Comment by CamelCaseCondo

Wind is not a homogeneous movement, there are highways and slow lanes. Spores (as from fungi), pollen (from wind pollinators such as grasses) and dust-like seeds (e.g. from orchids) are ideal nucleation points for condensation. So when wind is forced up (because of changes in the terrain) these are the particles that get filtered out: either physically as precipitation or functionally by freezing.

For those interested, there have been a number of studies that put numbers on the action radius. When genetic manipulation of wind pollinators (e.g. wheat, corn and others grasses) came in vogue they needed to put a number on the dispersal of modified pollen.