7
Transforming the Nation’s AQM System to Meet the Challenges of the Coming Decades

INTRODUCTION

The air quality management (AQM) system has been effective in addressing some of the most serious air quality problems confronting the United States in the latter half of the twentieth century. New technologies and fuels, developed largely in response to Clean Air Act (CAA) requirements, have substantially reduced emissions from mobile, stationary, and other sources. As a result, the U.S. population has experienced large reductions in ambient concentrations of lead (Pb), carbon monoxide (CO), sulfur dioxide (SO2), and, in some regions, ozone (O3) and particulate matter (PM10). These reductions in ambient concentrations have come despite substantial economic and population growth in the United States that brought about increases in power generation, vehicle miles traveled, and other activities that are traditionally associated with emissions of air pollutants.

However, significant and perhaps even more difficult challenges are to be met in the coming decades. In this chapter, a number of specific changes to the air quality management (AQM) system are recommended that would improve our ability to meet these challenges effectively. To place these recommendations in an appropriate context, this chapter begins with a brief discussion of some of the air quality challenges that the nation will need to confront in the future and then outlines a set of overarching principles that guided the committee in designing its recommendations (see Figure 7-1).



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Air Quality Management in the United States 7 Transforming the Nation’s AQM System to Meet the Challenges of the Coming Decades INTRODUCTION The air quality management (AQM) system has been effective in addressing some of the most serious air quality problems confronting the United States in the latter half of the twentieth century. New technologies and fuels, developed largely in response to Clean Air Act (CAA) requirements, have substantially reduced emissions from mobile, stationary, and other sources. As a result, the U.S. population has experienced large reductions in ambient concentrations of lead (Pb), carbon monoxide (CO), sulfur dioxide (SO2), and, in some regions, ozone (O3) and particulate matter (PM10). These reductions in ambient concentrations have come despite substantial economic and population growth in the United States that brought about increases in power generation, vehicle miles traveled, and other activities that are traditionally associated with emissions of air pollutants. However, significant and perhaps even more difficult challenges are to be met in the coming decades. In this chapter, a number of specific changes to the air quality management (AQM) system are recommended that would improve our ability to meet these challenges effectively. To place these recommendations in an appropriate context, this chapter begins with a brief discussion of some of the air quality challenges that the nation will need to confront in the future and then outlines a set of overarching principles that guided the committee in designing its recommendations (see Figure 7-1).

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Air Quality Management in the United States FIGURE 7-1 To meet the major challenges that will face air quality management (AQM) in the coming decade, the committee identified a set of overarching long-term objectives. Because immediate attainment of these objectives is unrealistic, the comm itteemade five interrelated recommendations to be implemented through specific actions.

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Air Quality Management in the United States THE CHALLENGES AHEAD Meeting NAAQS for O3 and PM2.5 and Reducing Regional Haze In 1997, the U.S. Environmental Protection Agency (EPA) promulgated new National Ambient Air Quality Standards (NAAQS) for two criteria pollutants: O3 and PM. These standards were developed because of new scientific data that indicated deleterious health effects from exposure to concentrations of the two pollutants that were below the current NAAQS. Meeting the new standards will require additional reductions in pollutant emissions. Moreover, because O3 and PM are secondary pollutants (produced in the atmosphere from reactions involving primary pollutants), it will be necessary to determine which pollutant emissions to reduce and to devise appropriate monitoring systems to assess progress toward meeting the new standards. All of these tasks will be major challenges for the AQM system in the United States over the next decade. The standard for O3 has been changed from a maximum 1-hr peak concentration of 120 parts per billion by volume (ppbv) to an 8-hr average concentration of 80 ppbv.1 It has proved to be extremely difficult to attain the previous (1-hr) O3 NAAQS. In the United States, approximately 56 areas composed of 233 counties have yet to attain it after decades of trying to do so (EPA 2003p). It will probably be even more difficult to meet the new O3 8-hr standard (NARSTO 2000). Retrospective analysis of air quality data indicates that there will be many more exceedances of the new 8-hr standard than the previous 1-hr standard. More frequent exceedances will occur in areas already in nonattainment of the 1-hr standard, and new exceedances will occur in areas currently in attainment of the 1-hr standard. Many of these new nonattainment areas will be in rural areas that do not have the major sources of the various air pollutants that produce O3. The decline of the 8-hr averaged O3 concentrations (11%) in the United States has been slower than that of the 1-hr averaged O3 concentrations (18%) over the past two decades (EPA 2002a). Therefore, additional pollution control strategies are likely to be needed to meet the new O3 NAAQS—for example, a further departure from the local emission-control approach demanded in the current state implementation plan (SIP) process and the enhanced development of multistate airshed2 management approaches, such as those embodied by the Ozone Transport Assessment Group (OTAG) and the resulting requirement to submit a revised NOx SIP. 1   EPA is phasing out the 1-hr 0.12-ppm standards (primary and secondary) and putting in place the 8-hr 0.08-ppm standards. However, the 0.12-ppm standards will not be revoked in a given area until that area has achieved 3 consecutive years of air quality data meeting the 1-hr standard (EPA 2001a). 2   The geographic extent of a pollutant or its precursor emissions in air is often referred to as an airshed.

