Ground-level ozone

Ground-level ozone, also called surface-level or tropospheric ozone, is a trace gas found in the troposphere, the lowest layer of Earth's atmosphere, typically present at 20 to 30 parts per billion by volume and close to 100 parts per billion in polluted areas. It is distinct from the ozone layer higher up in the stratosphere, and within the troposphere itself it is least concentrated near the ground, in the planetary boundary layer.