The monthly average this December marks a sharp reversal after relatively lower pollution levels last year.

Flagging the crisis, 80 Padma awardee doctors from across India said it is a “direct and ongoing threat to human life”, particularly for children, pregnant women, the elderly and those with chronic heart and lung conditions.

The latest spike coincides with a sharp rise in stubble burning cases in Punjab, which reported 442 farm fires on Saturday -- the highest single-day count so far this season

“An increase in PM 2.5 levels has occurred because all existing perennial sources of pollution haven’t been controlled in a systematic and comprehensive way. The base emissions load is already high so in episodic events, we can see this kind of spike,” explained Sunil Dahiya, founder and lead air quality analyst at Envirocatalysts.

The month is on its way to becoming the warmest October experienced by Delhi at least since 2011, from when India Meteorological Department (IMD) data on average maximum and minimum temperatures are available.