Carbon monoxide (CO) is a colorless, odorless gas that can produce serious adverse health effects. Exposure to high concentrations can be fatal. At lower concentrations that can occur in the ambient environment, the effects of CO include increased risk of chest pain and hospitalization for persons with coronary artery disease. Recognizing the public-health hazards of elevated ambient concentrations, the U.S. Environmental Protection Agency (EPA) set National Ambient Air Quality Standards (NAAQS) for CO in 1971.1 When the concentration of CO in ambient air exceeds health standards, it is due mainly to incomplete combustion of gasoline by light-duty vehicles, such as passenger cars and pickup trucks. EPA accordingly has set increasingly stringent standards for CO emissions from vehicles and has mandated vehicle emissions inspection and maintenance (I/M) programs and the use of oxygenated fuels to reduce emissions in areas with ambient-CO problems.
The controls are working. In the 1970s, numerous cities exceeded the CO health standards. Now, only a handful of areas fail to meet the NAAQS for
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-
oxide Episodes in Meteorological and Topographical Problem Areas, which has prepared this interim report. The final report will more broadly address approaches to predicting, assessing, and managing CO episodes in other problem areas in addition to Fairbanks.
THE COMMITTEE’S APPROACH TO ITS CHARGE
In this interim report on Fairbanks, the committee addresses meteorological and topographical conditions that foster pollution episodes, wintertime CO emissions frommobile sources, air quality management options, and statistical methods for tracking progress. The committee also examined monitoring data for ambient CO, including episodes when 8-hour (h) average concentrations exceeded the NAAQS. Although Fairbanks has monitored CO in three downtown locations since 1972 and has a laboratory to study vehicle emissions under cold-weather conditions, data and modeling to assess the spatial and temporal extent of high-CO events are limited for the city. This reduced the ability of the committee to assess the exposure of residents during high-CO episodes. In addition, little exposure or epidemiological data specific to Fairbanks were available to assess the public health impact of those high ambient CO episodes. In the absence of such data, the committee reviewed relevant clinical and epidemiological studies presented in the scientific literature and considered by EPA in assessing the health impact of exposure to ambient CO at concentrations and durations exceeding the NAAQS. In addition, the technical feasibility and potential for emissions reductions of a number of air quality management options are discussed in the body of this report. Promising options available for implementation at the state and local levels are presented in this summary. The committee’s recommendations follow and can be found in the body of the report adjacent to further supporting evidence.
FINDINGS AND RECOMMENDATIONS
CO Concentration Trends in Fairbanks
Fairbanks has made great progress in reducing its violations of the 8-h CO health standard. The Fairbanks North Star Borough has worked effectively to reduce CO emissions. It has also benefited greatly from stringent federal vehicle-emissions standards for CO, and the borough and Alaska have in-
vested more resources in studying and characterizing the air quality problem in Fairbanks than other cities of this size in the United States. The number of days annually with violations has been reduced from over 130 during 1973 and 1974 to zero over the last 2 years;4 that demonstrates the effectiveness of new-vehicle emissions standards, including requirements for certifying vehicles at a low temperature (20°F [−6.7°C]), and of local controls to reduce motor-vehicle emissions.
Despite those efforts, Fairbanks will continue to be susceptible to violating the 8-h CO health standard on some occasions for many years to come because of its unfavorable meteorological and topographical conditions. Those adverse natural conditions might be compounded by future increases in the population of Fairbanks brought about by large pipeline or military construction projects. In such cases, emissions controls may have to be enhanced to offset increases.
Borough officials have argued that Fairbanks should be granted an exemption from the Clean Air Act with regard to the ambient CO health standards because of its extreme meteorological and topographical conditions. However, a similar argument could be made for other regions with regard to a variety of air pollutants. Furthermore, the ambient concentrations of CO observed in Fairbanks have exceeded the level that EPA identified in the health-based standards for the protection of the general population and susceptible individuals.
Health and Exposure
The committee finds that EPA has presented strong scientific evidence in support of the NAAQS describing the health effects of CO on the general population and susceptible individuals. Although ambient CO concentrations observed in Fairbanks have exceeded the NAAQS, the lack of exposure data makes it impossible for the committee to comment on the actual health impacts in Fairbanks from CO episodes. Nevertheless, given the strong health basis of the NAAQS and the observed ambient CO concentrations in Fair-
banks, the committee finds that there are potential health benefits from lowering exposure to CO.
