Worldwide CFC and halon production peaked in 1974 at nearly a million tons per year, declined slightly during the later 1970s, then by the late 1980s had again increased to near the million ton mark. Beginning in 1987, scores of nations, including the United States, entered into international agreements to reduce the production of ozone-depleting chemicals. Near the earth's surface, small amounts of ozone are continuously created and destroyed in ongoing natural cycles. The balance of ozone creation and destruction shifts drastically, however, when hydrocarbons are added to the atmospheric mix. Summer heat and the increase in sunlight intensity speed the rate of these chemical reactions, triggering rapid formation of ozone.
Ozone can have an adverse effect on the human body.
High ozone concentrations irritate nasal, throat and bronchial tissues. Ozone attacks certain components of the body's defense system, raising concerns about the effects of ozone exposure on the human immune system. High concentrations of ozone can also harm forests, thereby altering wildlife habitats, lowering crop yields, and damaging materials such as rubber, plastics, synthetic fibers, dyes and paints. This occurs because hydrocarbons, nitrogen oxides and ozone itself are carried by the wind many hundreds of miles from their city origins, polluting rural areas. In large urban areas, ozone mixes with other pollutants to create the air pollution condition known as smog.