Delhi's air quality fell into the 'very poor' category on Monday, the morning after Diwali, according to the Central Pollution Control Board. Its daily bulletin put the capital's average air quality index above 300. Several monitoring stations, including Anand Vihar and Wazirpur, recorded 'severe' readings above 400.

The festival fell on Sunday, November 8, and residents in many neighbourhoods reported fireworks well into the night despite official curbs on firecracker use. Data from the CPCB's continuous monitoring network showed concentrations of fine PM2.5 particles climbing sharply after 10pm. The haze persisted into the morning rush hour, cutting visibility around the Ring Road and near Indira Gandhi International Airport, according to the India Meteorological Department.

The Decision Support System run by the Indian Institute of Tropical Meteorology in Pune estimated that farm fires in Punjab and Haryana contributed a significant share of the capital's pollution load. Forecasters at the IMD said calm winds and falling night-time temperatures had trapped pollutants close to the ground. The ministry of earth sciences' early warning system forecast that air quality would stay 'very poor' for at least the next two days.

The Commission for Air Quality Management said its sub-committee on the Graded Response Action Plan had already invoked Stage III across the region on November 6 as a precautionary measure, keeping restrictions on construction and vehicles in force, and would keep conditions under review; only Stage IV remained as a further step if readings deteriorated. Doctors at the All India Institute of Medical Sciences advised children, older people and those with asthma or heart conditions to limit time outdoors. Schools across the National Capital Region reported a drop in attendance for morning sessions.

The post-Diwali spike has become an annual fixture in north India's winter pollution season. Readings the day after the festival have landed in the 'very poor' band in most recent years, according to CPCB records. Environmental groups, including the Centre for Science and Environment, have argued that festival smoke worsens an emergency driven chiefly by vehicles, industry and crop burning.