Health Benefits from Meeting CO Standards
Evidence in the scientific medical literature indicates that attainment of the ambient CO health standards should decrease morbidity and mortality from heart disease. Epidemiological studies at various locations have confirmed that ambient CO concentrations similar to those observed in Fairbanks are associated with increased hospital admissions and increased mortality. For example, one epidemiological study of elderly patients in eight United States counties reported that daily variations in ambient CO concentrations had a statistically significant impact on daily cardiovascular hospital admissions. Another study found a statistically significant relationship between CO and hospital admissions for congestive heart failure in six United States cities. Evidence also suggests that attainment of the 8-h CO standard should generally decrease morbidity from neurological disease, fetal loss, and childhood developmental abnormalities.
To reduce the potential adverse health effects of CO, the borough will need to continue to make progress in meeting the NAAQS for CO. Public-awareness campaigns regarding the public-health issues associated with ambient CO should be enhanced.
Exposure During Episodes
Human exposure to CO takes place both indoors and outdoors. Air pollution in buildings can come from a combination of the intake of ambient air and indoor sources. In the case of CO, buildings do not provide protection from
high outdoor concentrations because the gas is chemically stable, penetrates freely with infiltration air from the outside, and is not removed by building materials or ventilation systems. Indoor sources of CO (for instance, a faulty furnace, an underground parking garage, a kerosene heater, or a smoker), add to the background concentration from the outdoor air. Therefore, concentrations of CO indoors, where people spend the vast majority of their time, can be even higher than those outside. For these reasons, human exposure to high concentrations of CO is likely during episode conditions in Fairbanks, although insufficient exposure data are available to verify this statement.
Additional efforts should be made to monitor personal exposures to CO in buildings and garages near high-CO areas, outside in residential locations, and in motor vehicles. Sampling of human exposure with personal monitoring, blood carboxyhemoglobin measurements, or breath samples is recommended. Monitoring of CO concentrations in microenvironments and of human exposure to CO should be performed in conjunction with improved ambient monitoring to better characterize the CO problem in Fairbanks.
CO is often an indicator of several less well-characterized pollutants (“copollutants”) that are generated and transported with it, especially airborne particulate matter (PM) smaller than 2.5 microns in diameter (PM2.5) and toxic organic air contaminants, such as benzene, 1,3-butadiene, and aldehydes. Many of the efforts taken to reduce CO emissions will also reduce emissions of copollutants and their corresponding health effects.
The expected adverse health effects of exposures to copollutants is another reason to consider enhanced CO controls. To assess the relationship between CO and copollutants in Fairbanks during winter, Alaska and the
borough should implement an ambient monitoring program for toxic organic compounds and expand the monitoring of PM2.5.
Meteorological Conditions of Primary Concern
When CO concentrations exceed the health standard in Fairbanks, the ambient temperatures are typically between −20° and 20°F (−28.9° and −6.7°C). The combination of high albedo (reflection of sunlight due to snow cover) and the low solar elevation (the sun remains low in the sky) characteristic of northern latitudes in winter creates little heating of the ground and weak vertical mixing between the surface and overlying air. In Fairbanks, that frequently results in ground-based inversions of considerable strength topped by weaker inversions reaching as high as 1–2 km. Human behavior and motor-vehicle technology further narrow the primary temperatures of concern to 0° to 20°F (−17.8° and −6.7°C). In the 0° to 20°F temperature range, preheating a vehicle’s engine with electric plug-in devices is not necessary to ensure that it will start, so drivers do not plug in as often as they do when temperatures are below 0°F. The higher emissions that result from starting nonpreheated vehicles is thought to be the reason why five of the last six episodes exceeding the CO standard occurred in this temperature range.
Air quality management in Fairbanks should focus on the 0° to 20 °F (−17.8° to −6.7°C) temperature range. Emissions inventories should be refined and verified and control programs evaluated for their effectiveness with emphasis on that temperature range. In addition, air quality modeling should be developed, conducted, and evaluated for the extreme conditions found in Fairbanks in winter.
I/M Programs in the Fairbanks North Star Borough
The vehicle emissions inspection and maintenance (I/M) program is a
central element of the borough’s plans to comply with the 8-h ambient CO health standard. Emissions models estimate that improved vehicle testing and increased enforcement provide the largest emissions reductions beyond those attributed to increasingly stringent federal motor-vehicle emissions standards. However, the emissions reductions resulting from the I/M program in the borough have not been evaluated with in-use vehicle emissions data. Moreover, the I/M program could be improved. The issues deemed most important by the committee are inspection frequency, exemptions, testing improvements, remote sensing, and continuing program evaluation.
