Delhi’s air quality took a sharp nosedive following Diwali celebrations, deteriorating to the ‘very poor’ category. This alarming shift is attributed to extensive firecracker use that continued well beyond the time restrictions set by the Supreme Court. The skies filled with a noxious mix of pollutants and heavy metals, causing hourly PM 2.5 levels to spike to approximately 29 times the safe standard for these ultra-fine particles. Experts predict the air quality could worsen to ‘severe’ levels later in the day and persist through Wednesday, with a potential return to ‘very poor’ by Thursday.
On Tuesday morning, the average Air Quality Index (AQI) stood at 350, classifying it as ‘very poor’. This marks a slight increase from Monday’s average of 345. While the Supreme Court had permitted the use of ‘green firecrackers’ during specific windows – 6am to 7am and 8pm to 10pm on October 20 and 21 – widespread violations were observed. Many areas experienced firecracker bursts throughout the day on Monday, with a significant surge in intensity starting around 8pm and continuing past midnight.
Data from the Central Pollution Control Board (CPCB) indicated a fluctuating AQI trend on Monday. It improved slightly from 345 at 4pm to 340 by 7pm, but began to climb again as midnight approached, reaching 349 due to the accumulating emissions from firecrackers.
The CPCB categorizes AQI levels as follows: 0-50 is ‘good’, 51-100 is ‘satisfactory’, 101-200 is ‘moderate’, 201-300 is ‘poor’, 301-400 is ‘very poor’, and anything above 400 is ‘severe’.
Measurements from the Delhi Pollution Control Committee highlighted the severity of the pollution. In Nehru Nagar, hourly PM 2.5 concentration reached a staggering 1,763 micrograms per cubic meter (µg/m³), nearly 29 times the national 24-hour standard of 60 µg/m³. East Delhi’s Anand Vihar, a known pollution hotspot, recorded a peak of 1,710 µg/m³.
The highest pollution levels were recorded across Delhi between midnight and 1am. While PM 2.5 concentrations gradually decreased as firecracker activity subsided, the overall average PM 2.5 level at midnight was 675µg/m³, more than 11 times the standard. Earlier in the day, at 4pm on Monday, the average was 91µg/m³, rising to 223µg/m³ by 8pm.
These peak pollution figures surpass those of the previous year, when Delhi’s average PM 2.5 levels peaked at 609µg/m³ and 570µg/m³. It’s important to note that a complete ban on all types of firecrackers, including green ones, was in effect for the two years prior to this Diwali.
Adding to the poor air quality, shallow fog was reported in the Palam area between 3:30am and 5am on Tuesday, with visibility dropping to 600 meters. This fog, combined with the airborne pollutants, created a dense smog. Moderate easterly winds of 5-7 km per hour, beginning around 5:30am, offered some relief by gradually improving visibility.
Meteorologists anticipate wind speeds of 5-10 km per hour throughout Tuesday, which may help disperse pollutants once the sun is out. The current warmer temperatures, with Diwali falling earlier in the year, contribute to a higher atmospheric mixing height, allowing particles to move more freely. However, lower temperatures typically reduce this mixing height and slow down pollutant dispersal.
Delhi recorded a maximum temperature of 33.5°C on Diwali day, one degree above normal, with a minimum of 20.2°C, two degrees higher than usual. Similar temperatures are expected for Tuesday. Historical data shows a significant dip in air quality post-Diwali: last year’s AQI was 328 on Diwali day, rising to 339 the next day. In 2023, it was 218 on Diwali day, jumping to 358 the following day. The most severe air quality was recorded in 2021, when the AQI reached 462 (severe) after Diwali.
Current data from the Decision Support System indicates that stubble burning has not yet significantly impacted Delhi’s air quality, contributing only 0.8% to the city’s PM 2.5 levels on Diwali day.