If we separated the ozone from the rest of the air and brought it all together at sea-level pressure and temperature it would form a layer just about 3 mm thick. But that’s not how ozone is found.
This is the ‘ozone layer’ – the diaphanous region of the stratosphere that filters out 99% of the harmful UV-B radiation in sunlight. Ozone is continually created and destroyed in the atmosphere as oxygen interacts with UV. It is a dynamic process, but man-made chemicals can break the cycle.