Ozone (O3) is a gas - a form of oxygen (O2) with an extra oxygen molecule attached. It is an unstable molecule (it changes to O2 quite easily), and reacts easily with other substances.
Oxygen (O2) becomes ozone (O3) by means of the ultraviolet rays of the sun, approximately 20 to 30km above the earth. Ozone can form lower down that that: in the lower layer of the atmosphere it is a pollutant that contributes to smog; from about 10 to 15km upwards it is protective against UV (the ozone layer).
Ozone also forms when there is a storm and lightning comes into contact with oxygen in the air. This is why the air smells so clean after a thunderstorm. Ozone also forms when waterfalls and waves (H2O) crash onto rocks.
Environmental ozone can be ‘good’ or ‘bad’, depending on where it occurs in the atmosphere, says Olivia Rose-Innes, Health24's EnviroHealth expert.
In the lower layer of the atmosphere, the troposphere, where we live and breathe, ozone is ‘bad’: it’s an air pollutant damaging to human health and the environment. Pollution from industries and motor vehicles lead to unhealthy levels of ozone.
In the higher layer of the atmosphere, the stratosphere, ozone is ‘good’: it protects us from excessive exposure to the sun’s rays. This protective layer has been damaged by the production of ozone-depleting gases, like CFCs, which end up in the stratosphere.
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