Here’s some uncalibrated lidar measurements from the night of 21 June, 2013 which show what appears to be a faint smoke layer around 13 km. I did a quick and dirty run of HYSPLIT and the trajectories go back to Colorado in about 2 days. They descend about 25% of their initial height, e.g. as they go across the prairies they drop, for instance, from 10,000 m to 7,500 m elevation.
Uncalibrated returns from The University of Western Ontario’s Purple Crow Lidar, shows an apparent thin smoke layer around 13 km altitude. Full size image available here.
