Delhi's air quality rapidly deteriorated to the severe category on Sunday, but the Commission for Air Quality Management (CAQM) chose not to invoke curbs under stage-III of the Graded Response Action Plan in view of a prediction of "immediate improvement".
The action plan is a set of anti-air pollution measures followed in the national capital and its vicinity according to the severity of the situation.
Delhi's 24-hour average air quality index (AQI) stood at 407 on Sunday, worsening from 294 on Saturday, amid calm winds.
The stable atmospheric conditions allowed accumulation of pollutants from highly localised sources, such as a fire in central Delhi on Saturday, an official of the India Meteorological Department (IMD) said.