I taped a piece of a gelatin filter behind the pinhole in my Zero Image 2-1/4 sq camera once to try to separate the sky & clouds... every scratch, dust speck, fingerprint etc showed up... didn't try it again.

As far as dust particulates in the sky... I am not sure that any type of filter will help eliminate that. Polarizers can help reduce fog and atmospheric haze, but not smoke or dust... I seem to remember reading that somewhere some time ago.