Ninety percent of the ozone in the atmosphere sits in the stratosphere, the layer of atmosphere between about 10 and 50 kilometers altitude. Ozone in the stratosphere is created when the kind of oxygen we breathe - O2 - is split apart by sunlight into single oxygen atoms. Single oxygen atoms can re-join to make O2, or they can join with O2 molecules to make ozone (O3)
Ozone is found in two places in the Earth's atmosphere. Ozone in the Earth's upper atmosphere (stratosphere) protects life from harmful ultraviolet (UV) rays from the sun. High concentrations of ozone found in the Earth's lower atmosphere (troposphere) are hazardous to life.
Ozone in the lower atmosphere (troposphere) is created through a series of reactions involving man-made chemical species such as Nitrogen oxides (NOx) and volatile organic compounds (VOCs). Chemical species that contribute to ground level ozone.
In high concentrations, ground level ozone is toxic to human tissue. When ozone levels get too high, the EPA issues "Code Red" days, on which humans should limit their time outdoors.
You can help reduce the amount of ozone in the troposphere by taking some simple steps:
You can monitor ozone by planting ozone-sensitive species in your own garden.
+ Getting Involved in ozone monitoring