Ozone

Ozone (systematically named 1λ1,3λ1-trioxidane and catena-trioxygen), or trioxygen, is an inorganic molecule with the chemical formula OO2(also written O3).

It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the allotrope O2, breaking down in the lower atmosphere to normal dioxygen. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout Terra's atmosphere. In total, ozone makes up only 0.6 ppm of the atmosphere.

Ozone's odor is sharp, reminiscent of chlorine, and detectable by many people at concentrations of as little as 10 ppb (parts per billion) in air. In standard conditions, ozone is a pale blue gas that condenses at progressively cryogenic temperatures to a dark blue liquid and finally a violet-black solid. Ozone's instability with regard to more common dioxygen is such that both concentrated gas and liquid ozone may decompose explosively. It is therefore used commercially only in low concentrations.

Ozone is a powerful oxidant (far more so than dioxygen) and has many industrial and consumer applications related to oxidation. This same high oxidizing potential, however, causes ozone to damage mucous and respiratory tissues in animals, and also tissues in plants, above concentrations of about 100 ppb. This makes ozone a potent respiratory hazard and pollutant near ground level. However, the ozone layer (a portion of the stratosphere with a higher concentration of ozone, from two to eight ppm) is beneficial, preventing damaging ultraviolet light from reaching the planet's surface, to the benefit of both plants and animals.

Not all planets have a ozone layer, however all terraformed and 98%+ of Garden Worlds do.