Now it's ground-level ozone

Hundreds of deaths from ozone predicted - Telegraph

Hundreds more people could die because of increasing levels of ozone at street level, according to scientists.

A study by the Royal Society found ground levels of ozone, the pollutant caused when sunlight hits a mixture of gases in the air, has risen by six per cent per decade since the 1980s.

Although the ozone layer protects the planet at a higher level, at ground level it is damaging to human health.

More on ozone:

Ozone (O3) or enriched oxygen is a powerful oxidizing gas that has been in use since the early 1800's. Ozone is sometimes referred to as "triatomic oxygen" since it contains three atoms of oxygen rather than two.

Ozone occurs quite readily in nature, most often as a result of lightning strikes that occur during thunderstorms. That "fresh, clean, spring-like rain" smell that we notice after a storm most often results from nature's creation of ozone.
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Ozone is a toxic gas. However, it can be used safely when deployed by specialized generators under proper considerations.
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One of the most positive features about ozone is that is performs work and then reverts back to normal oxygen within 15 to 30 minutes.