Bracing air a person found round most of animal park (5)
I believe the answer is:
ozone
'bracing air' is the definition.
(I've seen this before)
'a person found round most of animal park' is the wordplay.
'a person' becomes 'one' (an individual).
'found round' means one lot of letters goes inside another.
'most of' means to remove the last letter.
'animal park' becomes 'zoo' (I've seen this before).
'zoo' with its final letter removed is 'zo'.
'one' placed around 'zo' is 'OZONE'.
(Other definitions for ozone that I've seen before include "(Depleted) layer of gas" , "invigorating British air" , "Gas formed from oxygen" , "Stratospheric layer of gas -- invigorating sea air" , "Clean, bracing air" .)