According to Wednesday's official data by the Central Pollution Control Board (CPCB), Ambala in Haryana recorded the worst Air Quality Index (AQI) of 452 in the country and was under 'severe' category. While three out of 10 most polluted cities were in Haryana, seven were in UP. Fatehabad was another Haryana city under 'severe' category with AQI at 413.