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Air Quality Management in the United States Developing effective strategies to attain the new PM2.5 standard may also prove to be difficult. Atmospheric PM is a complex mixture of solid and liquid particles suspended in air; PM2.5 is a subset of PM in the atmosphere with (aerodynamic) diameters of less than 2.5 × 10–6 m (or 2.5 μm). Modern instrumentation capable of characterizing individual particles in the atmosphere confirms that PM2.5 within any airshed comprises numerous particles having different sizes, shapes, and chemical components (NARSTO 2003). Some actions are already under way or proposed to reduce these emissions (for example, the existing 2007 heavy-duty on-road diesel requirements and the proposed multipollutant controls on electric utilities). However, for the nation’s AQM system to protect human health from PM2.5 pollution over the long term, the specific characteristics of PM2.5 that negatively affect health need to be identified, the sources of emissions and the atmospheric processes responsible for the ambient concentrations of particles with these characteristics need to be determined, and new control technologies will need to be developed and implemented. These tasks will require a major investment in research (as outlined in NRC 1998b) and close collaboration between the policy-making and scientific and engineering communities in the United States. Reducing regional haze to improve visibility in scenic areas, such as national parks, is another difficulty that the U.S. AQM system will be confronting for decades to come. As discussed in Chapters 2 and 5, EPA’s regional haze regulations call for states to develop strategies that will bring about interim improvements by 2018 but do not project attainment of the stated goal of returning national parks and wilderness areas to their natural visibility conditions until 2065. O3, PM2.5, and regional haze share, to some extent, common precursor emissions and chemical pathways for the generation of these pollutants and are all to greater or lesser extents affected by long-range transport. For those reasons, it is critically important that pollution control strategies targeted for mitigation of O3, PM2.5, and regional haze be developed in tandem and on a multistate basis. Such a multipollutant, multistate approach should minimize the possibility that control strategies implemented for one pollutant will inadvertently increase the concentrations of another pollutant3 and should enhance the ability of policy-makers to maximize the cost-effectiveness of their overall air pollution control strategies. The one-pollutant-at-a-time approach that is currently used to develop SIPs may substantially hinder the development of multipollutant control strategies. 3   In some cases, reducing sulfate emissions can increase concentrations of nitrate-containing PM (NARSTO 2003).

