Urban haze (4)
I believe the answer is:
smog
'urban haze' 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 "Smoky haze" , "Smokey fog" , "Dirty mixture of smoke and fog" , "Thick polluted mist" , "Fog and smoke mix" .)