Ozone is also toxic to plants at levels of 0.01 to 0.05 parts per million with an exposure time of several hours. Ozone can also cause breathing disorders such as bronchitis. Parts per million is a way of measuring the concentration of a gas. An ozone concentration of 0.01 parts per million means that for every 100 million particles there will be 1 ozone molecule. This is not very much ozone and it is still harmful to plants.
Ozone does exist in the atmosphere.
Everyone has heard discussions of the problems with the ozone layer. The ozone layer in the atmosphere exists at a very large distance from the earth. We do not breathe this ozone. The atmospheric ozone shields us from some of the Sun's radiation. Ozone is also generated when an electrical spark passes an atmosphere containing oxygen.