At this time of year, I keep all windows closed except those with fly mesh netting on them - that seems to help a little.

I also have "air washing" machines running on each level of the house - that also seems to help keep the dust down a little. I think the German is Luftreiniger? Basically they suck the air in, put it through fabric filters, or plastic filters being washed constantly by water, and then push it out again. Not very expensive in the scheme of things (and the ones I have are a godsend for alleviating hayfever symptoms)

I always thought the pollen came from the millions of dandelion flowers blooming across our mountains, but the locals assure me that right now, the yellow dust is from the birch trees.

For sure I don't bother washing the cars or cleaning the windows or hanging washing outside at this time of year...