The chemical compound ozone is composed of 3 oxygen atoms.  At the level of us humans, ozone is a dangerous pollutant to our health.  It negatively effects plants and buildings, as well as human health.  It is important to the atmosphere because it forms a protective shield that prevents certain wavelengths of sunlight from entering the earth's atmosphere.
 

These wavelengths are generally those wavelengths that are shorter, which generally pack more energy than wavelengths such as visible light or heat.  One example that is probably familiar to most of you is ultraviolet radiation.  This radiation is of great concern to humans because of the harmful effects on human beings.  These effects include melanoma (skin cancer), glaucoma, genetic damage, radiation burns.  The graphic below illustrates the correlation between the depletion of the ozone layer and skin cancer rates.

A 1% loss in the ozone layer results in an increase in ultraviolet radiation of 2%.