Vista spoiler (4)
I believe the answer is:
smog
'vista spoiler' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for smog that I've seen before include "Pollution haze/fog" , "Polluted atmosphere" , "Pollutant haze" , "Industrially polluted air" , "Pollutant fog" .)