (poor) at the same time a day before.

CPCB classifies AQI between 101 and 200 as “moderate”; 201 and 300 as “poor” , 301 and 400 as “very poor” and beyond 400 as “severe”.

Centre’s Air Quality Early Warning System (EWS) bulletin for Delhi said, “The air quality is likely to be in the ‘poor’ category on Thursday. The air quality is likely to be in the ‘moderate’ category from Friday to Saturday.”

Over the subsequent six days is that the air quality is likely to be in the “moderate” to “poor” category, it said.

Sunil Dahiya, founder and lead analyst at environmental think-tank Envirocatalysts, said “The PM 2.5 build up was very high through Tuesday night, as a result of which the initial load was very high to begin with. So even as the wind speed started picking up on Wednesday, the dispersion rate was not enough to bring down the pollution level.”

“Major sources for PM 2.5 are transportation, industries, and energy sources,” he added.

Dahiya said “shallow” to “moderate” fog in isolated parts of the city on Wednesday morning added to the spike in the pollution, as a result of the added humidity.

As a result of the fog, the India Meteorological department (IMD) said, visibility at Safdarjung, the city’s base weather station, dropped to as low as 450 m at 9 am and 600 m at Palam.

According to flight tracking website FlightRadar24, at least 500 flight at Delhi’s Indira Gandhi International (IGI) airport were delayed as a result, with no cancellations or diversions.

Fog intensity is likely to reduce in the coming days with a fresh western disturbance is expected to influence the region from February 5, raising surface wind speeds.

The minimum temperature on Wednesday was 8.2°C, nearly normal for this time of the year and a 1.2°C drop from a day earlier.

“Sustained surface winds of speed 10-20 kmph is expected to continue on Thursday, with ‘shallow’ to ‘moderate’ fog conditions possible in parts of the city on Thursday morning,” said an IMD official, adding that the minimum is expected to be around 7-9°C on Thursday and subsequently increase by a couple notches due to the influence of the western disturbance.