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1 Ambient Carbon Monoxide Pollution in the United States INTRODUCTION Carbon monoxide (CO) has been central to the evolution of air quality management in the United States. CO is produced primarily by the incom- plete combustion of carbon-containing fuels, such as gasoline, natural gas, oil, coal, and wood. In a 1977 National Research Council (NRC) report, CO was declared "probably the most publicized and best known criteria pollutant" (NBC 1977~. The NBC attributed this recognition to the severe adverse health effects (including death) that result from acute exposure, which have been observed for centuries. Reducing human exposure to the products of incomplete combustion was an early objective of air quality management in the United States. CO was and still is the most recogniz- able indicator of incomplete combustion and has Tong been viewed as one of the most fundamental indicators of ambient air quality. When continu- ous monitors were first installed in some cities in the early 1960s, maxi- mum 8-hour average concentrations in excess of 30 parts per million (ppm) were not unusual (DHEW 1970, EPA 19791. National Ambient Air Quality Standards (N~AQS) for ambient con- centrations of CO (9 ppm for an 8-hour average and 35 ppm for a 1 -hour average) were instituted in ~ 97 ~ on the basis of studies linking ambient CO concentrations with neurobehavioral effects. Although neurobehavioral 16

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Ambient CO Pollution in the United States 17 effects no longer serve as the basis for the standards, subsequent studies linking CO to increased risk of chest pain and hospitalization for persons with coronary artery disease have supported retention of the regulation. In the early 1970s, monitoring of CO indicated that exceedances ofthe 8-hour standard were common. The first comprehensive national report on emissions and air quality trends found that over 90% of monitors operating in 1971 recorded exceedances of the 8-hour NAAQS (EPA 1973~. How- ever, the situation improved fairly rapidly, primarily due to vehicle pollu- tion controls. By the year 2000, only four locations (Birmingham, Ala- bama; CaTexico, California; Lynwood, California; and Fairbanks, Alaska) reported exceedances ofthe 8-hour standard (Table 1-~. As ofthe end of 2002, both Lynwood and Fairbanks reported 2 years with no violation of the CO standard. The locations that continue to have high concentrations of CO also tend to have topographical and meteorological characteristics that exacerbate pollution (e.g., nearby hills that inhibit wind flow and temperature inver- sions that inhibit vertical pollutant dispersion). Attainment of the health- based NAAQS for CO has proved somewhat difficult under those condi- tions. The question arises whether unique approaches are necessary to manage CO in such problem areas or the current policies will ultimately achieve good air quality. An issue for areas that now meet the NAAQS is their vulnerability to future exceedances as a result of increases in vehicle- miles traveled (VMT) or unusual meteorological conditions favoring CO accumulation. STUDY BACKGROUND AND CHARGE in response to the challenges posed for some locations by the NAAQS for CO, a committee was established by the NRC to investigate the problem of CO in areas with meteorological and topographical problems. The com- mittee's statement of task was as follows: An NRC committee will assess various potential approaches to predict- ing, assessing, and managing episodes of high concentrations of CO in meteorological or topographical problem areas. The committee will con- sider interrelationships among emission 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

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20 Managing CO in Meteorological and Topographical Problem Areas relationships between episodes of high ambient CO, personal exposure, and the public-health impact of such episodes and alternative ways to measure progress in controlling ambient CO. An interim report dealing with Fair- banks, Alaska, as a case study was completed in May of 2002. A final report, including other CO problem areas, will be completed by the end of the study. The committee will address the following specific issues: · Types of emission sources and operating conditions that contribute most to episodes of high ambient CO. · Scientific bases of current and potential additional approaches for developing and implementing plans to manage CO air quality, including the possibility of new catalyst technology, alternative fuels, cold-start technol- ogy, as well as traffic and other management programs for motor vehicle sources. Control of stationary source contributions to CO air quality also will be considered. . Assessing the effectiveness of CO emissions control programs, including comparisons among areas with and without unusual toco~rachi- -r -en- ~r- cal or meteorological conditions. · Relationships between monitored episodes of high ambient CO concentrations and personal human exposure. The public-health impact of such episodes. Statistically robust alternative methods to assist in tracking prog- ress in reducing CO that bear a relation to the CO concentrations consid- ered harmful to human health. This study provides scientific and technical information potentially helpful in the development of state implementation plans (SIPs); however, the committee does not provide prescriptive advice on the development of specific SIPs for achieving CO attainment. In addition, the committee does not suggest changes in regulatory compliance requirements for areas in nonattainment of the NAAQS, and it does not recommend changes in the NAAQS for CO. Fairbanks, Alaska, was chosen as a case study for the interim report because its meteorological and topographical characteristics make it sus- ceptible to severe winter inversions that trap CO and other pollutants at ground level (NRC 2002~.

