mer ozone (O3) and year-round particulate matter (PM).1 Low temperatures also contribute to high CO concentrations. Engines and vehicle emissions-control equipment operate less efficiently when cold: Air-to-fuel ratios are lower, combustion is less complete, and catalysts take longer to become fully operational. The result is that products of incomplete combustion, including CO, are formed in higher concentrations. Sometimes, topography, meteorology, and emissions combine to cause high concentrations of CO. Compliance with the health-based National Ambient Air Quality Standards (NAAQS) for CO has proved difficult under those circumstances. The question arises as to whether unique methods are necessary to manage CO in such problem areas, or whether the current policies will ultimately achieve good air quality.


In response to the challenges posed for some areas by having to come into compliance with the NAAQS for CO, a committee was established by the National Research Council (NRC) to investigate the problem of CO in areas with meteorological and topographical problems. The committee’s statement of task is as follows:

An NRC committee will assess various potential approaches to predicting, assessing, and managing episodes of high concentrations of CO in meteorological or topographical problem areas. The committee will consider interrelationships among emissions sources, patterns of peak ambient CO concentrations, and various CO emissions-control measures in such areas. In addition, the committee will consider ways to better understand relationships between episodes of high ambient CO and personal exposure, the public-health impact of such episodes, and alternative ways to measure progress in controlling ambient CO. An interim report dealing with Fairbanks, Alaska, as a case study is to be completed. A final report, including other CO problem areas, will be completed by the end of the study.


Of the seven areas currently in serious nonattainment for CO, five (Anchorage, Denver-Boulder, Los Angeles, Phoenix, and Spokane) are also in nonattainment for PM10, and three (Denver-Boulder, Los Angeles, and Phoenix) are in nonattainment for ozone (O3). O3 formation is promoted by sunlight and high temperatures and is a summer problem.

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