ozone
n. uncountablen. a form of oxygen that protects the Earth from the sun's harmful rays. It is also a type of air pollution when it is found close to the ground.
n. an allotrope of oxygen consisting of three atoms per molecule. It exists as a protective layer in the stratosphere but acts as a respiratory irritant and pollutant in the lower atmosphere.
The ozone layer protects us from the sun.
Scientists monitored the hole in the ozone layer to see if the new environmental laws were working.
While stratospheric ozone is essential for filtering ultraviolet radiation, ground-level ozone is a primary component of urban smog and can cause significant respiratory distress in vulnerable populations.
From German Ozon, coined 1840 by Christian Friedrich Schönbein, from Ancient Greek ὄζον (ózon), neuter participle of ὄζω (ózō, “I smell”), in reference to its pungent odour. The “fresh air” sense is from an erroneous former belief that seaweed contains and releases ozone.
Typically used without an article when referring to the gas itself, but takes 'the' when referring to 'the ozone layer'.