How speed, direction of wind dictate quality of air we breathe

This year, like clockwork, Delhi began choking on a toxic cocktail of pollutants in early November, as smoke from scorched paddy fields in Punjab wafted towards the Capital and blanketed its air.

- Jasjeev Gandhiok

The city’s tryst with hazardous air pollution levels has become an annual affair, and even as emissions (local and external) play a key role in regulating Delhi’s air quality, one weather factor plays a key role in pushing the pollution needles one way or the other — winds.

The speed and direction of winds — specifically the high, long-range transport winds — can either wash pollutants away and clean up the air, or keep emissions trapped in Delhi and worsen the pollution.

Delhi’s 12 “severe” or “near severe” air days so far in November — when the air quality index (AQI) is over 390 — is an example of the latter, with calm, predominantly northwesterly winds bringing smoke from farm fires in Punjab and Haryana to the Capital and trapping pollutants locally. However, on the flip side, the Capital has also seen the winds lend a helping hand. November 18 was the latest such instance, when a change in wind direction from northwesterly to easterly improved Delhi’s average AQI from 405 (severe) a day earlier to 319 (very poor).