Delhi records poor air quality as minimum temperature dips to lowest this season

A dip in temperature slows down the dispersion of pollutants and also brings smoke from the fields of Haryana and Punjab, where farm fires are recorded around this time of the year

Delhi’s air quality deteriorated to the poor category on Thursday while the minimum temperature dipped to the lowest so far this season to 16.4°C, a day after the change in wind direction brought the mercury below 20°C (19.4°C) after five days.

The hourly AQI was 204 at 9am in the lower end of the poor category. (AFP)

According to the Central Pollution Control Board, the hourly air quality index (AQI) was 204 at 9am in the lower end of the poor category. On Wednesday, the average 24-hour AQI was 193 in the higher end of the moderate category.

An AQI between 0-50 is considered 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.

An AQI of 196 (moderate) was recorded at 8am on Wednesday, compared to 180 (moderate) a day earlier. The change in the wind direction to northwesterly and a drop in local wind speed was likely to keep the air quality poor until Friday.

Cold northwesterly winds negatively impact air quality. A dip in temperature slows down the dispersion of pollutants and also brings smoke from the fields of Haryana and Punjab, where farm fires are recorded around this time of the year.

The minimum temperature dipped below 20°C first last week when it was 18.6°C. A change in wind direction followed and the minimum temperature rose to 20.9°C on Saturday. On Sunday, it rose to 23.1 and to 24.4°C on Monday. Delhi’s minimum on Tuesday was 22.7°C, two degrees above normal.

The minimum temperature on Wednesday was two degrees below normal and the maximum was 35°C, a degree above normal. The previous lowest temperature was recorded this season (18.3°C) on October 3.

According to an Air Quality Early Warning System (AQEWS) forecast, the air quality was likely to be in the lower end of the poor category until Friday. The outlook for the subsequent six days showed the air quality was likely to hover between poor and moderate.

AQEWS is a forecasting system under the Union earth sciences ministry. The Commission for Air Quality Management (CAQM) relies on AQEWS for pre-emptive action to check pollution.

Delhi recorded its first poor air day this winter season on Friday last when the AQI was recorded at 212. On the same day, CAQM invoked stage-I measures of the Graded Response Action Plan. The measures include shutting down construction and demolition sites over 500 sqm not registered with the government, reduction of road traffic, periodic mechanised sweeping, and water sprinkling on roads, etc.

On Saturday, the AQI deteriorated to 216 (poor) before improving to the moderate range.

On Monday, CAQM said Delhi recorded 200 good to moderate air days this year, making it only the second time since 2015. The only other time this has happened in the last eight years was in 2020 when the Covid-19 pandemic prompted lockdowns.

On Wednesday, the AQEWS said that the predominant surface wind was likely to come from the northwest with speeds of 8-14 km per hour. The surface wind was likely to be from west/north with speeds of 6-12 km per hour on Thursday. The wind is likely to be from west/northwest with speeds of 8-16 km per hour on Friday.