Gas that filters out UV rays (5)

I believe the answer is:

ozone

(Other definitions for ozone that I've seen before include "Atmospheric gas shielding us from ultraviolet radiation" , "That precious layer" , "Bracing air of old, now seen as potentially toxic" , "Toxic form of oxygen" , "Sea air (found in layer?)" .)

I've seen this clue in The Wall Street Journal.

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