How to protect my LEGO city from the dust?
Where I'm from it's called Plexiglas. Other tradenames are Crylux, Acrylite, Lucite or Perspex...
Anyway, you can get sheets of it cut to size in D.I.Y-shops or hardware stores to build your own domes.
If you are less handy, you can find lots of shops offering standard or custom solutions.
If I google "plexiglas", I find dozens of solutions near where I live.
I know of one person who had a custom pyramid shaped Plexiglas dome made for the 10181 set (Eiffel tower)