Photochemical reactions in the stratosphere lead to the build up of ozone molecules.
This accumulation of ozone is known as the Ozone Layer.
The ozone layer occurs between about 20 and 40 km above sea level.
The maximum concentration of ozone in this layer is only about 10 ppmv (parts per million by volume).
If the entire Ozone Layer was brought down to sea level where the pressure is 1 atmosphere and the temperature is 273 K, the resulting layer would only be about 3 mm thick.