Dust!
The particles are by themselves small insignificant things, but in quantity they can be a pain in the rear.
With the onset of sunny days I tend to open the window of the computer room and the result is that the screens all get covered in dust. I am getting through screen wipes at a rapid rate of knots.
I mean I leave the room with nice shiny screens and when I return they all have varying degrees of a matt finish on them.
Roll on autumn.