Atmospheric Pressure — Definition & Overview

The ozone layer is a region of the Earth's atmosphere with a high concentration of ozone that blocks most of the sun's harmful UV radiation. The ozone concentration is greatest at altitudes of between $20$km and $40$km above the surface of the Earth, where concentrations are between $2$ and $8$ parts per million. If all of the ozone layer were compressed to atmospheric pressure at sea level, approximately how thick would it be?