Australia has a certain invigorating air (5)
I believe the answer is:
ozone
'invigorating air' is the definition.
(I've seen this before)
'australia has a certain' is the wordplay.
'australia' becomes 'oz' (informal name for Australia).
'has' is a charade indicator (letters next to each other).
'a certain' becomes 'one' (ie one particular example of something).
'oz'+'one'='OZONE'
(Other definitions for ozone that I've seen before include "Form of oxygen, O3" , "That precious layer" , "Gas in upper atmosphere" , "Shield against radiation" , "Seaside air, maybe" .)