Once particles reach the jet stream, my understanding is that they're likely to stay up there a VERY long time. It's this dust that's supposed to cause the nuclear winter and we all know how long some estimates say that'll last.....
The biggest, or at least more immediate threat from fallout will probably be in the first few weeks. After that time, most of the airborne particles are likely to be coating the ground and just about every other surface only causing significant immediate problems if it's stirred up (which normal winds are certain to do, not to mention people walking through it).
Fallout (ie particles falling from the sky) is likely to remain a danger for as long as there's dust in the upper atmosphere. Without rain to flush it clear (it's WELL above cloud level), this could be generations. Fortunately the amount of dust isn't going to be anything like directly after the initial bursts.
|