Gas round region (5)

I believe the answer is:

ozone

'gas' is the definition.
(I know that ozone is a type of gas)

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

(Other definitions for ozone that I've seen before include "Colourless gas, O3" , "Invigorating air of the seaside" , "Fresh, bracing sea air" , "Gas forming screen against ultraviolet radiation in the stratosphere" , "Seaside air, maybe" .)

I've seen this clue in The Sun, The Mirror and The Telegraph.

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