Crossword Genius

Gas round the region (5)

Ross

I believe the answer is:

ozone

'gas' is the definition.
(I've seen this before)

'round the region' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'the region' becomes 'zone' (zone is a kind of region).
'o'+'zone'='OZONE'

(Other definitions for ozone that I've seen before include "It's said to brace" , "Bracing air of old, now seen as potentially toxic" , "A gas; threatened layer in air" , "Stratospheric layer of gas -- invigorating sea air" , "Gas in upper atmosphere" .)

I've seen this clue in The Mirror.
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