Foul air in Nov, Dec offsets AQI gains made throughout 2023

In 2023, Delhi was on course to record its cleanest year in terms of air quality since 2020, but a polluted November and December negated these gains, with the Capital ending the year with an annual PM2.5 concentration of 101 micrograms per cubic metre (ug/m3) - more polluted than 2022's average of 99 µg/m3.

- Jasjeev Gandhiok

The annual PM2.5 national standard set by the Central Pollution Control Board (CPCB) is 40µg/m3, meaning Delhi ended the year at over 2.5 times the safe limit.

CPCB's PM2.5 data from the 40 continuous ambient air quality monitoring stations in Delhi, showed the annual PM2.5 average till December 29 this year has been 101µg/m3. It was 99µg/ m3 last year; 106µg/m3 in 2021; 95µg/m3 in 2020-a lockdown year; 109µg/m3 in 2019 and 116µg/m3 in 2018. Prior to 2018, Delhi had less than half of the ambient air quality stations it has now, making a comparison unfair.

Barring 2020, Delhi's annual PM2.5 concentration had been dipping each year, a trend that was on course till October, 2023. However, a spike in pollution levels from the start of November appeared to have prevented that from happening. CPCB data showed Delhi's average PM2.5 concentration till the end of October had been 77µg/m3 Delhi's lowest since it was 73 µg/m3 in 2020 for the corresponding period. The PM2.5 concentration for the first 10 months in 2021 and 2022 had been 83 µg/m3 each.

However, a fairly polluted November brought up the average air quality index (AQI) to the dirtier end of "very poor" at 390, and 17 out of 30 days in the month recorded a near severed AQI. The average PM2.5 concentration rose to 92µg/m3 by the end of the month, compared to 91µg/m3 for the corresponding period last year; 98µg/m3 in 2021 and 86µg/m3 in 2020.

The average PM2.5 concentration till December 29 was 199µg/m3. It was 177 µg/m3 in all of December last year; 203µg/ m3 in December 2021 and 195µg/m3 in December 2020.