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Southeastern Geographer Vol. XXXI, No. 2, November 1991, pp. 90-102 IDENTIFYING SURFACE OZONE TRENDS: A CASE STUDY OF CHARLOTTE, NORTH CAROLINA* Walter Martin The Clean Air Act (CAA) amendment of 1970 charged the federal government with the responsibility of developing uniform National Ambient Air Quality Standards (NAAQS) to protect health and public welfare . A year later the U.S. Environmental Protection Agency (EPA) promulgated air quality standards for six classes of air pollutants: carbon monoxide, nitrogen dioxide, sulfur dioxide, particulates, hydrocarbons, and ozone. Although considerable progress has since been achieved, air quality in many areas remains stubbornly worse than the NAAQS. One of the most intractable air pollution problems has been widespread "nonattainment" ofthe ozone standard. The current standard permits no more than one day per year (on average) with a maximum one-hour ozone concentration of 120 parts per billion (ppb). Because the original 1977 target for attainment of the ozone standard was not achieved, the deadline was postponed first to 1982 and then to 1988. In 1988 more than 120 million Americans were living in areas that failed to meet the ozone standard, and it appears that attainment will continue to be elusive through the 1990s and beyond. The CAA amendments of 1990 extend deadlines for meeting NAAQS but call for stricter tailpipe emissions standards and more stringent pollution controls on point sources. Charlotte , like many metropolitan areas throughout the Southeast, is not compliant with the NAAQS for ozone and faces more stringent and costly state and local air quality programs to abide by the 1990 amendments. Although the framework for ambient pollution control is established by Congress, pollution control policy and implementation are continuously evolving to reflect legal decisions, new problems, new data, and reappraisal of recent control tactics. Assessment of local air quality trends can be useful for state and local agencies that must evaluate the performance of existing controls and * This work was supported in part by funds from the Foundation of the University of North Carolina at Charlotte and from the State of North Carolina. Dr. Martin is Assistant Professor of Geography and Earth Sciences at the University ofNorth Carolina at Charlotte in Charlotte, NC 28223. Vol. XXXI, No. 2 91 recommend implementation strategies. Trends in ozone concentrations have been notably difficult to discern because ozone formation depends strongly on meteorologie factors, especially temperature, and consequently are often obscured by the influence of annual or seasonal climatic variability. During the warm summers of the past decade it has been difficult to distinguish high ozone levels which result from inadequate emission controls from those which result from weather episodes favorable to ozone formation. The primary objective of this study is to identify a series of mean annual ozone concentrations that are adjusted to control for meteorological influences. A secondary objective is to measure the influence of meteorological factors associated with high ozone concentrations. By excluding the meteorological component, a temporal trend of ozone levels emerges that serves as a useful yardstick by which local control efforts can be gauged. As the CAA amendments of 1990 are promulgated and state and local agencies collaborate to amend state implementation plans (SIPs), the adjusted trend can provide insight on how well local ozone has been controlled and how much remains to be done. Ozone pollution is a byproduct of photochemical reactions between nitrogen oxides, hydrocarbons, and ultraviolet light. Although ozone occurs naturally, increases in the amount of nitrogen oxides and volatile hydrocarbons result in increased ozone generation. (I) Sources of reactive hydrocarbons include unburned gasoline in automobile emissions and evaporative emissions from fuel storage tanks, dry cleaners, printing plants, furniture finishing, automobile body shops, and in the Southeast even trees. (2) The major anthropogenic source of nitrogen oxides is exhaust from high temperature combustion. The availability of solar ultraviolet radiation and precursory nitrogen oxides and hydrocarbons limit the rate of ozone formation in the atmospheric boundary layer. Data for Mecklenburg County between 1981 and 1989 were analyzed . Principal components and stepwise multiple linear regression analysis were used to reduce the number of independent meteorological variables to a small coherent variable set associated with changes in ozone levels. (3) Analysis ofcovariance (ANCOVA) was used to calculate mean annual...

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