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Ambient CO Pollution in the United States 21 SUMMARY OF INTERIM REPORT Fairbanks, Alaska, was chosen as a case study for the interim report because its meteorological and topographical characteristics make it sus- ceptible to severe winter inversions that trap CO and other pollutants at ground level. The committee's interim report, entitled The Ongoing Chal- lenge of Managing Carbon Monoxide Pollution in Fairbanks, Alaska, was completed in 2002 (NRC 2002~. The interim report allowed the committee to assess the characteristics ofthe CO problem in detail in one meteorologi- cal and topographical problem area. It provided the committee with general lessons applicable to other locations as well as characteristics of the prob- lem that were unique to Fairbanks. Because the committee devoted signifi- cant effort to assessing CO episodes in Fairbanks, the final report also draws on the Fairbanks case study. In the interim report, the committee found that Fairbanks has made great progress in reducing its violations of the 8-hour CO health standard, and has reduced the number of days annually with violations from over 130 during 1973 and 1974 to zero over the last 2 years (2001 and 2002~. De- spite this progress, the committee also concluded that Fairbanks will con- tinue to be susceptible to violating the 8-hour CO health standard on some occasions for many years to come because of its unfavorable meteorologi- cal 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. The findings associated with the progress on reducing CO violations and vulnerability to future violations are relevant to CO episodes in other meteorological and topographical problem areas. The committee recommended that there be improvements to local emis- signs controls, including vehicle emissions inspection and maintenance (I/M) programs, low-sulfur gasoline, and traffic control strategies. In par- ticular, the committee found that the Fairbanks North Star Borough is mak- ing substantial efforts to characterize and control cold-start emissions, despite the difficulty in quantifying emissions-reduction credits in its CO- attainment plan. The main method for controlling these emissions is through electrical heating devices known as plug-ins that preheat the engine coolant or lubricant of parked motor vehicles. Plug-ins substantially reduce CO emissions during the cold-start phase of engine operations by reducing the length of time needed for the catalyst to become fully operational. The committee recommended that the borough continue to expand the plug-in program by requiring or encouraging the equipping of more parking spaces

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22 Managing CO in Meteorological and Topographical Problem Areas with electric outlets for plug-ins. The committee noted that the alert-day program, where the public is alerted on days when CO is forecasted to exceed the standard, was important in Fairbanks because it was part of a larger public information campaign to encourage motorists to use plug-ins. The emphasis on controlling cold-start emissions through plug-ins is gener- ally limited to Fairbanks and likely does not translate well to the lower 48 states. ~ its interim report, the committee noted that officials with the bor- ough argued that Fairbanks should be granted an exemption from the Clean Air Act with regard to the ambient CO health standards because of its ex- treme meteorological and topographical conditions. However, the commit- tee concluded that a similar argument could be made for other regions with regard to a variety of air pollutants. Furthermore, the ambient concentra- tions of CO observed in Fairbanks have exceeded the level that EPA identi- fied in the health-based standard for the protection of the general popula- tion and susceptible individuals. Thus, the committee concluded that ef- forts to control CO be continued and improved. TH:E COMMITTEE'S APPROACH TO ITS CHARGE In this final report, the committee addressed meteorological and topo- graphical conditions that foster pollution episodes, CO and related emis- sions from mobile and other sources, and air quality management options. The committee also examined monitoring data for ambient CO, including episodes when 8-hour average concentrations exceeded the NAAQS. In general, although monitoring of CO at locations with problems has oc- curred for an extended period of time, data and modeling to assess the spatial end temporal extent of high-CO events are limited. The limited data reduced the committee' s ability to assess human exposures during high-CO episodes. In addition, little exposure or epidemiological data specific to locations with high-CO episodes resulting from meteorological and topo- graphical conditions were available to assess the public health effects of those episodes. In the absence of such data, the committee reviewed rele- vant clinical and epidemiological studies presented in the scientific litera- ture and considered by EPA in assessing the health effects of exposure to ambient CO at concentrations and durations exceeding the NAAQS. Thus the committee did not conduct a comprehensive examination of the health effects of CO and did not examine the likelihood or actual risk of adverse health effects from exposure to ambient CO concentrations in these meteo-