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Air Quality Management in the United States Toxic Air Pollutants The health risks faced by U.S. citizens from exposure to toxic air pollutants remain an important concern, albeit one that is not well quantified. The National Air Toxics Assessment (NATA) estimates that most Americans face cancer and noncancer risks of public health concern from exposure to hazardous air pollutants (HAPs) (EPA 2002e). Moreover, these estimates do not consider the risks associated with exposures to numerous poorly characterized HAPs, or to the large number of chemicals that are not identified as HAPs but that might pose a health hazard. Although some monitoring data suggest that concentrations of commonly measured HAPs are declining and the implementation of planned maximum achievable control technology (MACT) and other regulations is expected to substantially reduce toxic emissions, significant residual risk is predicted to remain (EPA 2000a). Given the multitude of sources of toxic air pollutants in the nation and the variety and complexity of the risks they pose, protection of human health and ecosystems from exposure to HAPs will continue to challenge the AQM system over the coming decades. Ideally, control strategies for HAPs would be scaled to the degree, severity, and pervasiveness of the risks posed. The difficulty in developing such strategies has been and will probably continue to be a lack of sufficient information on the sources, atmospheric distribution, and effects of most HAPs. Evidence regarding risks for the majority of HAPs, unlike the criteria pollutants, is often indirect (that is, from animal studies rather than human laboratory or epidemiological studies) and extrapolated from effects reported for HAPs at concentrations much higher than typical ambient concentrations. In addition, current efforts to monitor HAPs fall far short of that needed to characterize HAP exposures adequately. There is a clear need to enhance resources for research, data collection, and analysis efforts on HAPs. However, in the past, priority for these resources has generally been given to criteria pollutants. A large number of potentially toxic pollutants in the atmosphere are unregulated and, in most cases, poorly characterized in terms of environmental concentrations and subsequent health and ecological effects. An illustration of the enormity of this problem is that while 188 compounds are officially designated as HAPs by EPA, an estimate of approximately 300 compounds with varying tendencies to exist in the atmosphere as gases or particles are introduced into commerce each year by U.S. industries.4 A major challenge for the nation’s AQM system over the coming 4   Information obtained from the Notice of Commencement Database maintained by the inventory section in EPA’s Office of Pollution Prevention and Toxics.

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Air Quality Management in the United States decades will be the development of a research and regulatory infrastructure capable of protecting human health and welfare from the increasing number of potentially toxic pollutants in the atmosphere in an effective and timely manner while not unnecessarily impeding economic activity and technological progress. Protecting Human Health and Welfare in the Absence of a Threshold Exposure There is increasing evidence that for some criteria pollutants and subsets of the population, any exposure is harmful—that is, there is no threshold exposure below which harmful effects cease to occur (Daniels et al. 2000). Under these circumstances, there is a tendency to set air quality goals and standards at ever lower concentrations—concentrations so low, in fact, that they approach what might be considered the irreducible background concentration that is unaffected by human pollutant emissions and thus impervious to even the most aggressive air pollution control efforts. To address this challenge, AQM needs to develop a better understanding of the reducible (human-induced) and irreducible components of pollution in the United States (NARSTO 2000). Achievement of this understanding will require a substantial expansion of monitoring networks into rural and remote regions, as well as in cities (see Chapter 6). Enhanced tools will also be required for exposure assessment and health and ecosystem impact analysis to better characterize risks at low levels of exposure. When scientific understanding is improved, it might be necessary to reconsider how to set standards to protect public health from those pollutants with no established thresholds. Ensuring Environmental Justice The CAA Amendments of 1990 make no direct or specific reference to environmental justice. Nevertheless, environmental justice issues clearly can arise in the implementation of the CAA, and for this reason, environmental justice is a goal of the nation’s AQM system (see Chapter 2). Addressing environmental justice in the nation’s AQM system will require actions on a number of levels. First, environmental justice concerns reinforce the need to monitor and model the distribution of HAPs and other pollutants in microenvironments and to use those results to estimate exposures to the populations in those microenvironments. Second, the concept of environmental justice will need to be incorporated in the earliest stages of air quality planning and management. Implementation planning has a critical role in the CAA, and issues of environmental justice often can be addressed most effectively during development of these plans especially if

