Destruction of atmosphere reversed (4)
I believe the answer is:
doom
'destruction' is the definition.
(I've seen this in another clue)
'atmosphere reversed' is the wordplay.
'atmosphere' becomes 'mood' (I've seen this in another clue).
'reversed' says the letters should be written backwards.
'mood' written backwards gives 'DOOM'.
'of' is the link.
(Other definitions for doom that I've seen before include "Inevitable ruin" , "Day of reckoning" , "Death, destruction" , "Bad destiny" , "Catastrophe" .)