Delhi’s air quality has remained in the ‘very poor’ category for the third consecutive day as of Wednesday. The 24-hour average Air Quality Index (AQI) was recorded at 333 at 10 am, a slight improvement from 351 at 4 pm on Tuesday, which marked the season’s highest reading so far. On Diwali day itself, the AQI had reached 345, indicating a deterioration into the ‘very poor’ zone for the first time this season.
The city experienced relatively mild temperatures, with the minimum temperature on Wednesday at 21.8°C, three degrees above normal. The previous day saw a high of 32.9°C. Both maximum and minimum temperatures are expected to hover around this range through the weekend.
Fortunately, favorable meteorological conditions have aided in the dispersion of pollutants generated by firecrackers. Consistent easterly to south-easterly winds, blowing at speeds up to 10 km/h since Tuesday morning, have helped clear the accumulated smog post-Diwali. An India Meteorological Department official noted that winds ranging from 5-7 km/h on Tuesday morning increased to 10 km/h during the day, contributing to significant dispersion, further aided by high daytime temperatures and sunshine allowing for vertical and horizontal pollutant movement.
However, the impact of Diwali celebrations was stark. PM 2.5 levels in parts of Delhi surged to over 29 times the national permissible limit of 60 micrograms per cubic meter on Diwali night. The city’s overall average PM 2.5 concentration peaked at a concerning 675µg/m³ at midnight on Diwali, the highest recorded in four years since 2021, when the average reached 728µg/m³ on the same occasion.
There was a notable improvement throughout Diwali day and into the next. PM 2.5 concentrations were 91µg/m³ at 4 pm and 223µg/m³ at 8 pm on Monday. By Tuesday morning, levels had dropped from 510µg/m³ at 6 am to 438µg/m³ at 8 am, further decreasing to 135µg/m³ by noon and 89µg/m³ by 3 pm, demonstrating the effectiveness of wind dispersion in clearing firecracker emissions.
The contribution of stubble burning to Delhi’s PM 2.5 levels remained minimal due to the dominant easterly winds, accounting for only 0.8% on Diwali day and 1% on Tuesday, according to the Centre’s Decision Support System. This contribution is projected to increase slightly to 2.6% on Wednesday and 4.4% on Thursday.
Current forecasts from the Early Warning System indicate that the AQI is likely to persist in the ‘very poor’ range until at least Friday. Over the following six days, the air quality is expected to fluctuate between ‘poor’ and ‘very poor’ conditions, with northeasterly winds continuing to help mitigate the impact of stubble burning emissions.
Mukesh Khare, an air pollution expert from the Indian Institute of Technology Delhi, commented that stubble burning’s contribution is currently negligible. He added, “If the contribution was over 10%, the AQI would have shot up to close to severe, or possibly in that range. Favourable meteorological conditions have helped disperse pollutants swiftly, which was clearly from firecrackers.”