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Air Quality Management in the United States they begin to address multiple pollutants and hot spots,5 as proposed in the third and fourth recommendations in Recommendations for an Enhanced AQM System later in this chapter. In one instance, the California Air Resources Board (CARB) led in establishing a framework for incorporating environmental justice into its programs consistent with the directives of state law (CARB 2001). Third, new proposals for pollutant reduction (cap-and-trade programs, for example) should be judged in terms of the environmental justice impact and the efficacy of the reduction and should be designed to include sufficient local emission-control requirements to minimize the possibility that hot spots will result, especially in disadvantaged communities. Fourth, Native American tribes should be given help to develop and implement AQM programs for reasons of environmental justice and tribal self-determination. The recommendations advanced later in this chapter, specifically those that allow AQM to target the most significant exposures and risks, are designed in part to address these issues. Assessing and Protecting Ecosystem Health The goal of protecting ecosystems is clearly enunciated in the CAA under the proviso to protect public welfare through the promulgation and implementation of secondary standards. The protection and maintenance of ecosystems is critical not only because of a general desire to protect and preserve forests and undeveloped spaces in the United States but also because ecosystems provide invaluable services (for example, water purification, water supply, forest production, and carbon and nitrogen fixation) that are essential to our economy and the public health (Daily 1997; ESA 1997a; Balmford et al. 2002). Indeed, provisions to mitigate ecosystem impairment in wilderness areas and national parks in the 1977 CAA Amendments and to mitigate the effects of acid rain in Title IV of the 1990 CAA Amendments are proactive steps taken by Congress to protect public welfare in the absence of formally established secondary standards. Despite the mandate in the CAA to protect welfare, protection of ecosystem health has not received adequate attention in the implementation of 5   Hot spots are locales where pollutant concentrations are substantially higher than concentrations indicated by ambient outdoor monitors located in adjacent or surrounding areas. Hot spots can occur in indoor areas (for example, public buildings, schools, homes, and factories), inside vehicles (for example, cars, buses, and airplanes), and outdoor microenvironments (for example, a busy intersection, a tunnel, a depressed roadway canyon, toll plazas, truck terminals, airport aprons, or nearby one or many stationary sources). The pollutant concentrations within hot spots can vary over time depending on various factors including the emission rates, activity levels of contributing sources, and meteorological conditions.

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Air Quality Management in the United States the act (see Chapter 2). Nevertheless, research over the past 30 years suggests that there is a critical need to protect ecosystems from the damaging effects of air pollution. In addition to impairment of visibility, air pollution can have far-reaching effects on ecosystems, including damage to trees and crops; degradation of soil quality (particularly shallow forest soils); acidification of surface waters; and a resulting decrease in the diversity of biota, contamination of fish tissue (for example, by mercury and polychlorinated biphenyls), and eutrophication of coastal waters. Those ecological effects have an impact on humans through decreases in the productivity of forests and crops, increased advisories on consumption of contaminated fish, loss of fisheries in waters located in upland forests and in estuaries, and a deterioration of the quality of recreational activities. A major goal of the nation’s AQM system in the coming decades should be to establish an appropriate research and monitoring program that can quantitatively document the links between air pollution and the structure and function of ecosystems and use that information to establish realistic standards and goals for the protection of ecosystems and implement strategies to attain those standards and goals. Addressing Multistate, Cross-Border, and Intercontinental Transport Historically, the primary emphasis of AQM in the United States has been on controlling emissions in and nearby urban and industrial centers where pollutant concentrations are generally the highest; this approach is often referred to as a local pollution control strategy. During the late 1980s and 1990s, it was realized that controlling local emissions alone was insufficient to meet the NAAQS for some air pollutants in some areas. In response, regional planning organizations were created to devise multistate AQM strategies. As discussed in Chapter 3, some of these regional planning organizations were created in response to specific requirements of the 1990 CAA Amendments (for example, the Ozone Transport Commission and the Grand Canyon Visibility Transport Commission), and others were formed on a more ad hoc basis (for example, the Ozone Transport Assessment Group). Whatever the mechanism that led to their formation, these regional planning organizations all shared a common purpose: to fill the gap in the nation’s AQM system that has historically fallen between the responsibilities and regulatory authority vested with state governments and those vested with the federal government. To better fill this gap and thereby facilitate the development and implementation of multistate AQM plans in the future, the recommendations section of this chapter proposes that EPA’s role in addressing regional problems be enhanced. As more is learned about the atmosphere, it has become more apparent that air quality in a locale (even an urban locale) can be influenced by even

