CO,2 and they are experiencing fewer violations as automotive controls continue to reduce emissions. However, a few areas, including Lynwood and Calexico, California, and Fairbanks, Alaska, have continued to experience violations over the last five years. Those three areas have very different physical and demographic characteristics, and the reasons for their continuing problems differ greatly.

Fairbanks is an extreme example of the roles that meteorology and land topography play in producing air quality problems. In winter, Fairbanks is subject to extreme atmosphere inversions, at times recording inversion strengths of as much as 30°C (86°F) per 100 m of altitude.3 In addition, Fairbanks is situated in a three-sided bowl, surrounded by the Yukon-Tanana uplands; the bowl opens to the Tanana River Flats toward the south and southeast. Although Fairbanks is not heavily populated and has no major air-pollution-producing industries, its meteorological and topographical characteristics make the city susceptible to high ambient CO concentrations in winter. The atmospheric inversions and low windspeeds that commonly occur during winter are extremely effective in trapping the products of incomplete combustion, including CO, that are emitted at ground level.

The Fairbanks North Star Borough, Alaska Department of Environmental Conservation (ADEC), and EPA have been concerned about the inability of Fairbanks to attain the CO health standard. In the fiscal year 2001 appropriations for EPA, Congress called for the National Research Council (NRC) to conduct an independent study of CO episodes in meteorological and topographical problem areas. The study is to address various potential approaches to predicting, assessing, and managing episodes of high concentrations of CO in such areas. The complete study charge is contained in Chapter 1. Congress also requested that the Fairbanks area be the subject of a case study in an interim report. In response, the NRC formed the Committee on Carbon Mon-

2  

Areas that violate an NAAQS for a given pollutant are designated as being in nonattainment for that pollutant. Their nonattainment status triggers many regulatory requirements, including the submission to EPA of an attainment plan, known as a state implementation plan (SIP), which describes the strategies an area will use to come into compliance.

3  

Inversions occur when the temperature of the atmosphere increases with height. Combined with low windspeeds, this prevents air circulation because colder air is trapped near the ground by the warmer air above. A temperature increase of several degrees per 100 m is considered a strong inversion.



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