Delhi's air quality declines, anticipated to deteriorate to 'poor' category

On Wednesday morning, Delhi witnessed a decline in air quality, and by the end of the day, it was likely to dip into the 'poor' category. This deterioration occurred as a change in wind direction brought the minimum temperature below 20°C (19.4°C) for the first time in five days.

At 8 am, the average Air Quality Index (AQI) stood at 196, indicating a 'moderate' level of air quality. The previous day, the AQI was also in the 'moderate' category at 180. Unfortunately, the change in wind direction to northwesterly, coupled with a decrease in local wind speed, was expected to keep the air quality poor over the next two days.

Impact of cold Northwesterly winds

Cold northwesterly winds have a negative impact on air quality. They slow down the dispersion of pollutants and carry smoke from the fields of Haryana and Punjab, where crop residue burning is common during this time of the year.

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The minimum temperature in Delhi dipped below 20°C for the first time since the previous Friday when it reached 18.6°C. After that, a shift in wind direction led to a rise in minimum temperature, reaching 20.9°C on Saturday, 23.1°C on Sunday, and 24.4°C on Monday. On Tuesday, the minimum temperature was 22.7°C, which was two degrees above the normal range.

Air quality forecast

According to the Early Warning System (EWS) forecast, the air quality was expected to remain at the lower end of the 'poor' category until Friday, with fluctuations between 'poor' and 'moderate' in the subsequent six days.

The Commission for Air Quality Management (CAQM) relies on the EWS for proactive measures to control pollution. Delhi recorded its first 'poor' air quality day this winter on the previous Friday, prompting stage-I measures of the Graded Response Action Plan, including construction site closures, traffic reduction, and road cleaning, among other actions.

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Delhi's AQI has been in the 'moderate' category since Sunday. For reference, an AQI between 0-50 is considered 'good,' between 51 and 100 is 'satisfactory,' between 101 and 200 is 'moderate,' between 201 and 300 is 'poor,' between 301 and 400 is 'very poor,' and over 400 is 'severe.' In other recent data, CAQM reported that Delhi had experienced 200 days of 'good to moderate' air quality this year, which has occurred only for the second time since 2015, with the first instance being in 2020 during the COVID-19 pandemic lockdowns.