Ozone (O3).. Yesterday's Dream, Today's Reality, Tomorrow's Future Is ozone (O3) Safe? The town of Payson, Arizona claims some of the purest air in the world. Why? Because Payson is in the center of the largest concentration of ponderosa pines on earth, which help create a higher than usual level of ozone. Ozone is nature's way of cleaning the air. It is nature's best tool for cleaning the environment. The earth's ozone layer protects us from the suns harmful ultraviolet rays. But also helps reduce pollution, while actively working at creating a healthier working and living environment. Ozone is measured in "parts per million" (ppm). Normal ozone levels on the earth's surface range from .017 ppm to .034 ppm. Like most things, an over abundance of ozone can be harmful. In some heavy smog areas, ozone levels can approach .2 ppm to .65 ppm. Away from areas of industrial pollution, we are generally exposed to healthy levels of.04 ppm. Unfortunately, indoor air lacks ozone concentrations that exist in normal outdoor environments. Therefore, indoor ozone levels must be supplemented to achieve the desirable benefits of ozone. Maximum levels of indoor ozone have been set, however, by a variety of government organizations to ensure safety. The CSA recommends maximum limits for household use at .04ppm. The FCA and ASHRAE recommend maximum concentrations of .05 ppm. The level of ozone needed to clean air in a typical home or business is approximately 20% of those allowable levels and less than you would find outdoors in a typical non-industrial, rural setting.