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Ambient CO Pollution in the United States 23 rological and topographical problem areas. In addition, the committee did not consider other CO sources such as cigarettes and therefore did not attempt to put the risks of ambient CO exposure into the context of other CO sources. The technical feasibility and potential for emissions reductions of a number of air quality management options are also discussed in the body of this report. Promising options available for controls at the federal, state, and local levels are presented in the summary. The committee found that light-duty vehicles are the primary source of emissions and potential emis- sions reductions, so most options focused on control of emissions from those vehicles. The committee's recommendations follow the relevant supporting evidence. REPORT CONTENTS This final report documents the committee's response to the charge described above. The report consists of four chapters and a summary. Chapter 1 provides background information on the regulation and sources of ambient CO pollution in the United States necessary to characterize the key issues stated in the committee's charge. The main topics include the NAAQS and areas exceeding CO standards, sources of CO emissions, health effects of CO, relationship of CO to other air pollutants, and issues relating to the spatial distribution of CO. Chapter 2 describes the meteoro- logical and topographical conditions that foster pollution episodes in CO problem areas. Temperature inversions, Tong-term meteorological trends, temporalpatterns of CO concentrations, end vulnerability of areas to future exceedances are discussed in detail. Chapter 3 discusses CO management and the tools needed to implement CO standards, such as emissions control strategies and monitoring and modeling tools. Some control strategies de- scribed include emissions standards, I/M programs, fuels, and transpor- tation-conkol measures. Finally, Chapter 4 focuses on long-term issues related to exposures, controls, and management of CO. NATIONAL REGULATORY SETTING FOR AMBIENT CO National Ambient Air Quality Standards To control adverse health effects from CO exposure, the U.S. Environ-

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24 Managing CO in Meteorological and Topographical Problem Areas mental Protection Agency (EPA), acting per Sections 108 and 109 of the Clean Air Act (CAA), established the NAAQS for CO in 197 ~ . Recogniz- ing that exposure can have both acute and longer-term effects, the NAAQS for CO have two criteria with different averaging periods: 35 ppm averaged over ~ hour, and 9 ppm averaged over ~ hours.) Each criterion is not to be exceeded more than once per year; the second and subsequent exceedances within a year are considered violations of the standard. The 8-hour stan- dard has proven to be more difficult to meet than the 1-hour, especially for a handful of cities. The standard has been periodically reviewed on the basis of new scientific findings, as mandated by the CAA. The most recent review was published in 2000 (EPA 2000a). EPA originally designated an area as being in "nonattainment" of the S-hour standard if the second-highest 8-hour average CO concentration measured during a calendar year (known as the "design value") was greater than 9 ppm. After the Clean Air Act Amendments of 1990 (CAAA90), EPA designated areas that had previously been in nonattainment as "seri- ous" if the design value was ~ 6.5 ppm or greater, "moderate" if the design value was 9.1-16.4 ppm, and "not classified" if recent data were insuffi- cient to determine whether the standard was met. Moderate areas that did not reach attainment by July 1996 could be reclassified by EPA as serious. Nonattainment areas are required to submit a state implementation plan (SIP) to EPA that includes a characterization of pollutant concentrations and emissions, a description of the emissions reductions the area plans to make, and an "attainment demonstration" showing how the emissions re- ductions will enable the area to attain and maintain compliance with the NAAQS. To be eligible for reclassification from nonattainment to attain- ment status for CO, an area must have air quality monitoring data indicating that it did not violate the NAAQS during the previous 2 years. Though areas typically apply forreciassification immediately, Smith and Woodruff (200~ discussed how Fort Collins, Colorado, has delayed their application for reclassification since ~ 994 to pursue wider air quality goals. To meet the city's goal of continually improving air quality as described in the City of Fort Collins Air Quality Action Plan (2001), the city used their non- attainment status to pursue emissions control strategies that are not tradi- tionally implemented in attainment areas. One example is the vehicle emis- sions FM program, which currently is not required when a city is in attain- ~Thoughthe standard is 9.0ppm, in practice anexceedance does not occur until the 8-hour average is greater than 9.4 ppm. Values between 9.1 ppm and 9.4 ppm are rounded down to 9.0 ppm.

