Implications of the Fairbanks Case Study
PROSPECTS FOR CONTINUED ATTAINMENT
Ambient carbon monoxide (CO) concentrations in Fairbanks are the result of human activities, especially the use of motor vehicles, and of regional and local meteorology and topography. Severe temperature inversions and low windspeeds, prevalent in Fairbanks during winter, trap CO emitted close to the ground. Although the number of violations of the 8-h National Ambient Air Quality Standard (NAAQS) for CO has declined substantially over the past 25–30 y, the inversion conditions experienced in Fairbanks are among the most severe in the United States. The prospects for continued attainment in Fairbanks depend essentially upon whether the current understanding of the cause-effect relationships at work in the region is accurate, whether observed trends in human activity and emissions continue as expected, and whether meteorological conditions are favorable for CO dispersal.
As stated earlier, maintaining compliance with the NAAQS for CO will be unlikely without an accurate understanding of cause-effect relationships and will depend on how this understanding is translated into control policies. The Fairbanks North Star Borough and Alaska have invested more resources in characterizing the cause-effect relationships involved in Fairbanks’s CO problem than have other cities of similar size in the United States. Management of CO in the borough has focused on control strategies that reduce overall emissions from motor vehicles (primarily through the I/M program) and that reduce cold-start emissions (primarily through vehicle plug-ins). Analysis has focused on how the coincidence of cold starts and the strengthening of
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
standard in Anchorage, which had no violations over the last 3 y. A modest change in regional or local meteorology or unforeseen growth in vehicle activity or emissions could readily cause Fairbanks to violate the standard again. Sustained efforts will be required if Fairbanks is to maintain compliance with the standard over the long term.
Nonetheless, Fairbanks has made great progress in reducing its violations of the 8-h CO standard. The success in reducing the number of days of violations from over 130 during 1973–1974 to below 4 per year over the last 5 y (and none in the last 2 y) demonstrates the ability of new vehicle-emissions standards and local controls to reduce motor-vehicle emissions. That improvement has reduced population exposures to CO and related pollutants, but some probably remain.
RELATIONSHIP OF FAIRBANKS CASE STUDY TO OTHER NONATTAINMENT AREAS
A number of other areas in the United States are struggling to attain the CO NAAQS, but Fairbanks is unique in the severity of its inversions. The Fairbanks area is subject to strongly inhibited mixing in winter because it has little solar heating, which prevents deepening of the mixing layer during day-time, and very light winds, which result in slow exchange of air between the city and its surroundings. Such an environment is conducive to the accumulation of pollution released near the ground. Nonattainment areas farther south have similar conditions in winter but benefit from additional sunlight that allows more vertical turbulent mixing. Although such mixing may not occur on cloudy days, these conditions rarely persist for long periods in association with light or calm winds. Even in mountain valleys, where terrain can be effective in trapping pollution, the solar heating of the surface and the relatively frequent windy conditions provide better dilution of pollutants than that in the Fairbanks area.
Other areas in nonattainment for CO must address unique conditions that contribute to their own CO problems. For example, Calexico, California, is close to the U.S.-Mexico border, where pollution from vehicles waiting to cross the border is thought to be the primary cause of high CO concentrations. Las Vegas, Nevada, not only has problematic meteorological and topographical conditions but is also one of the fastest-growing areas in the United States. Lynwood, California, has both severe inversion conditions and higher than average vehicle emissions that contribute to CO violations.
In many areas of the Unites States that have air quality problems related to CO and other pollutants, meteorological or topographical conditions exacerbate the accumulation of pollution. But health benefits can still be gained by meeting the health standards set by EPA. Although the conditions in Fairbanks are severe, Fairbanks is in no way unique in having natural conditions that contribute substantially to its air quality problem.