NEW DELHI — For days, many in Delhi have been living as if under siege, trying to keep the dirty air away from their children and older parents.

But it is not easy: Open a window or a door, and the haze enters the room within seconds. Outside, the sky is white, the sun a white circle so pale that you can barely make it out. The smog is acrid, eye-stinging and throat-burning, and so thick that it is being blamed for a 70-vehicle pileup north of the city.

If in past years Delhi’s roughly 20 million residents shrugged off wintertime pollution as fog, over the past week they viewed it as a crisis. Schools have been ordered closed for three days — an unprecedented measure, but not a reassuring one because experts say the concentration of pollutants inside Indian homes is typically not much lower than outside.