Delhi's air quality deteriorated to "severe" on Tuesday morning, prompting the Centre's air quality panel to impose the strictest Stage 4 curbs under the winter air pollution control plan. The AQI reached 427, with 28 out of 35 monitoring stations recording "severe" levels, some even breaching the 450 mark, classified as "severe plus." The restrictions include a ban on all construction activities, entry of polluting trucks into Delhi, and mandatory hybrid learning for school classes except X and XII.