Pollen particles range in size from 10-200 microns. The size of the pollen particle depends on the flower or plant. If you can see the pollen floating in the air, this means the particle is quite big, at least 60 microns in size.
Despite some pollen particles being as small as 10 microns, pollen can easily be removed from the air with HEPA filters.
And when outside, masks are highly effective at filtering pollen.