Frequency and Exemptions
The 1997 change in the borough’s I/M program from annual to biennial inspections lacked technical justification and has resulted in an increase in the rate of vehicles failing inspection. Assuming that the quality of vehicle repairs did not change, the increased failure rate implies that the switch to a longer interval has reduced the benefits associated with the I/M program. Returning from biennial to annual inspections will increase the emissions-reduction benefits of the I/M program and help to ensure that the reduction targets of the program are met.
Fairbanks exempts pre-1975 model-year vehicles from its I/M program, although Anchorage tests model years 1968 and newer. Including older vehicles in the Fairbanks program might help to reduce CO emissions from the onroad fleet. Because of the low rates of failure of newer vehicles, studies have shown a minimal loss of program benefits when newer vehicles (vehicles less than 2 or 4 years old) are exempted from the inspection requirement.
The borough should consider resuming annual inspections. The committee is aware that this may require state legislation. The borough should also expand the coverage of its I/M program to include 1968–1974 model-year vehicles. The current new-car testing exemption is reasonable; it may also be cost-effective, starting with the 2000 model year, to expand the exemption to cover the four most recent model years.
Improvements in Emissions Testing
It is important that the emissions-test procedure be compatible with vehicle technology. The current two-speed idle test for 1982–1995 model-year vehicles is not capable of identifying many of the problems that will cause a vehicle to emit CO at high rates in advanced emissions-control systems, such as a defective oxygen (O2) sensor, one of the most common significant emissions-producing defects. The committee notes that the borough incorporated advanced onboard diagnostic (OBDII) testing beginning in July 2001 for 1996-model-year and newer vehicles. The OBDII system uses sensors to monitor and modify the performance of the engine and emissions-control components.
The borough should comprehensively assess emissions-testing methods to determine appropriate inspection procedures for various vehicle technologies. This assessment should consider the use of annual two-speed idle tests for pre-1982 vehicles and biennial or annual testing under driving-load conditions for 1982–19965 vehicles. The assessment should also consider the issues associated with using OBDII testing in cold climates. Because of the frequency of O2-sensor failure, the borough should also evaluate the potential emissions-reduction effectiveness of a mandatory O2-sensor replacement program for older, high-mileage vehicles and implement such a program if it is found to be effective.
Remote sensing is a noninvasive roadside monitoring technology used to estimate the concentration of CO in the exhaust plume of a vehicle as it passes
a monitored location. Remote-sensing technologies are used in many areas of the United States to track the distribution of vehicle emissions in the onroad fleet and to evaluate the effectiveness of I/M and other emissions-control programs. Although the technology is not typically deployed in the winter because of the effect of extreme cold and other meteorological factors on the performance of remote-sensing equipment, it can be used for part of the year. Vehicles that are high-emitting during the summer are often high-emitting during the winter, so the use of remote sensing could help the borough to evaluate the success of its I/M programs.
Use of remote-sensing capabilities should be considered for the borough’s I/M program, as temperatures and atmospheric conditions permit, to help characterize emissions of the vehicle fleet. A continuing remote-sensing program should be considered to evaluate the potential effectiveness of the I/M program, as is done in other regions. The borough could also consider using remote sensing to identify vehicles that must be tested or vehicles that could be given an exemption.
Ongoing Evaluation of I/M
The I/M program has been predicted to produce substantial reductions in emissions in the Fairbanks area, but the borough has not actually evaluated the effectiveness of the program. Evaluation is especially needed given the borough’s claim that the program is much more effective than the federal performance standard for such a program.
The borough should evaluate the I/M program more rigorously to estimate its emissions-reduction benefits and to identify where improvements to the program are needed. The evaluation should allow the direct comparison of the emissions reductions achieved by the program with those estimated in the
borough’s attainment plan. It should also look for methods to improve the effectiveness of I/M.
Cold-start emissions occur during the first minutes of vehicle operation—until the engine warms up and the emissions-control catalyst is operating at full efficiency. As the ambient temperature drops, vehicles take longer to warm up, and cold-start emissions increase. Cold-start emissions are especially a problem in Fairbanks during the winter, contributing an estimated 45% of all motor-vehicle emissions. The borough is making substantial efforts to characterize and control these emissions, despite the difficulty in quantifying emissions-reduction credits in its CO-attainment plan.
Electrical heating devices known as plug-ins preheat the engine coolant or lubricant in parked motor vehicles. Plug-ins reduce the amount of time that an engine takes to warm up, reduce fuel consumption, and reduce the length of time needed for the catalyst to become fully operational. Engine preheating can substantially reduce CO emissions during the cold-start phase of engine operations, as well as warming the rider compartment more quickly. The borough is now mandating that parking lots of major employers be equipped with electrical outlets for preheating and is conducting mass-media campaigns to encourage the use of plug-ins during winter.