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Ambient CO Pollution in the United States 25 meet. However, Fort Collins has recently applied to be reclassified and may discontinue some emissions control programs. Officials in Fort Col- lins are undertaking a feasibility study to explore both the voluntary and/or mandatory control programs after the state mandatory I/M program is elimi- nated. Throughout the report, the terms exceedance, exceedance days, and violation are used. They are defined as follows: an exceedance of the CO standard is any CO concentration measurement of 9.5 ppm or above for an 8-hour average;2 exceedance days are days on which one or more nonover- lapping 8-hour average CO concentration was 9.5 ppm or greater; and a violation is two or more exceedances within a calendar year. Note that more than one exceedance can occur in a day if there is more than one nonoverIapping S-hour period with an average CO concentration of 9.5 ppm or greater. Vulnerable Areas and the Form of the CO Standard The form ofthe CO standard, where a violation occurs upon the second and all subsequent exceedances in a calendar year, contributes to the diff~- culties that meteorological and topographical problem areas have in attain- ing the standard. A significant probability of an exceedance exists with the current attainment test because of the stochastic nature of ambient air pol- lutant concentrations (Gibbons 2002~. Areas must control CO under very infrequent, though not uncommon, meteorological conditions. The for ~~ of the new 8-hour ozone standard (the 3-year average of the fourth highest annual value) was changed from the form ofthe 1 -hour standard (the fourth highest value over 3 years) in part because the latter form is more suscepti- ble to extreme meteorological conditions. Conformity Requirements Transportation conformity requirements were originally developed to ensure that federal funding and approval was given to those transportation Although the 8-hour NAAQS for CO is 9 ppm, because early monitoring instruments had limited precision of about 1 ppm it has been the practice to consider an 8-hour average an exceedance only if it is 9.5 ppm or greater.

