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Winds improve AQI from ‘very poor’ to ‘moderate’, Delhi logs lowest maximum of season

Dec 10, 2024 05:52 AM IST

Delhi also recorded its lowest maximum temperature of the season, at 21.6°C, which was three degrees below the normal for this time of the year

New Delhi

A destitute man sits huddled during chilly early morning hours at Rajendra Nagar on Monday. (Sanchit Khanna/HT Photo)
A destitute man sits huddled during chilly early morning hours at Rajendra Nagar on Monday. (Sanchit Khanna/HT Photo)

Buoyed by fast winds and light rainfall over the weekend, Delhi’s air quality improved dramatically—by 116 points and two categories—between Sunday and Monday, paving the way for one of the best starts to December in terms of air Delhi has breathed since 2015, according to data shared by the Central Pollution Control Board (CPCB).

An air quality index (AQI) reading of 302 (“very poor”) recorded at 4pm on Sunday moved up significantly, clocking a reading of 186 (“moderate”) at 4pm on Monday, marking the fourth “moderate” air day this month, which is the highest number of “moderate” air days recorded in any December since 2015.

To be sure, there has been no “good” or “satisfactory” air day recorded in December. 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”

On the day, Delhi also recorded its lowest maximum temperature of the season, at 21.6°C, which was three degrees below the normal for this time of the year. Before this, the lowest maximum temperature was 23.5°C, recorded on November 17. The minimum temperature, meanwhile, increased from 7.4°C to 8.2°C on Monday.

Air improves

Previously, three “moderate” air days each were recorded in December 2022, 2019 and 2015. The AQI has never gone below the “moderate” category in December, with the lowest reading being 140 (“moderate”), which was recorded on December 26, 2015.

This year, Delhi recorded “moderate” AQI on December 4 (178), December 5 (165) and December 6 (197) too, in what has been a fairly clean start to the month.

The AQI on Monday was calculated on the basis of data from 38 ambient air quality monitoring stations. Of them, only the Shadipur weather station recorded a “very poor” AQI, of 315; 13 stations clocked “poor” AQIs and 24 stations recorded “moderate” AQIs. The lowest AQI, of 113, was recorded at the Lodhi Road station.

Data from December 2023 showed the average AQI was 348, with three “severe” air days recorded. In 2023, the lowest AQI was 286 (“poor”), recorded on December 19, and the highest was 450 (“severe”), recorded on December 23. Typically, the second half of December witnesses a spike in pollution due to plummeting temperatures, low wind speed, and the return of dense fog.

Days to get colder

Strong winds of speeds up to 18km/hr were recorded on Sunday, with a drizzle recorded in parts of NCR towards the evening. Meteorological experts said cold northwesterly winds with speeds of up to 15km/hr were also blowing on Monday, leading to a drop in the maximum temperature.

“We have recorded fresh snowfall across the Himalayas due to this prevailing western disturbance. This will now impact the plains and lead to cooler days and nights,” said Mahesh Palawat, vice president at Skymet meteorology, adding that although wind speed will dip marginally, it will still hover around 8-10km/hr on Tuesday and Wednesday.

Delhi’s minimum temperature, meanwhile, rose marginally and was recorded at 8.2°C, which was a degree below the normal for this time of the year. The minimum is forecast to drop to around 7°C by Tuesday and further to 6°C by Wednesday.

The maximum is also forecast to remain below normal levels; despite sunshine predicted, the maximum is expected to hover around 23°C till Thursday.

The lowest maximum temperature on the day was recorded at 19°C, recorded at the Palam station, and the lowest minimum was 6.4°C, recorded at the Ayanagar weather station.

Long-term data shows minimum temperature in December usually dips below normal levels in the second half of the month. Last year, the lowest minimum in December was 4.9°C, recorded on December 15. It was 5°C on December 26, 2022, and 3.2°C on December 20, 2021. The lowest minimum in the last decade in December was 2.4°C, recorded on December 28, 2019.

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