inversion conditions during winter afternoons can play a major role in CO exceedances. However, little attention has been paid to characterizing other sources of CO, which may be highly uncertain. The spatial extent of the CO problem, and the understanding of the microscale and regional meteorological conditions that are associated with exceedances, also are poorly characterized. Data on emissions from vehicles operating under winter conditions in Fairbanks are sparse, so it is difficult to predict the effects of future vehicle emissions-control strategies.

The borough recently has experienced decreasing emissions from motor vehicles, and this contributes to a higher likelihood of attaining and maintaining compliance. Federal controls on vehicles and fuels have had by far the largest effects in reducing CO emissions. Most of the recent reductions have been attributed to more stringent new-vehicle certification standards for CO. State and local programs generally help to reduce emissions but do not have the same impact. Nonetheless, in the absence of further federal mandates designed to yield additional emissions reductions in cold climates, enhancement of state or local controls is essential for achieving and maintaining CO concentration standards.

Long-term population growth in the area remains an issue. It is likely that a natural-gas pipeline or missile-defense initiative in Alaska will be approved and funded. If either of those activities occur, the growth in population, in vehicle-miles traveled, in service-industry activity, and in construction activities would substantially increase the probability of a CO-attainment lapse in Fairbanks in the future.

Finally, the prospects for continued attainment in Fairbanks depend on meteorological conditions. Severe inversions are inevitable. Exceedances could be avoided if such inversions occurred on days when emissions-producing activities were at a minimum or if emissions were minimized on days with severe inversions. If researchers could reliably discern the meteorological patterns that cause severe inversions, short-term mitigation strategies could be developed and used. But there is insufficient knowledge to understand the microclimate of the Fairbanks basin, let alone to understand how large-scale weather patterns in Alaska influence inversion conditions. Without improved meteorological understanding, the region cannot know whether additional emissions-reduction efforts or other mitigation strategies will be necessary until it is too late to prevent the area from slipping back into nonattainment.

The committee concludes that Fairbanks will be susceptible to violating the CO health standards for many years because of its severe meteorological conditions. That point is underscored by a December 2001 exceedance of the

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