New Delhi: A thick layer of smog enveloped the national capital on Tuesday morning, with air quality deteriorating to the ‘very poor’ category just days ahead of Diwali. Jahangirpuri recorded the highest Air Quality Index (AQI) at 451, placing it in the ‘severe’ category. Delhi's average AQI stood at 330 at 8 a.m., according to data from the Central Pollution Control Board (CPCB).