Stratospheric OZONE - O 3 Forms km above the earth’s surface. Blocks harmful % of UV radiation from reaching earth’s surface. Chemistry: Up to 98% of the sun's high-energy ultraviolet light(UV-B and UV- C) are absorbed by the destruction and formation of atmospheric ozone. The global exchange between ozone and oxygen is on the order of 300 million tons per day.

Our Global Sunscreen at Work Filters UVB radiation (biologically damaging) Absorbs/blocks UVC radiation Allows UVA through the atmosphere (longest wavelength – lowest energy) Reduction in stratospheric ozone results in biological damage & DNA mutation (cataracts & skin cancers) Measured in the units “Dobson” 1Db = 1ppb O 3 Seasonal – fluctuates with summer & winter intensities of the sun. Most dramatic fluctuations over the poles. “Artic Hole”

In the 1970s, scientists observed a thinning in the ozone layer over Antarctica, inaccurately, called an "ozone hole" and concerns arose that emissions from human activities were implicated in ozone depletion. The concern was that chlorofluorocarbons (CFCs), which had been widely used as refrigerants and in aerosols because they are inert and non-toxic, might be capable of depleting the ozone layer. Occurs during the artic spring – 50% reduction in ozone during that time Photochemical

Halogens are a chemical family containing fluorine, chlorine, bromine and iodine; any carbon compound containing them is known as a halocarbon. ~ one molecule of chlorine can degrade over 100,000 molecules of ozone before it is removed from the stratosphere or becomes part of an inactive compound. These inactive compounds, for example ClONO 2, are collectively called 'resevoirs'. They hold chlorine in an inactive form but can release an active chlorine when stuck by sunlight.