The contribution of stubble burning to Delhi's PM2.5 pollution has so far remained low.
Starting the day with "poor" air quality -- overall Air Quality Index (AQI) of 251 at 6.30 am -- Delhi's air slightly worsened during the day, but eventually recorded its lowest AQI for the day before Diwali in seven years. Central Pollution Control Board (CPCB) data showed the AQI of 265 on Sunday.
Diwali will be celebrated across the country on Monday. An AQI between zero and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".
Last year, the AQI on November 3 (a day before Diwali) was 314. It had shot up to 382 on the Diwali day and 462 the next day.
In 2020, Delhi recorded an AQI of 296 a day before Diwali (November 13), while it worsened to 414 on Diwali and 435 the day after.
The capital logged an AQI of 287 on the day before the festival in 2019. It worsened to 337 on Diwali (October 27) and further to 368 the next day.
The AQI was 338 on the day before Diwali in 2018. Interestingly, it improved to 281 on the Diwali day before aggravating to 390 the next day.
The AQI was 302 and 404 on the day before Diwali in 2017 and 2016, the CPCB data showed.
The air quality in the capital is predicted to turn "very poor" on Monday morning, while it could worsen to the "severe" category on Tuesday due to emissions from firecrackers and an increase in the share of smoke from stubble burning because of a favourable wind speed and direction.
SAFAR, a forecasting agency under the Union Ministry of Earth Sciences, said the air quality may deteriorate to "very poor" levels even if no firecrackers are burst.
In case firecrackers are burst like last year, the air quality may plunge to "severe" levels on the night of Diwali itself and remain in the "red" zone for another day.
The contribution of stubble burning to Delhi's PM2.5 pollution has so far remained low (up to 5 per cent) due to a slow transport-level wind speed.
"However, the transport-level wind direction and speed is likely to become very favourable from Monday afternoon. It will increase the share of stubble burning in Delhi's PM2.5 pollution to 15-18 per cent on October 25 and push the air quality into the 'severe' category," said Gufran Beig, founder project director, SAFAR.
Paddy straw burning accounted for 25 per cent of Delhi's PM2.5 pollution on Diwali last year.
The share of smoke from farm fires in Delhi's pollution stood at 32 per cent in 2020 and 19 per cent in 2019.