A thick blanket of smog engulfed Delhi on Monday with the pollution level falling to the “severe” category. The air quality deteriorated a day after having shown marginal improvement.

The overall Air Quality Index of the city was registered at 345, which falls in the “very poor” category, according to data from the Central Pollution Control Board. The AQI on Sunday was recorded at a “moderate” 171, the lowest in three weeks. The System of Air Quality Forecasting and Research had predicted a deterioration in air quality from Monday.

Authorities said an increase in stubble burning in the neighbouring states contributed to the decline in air quality.

Residential buildings are seen shrouded in smog in Noida on Monday. (Photo credit: Reuters)
People walk along a busy road as smog covers the city on Monday. (Photo credit: Dominique Faget/AFP)
A worker of the Municipal Corporation of Delhi sprays water onto roadside trees in a bid to curb air pollution. (Photo credit: Money Sharma/AFP)
Schoolchildren hold placards as they stage a demonstration against the use of fireworks and crackers to avoid air pollution during Diwali celebrations, in Amritsar on Monday. (Photo credit: Narinder Nanu/AFP)

On Monday, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level was recorded at 268 while the PM10 (particles in the air with a diameter of less than 10 micrometres) was recorded at 391. Delhi authorities have intensified efforts to combat pollution, including measures like halting construction activities and regulating vehicular traffic.