Delhi has achieved its cleanest December air since the Air Quality Index (AQI) system was introduced in 2015, with an average AQI of 294. The feat is remarkable for the national capital as it ends the year on a high note.
This remarkable improvement is attributed to strong, consistent winds during the first half of the month and record-breaking rainfall in the second half, officials said.
Data from the Central Pollution Control Board (CPCB) shows that December 2024 saw the cleanest first half of the month ever with only one “very poor” air quality day recorded between December 1 and 15.
On December 30, the AQI was recorded at 173, classified as “moderate”, a significant improvement from 225 (poor) recorded a day earlier. This marked the eighth moderate air quality day in December compared to no more than three in previous Decembers.
The cleanest day of the month came on December 28, with the lowest AQI of 139. During this period, the average AQI was 238, notably lower than the usual AQI of over 300 typically seen in December.
For comparison, Delhi’s average AQI last December was 348, 319 in 2022, and 336 in 2021. The previous lowest December AQI was 300, recorded in 2015.
Additionally, December 2024 is set to close with at least 53.5 mm of rainfall, making it the fifth-wettest December since 1901. The city also recorded its highest single-day December rainfall in 101 years on December 28, with 41.2 mm of rain.
This December saw six rainy days, a sharp contrast to just one rainy day in December 2023, none in 2022, and four in 2021.
The total rainfall for December was 53.5 mm, with 41.2 mm falling in a single day. In comparison, December 2023 and 2022 had no rainfall, while 2021 saw 9.6 mm, and 2020 recorded 1.6 mm.
According to the India Meteorological Department (IMD), the highest-ever single-day rainfall in December occurred on December 3, 1923, with 75.7 mm.
The nights in Delhi were pleasant, with an average minimum temperature of 8.4°C, matching the long-period average (LPA) for December. Daytime temperatures were slightly warmer, with an average maximum of 23.1°C, 0.3°C above the LPA.
This December has been the coldest since 2021 when the average maximum temperature was 22.4°C, according to IMD officials.
Experts attribute the favorable air quality in December to the effective dispersion of pollutants, especially during the first two weeks of the month. However, the third week saw a slowdown in winds, leading to six days of severe air quality between December 17 and 23. This stagnation was caused by a western disturbance that brought additional moisture.
Mahesh Palawat, vice president at Skymet, explained that the strong winds in early December played a crucial role in dispersing pollutants, preventing dense fog, and keeping the air relatively clean.
On Monday, Delhi's AQI stood at 173, in the "moderate" range, a significant improvement from Sunday’s 225 (poor).
The lowest AQI of the month was recorded on December 28 at 139, marking the cleanest December day on record. The highest AQI in December was 451, recorded on December 19.
The CPCB categorizes AQI as follows: 0-50 (Good), 51-100 (Satisfactory), 101-200 (Moderate), 201-300 (Poor), 301-400 (Very Poor), and above 400 (Severe).
(With inputs from PTI)