Poison air cocktail: Ozone gives way to PM2.5, PMI10 post Diwali

As Delhi grapples with its annual pollution crisis, a subtle but significant shift has occurred in the cocktail of pollutants that cloud its skies. For the first19 days of October, Delhi's air has been dominated by photo-chemical pollutants such as ozone (O,) and carbon monoxide (CO) before dramatically shifting to particulate matter (PM2.5 and PMIO) since Diwali.

- Jasjeev Gandhiok

Experts said the shift reflects a sharp rise in combustion-driven emissions — largely from firecrackers — compounded by ongoing contributions from vehicles, industries, and other sources.

Between October land 19, data from Central Pollution Control Board’s (CPCB) Sameer app showed that ground-level ozone was the primary pollutant on 12 of the 19 days, with CO and NO2 also contributing significantly to the overall air quality index (AQN.

Ozone, a secondary pollutant, is not directly emitted but formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) from vehicles, factories, and power plants react in bright sunlight. CO, meanwhile, is a direct byproduct of incomplete combustion from similar sources.