Ozone: useful high up, harmful near the ground

The stratospheric ozone layer absorbs much harmful ultraviolet radiation, helping protect living organisms. Ground-level ozone is an air pollutant that can irritate the respiratory system. Saying ozone is always beneficial or always harmful ignores its location.

Chlorofluorocarbons, CFCs, are chlorine-containing compounds that can persist long enough to reach the upper atmosphere. Ultraviolet radiation can release reactive chlorine species, which react with ozone and promote its destruction. Chlorine can be regenerated, allowing repeated ozone breakdown rather than only a one-for-one removal.

Ozone depletion allows more harmful ultraviolet radiation to reach the surface, increasing risks to living organisms. It is a different issue from greenhouse warming: ozone loss concerns UV protection, while greenhouse gases affect the escape of outgoing infrared radiation.

More ultraviolet radiation can damage cells and genetic material, increasing risks such as skin cancer and cataracts. It can also damage plants and plankton, affecting growth and food chains. CFCs persist for a long time, so reducing new releases does not instantly remove the compounds already in the atmosphere; ozone protection addresses a long-lived cause as well as its present effects.