Delhi air quality improves, lowest AQI recorded since Dec 2015

The data from the Central Pollution Control Board (CPCB) reveals that the national capital had its cleanest first half of Dec since the air quality index (AQI) was initially compiled in 2015.

There was just one "very poor" air day during the first half of the month and no "severe" air day. Additionally, according to CPCB, there were eight "poor" air days and six "moderate" air days—the highest number for Dec.

Delhi had its lowest-ever Dec AQI of 238 between Dec 1 and Dec 15 of this year. The first half of Dec is noticeably cleaner than it has been in the previous nine years, when the average AQI was over 300.

The lowest average AQI for the first half of the month prior to this was 301 in 2022. During the same time last year, the average AQI was 327.

According to the CPCB, an AQI of 0 to 50 is considered "good," 51 to 100 is "satisfactory," 101 to 200 is "moderate," 201 to 300 is "poor," 301 to 400 is "very poor," and more than 400 is "severe."

Strong and steady winds have been observed throughout the month in northwest India, according to meteorological experts, and the absence of fog and moisture has also helped to enhance the air quality.

“Generally in December, we see moderate to dense fog, which makes dispersion of pollutants difficult. At the same time, winds are also slow. On average, winds have been blowing at speeds of over 8-10 km/hr on most days, with this regularly touching 20 km/hr on multiple days,” said Mahesh Palawat, vice president at Skymet meteorology.

According to him, the majority of the days in Delhi-NCR had seen clear skies. “There has not been enough moisture in the plains, barring a few days. This has meant fog is not forming with the same intensity it was seen in mid-November,” he said.

In the preceding years, the average AQIs from Dec 1 to Dec 15 were 322 in 2021, 335 in 2020, 321 in 2019, 330 in 2018, 304 in 2017, 367 in 2016, and 323 in 2015.

Prior to this year, 2022, 2019, and 2015 had the most "moderate" air days in Dec, with three each.

On Dec 8, the AQI reached 302, marking the sole "very poor" air day in the Capital this month.

According to the Center's Early Warning System for Delhi (EWS), a predicted decrease in wind speeds is expected to cause the AQI to worsen to "very poor" by Dec 16.

Meteorological factors have proven crucial thus far, according to Sunil Dahiya, principal analyst at the think tank Envirocatalysts, who pointed out that even under favorable circumstances, Delhi's AQI did not fall below "moderate."

“This shows our background emissions are fairly high, and the PM2.5 concentration did not dip below 110 micrograms per cubic meter during this period. So, while comparatively it may be somewhat cleaner, this is still over two times the permissible standard for PM2.5, which is 60 micrograms per cubic meter. If conditions become adverse again, all this pollution will again get trapped in Delhi,” he said.