Several gates at Dulles International Airport were closed Thursday morning to ventilate hazy smoke, according an airport spokesman.

The smoke closed gates A1 through A6 around 9 a.m. and airport officials moved passengers and some United Express flights to other gates, said Robert Yingling, a spokesman for the Metropolitan Washington Airports Authority. The gates reopened by 10 a.m.

Yingling said a rooftop heating, ventilation and air conditioning unit was the source of the smoke. Officials turned off the unit so it could be examined by airport maintenance, he said.

Fans were positioned throughout the terminal to move the smoke out of the building, Yingling said.

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