Measures fail but rain steps in: AQI improves from 437 to 279

After gasping under its longest spell of bad air days this year, the Capital's air quality improved and moved out of the deep red zone on Friday following unexpected showers and strong winds that swept the city and its adjoining regions overnight.

- Jasjeev Gandhiok

The 24-hour average air quality index (AQI) was recorded at 279 (poor) according to the Central Pollution Control Board's (CPCB) national bulletin at 4 pm - a tremendous dip of over 150 points from Thursday's 437 (severe). By 9pm, the AQI had improved further to 239, due to the meteorological factors that naturally flushed out pollutants.

Though Delhi's average AQI is calculated over 24 hours, its realtime particulate matter (PM) 2.5 concentration data showed the level at lam on Friday was 398 micrograms (ug) per cubic metre over six times the national standard of 60µg per cubic metre. The drizzle began in parts of Delhi between 11pm on Thursday and lam on Friday, but the rain clouds gathered significant momentum by 3am. CPCB data showed an immense dip in PM2.5 concentration in a span of three hours - at 3am it was 322µg per cubic metre, plunging to 194µg per cubic metre at 4am and a mere 88µg per cubic metre at 5am.