Here’s a sequence of photographs from an apartment across the water showing the collapses of both the Twin Towers. Note, as I keep saying, that the major dust cloud starts welling up from lower levels as the collapse reaches ground. Comparatively, hardly any dust is left higher up in the space just vacated by the collapsing tower. There is much grey material during collapse, but it must be larger debris because it falls, leaving the air relatively clear. This effect is most clearly seen for the first collapse; wtc-44.jpg and wtc-45.jpg show it very clearly; just a wisp of smoke left above building height where the top two thirds of WTC2 was, and lower, among the buildings still standing, an enormous billowing, spreading cloud of dust:
http://www.amanzafar.com/WTC/index.html
The Twin Towers were NOT “blasted into dust in mid air”. Their remnants crushed themselves into dust as they hit the ground, just as would be expected.