For plug-ins to be effective in CO control, an electric outlet must be present and operational at the parking space, and the driver must take the time and effort to plug the vehicle in. In the temperature range of 0°F to 20°F (−17.8° to −6.7°C), drivers may make a convenience decision and not plug in if they believe that the temperature will not go below 0°F. Hence, human behavior is a major factor in the effectiveness of this voluntary program. Plug-in use is not being monitored systematically in Fairbanks to demonstrate its emissions-reduction benefits.
The borough should continue to expand the plug-in program by requiring or encouraging the equipping of more parking spaces with electric outlets for
plug-ins. Efforts to increase the use of plug-ins at 0° to 20°F (−17.8° to −6.7°C) are especially warranted. Public-education campaigns should continue. Adoption and enforcement of engine-preheating regulations on days expected to have high ambient CO concentrations should be considered. However, further analyses could determine the factors that motivate the voluntary use of plug-ins and the incentives that will expand their use. Additional effort should be directed toward understanding the relationships among engine size, heater power, and the heating time required to substantially reduce cold-start emissions.
Fuel Sulfur Content
Modern vehicles are equipped with three-way catalytic converters that reduce emissions of organic compounds (including unburned fuel and air toxics), CO, and nitrogen oxides from the engine. High concentrations of sulfur in gasoline decrease the efficiency of the catalytic converter and impair its ability to oxidize CO to carbon dioxide. Switching back and forth between high- and low-sulfur fuels reduces the effectiveness of low-sulfur gasoline.
Two refineries supply the gasoline sold in the Fairbanks region—one with a reported sulfur content of about 200 parts per million (ppm) and the other with a reported sulfur content of less than 1 ppm. The refinery supplying the high-sulfur gasoline is expected to meet the federal regulations for lowering average sulfur content to 180 ppm in 2004 and 30 ppm in 2007. Requiring year-round sale of low-sulfur gasoline in Fairbanks earlier than the federal mandate would help in attaining the CO health standard.
The borough should consider requiring the sale of low-sulfur gasoline as soon as possible. Introduction of lower-sulfur gasoline could be facilitated through accelerated approval of refinery-construction permits and through a state-brokered gasoline-exchange program. Policy and economic analyses, in consultation with the two local refiners, are needed to determine the best approach to ensure that this mandate will not substantially increase the cost of gasoline to Fairbanks residents or compromise the air quality in other parts of the state. A public-awareness campaign to explain the benefits of low-
sulfur fuels is needed, and the sulfur content of fuels should be posted at gasoline stations.
Reductions in CO and in some other toxic emissions from oxygenated fuel6 have been observed at ambient temperatures down to 30°F (−1.1°C). Oxygenated fuels may also provide benefits at temperatures below 30°F, but the effects are uncertain because there has not been much testing in cold climates. Use of oxygenated fuels is highly controversial in the Fairbanks North Star Borough. The decision to use fuels containing the oxygenate methyl tertiary-butyl ether (MTBE) in October 1992 was rescinded because of public concerns about odor and possible health effects. There is a reluctance to introduce other oxygenated fuels, such as gasoline containing 10% ethanol, even though such fuels are mandated for Anchorage and estimated by the state to yield the greatest emissions reductions there.
Alaska, EPA, and others should conduct additional research and vehicle testing to assess the effectiveness of ethanol in gasoline for decreasing CO and air-toxics emissions during cold starts and operation at ambient temperatures below 20°F (−6.7°C). If such research indicates that substantial benefits can be achieved, ethanol blending should be considered for Fairbanks.
Traffic Flow and Motorist-Directed Control Strategies
The borough has implemented several control measures directed at improving traffic flow and modifying motorists’ travel behavior, including high-
way and intersection improvements, transit-system expansion and free transit services, an “alert-day” program, and a public-information campaign. The borough is working on an improved traffic-signal coordination plan. Those measures have contributed to improvements in air quality. Most other transportation control measures (TCMs) recommended by EPA for other areas are clearly not appropriate for Fairbanks given the low levels of congestion, low-density development, and severe winter conditions. It may be possible to achieve marginal reductions in ambient CO, beyond those achieved by plug-ins, with creative and innovative TCMs designed for Fairbanks. However, without sufficient household travel data or a travel-demand forecasting model, the borough does not have the information needed to evaluate the potential effectiveness of alternative TCMs.
The borough should explore parking pricing, telecommuting, and teleservices strategies. The borough should evaluate the effectiveness of its “alert-day” program and consider enhancing it. In addition, a travel-demand study, including a winter travel diary and transit-ridership survey, should be undertaken to provide a basis for evaluating the potential effectiveness of proposed TCMs.
