Air quality worsens again in Delhi, enters upper end of ‘poor’

The air quality in Delhi deteriorated significantly on Thursday and reached the higher end of the “poor” category, impacted by a drop in temperature. The 24-hour average air quality index (AQI) stood at 288 (poor) at 4pm on Thursday, from Wednesday’s 4pm reading of 199 (moderate).

Forecasts suggest that wind speeds are likely to drop at night-time, but will remain around 10-15km/hr during the day, likely keeping AQI in the ‘poor’ category till Sunday.

“Delhi’s air quality is likely to be in the ‘poor’ category from December 13 to December 15. The outlook for the subsequent six days shows the air quality is likely to be in ‘poor’ to ‘very poor’ range,” said the Early Warning System for Delhi (EWS), a forecasting model under the Ministry of Earth Sciences.

The Central Pollution Control Bureau (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”.

CPCB’s data showed that the day’s average AQI was calculated on the basis of 38 ambient air quality stations, with both PM 2.5 and PM 10 emerging as the lead pollutants of the day. This indicated that both combustion sources and dust were impacting the Capital’s air. Out of the 38 stations, 19 were in the “very poor” zone with the highest AQI recorded at Mundka (361). Only one station – Lodhi road (197) was in “moderate”, with the rest in the “poor” range.

Mahesh Palawat, vice president at Skymet meteorology explained that low temperatures negatively impact air quality. “The lower the temperature, the more unfavourable conditions become for dispersion of pollutants. Wind speeds also drop and so we are now seeing a dip in winds at night-time. What is still helping Delhi are the strong and consistent winds of 10-15km/hr during the day, which then ensure that the AQI does not deteriorate too rapidly,” said Palawat, stating a similar pattern is expected to continue where winds become calm at night but pick up during the day.

Monday was the fifth “moderate” air day this month so far – the highest number of such days in a month’s span. The previous record was three days each in December 2022, 2019 and 2015. Delhi has never recorded a “satisfactory” or “good” air day in December.

The average AQI in Delhi this month so far is 235. In comparison, the average AQI in the corresponding period last year was 324. In the entire month, December’s average AQI was 348 last year, which included three severe air days and a peak AQI of 450.

Typically, Delhi’s AQI worsens in the second half of December, when low temperatures, calm winds and dense fog combine.