Delhi’s AQI in poor category as mercury dips to 9 degrees Celsius

Delhi recorded an Air Quality Index (AQI) of 281 in the poor category at 7am on Tuesday as the mercury dipped to 9 degrees Celsius.

The AQI was 310 in the very poor category at 4 pm on Monday. It was likely to remain poor till at least Thursday as strong surface winds allowed pollutants to disperse.

Low temperatures, particularly at night, lead to a drop in mixing height – a layer of the atmosphere within which pollutants can get trapped. But strong surface winds during the day and a good mixing height – an invisible layer of the atmosphere within which pollutants get trapped –are both likely to help pollutants disperse.

Delhi’s AQI is unlikely to touch the severe level by the end of the month, according to the Early Warning System for Delhi which the Commission for Air Quality Management in NCR uses for pre-emptive action against pollution.

The AQI is expected to be in the poor category until Thursday and the outlook for the subsequent six days shows the air quality is likely to remain largely in the between poor to very poor categories.

On Monday, the minimum temperature was 8.9 degrees Celsius, three notches above normal and the lowest so far this season. This was the first time mercury dipped below the 9-degree mark.

Delhi’s minimum temperature has been below 10 degrees Celsius since Friday when it dipped to 9.6 degrees. It was 9.0 degrees on Saturday, 9.6 degrees on Sunday, and 8.9 degrees on Monday. The drop in the mercury is largely due to cold northwesterly winds blowing towards the capital. A further drop was possible.

“The longer these northwesterly winds prevail, the greater is the impact on temperature, particularly at night. The minimum could touch the 8-degree mark by Thursday,” said an official.

Last November, Delhi’s lowest minimum temperature was 9.2 degrees Celsius on November 24. In 2020, it fell to as low as 6.3 degrees Celsius (November 23). In 2019, the lowest minimum in November was 11.4 degrees (November 20).