Australian figure in fresh air (5)
I believe the answer is:
ozone
'fresh air' is the definition.
(ozone can informally mean fresh air)
'australian figure' is the wordplay.
'australian' becomes 'Oz' (nickname for Australia).
'figure' becomes 'one' (a numerical figure).
'oz'+'one'='OZONE'
'in' acts as a link.
(Other definitions for ozone that I've seen before include "A poisonous gas; seaside air" , "That precious layer" , "invigorating British air" , "Atmospheric gas shielding us from ultraviolet radiation" , "Gas forming protective layer" .)