Delhi AQI: This year’s Diwali day AQI was the lowest the city has experienced since 2019.
This year, Delhi’s post-Diwali air was the cleanest it had been since 2015. This is true even though the air quality index (AQI) remained in the “extremely bad” category on both Diwali and the day following, and pollution levels spiked when firecrackers were lit in defiance of the Delhi government’s ban.
Delhi AQI: According to information from the Central Pollution Control Board, the AQI (air quality index) on Diwali day was 312 while it was 303 on Tuesday (CPCB). An AQI of 301 to 400 is regarded as “extremely poor.” This year’s Diwali day AQI was the lowest the city has experienced since 2019.
The worst post-Diwali air quality was reported last year, when the day after Diwali recorded an AQI of 462, in the “severe” category, according to CPCB data available from 2015 on. Last year, the AQI on the day of Diwali was 382. Since 2015, the day following Diwali has seen “severe” air quality four times.
This time, the air quality was better due to meteorological circumstances. Due to an early Diwali this year, the wind speed helped limit the accumulation of pollution, and the temperature is still comparatively warm, according to Gufran Beig, founder project director of SAFAR.
“On Tuesday, wind speed increased at 2:00 a.m. When the temperature is cooler, the boundary layer lowers, and the winds slow down in the early morning, pollutants would often have accumulated. However, the wind picked up, which aided in dispersion. The AQI reached its peak about midnight, then began to decline and stabilize around 323 in the morning, according to Beig.
“Compared to last year, it appears that there may have been a decrease in firecracker emissions. Not as much as it could have, the air quality did not degrade. However, it may take a few days to ascertain how much the pollution load from firecrackers is, according to Beig.
Burning crop residue hasn’t contributed much so far this year in Punjab or Haryana either. According to Beig, the wind, which has been blowing from Delhi’s west-southwest direction since Monday, has not been conducive to carrying smoke from stubble burning in the northwest. According to a SAFAR forecasting system update, Delhi’s contribution of stubble burning to PM2.5 levels on Tuesday was roughly 5.6%. In contrast, data from SAFAR show that stubble burning contributed 25% to Delhi’s air on Diwali day (November 4) and 36% the day after Diwali last year.
“Some of the controls may have been effective. It’s possible that people choose firecrackers since they make less harmful gases while still making noise, according to Beig.
Professor Sachchida Nand Tripathi of IIT Kanpur also suggested that meteorology may have played a role in some way. Burning of crop residue has also not increased in intensity compared to prior years. Lower temperatures would also result in a thinner boundary layer and slower dispersion of particulate particles. However, the high wind has cancelled this out, he said.
A number of factors were mentioned by Anumita Roychowdhury, executive director of research and advocacy at the Centre for Science and Environment. Diwali occurred earlier than usual, in warmer weather, and well before the extreme inversion conditions began. Better wind speeds and less violent crop fires have both been observed in comparison. It’s challenging to determine whether firecracker emissions have decreased, she added.