The ozone blocks out the harmful UV b rays that cause skin cancer. The production of ozone is dependent on the amount of the suns energy. This helps explain the shortage of ozone over the poles in the winter months when there is a lack of sunshine. Ozone, being heavier than air, is carried in down drafts into the lower atmosphere. As the ozone falls it oxidizes any pollutant or contaminate with which it comes into contact, turning it into a safer compound.
Chlorine is the main compound which reduces the ozone layer in the upper atmosphere.
If ozone comes into contact with water vapor during storms it forms hydrogen peroxide. This is why plants flourish better with rainwater than with irrigation water. This is natures way of cleaning the environment. Natural ozone concentrations can vary between .01 ppm to .05 ppm, depending on geographic location, altitude and season. The cycle of oxygen and ozone is just like the cycle of water in nature.