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Air Quality Management in the United States FIGURE 7-2 Contribution to the sulfate column burden for July 15, 1997, at 00UT (vertical integral of the concentration) from different source regions showing intercontinental transport. Data are in micromoles per square meter. Source regions are (A) Asia (anthropogenic), (B) North America (anthropogenic), (C) Europe (anthropogenic), (D) biogenic (dimethyl suflide and hydrogen sulfide from natural sources), (E) volcanoes, and (F) total. Results from the Brookhaven National Laboratory chemical transport and transformation model for sulfate. SOURCES: Data from Benkovitz et al. 2003; and from C.M. Benkovitz, Brookhaven National Laboratory; S.E. Schwartz, Brookhaven National Laboratory; M.P. Jensen, Columbia University; M.A. Miller, Brookhaven National Laboratory; R.C. Easter, Pacific Northwest National Laboratory; and T.S. Bates, Pacific Marine Environmental Laboratory; unpublished material, 2004. longer range pollutant transport; namely, transport across national boundaries and even between continents. Analyses of data sets gathered from space-based and airborne platforms in combination with sophisticated computer models indicate that air pollutants from Central America, Asia, Africa, and Europe reach North America, and, in turn, pollutants from North America reach Europe (Figure 7-2). The implications for AQM in the United States are 2-fold: International and intercontinental transport of pollutants can significantly degrade air quality in the United States, particularly over the short term. For example, in April and May 1998, large amounts of smoke were observed by the total O3 mapping spectrometer (TOMS) satellite in

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Air Quality Management in the United States plumes emanating from fires in Mexico and extending into Florida, Texas, New Mexico, California, and Wisconsin. Along the Gulf Coast of Texas, a public health alert was issued advising residents to stay indoors to avoid the smoke. Similarly, chemical measurements have documented the import of pollutants transported from the Eurasian continent across the Pacific Ocean into the western part of North America (Jaffe et al. 1999; Wilkening et al. 2000). The rapid industrialization of the Asian continent could conceivably exacerbate this phenomenon. Pollutant emissions from North America, Europe, and Asia are probably causing an increase in the so-called background concentrations of pollutants in the northern hemisphere. For example, there is evidence that the background concentration of tropospheric (lower atmospheric) O3 in the northern hemisphere has increased by as much as a factor of 3 in the past 100 years, presumably in response to growing pollutant emissions from throughout the hemisphere, including the United States (Volz and Kley 1988; Staehelin et al. 1994). In addition, the mean summer afternoon concentration in rural areas of the United States (Logan 1988) and Europe (Scheel et al. 1997) have grown by a factor of 4 to 6. As standards for PM and O3 become more stringent and the thresholds for health effects from air pollution are found to be lower or nonexistent, the increasing level of background pollution causes difficulty in separating the effects of local and regional air pollution from global problems. To address these international aspects of air pollution, the AQM system will need to continue to develop, implement, and utilize sophisticated remote-sensing technology to document and track the phenomena. It will also be necessary for the United States to continue to pursue collaborative projects and enter into agreements and treaties with other nations (especially developing nations) to help minimize the emissions of pollutants that can degrade air quality on continental and intercontinental scales. Examples of past initiatives and treaties undertaken by the United States to mitigate atmospheric problems of international concern include the development and implementation of the Montreal Protocol to address stratospheric O3 depletion, the Convention on the Long-Range Transport of Transboundary Air Pollution (CLTRAP) to mitigate a wide range of air quality problems, and NARSTO to develop a coordinated program of research on the causes of and remedies to ground-level O3 and PM pollution in Canada, Mexico, and the United States. Adapting the AQM System to Climate Change The earth’s climate is warming (IPCC 2001). Although uncertainties exist, the general consensus within the scientific community is that this

