the standards are for outdoor air, they help to improve indoor air. CO remains in the outdoor air long enough to penetrate the indoor environment and is not removed by filtration. Because the measures taken to reduce CO emissions typically result in reduced emissions of copollutants, such as PM_2.5 and air toxics, the health benefits of CO reductions can be greater than those associated with reduced CO concentrations alone.

Controls on CO emissions, particularly in the form of improved vehicle technology, have led to significant reductions in ambient CO concentrations throughout the United States. However, a few locations still experience concentrations that approach or exceed the CO 8-h health standard. Most of those areas have meteorological conditions (such as frequent inversion or stagnation conditions) or topography (such as being situated in a mountain valley) that inhibit ventilation and allow CO to accumulate at high concentrations near the surface. One such location is Fairbanks, Alaska. The task of the Committee on Carbon Monoxide Episodes in Meteorological and Topographical Problem Areas was to assess approaches for predicting, assessing, and managing episodes of high CO concentrations in meteorological or topographical problem areas. The committee’s charge called for Fairbanks to be the focus of this interim report. The rest of this report describes the CO problem there, including its physical characteristics, the emissions-control strategies used there, and the prospects for the area to remain in attainment with the NAAQS for CO.