Some of the cameras show either a lot of fog or a lot of smoke. Earlier it really didn't look like fog because of how quick it was moving and it was not spread out like fog would be.
Live Webcam 1 - Reagan National Airport - Washington D.C.
Live Webcam 2 - 4K - Reagan National Airport - Washington D.C.
Live Webcam 3 - 4K - Reagan National Airport - Washington D.C.
The Runway 1 Approach camera shows the smoke starting around 5-6 hours ago, much lighter and only localized in the left corner. At that time, its very clear that its smoke and not fog. And then as time goes by the smoke gets heavier