Respite from extreme pollution as air quality limps to ‘very poor’ in Delhi

Strong and consistent winds of 10-15 km/hr came to Delhi’s rescue on Sunday, leading to a sharp improvement in the air quality, propelling the air quality index (AQI) from a 24-hour average of 412 (“severe”) at 4pm on Saturday to 318 (“very poor”) on Sunday, according to the Central Pollution Control Board (CPCB).

Although the AQI was far off from the “moderate” or “good” category, the improvement continued throughout the day, improving to 308 (“very poor”) at 6pm and further to 294 (“poor”)at 10pm.

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”.

Meteorological experts said that even though winds were predominantly calm on Saturday, they picked up late in the evening, with similarly strong winds recorded on Sunday. Fog also reduced visibly in the Capital, with the lowest visibility recorded at 800 metres (“shallow fog”) at the Safdarjung weather station.

“A western disturbance was influencing northwest India, which led to almost calm winds conditions on Saturday. Late towards the night and in the early hours of Sunday, we began to see the impact of this western disturbance weaken and a subsequent increase in wind speeds again. On Sunday, during the day, winds touched 15km/hr, which led to a significant improvement in AQI,” said Mahesh Palawat, vice president at Skymet meteorology.

Palawat said winds would remain consistent on Monday and Tuesday too. Forecasts by the Centre’s Early Warning System for Delhi (EWS) also predicted similar meteorological conditions over the next two days, with the AQI expected to persist in the “very poor” category till at least Wednesday.

The average AQI on Sunday was calculated on the basis of 38 of Delhi’s 40 air quality stations, with PM2.5 (particulate matter having a diameter of 2.5 microns or less) emerging as the lead pollutant. Data showed no station was in the “severe” zone at 4 pm, with 21 stations clocking “very poor” AQIs and the remaining 17 clocking “poor” AQIs, data showed. The highest AQI, 367, was recorded at Anand Vihar, while the lowest, 246, was recorded at the ITO station.

Saturday was Delhi’s eighth “severe” air day of this winter. The first “severe” day was recorded on November 13, with the AQI touching 494 on November 18 — the joint second-highest ever recorded in the Capital.

Although northwesterly winds were persisting, the maximum and minimum temperatures were over the normal levels. The maximum temperature was 29.1°C, two degrees above normal and marginally lower than 29.4°C recorded a day earlier. The minimum temperature, meanwhile, was 12°C, which was a degree above the normal and marginally lower than the 12.2°C recorded a day earlier.

Forecasts by the India Meteorological Department (IMD) predicted shallow to moderate fog to persist in the region for the next five days, with consistent northwesterly winds likely to lead to a drop in both maximum and minimum temperatures. It said the maximum may dip to 25°C by Friday and the minimum to around 10°C.

“Winds of 8-10 km/hr are likely on Monday, with shallow to moderate fog. We should also see smog towards the evening and night-time,” an IMD official said.