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26 Managing CO in Meteorological and Topographical Problem Areas activities consistent with air quality goals. Transportation conformity was first introduced in the CAA Amendments of ~ 977, which included a provi- sion linking air quality to transportation planning by ensuring that transpor- tation investments conform with STPs (DOT 2000~. Conformity require- ments were made more rigorous in the CAAA90 and in the regulations EPA issuedin 1993 to implement the requirements (40 CFR § 51 and 93 tI9933~. The CAAA90's conformity mandate requires that transportation plans, programs, and projects in nonattainment or maintenance areas funded or approved by the Federal Highway Administration (FHWA) or the Federal Transit Agency (FTA) do not: (1) create new violations of the federal air quality standards; (2) increase the frequency or severity of existing viola- tions; or (3) delay timely attainment of CAA standards. Metropolitan planning organizations (MPOs) are responsible for per- forming air quality conformity analyses. MPOs must have transportation plans in place that present a 20-year perspective on transportation invest- ments for their region as well as a short-term transportation improvement program (TIP). The TIP is a multi-year prioritized list of projects (3 years at a minimum) proposed to be funded or approved by FHWA or ETA. The conformity analysis is done for the system of projects contained in a re- gion's TIP and transportation plan, and must show emissions consistent with those allowed in the SIP. Conformity determinations must be made at least every 3 years, or as changes are made to plans, TIPs, or projects. A formal interagency process is required to establish procedures for consultation between MPOs, EPA, FHWA, ETA, and state and local transportation and air quality agencies. These procedures apply to the development of the SIP, the transportation plan, the TIP, and conformity determinations. The sIP must establish interagency consultation procedures for the coordinating agencies and include schedules for implementation of all strategies. Once EPA approves the part ofthe SIP that describes the interagency consultation process (the conformity SIP), it is then enforceable by EPA as a federal regulation. One of the key components of the conformity determination for CO is the application of project-level emissions analysis and, on occasion, hot- spot analysis. During SIP preparation, emissions budgets are created for nonattainment areas. These budgets set limits on the mass of the criteria pollutant that can be emitted in the area and are usually broken into general and transportation budgets. For an area to be in conformity with the SIP, the sum of the emissions from all transportation projects may not exceed the transportation budget., unless reductions in the general budget are made to compensate In cases where a project could create a local violation or

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Ambient CO Pollution in the United States 61 3.0 - . Correlation Coeffecient = 0.70 2.5 E Q 2.0- ._ ._ `,, 1.5 - In s ,'5 1.0- o . · ~ · ~ . . 1 · ~ . . . · . ~ . . . · . , · ~ · _ ~ ·. . . o 5 10 15 20 25 30 35 40 45 50 PM2.5 ,ug/m3 FIGURE 1-15 Correlation of daily average CO and PM2 5 concentrations at the state building, Fairbanks, Alaska, November 2000 to February 2001. are lower, and CO concentrations are high. A hypothesis explaining these observations might be that during inversions with fog, aqueous reactions in the fog form secondary PM2 s more quickly, and during clear inversions stratification in the inversion traps CO closer to the ground. However, this conclusion has not been confirmed. Roles of CO in Tropospheric Ozone and Climate Change Tropospheric Ozone In the atmosphere, the only chemical loss process for CO is by reaction with the hydroxy! (OH) radical. The overall reaction is OH + CO (+ 02) = HO2 + CO2. Using a global average tropospheric OH radical concentration of 9.4 x 105 molecule cm~3 (Prinn et al. 2001), the average CO lifetime is calculated

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62 Managing CO in Meteorological and Topographical Problem Areas to be 2 months, which is sufficiently long for CO emitted in the United States to be mixed throughout the northern hemisphere. When enough NO is present that HO2 radicals react only with it, HO2 + NO = OH + NO2, the photolysis of NO2 and the rapid reaction of the oxygen, CHOP), atom with 02, NO2 + sunlight = NO + 0~3P) 0~3P)+O2+M=O3+M(M=air), leads to net formation of ozone from the reaction of OH radicals with CO (in the presence of NO such that HO2 radicals react dominantly with NO), CO+2O2=CO2+O3 Therefore, CO can be viewed as the simplest ozone-forming "hydrocar- bon." Because CO reacts rather slowly in the atmosphere, and its photo-oxi- dation results in the conversion of only one molecule of NO to NO2 per molecule of CO oxidized (see above), CO has a significantly lower ozone- forming potential (grams of O3 foe per grams of reactant emitted) than the HC mix in vehicle exhaust (Carter ~ 998~. The ~ 997 maximum incre- mental reactivity (MIR) scale (Carter 1998) of CO is 0.065 g of O3 per gram of CO emitted, which can be compared to the MIR of exhaust emis- sions from vehicles fueled with two gasolines representative of California reformulated gasoline (testing conducted during the Auto/OiT Air Quality Improvement Research Program) of approximately 3.5 g of O3 per gram of HO emitted (NRC ~ 999~. However, because of the amount of CO and HCs emitted in vehicle exhaust, NBC (1999) concluded that CO from LDVs contributes 15-25% of the total ozone-forming potential of exhaust emis- sions. Therefore, despite its Tow ozone-forming potential, CO contributes to ozone formation in polluted atmospheres. Keep in mind however that ozone formation requires sunlight and is strongly temperature dependent, so it tends to be more of a problem during the summer months and not during the winter months when CO exposure tends to be a problem.

