Ozone Structure, O3: ozone gas consists of three oxygen atoms covalently joined. Ozone is an allotrope of oxygen. It absorbs ultraviolet light and so protects us from the intense UV from the sun (the ozone layer). Oxygen molecules (O2) are hit by a high energy photons which split them into two oxygen atoms (photo-dissociation of oxygen). Individual oxygen atoms can then combine with oxygen molecules (O2) to create ozone (O3). The ozone molecules absorb ultraviolet (UV) radiation and in so doing split into an oxygen molecule and an oxygen atom (which can then recombine to create more ozone). Depletion of the ozone layer creating a so called ozone hole is a worry because the UV that reaches the surface can damage DNA and cause skin cancer. Ozone is also a greenhouse gas.