Improving Ambient Monitoring in the Borough
Ambient air monitoring data are available to characterize long-term CO trends over a limited area in the city of Fairbanks but are inadequate to understand the temporal trends across the entire city and at different heights above the ground. Such data are needed to quantify source contributions to human exposure and to evaluate air quality models.
In the short term, the ambient-CO monitoring network in the borough should be expanded to measure concentrations over a wider area. In the lon-
ger term, the vertical distributions of CO concentrations and the wind field should be characterized to support the development and application of modeling approaches better than those now available.
Improving Ambient-CO Modeling in the Borough
Air quality models are important tools for air quality planning and for forecasting severe CO events. A variety of modeling techniques have been used in other areas to plan strategies for controlling ambient CO, but the extreme conditions in Fairbanks limit the applicability of many of those techniques. In developing Fairbanks’s most recent state implementation plan (SIP), Alaska used a relatively simple model, referred to as a statistical rollback model, to estimate the emissions reductions needed to lower ambient CO to achieve the CO health standards. More sophisticated tools could not be used because meteorological data and emissions inventories were insufficient.
In the near term, Alaska should use a simple box-model approach, which simulates the effects of emissions and meteorology in a well-mixed, controlled volume, for air quality planning purposes in Fairbanks. Such an approach could provide greater insights into the effects of the timing of CO emissions and meteorological variables. The relative contributions of mobile and stationary sources to CO episodes could also be assessed with this type of model. Enhanced data-collection efforts are required to support this and more sophisticated modeling efforts.
Improvements in the statistical forecasting approach used by the borough might help in forecasting episodes of high CO concentrations. More work is also needed to develop, apply, and evaluate more sophisticated, physically comprehensive models that would simulate how CO concentrations vary with time and space over the entire borough. Such models could be used for planning, forecasting, and assessing human exposure to high CO concentrations. It is important that model development and testing be specific to the extreme conditions that occur in Fairbanks. Model development must occur in concert with improved monitoring to enable model evaluation.
Successful control of ambient CO requires a community effort. The borough’s public-education efforts, aimed at increasing awareness of the CO problem and of how using plug-ins and mass transit may help to alleviate it, have included paid television and radio announcements during heavy viewing and listening times. The committee is concerned, however, that the public-education campaign has not sufficiently emphasized the potential health effects associated with high ambient-CO exposure.
Misconceptions about the relationship between high CO concentrations and public health can be a major barrier to the success of air quality improvement strategies. Policy-makers and the public should understand the health benefits of air quality improvement and accept the need to implement, enforce, participate in, and support these strategies.
Public-education programs should be continued and expanded to increase public awareness of the potential health effects of high ambient CO concentrations and to increase public participation in efforts to improve air quality. Surveys of public opinion should be used in designing the programs and assessing their effectiveness.
Fairbanks has succeeded in reducing the number of days that violate the 8-h CO standard from over 130 per year in the 1970s to none during the last 2 years. Despite this improvement, it is likely that, under severe inversion conditions, Fairbanks will again exceed the 8-h CO standard, particularly if the area experiences significant growth due to pipeline or military construction. To further improve air quality in Fairbanks, the borough should continue to use, and possibly expand, effective current control strategies. The committee concludes that pursuit of cold-start emissions controls through the plug-in program should continue to be a priority. For its final report, the committee will consider the extent to which the federal government could aid Fairbanks
and other areas in improving air quality by mandating stricter vehicle-certification standards for starts during cold conditions. The committee sees such standards as possibly a very effective means for the borough to reduce emissions in the future but also recognizes that national vehicle-emissions standards cannot be set for a single area.
In addition, the borough should undertake a cost-effectiveness analysis to help determine which of the other emissions-control strategies discussed in this report should be pursued. Efforts to control CO in the borough should be accompanied by public-education campaigns to improve public awareness of and participation in efforts to improve air quality.
The committee also sees potential benefits from additional studies to improve the spatial characterization of CO during episodes of high ambient concentrations. In the short-term, continuing to conduct a basic assessment of the spatial variability of CO during such episodes should be a priority. The long-term priority should be to develop a three-dimensional characterization of CO episodes; that would require long-term monitoring commitments and the development of modeling capabilities. Such work would probably require local and state commitments in combination with federal research support.
Further study of the Fairbanks CO problem could provide useful insights to scientists and regulators in the wider air quality community. Fairbanks constitutes a natural laboratory for understanding influences of meteorology and topography on air quality in regard to CO and for understanding the effectiveness of emissions-control technologies at low temperatures.