I don't think there is any out-of-the box solution that works. I think it would be possible to write a particle system that spawns dust particles within a bounding box defined by contrtol points, and then set the control points to the bounds of a mesh using a VScript. The particle editor is not well documented, so it would take a lot of experimenting finding the right settings.

Do you know how they did the snow in the winter peak destination.
That is somewhat what im looking for.
Most particle systems i work with (AE,Max, Blender,..) have point, plane, sphere and box emitters. Maybe this is possible in the hammer particle editor as well ?

It does have a box emitter, so if you want to input the local space box extents in the particle editor directly, it is possible to do.

I'll have to give that a go.
The PE is nothing i'm used to in terms of particle systems, and i'm used to some quite nice ones. Let's see...

Pitty this one doesn't work https://developer.valvesoftware.com/wiki/Func_dustmotes

Created a particle system from scratch and i think it worked out exactly as i intenden.
Still a bit weird to work with but it does work !
Quite happy with the result in the cellar of my cabin map.
Feel free to let me know what you think.