Those of us who happened to be in the Northeast on 9/11 clearly remember that it was a crystal clear day with a bit of a nip in the air.
One might think that a pilot flying at 10,000 feet in the region could have seen clearly for 100 miles or more.
I don't want to write about 9/11 - not ready yet. But yes, it was a clear, crisp day. Until the smoke started. Then it got foggy.