Where air's kept awfully volatile after temperature drops (7)
I believe the answer is:
alveoli
'where air's kept' is the definition.
(air sacs in the lungs)
I don't understand the rest of the clue.
(Other definitions for alveoli that I've seen before include "providing lung processes" , "Bit of lung" , "Parts of lungs" , "Sockets for tooth roots" .)