NEW DELHI: Delhi’s air pollution levels deteriorated sharply ahead of Diwali, with the city recording its worst pre-Diwali pollution spike since 2019, according. The national capital was also the only megacity among five assessed to record a monthly average PM2.5 concentration exceeding the daily National Ambient Air Quality Standards (NAAQS) in October.CREA’s pre-Diwali air quality analysis found that PM2.