means A pale-blue, sharp-smelling gas made of three oxygen atoms (O₃), which protects life as a high-altitude layer but acts as a harmful pollutant down at ground level.

from From German Ozon, coined in the mid-19th century by the chemist Christian Friedrich Schönbein, who took it from the Greek ozein, 'to smell' — because he first noticed the gas by its distinctive sharp odor, the same electric tang you catch after a thunderstorm or near sparking machinery.