Weather saves Delhi from becoming a gas chamber

A combination of unseasonably warm temperatures and persistent winds helped the Capital avoid a severe pollution crisis on Friday — despite widespread violation of the firecracker ban during Diwali celebrations.

While the 24-hour air quality index (AQI) climbed steadily through Thursday night — from 328 in the early evening to 338 at midnight, reaching 362 by 9am Friday — the city experienced an unexpected respite. Strong, sustained winds swept through Delhi, rapidly dispersing the dense smoke layer and bringing the AQI down to 339 by 4pm Friday, further improving to 323 by 7pm.
This remarkable turnaround was orchestrated by two key meteorological factors: temperatures that remained significantly above normal and steady winds maintaining speeds of 10-15 kilometers per hour. These conditions helped maintain what meteorologists term a high “mixing height”, allowing pollutants to be lifted higher into the atmosphere and transported away from the city rather than settling near the ground.
The timing of these favourable conditions was particularly crucial. Typically, late October in Delhi marks the onset of a phenomenon known as thermal inversion — a wintertime occurrence where cold air becomes trapped near the ground beneath a layer of warmer air above. This natural phenomenon usually creates an invisible ceiling, trapping pollutants in a persistent haze layer that blocks sunlight, creating a self-reinforcing cycle of pollution accumulation.
Mahesh Palawat, vice president at Skymet meteorology, explained this complex interaction between temperature and pollution: “Higher temperature keeps mixing height high and allows pollutants to move and disperse freely. Low temperature slows down wind speed and also traps pollutants closer to the surface through a phenomena called inversion.” He noted that while winter months typically see the mixing height drop to a mere 200-300 metres, Thursday maintained mixing height of 2,100 metres.
These unusual conditions are part of a larger temperature anomaly this year. The India Meteorological Department (IMD) confirmed that October was Delhi’s warmest in 73 years.
An IMD official, speaking on condition of anonymity, detailed the wind patterns: “We have had good wind speed over the last few days, but winds picked up especially on Thursday. We had forecast winds of up to 15 km/hr and the maximum wind speed was 16 km/hr. The maximum and minimum meanwhile remain above normal due to lack of snow in the mountains.”
Palawat’s Skymet predicted winds on Saturday to remain as they were the previous day, but taper off by Sunday. “We will see wind direction change once again to easterly on Sunday, but only for one or two days. We will then see calm winds that may trap local pollutants again,” he added.
The temperature deviation from seasonal norms was striking. Friday’s maximum temperature reached 33.6°C, three degrees above normal, following Thursday’s 34.1°C. Night-time temperatures also remained elevated, with Thursday’s minimum at 21.1°C—five degrees above normal—and Friday’s at 18.4°C, still two degrees above typical levels.
This presents a stark contrast to last year’s Diwali, celebrated on November 12, when the maximum temperature was 27.5°C and the minimum 12.4°C. Those conditions had led to significant thermal inversion, causing Delhi’s AQI to spike by 140 points, from 218 (poor) to 358 (very poor).
Environmental analyst Sunil Dahiya, founder of think-tank Envirocatalysts, highlighted the timing’s significance: “An early Diwali helps Delhi as often, temperatures are higher and inversion is missing. This year, October temperature has been even warmer than usual. We have also seen strong winds on Diwali, which can again quickly ensure firecracker emissions dissipate.”
Weekend forecasts suggest the unusually warm spell will continue, with maximum temperatures expected to remain around 33-34°C and minimum temperatures between 18-19°C.
Wind direction, like on Thursday, remained northwesterly on Friday, meaning smoke from farm fires in Punjab and Haryana was likely reaching the capital. As per the Centre’s Decision Support System (DSS), the contribution of farm fires to Delhi’s PM 2.5 was 27.61% on Friday — the highest so far this season. DSS only releases the actual contribution from the previous day after incorporating the actual fire count in its model. Though contribution should remain high for Friday, this is likely to dip from Saturday onwards, with the wind direction likely to transition towards easterly.