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Ambient CO Pollution in the United States 63 Climate Change CO contributes to climate change in four ways: (~) it is itself a green- house gas (GHG), though its warming potential is much less than that of CO2; (2) CO is oxidized to CO2, as shown above, noting that direct emis- sions of CO from vehicles are an order of magnitude or more lower than those of CO2; (3) at low NOx concentrations, reaction of CO with OH radi- cals results in loss of OH radicals, and by removing OH from the atmo- sphere CO tends to increase the lifetime of methane (CH4), a powerful GHG; and (4) CO contributes to the formation of ozone (03), another GHG. Using CO As an Indicator of Other Pollutants In urban environments, CO can serve as an indicator of motor vehicle emissions from gasoline-fueled vehicles. The observed spatial and tempo- ral variability of CO shows that the effects of motor-vehicle pollution are heterogeneously distributed in urban areas and that CO can be a useful gauge of long-term human exposure to other pollutants of concern, includ- ing certain mobile-source air tonics. CO levels also demonstrate the exis- tence of"hot spots" in urban environments where high concentrations of CO and other products of automobile exhaust occur. However, CO is not a perfect indicator. CO does not react on the time scales of concern for urban pollution, and it is not representative of the chemical reactivity of other pollutants. The weather conditions that pro- duce high CO concentrations are generally unrelated to those that produce ozone pollution, which is most severe during the summer months. Because CO pollution is primarily due to exhaust emissions from LDVs in the urban environment, it is not strongly correlated with evaporative toxic emissions, diesel PM emissions, or stationary- and area-source emissions. Because CO is formed with other products of incomplete combustion (including unburnt fuel), CO emissions from a specific vehicle often corre- late with emissions of HCs and organic compounds (including the air toxics formaldehyde, acetaldehyde, 1,3-butadiene, and benzene). Emissions of formaldehyde and acetaldehyde depend on the fuel used and, more specifi- cally, on the presence of MTBE or ethanol in the fuel. MTBE leads to higher emissions of formaldehyde, and ethanol leads to higher emissions of acetaldehyde ARC 1999~. The exhaust emissions of benzene and other

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64 Managing CO in Meteorological and Topographical Problem Areas higher emissions of formaldehyde, and ethanol leads to higher emissions of acetaldehyde (NRC 1999~. The exhaust emissions of benzene and other aromatic HCs depend on the fuel aromatic content, because benzene and other aromatic HCs are emitted as unburnt fuel and are formed in the com- bustion process. The precise correspondence of CO and other organic vehicle emissions depends on the fuel used (including the presence or absence of a fuel oxy- genate, the actual oxygenate used, end the aromatic content ofthe fuel) and onboard emissions control technologies and engine conditions (i.e., cold start, hard acceleration, etc.~. Furthermore, CO's relationship with other organic emissions varies as a function of time after emission. While CO is essentially nonreactive on day-Ion" time scales, most other organic com- pounds in vehicle exhaust are significantly more reactive than CO, and certain organic compounds (e.g., carbonyl compounds, alkyl nitrates, and peroxyacyl nitrates) are later formed in the atmosphere from atmospheric reactions of other HCs (Atkinson 2000~. For example, formaldehyde is removed rapidly by photolysis (and less rapidly by reaction with OH radi- cals) and has a lifetime of about 4 hours in overhead sun. It is also formed in the atmosphere from the photooxidation of almost all other HCs (Atkinson 2000~. Therefore, although CO can serve as a general indicator of motor-vehi- cle exhaust (and hence of exposure to vehicle exhaust and/or to photochem- ically processed vehicle exhaust), CO concentrations alone are uncertain estimators for concentrations of other organic compounds in the same air

