Firecracker ban flouted; Delhi’s air quality likely to worsen to ‘severe’

Delhi’s air quality deteriorated to the higher end of the “very poor” category and was likely to inch close to the “severe” zone later on Friday as the annual winter ban on firecrackers was flouted again amid Diwali celebrations. Plumes of a toxic cocktail of pollutants and heavy metals enveloped the city with hourly PM 2.5 levels shooting up in parts of the city to around 31 times the permissible standards for the ultrafine particles.
The average air quality index (AQI) was 361 (very poor) at 7am on Friday compared to 328 (very poor) at 4pm on Thursday. Fireworks began from 6pm onwards and continued well past midnight in most places.
Last year, Delhi’s AQI on Diwali day (November 12) was significantly better at just 218 (poor). This deteriorated to 358 (very poor) the day after Diwali by 4pm. Delhi is expected to cross this later on Friday, likely making it Delhi’s worst day after Diwali since 2021, when the AQI was 462 (severe). The AQI the day after in 2022 was 302 (very poor).
The Central Pollution Control Board (CPCB) data showed Delhi’s AQI remained steady at 327 between 6pm and 9pm on Thursday, before rising every hour. It touched 330 at 10pm, 338 at midnight and 347 by 3am.
The CPCB classifies AQI between 0-50 as “good”, 51 and 100 as “satisfactory”, 101 and 200 as “moderate”, 201 and 300 as “poor”, 301 and 400 as “very poor”, and over 400 as “severe”.
The Delhi Pollution Control Committee (DPCC) data showed Delhi’s hourly PM 2.5 concentration was 1,853 micrograms per cubic metre at east Delhi’s Vivek Vihar. It was around 31 times the national 24-hour PM 2.5 standard of 60 micrograms per cubic metre (µg/m³). There was an hourly peak of 1,527 µg/m³ at Nehru Nagar near Lajpat Nagar. Data showed both these values peaked at midnight, as did most other stations, with PM 2.5 concentration then gradually dipping as the bursting of firecrackers waned.
Delhi’s average PM 2.5 concentration was 609µg/m³ at midnight, 10 times the standard. The same concentration was 96µg/m³ at 4pm on Thursday and 194µg/m³ at 8 pm, CPCB data showed.
The India Meteorological Department (IMD) said wind speed, which was predominantly calm on Thursday, is likely to pick up once again and could hover around 10-12 km/hr during the day on Friday, partially helping disperse pollutants. The wind direction remained northwesterly, as it was on Thursday allowing long-range transport of stubble smoke to the Capital. Another factor that may help is unusually warm weather for this time of the year. The maximum temperature on Diwali day was 34.1°C, three degrees above normal. The minimum was 21.1°C, five degrees higher than normal. The minimum is forecast to hover around 19°C on Friday, while the maximum should remain around 34°C. The higher the temperature, the higher the mixing height of the atmosphere, an invisible layer of the atmosphere within which particles move freely. Low temperature brings down this mixing height while also slowing down the movement of such particles and pollutants.
Data from the Centre’s Decision Support System (DSS) showed stubble burning contributed a season high 27.61% to Delhi’s PM 2.5 on Thursday. A high contribution is likely on Friday too.