My brother-in-law lives in the neighborhood, 5 blocks from the WTC. His apartment has a rooftop patio that was covered in dust and debris. The largest particles were the size of large pebbles but mostly it was a fine dust over everything.   I remember going to visit him two months after the tragedy and you could still smell something in the air.   

In the days after 9/11 you could smell a burning rubber type smell from the fires where I live in NJ - about 15 miles from the WTC. There was more in the air than they are telling us, and we are slowing finding that out.

As to how the floors pulverised, I am not sure if the theory is correct, nor am I sure that explosives would have provided the same result. It seems like explosions would have thrown pieces in all directions rather than downward as it seems to have done. Who knows.

This was an unsual building and unusual circumstances. No building was larger, no building suffered that kind of stress, and the construction was unique. There were also no concrete walls as in other skyscrapers, just relatively thin concrete floors, glass and steel.