India, Dec. 17 -- The Centre's air quality panel for Delhi-NCR on Monday enforced GRAP 4 restrictions under the winter air pollution control plan, including a complete ban on construction activities, as the region's air quality worsened to the 'severe' category due to adverse weather conditions. The Stage 4 curbs were implemented just hours after GRAP Stage 3 measures were imposed in the capital.

Delhi's 24-hour average Air Quality Index (AQI), which stood at 379 by 4 pm, crossed 400 around 10 pm due to stagnant wind conditions and the formation of an inversion layer, which limits the vertical dispersion of pollutants.

GRAP Stage 4 was implemented in Delhi for the first time this season in November following persistently high pollution ...