Damaged layer: Australia has one (5)
I believe the answer is:
ozone
'damaged layer' is the definition.
(the Earth's ozone layer)
'australia has one' is the wordplay.
'australia' becomes 'oz' (informal name for Australia).
'has' says to put letters next to each other.
'oz'+'one'='OZONE'
(Other definitions for ozone that I've seen before include "Trioxygen" , "Bracing seaside air" , "Colourless gas, O3" , "Form of oxygen in earth's upper atmosphere - there's a hole in it" , "bracing atmosphere" .)