1)Ultraviolet 2)Absorbs ultraviolet radiation, so less ultraviolet reaches Earth. 3)It is not possible to reduce all risks (exposure to ultraviolet radiation is not the only cause of skin cancer); nor can we limit exposure to the sun to zero without suffering other health risks. 4)By studying the health records of thousands of people living in regions affected most by changes in the ozone layer. 5)Ozone is produced if high-energy ultraviolet radiation is absorbed; but ozone splits into oxygen if low-energy ultraviolet radiation is absorbed. 6)It is re-emitted as infrared radiation.