Sometimes the action is fast and effective (e. g. cfcs) Sometimes the action is not so effective and slow (e. g. global warming) Note when 03 formed in the atmosphere (about 2. 5 million years ago: slightly after atmosphere was oxygenated. Note how 03 forms in the atmosphere: cyanobacteria took in co2 and produced oxygen, sunlight hit the oxygen and broke it up into oxygen radicals, they combine to form ozone. Tropshpere ozone is a pollute: big component of smog. Absorption of uv: warm air over cold air caps troposphere. Chlorine and nitric oxide combining with ozone to form oxygen. Chlorine and nitric oxide work as a catalyst for ozone breakdown. Sunlight breaks apart cfc and freeze the chlorine radical that catalyzes ozone breakdown. Thinning was not evident in arctic until recently. Less ice crystals in the atmosphere where chlorine rest on to do their work. l yl : cfcs trapped in the cold air during the whole period.