Did a search on the distance between the two buildings, and it said 2.83 miles. Not sure if that’s within the range of soot being carried on the air. Perhaps the soot being spread as the result of the plane’s impact, and resulting fires, could make it feasible.
I’ll accept 2.83 miles between the buildings, as the crow or soot flies. By road it’s 4+ miles, with a river in between. And some highways and bridges. And a few parks. And several office buildings. Remember, too, it was a very calm day, blue sunny skies, no high winds.
I pass by both buildings several times a week, and have for nearly 50 years. I really cannot see how soot would travel that distance with all that comes between. Traverse it by Google and see what all is in between.
Now, if the story referred to plain old soot from the air around the Capitol, that’d be a different and more credible story. But a one-day accumulation of soot, even at the Capitol, wouldn’t warrant the drama/hysteria the article emits.