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Ambient CO Pollution in the United States 65 mass, except for other long-lived vehicle exhaust components such as ben- zene (and even then, only in the absence of other sources). However, rea- sonably strong correlations between CO and the shorter-lived volatile or- ganic compounds (VOCs) emitted from LDVs will still be observed over distance scales corresponding to travel times of the pollutants of approxi- mately a half-Tife or less (see Figure 1-14~. EQUITY CONSIDERATIONS IN THE SPATIAL DISTRIBUTION OF AMBIENT CO Because CO levels are not evenly distributed, exposure to CO within the population will vary. Individuals living in or near areas of high CO ("hot spots") are exposed to higher concentrations of CO and other mobile- source-related pollutants. Although the network of CO monitors is too sparse to identify all hot spots, the characteristics of the residents living near known hot spots can be examined. An analysis of data from the 2000 U.S. Census shows that the individual CO monitors that registered exceedances of the 9-ppm 8-hour average CO standard during the period 1995-2001 are often found in areas that have greater percentages of low- income and minority residents than their surrounding regions (Table 1-7~. All but six of the monitor areas, as defined by the census tract or tracts immediately surrounding each CO monitor, had higher percentages of nonwhite residents in 2000 than the region as a whole. In the area around the Sunrise Avenue monitor in Las Vegas, for example, 49.6% of residents are nonwhite, compared with 26.2% for the Las Vegas Metropolitan Statis- tical Area (MSA). Three monitor sites in Los Angeles have a Tower per- centage of nonwhite residents than the region as a whole, but even in those areas, over one-third of residents are nonwhite. The percentage of residents who are of Hispanic origin is higher than the regional share for all but three monitors. The differences are often dramatic. The population in the Las Vegas-Sunrise Avenue area is 68.7% Hispanic compared with 5.3% for the region, and percentages of Hispanic residents for the Phoenix monitor areas are over twice the percentage for the region. Per capita incomes were lower for residents in the monitor area than on average for the region (for all but four of the monitor areas) and were less than half of the regional average for the Las Vegas-Sunrise Avenue, Phoenix-Indian School Road, and Lynwood-Long Beach Avenue monitor areas. The monitor area in Denver at Speer and Auraria Parkway, where the per capita income is over twice

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66 of To To o .= U) U) au · _ no ·_. Cal C) · _ VO · _ C) Ct V o · _ Cd - o 1 EM a, ~ C A V Cal, crJ: ·C :t .= O a, O ~ O .0 Ct .= 'C ._ .= ~ ~ 'O .= .0 3 o Z 'C C) Cal ~ 5= o Ct o C) ~ ~ X ~ =\ Go Do ~4 Do o Go Do Go - Cal - lo Do lo oo c~ ~ cr cr~ o ~o _4 ~ 0 . . O 0 ~o oo oo o~ o ~o o cr~ _4 o - C~ (~) t_ oo ~ oo oo . . . ~ 0 ~ ~n ~ ~ ~ 0 . . . . ~ 0 ~ ~ ~ ~ ~ , ~ oo rn oo _ 0 0 0 0 0 , 0, O O — O u ° , e ° ,; 3 ° ~, ° ~ ° a ° x ~ ~~ ~ c w ~ ,, - ~~ ~ Y c ~

