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Delhi has been struggling with its air quality this season, as smog made an early appearance, blanketing the city since November 1. On Monday, the city recorded its highest Air Quality Index (AQI) this season at a hazardous 495. In response, India's Supreme Court enforced Graded Response Action Plan (GRAP) 4, implementing strict restrictions to tackle the alarming situation. Experts predict that Delhi's air quality will remain in the severe category until November 22 and may only slightly improve in the following days.
Why Did Smog Arrive So Early?
Smog forms when pollutants combine with fog, trapping harmful particles close to the ground. This season, meteorological conditions initially helped Delhi avoid severe pollution levels during Diwali. Strong wind speeds and easterly winds carried pollutants away from the city, providing some relief.
However, these same easterly winds later increased moisture levels, and the arrival of a Western Disturbance (WD) added humidity to the air. After the WD passed, clear skies and cool north-westerly winds caused temperatures to drop. This combination of high moisture, cool air, and stagnant conditions allowed smog to form earlier than usual.
According to Mahesh Palawat, Vice President of Skymet Weather, such conditions typically occur at the end of November or early December. This year, regular infusions of moisture from easterly winds and feeble western disturbances created the perfect environment for smog formation ahead of time.
Why Does Delhi Experience Smog Only in Winter?
During winter, the planetary boundary layer, the lowest part of the atmosphere, becomes thinner. The cooler, dense air near the surface is trapped under warmer air above, creating an atmospheric "lid." This phenomenon, known as winter inversion, limits vertical air movement and traps pollutants closer to the ground.
In addition, chilly and calm winds during winter fail to disperse pollutants, allowing them to linger in the air. High humidity further enhances fog formation, which traps even more pollution.
Professor S.N. Tripathi of IIT Kanpur explains that particulate matter (PM) reacts with fog, becoming more oxidized. This creates a vicious smog cycle where each day sees more smog than the previous one, as pollutants continue to accumulate without adequate dispersion.
Impact on Delhi
The early arrival of smog this year has not only reduced visibility but also caused health concerns for residents. With strict measures in place, Delhi aims to control the rising pollution levels, but meteorological challenges may prolong the battle against smog.
