The U.S. EPA (Environmental Protection Agency) has used the phrase "good up high, bad nearby" to describe the difference between good ozone and bad ozone, or ozone in the upper and lower atmospheres. Good ozone is the ozone in the upper atmosphere, which is also called stratospheric ozone. Stratospheric ozone protects us by helping to filter out damaging ultraviolet radiation from the sun.
The ozone in the lower atmosphere, which is the air we breathe, is considered to be bad ozone. It can be harmful to the respiratory system. The interaction of sunlight with chemicals such as automobile emissions and emissions from industrial plants can produce harmful levels of ozone. Then, other pollutants such as nitrogen dioxide, fine particles, and hydrocarbons join the high levels of ozone in the atmosphere, contaminating our breathing air even more. The bottom line is, ozone can be detrimental to your health whether it's in pure form or mixed with other chemicals.