Delhi breathes worst air on Diwali eve in 10 years

Delhi’s AQI of 369 means its average air pollution over the previous 24 hours was “very poor” under the Central Pollution Control Board’s 0–500 scale. It signals highly polluted air, but it had not yet crossed the scale’s “severe” threshold. The distinction matters because the city was close to the worst category before Diwali night began.

The AQI rose from 261 on November 1 to 369 at 4pm on Saturday. At one point, PM2.5 averaged 295 micrograms per cubic metre across Delhi, and 36 monitoring stations exceeded 250. CPCB places PM2.5 at 250 or above in its “severe” band.

For the overall AQI, the Indian Institute of Tropical Meteorology forecast a rise to 406 by 4am Monday. That would move Delhi beyond 400 into “severe”, the scale’s worst category. Weak winds and firecracker smoke were expected to push pollution higher overnight.

PM2.5 pollution rose to dangerous levels before Diwali night had even fully begun. Across Delhi’s monitoring stations, the Saturday morning average reached 295 micrograms per cubic metre. By 10pm, the reported average across 55 stations had climbed to 289, while Mundka recorded 718 and some neighbourhood readings exceeded 600.

The previous Diwali shows how high pollution can go when smoke accumulates. At 2am last year, the average PM2.5 reading across 27 stations reached 1,137 micrograms per cubic metre. That was up from 535 at 10pm, when firecracker bursting was supposed to end. India’s 24-hour PM2.5 limit is 60 micrograms per cubic metre.

The comparison is stark. Last year’s Diwali-night average was nearly 19 times the national limit. This year began with a higher pollution base, and weak winds were forecast. IITM therefore projected the overall AQI could reach 406 by early Monday.

The 30% jump followed the opening of the first permitted evening firecracker window at 8pm. Delhi already had a high pollution base, with farm fires in Punjab and Haryana at their highest level of the season on Saturday. After sunset, ground-level winds also weakened, reducing the air’s ability to carry pollution away.

PM2.5 rose from 177 micrograms per cubic metre at 7.45pm to 208 at 8pm. It then climbed every 15 minutes, reaching 289 by 10pm across 55 reporting stations. In Punjabi Bagh, PM2.5 nearly tripled from 208 at 7pm to 593 at 8pm. RK Puram reached 621 at 9pm.

The mechanism was a rapid addition of smoke during stagnant conditions. By 9pm, nine stations were above 400, compared with none on Friday. From 10pm, even the median station exceeded 250. The main Diwali night, when most crackers are burst, still lay ahead.

PM2.5 is fine particulate matter small enough to lodge deep in the lungs. That is why readings at Delhi’s reported levels are a health concern, not merely a visibility problem. The article specifically highlights the particles’ ability to penetrate deep into the respiratory system.

On Saturday morning, PM2.5 averaged 295 micrograms per cubic metre across Delhi’s 59 monitoring stations. During the evening, Mundka reached 718, while RK Puram recorded 621. Last year, the average reached 1,137 at 2am. These figures were far above India’s 24-hour limit of 60.

The article does not list specific symptoms or medical outcomes. Established health evidence indicates that very high PM2.5 exposure can worsen breathing problems and increase stress on the heart and blood vessels, especially for vulnerable people. Avoiding additional exposure is therefore important while pollution remains extreme.

Pollution spreads more effectively when winds move air and the atmosphere has a deep mixing layer. When winds weaken, that movement slows. A shallow mixing layer also means pollutants have less vertical space to dilute, so smoke remains concentrated near the ground where people breathe.

Delhi’s ground wind became calm after sunset on Saturday. The mixing layer had already spent four days at about half its usual depth before returning to normal on Saturday afternoon. Even during that better-ventilated afternoon, every hour from 11am to 5pm was dirtier than Friday.

The evening created worse conditions. Firecracker smoke entered the air at 8pm, while light winds were forecast for Sunday. With little ventilation, PM2.5 rose from 177 at 7.45pm to 289 at 10pm. IITM forecast the AQI reaching 406 by 4am Monday as pollution remained trapped.

The article establishes that farm fires were an important part of Delhi’s pollution backdrop, but it does not calculate their exact contribution. It reports that fires in Punjab and Haryana reached their highest level of the season on Saturday, while the Isro satellite count rose for a tenth straight day.

The clearest figure is 415 fire pixels counted in Punjab by INSAT-3DS, which scans the region every half hour. However, a fire-pixel count is not the same as a percentage of Delhi’s pollution. The article gives no comparable numbers for firecrackers, vehicles, waste burning, or other sources.

That means the sources cannot be ranked quantitatively from this article alone. It does show that several sources overlapped: farm fires were high, firecrackers sharply increased evening PM2.5, and weak winds trapped pollution. The article recommends reducing crackers, trucks, and waste burning together.

The measures identified as most likely to help are cutting firecracker use, sending fewer trucks into Delhi, and stopping waste burning. These actions would reduce new pollution entering the air while weak winds continue to limit dispersion. Preventing additional emissions matters because the city already began Diwali with a high pollution base.

The Supreme Court allowed certified green crackers for one hour in the morning and two hours in the evening on Saturday and Sunday. Delhi Police formed more than 250 special enforcement teams, with at least one in every police station. Yet officers said identifying whether a cracker was genuinely green was nearly impossible.

Enforcing the time limits across the city was also described as “not humanly possible.” Conventional crackers were already available in several markets, and some boxes lacked mandatory QR codes. With weak winds forecast and IITM projecting severe AQI, combined controls were especially important.