New Delhi, the Indian capital declared a pollution emergency on Thursday as toxic smog hung over the city for a third day and air quality worsened by the hour. From a report: Illegal crop burning in the farm states surrounding New Delhi, vehicle exhaust emissions in a city with limited public transport and swirling construction dust have caused the crisis, which arises every year. The problem has been compounded this year by still conditions, the weather office said. A U.S. embassy measure of tiny particulate matter PM 2.5 showed a reading of 608 at 10 a.m. when the safe limit is 25. An hour before it was 591.