The national capital is battling with severe air pollution, with AQI crossing the 450 mark, reaching the 'severe plus' category, prompting CAQM to impose stage IV restrictions of the Graded Response Action Plan (GRAP). The severe air pollution levels and dense smog, prompted Delhi airport, IndiGo and Air India to issue travel advisories, as flight operations are disrupted, with over 400 flights delayed and 61 cancelled at Indira Gandhi International Airport, according to reports.