New Delhi: With an average Air Quality Index (AQI) of 294, Delhi recorded its cleanest December air since the AQI system was introduced in 2015. Officials attributed the improvement to strong winds in the first half of the month and record-breaking rainfall in the second half.
According to data from the Central Pollution Control Board (CPCB), December’s first half marked a milestone for air quality, with only one ‘very poor’ air day recorded between December 1 and 15. On Monday, the AQI stood at 173, categorised as “moderate,” a significant improvement from Sunday’s 225 (“poor”). This was the eighth “moderate” air quality day this month, a stark contrast to previous Decembers, which typically saw no more than three such days.
The cleanest day of the month—and the cleanest December day on record—was December 28, when the AQI dropped to 139. The month’s average AQI of 238 was notably better than December 2023’s 348, 2022’s 319, and 2021’s 336. The previous record for the lowest December AQI was 300, set in 2015.
The India Meteorological Department (IMD) highlighted that December also witnessed the fifth-highest rainfall since 1901, with a total of 53.5 mm. On December 28 alone, Delhi experienced 41.2 mm of rain, the highest single-day December rainfall in 101 years. In comparison, December 2023 and 2022 recorded no rainfall, while 2021 and 2020 saw 9.6 mm and 1.6 mm, respectively.
IMD officials noted that while the average minimum temperature of 8.4°C matched the long-period average, the average maximum temperature of 23.1°C was slightly warmer, at 0.3°C above the norm. This December was the coldest since 2021, when the average maximum temperature stood at 22.4°C.
Experts pointed to weather patterns as key factors in the improved air quality. Mahesh Palawat, vice president at Skymet, explained that strong winds during early December effectively dispersed pollutants, preventing dense fog and maintaining relatively clean air. However, the third week saw six days of severe air quality due to a western disturbance that added moisture and led to stagnation.
Despite this temporary dip, Delhi’s air quality improved overall, with fewer “severe” and “very poor” days. The highest AQI of the month was recorded on December 19, at 451, categorised as “severe.”
The CPCB classifies AQI as follows: 0-50 (Good), 51-100 (Satisfactory), 101-200 (Moderate), 201-300 (Poor), 301-400 (Very Poor), and above 400 (Severe).