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Ambient CO Pollution' in the United States 69 the regional average, is an anomaly and reflects a recent influx of affluent residents to downtown Denver residents choosing to live in a high-den- sity, high-traffic area. In addition, the number of employed residents who do not drive to work is higher than for the region as a whole in all but three of the monitor areas and is four or more times higher in monitor areas in Spokane, Washington, Denver, Colorado, and Provo, Utah. Residents who walk, bike, or ride transit are likely to spend more time within the monitor area during their commutes and may experience greater exposure to high CO levels. To a limited degree, these demographics may explain the high levels of CO recorded in many monitor areas. Although the residents of these areas are less likely to drive to work, they are more likely to own older vehicles, which in turn are more likely to be high-emitters (Rajan 1993; Granell 2002~. For example, Singer and Harley (1996, 2000) observed a much higher fraction of older vehicles near the Lynwood monitor. The vehicles observed in their study included vehicles passing through the area as well as vehicles owned by local residents. The high emissions rates for older vehicles may offset lower total amounts of driving. In addition, the rela- tively high population densities in all but one monitor area (Table 1-7) suggest higher concentrations of traffic in these areas and thus higher con- centrations of pollutants. However, the traffic generated locally is likely to represent a small fraction of the total traffic in and around most of these monitor areas. These preceding demographics suggest the need for continued attention to the CO problem from the standpoint of environmental justice. In ~ 994, President Clinton signed Executive Order 12898, Federal Actions to Ad- dress Environmental Justice in Minority Populations and Low-Income Populations. The order was related to Title VI of the Civil Rights Act of 1964 and required federal agencies "to achieve environmental justice by identifying and addressing disproportionately high and adverse human health and environmental effects, including the interrelated social and economic effects of their programs, policies, and activities on minority populations and low-income populations in the United States." The order also stipulated that in reviewing other agencies' proposed actions under Section 309 of the CAA, "EPA must ensure that the agencies have fully analyzed environmental effects on minority communities and low-income communities, including human health, social, and economic effects " (EPA 1 998a). EPA and the FHWA have issued their own interpretations of the envi- ronmental justice requirement. EPA defines environmental justice as "the

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70 Managing CO in Meteorological and Topographical Problem Areas fair treatment of people of all races, cultures, and incomes with respect to the development, implementation, and enforcement of environmental laws and policies, and their meaningful involvement in the decision making processes of government" (emphasis in original). According to EPA, fair treatment requires that EPA conduct its "programs, policies, and activities that substantially affect human health and the environment in a manner that ensures the fair treatment of all people, including minority populations andlor low-income populations" and that EPA ensure "equal enforcement of protective environmental laws for all people, including minoritypopula- tions and/or low-income populations" (EPA 20016~. As interpreted by the FHWA, environmental justice includes notjust minimizing adverse effects but also the preventing of "the denial of, reduction in, or significant delay in the receipt of benefits by minority and low-income populations" (FHWA ~ 998~. This requirement should apply to benefits from federal policy such as improvements in air quality. Both ofthese interpretations suggest that the remaining locations expe- riencing high CO concentrations represent a potential environmental justice concern. According to EPA's final guidance for incorporating environmen- tal justice concerns into National Environmental Protection Act (NEPA) compliance analyses, a minority population is present "if the minority population percentage of the affected area is 'meaningfully greater' than the minority population percentage in the general population or other ' appro- priate unit of geographic analysis"' (EPA 1998a). This is clearly the case for areas surrounding most of the monitors registering CO exceedances since 1995. In addition, EPA notes the following: Minority communities and Tow-income communities are likely to be dependent upon their surrounding environment (e.g., subsis- tence living), more susceptible to pollution and environmental degradation (e.g., reduced access to health care), and are often less mobile or transient than other populations (e.g., unable to relocate to avoid potential impacts). Each of these factors can contribute to minority and/or low-income communities bearing disproportion- ately high and adverse effects (EPA 1998a, p. 571. The extent of the areas with CO concentrations that exceed the NAAQS is unclear because the number of monitors in each area is limited. Therefore, measures of the exposures to CO experienced by low-income and minority populations are imperfect. While the declining number of exceedances of the CO standard and the design of the standard to ensure a

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Ambient CO Pollution in the United States 71 reasonable margin of safety are encouraging, the correlation between CO and other pollutants creates uncertainty in the degree to which "adverse human health and environmental effects" might be occurring in these Tow- income and minority communities. Nevertheless, the demographic patterns suggest that the impacts that occur are disproportionately high in these areas. In addition to providing an important impetus for the continuation of efforts to eliminate CO exceedances, these results suggest a need for monitoring and personal exposure research programs designed to more fully characterize the distribution of CO and other mobile-source-related pollutants.