What is the difference between stratospheric and tropospheric ozone?
Ozone in the troposphere (the layer of atmosphere in which we live) is a toxic compound dangerous for breath. Its concentration doesn't should be over few ppb (part per billion) also if few quantities are producted for sterilization of air and water. It is a secondary pollutant, because produced from others pollutants like NOx.
On the other hand, ozone is very useful in stratosphere because it stops the UV rays, coming from the sun. It is produced from the sun rays themselves but it can be destroyed from chemical substances as chlorofluorocarbons used for refrigerators and other ones used as propellent for spay cans