Ozone, normally referred to in the context of the so-called ozone layer - a layer of concentrated ozone molecules in the stratosphere between 2ppm and 8ppm - that helps shield Earth's plant and animal life from harmful ultraviolet rays from the sun.
The ozone layer has been depleted in certain areas over time by anthropogenic sources, and has led to the banning of many substances, as well as, the signing of international laws restricting those substances among other things.
In 1987, the Montreal Protocol was signed to legislate a phase out of a group of halogenated hydrocarbons that contribute to stratospheric ozone depletion "in a manner that is likely to result in adverse effects on human health and the environment."
By controlling the production and consumption of certain chemicals, mainly chlorofluorocarbons (CFCs) that were once used widely as refrigerants and aerosols, the atmospheric levels of these have begun to decrease.
The protocol is widely seen as the most successful scientific and international environmental endeavor. The most ratified document of all time as far as the number of nation states to sign onto it. Also, it has had a direct benefit to the ozone depletion that threatens to harm humans and the environment.
(CC Image of ozone hole (October, 2013) by NASA/Ozone Hole Watch [Public domain], via Wikimedia Commons)