Ozone

A rare form of oxygen, ozone is a poisonous, faintly blue gas that is produced by the action of electrical discharges (such as lightning) on oxygen molecules. Ozone occurs naturally in the upper atmosphere, where it screens the Earth from most of the Sun’s harmful ultraviolet radiation. The ozone layer is being depleted by atmospheric pollutants, allowing increasing amounts of ultraviolet radiation to reach the Earth’s surface. This problem could lead to a rise in the incidence of skin cancer and cataracts, as well as having other potentially hazardous effects.