Atmospheric mist (4)
I believe the answer is:
haze
'atmospheric mist' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for haze that I've seen before include "Vapour" , "Lack of definition or precision" , "Daze, fog" , "Mist or shimmer due to heat" , "Film" .)