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Ozone Methodology: Future Predictions

Over the past century, industrial activity and automobile emissions have increased the atmospheric concentrations of O₃ precursors. As a result, typical ambient O₃ concentrations have increased from 0.02-0.04 to 0.04-0.06 ppm—a trend that is expected to continue into the 21^st century (National Academy of Science 1992). Assuming a 1- to 2-percent annual increase in tropospheric O₃, as estimated by Fishman (1991), the United States would achieve a 50-percent increase in ambient O₃ in 21 (base 1990) years and a doubling of O₃ concentrations in 35 years. The National Academy of Science (1992) estimated an increase of 40 percent by the year 2020. Thompson (1992) used several computer models to predict that O₃ concentrations will rise by 0.5 percent per year for the next 50 years, whereas Chameides and others (1994) suggested that the frequency of O₃ events with concentrations high enough to damage plants will triple over the next 30 years. However, more recent ozone modeling efforts by SAMI predicted a 10- to 15-percent reduction in maximum daily ozone levels between 1995 and 2010 for the Southern Appalachians based on current emissions controls (Southern Appalachian Mountains Initiative 2001).