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Air Quality Management in the United States warming trend will continue or even accelerate in the coming decades (IPCC 2001; NRC 2001b). Some forms of air pollution might be exacerbated by these climate changes. For example, precursor emissions and photochemical reactions that result in the production of O3 tend to increase with warmer temperatures (Carter et al. 1979; Tingey 1981; Chock et al. 1982; Halberstadt 1989; Cardelino and Chameides 1990; Bernard et al. 2001). The AQM system must be flexible and vigilant in the coming decades to ensure that pollution mitigation strategies remain effective and sufficient as our climate changes. At the same time, air pollution and human-induced climate change have one important common characteristic: they are both fostered by the burning of fossil fuels and other anthropogenic activities. Although some emissions contribute to climate warming (for example, CO2, soot, and upper tropospheric O3), others cool the climate (for example, sulfates formed from sulfur oxide emissions) (IPCC 2001; NRC 2001b; Hansen and Sato 2001). Thus, some efforts to mitigate air pollution may also help to mitigate climate warming (for example, reducing O3 precursor emissions), and others may inadvertently exacerbate climate warming (for example, reducing sulfur oxide emissions). If the current trends in climate continue, the air pollution and climate interactions will need to be considered in designing air pollution control strategies. Multipollutant approaches that include mitigation of climate warming as well as air pollution may be desirable, and some states have already considered implementing such programs (STAPPA/ALAPCO 1999). PRINCIPLES FOR ENHANCING THE AQM SYSTEM In the U.S. democratic system, the AQM system is designed and implemented by political decision-makers and is, therefore, greatly influenced by political and economic considerations. However, since its inception, the CAA has recognized that its effectiveness can be substantially enhanced by policies that are informed by and consistent with scientific and technological realities. On the basis of the committee’s analysis of the strengths and limitations of the AQM system (in Chapters 2 through 6), as well as the future challenges described above, the committee has identified a set of overarching scientific and system-design principles that should guide the improvement and development of the nation’s AQM system. One Atmosphere Approach for Assessing and Controlling Air Pollutants Air pollutants are constituents of the atmosphere and, as such, can be transported and mix freely in atmosphere and transfer to other environmental media. Air pollutants do not have political and statutory boundaries

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Air Quality Management in the United States Proposed Actions To address these deficiencies, the nation’s AQM system must begin the transition toward a risk-focused multipollutant approach to AQM. Several recommendations to initiate this transition are presented below. Develop System to Set HAP Priorities Many HAPs warrant increased resources for monitoring and research so that the risk HAPs pose to human health and welfare can be more accurately assessed and given the regulatory attention needed to protect human health and welfare. However, the statutory list of HAPs is long and may need to be expanded. It is unrealistic to expect that all HAPs can be monitored on a routine basis or that all HAPs can be placed under an aggressive regulatory framework. To ensure an appropriate allocation of resources and regulatory attention to the most dangerous HAPs, the committee recommends that the current system of setting priorities, embodied in EPA’s urban air toxics program (EPA 2000b), be continued and enhanced. One possible approach (using a three-tier system to set priorities) is described in Box 7-3 for illustrative purposes. Other approaches might involve further elaboration of EPA’s current list of 33 high-priority HAPs and a focus on ensuring that comprehensive strategies to monitor and address the sources of these pollutants are created and integrated into state and local AQMPs. Establish List of Potential Air Toxicants for Regulatory Attention Beyond the current list of HAPs, little information on a vast array of unregulated emitted substances is an important problem. Examples of such possible toxicants are substitutes for various toxicants, such as bromopropane, used as a substitute for tetrachloroethylene and flame retardant polybrominated diphenyl ethers; atmospheric transformation products, such as formylcinnamaldehyde; peroxyacyl nitrates; other oxides, such as 1,3-butadiene diepoxide and benzoic acid; vehicular emissions, such as 2-methylnapthalene, diesel exhaust mixture, polychlorinated dibenzodioxins, polychlorinated dibenzofurans, isobutylene, and black carbon; and a number of pesticides. Especially for high-volume emissions and hot spots, some reasonable level of regulatory response appears appropriate to curtail exposure to unregulated chemicals with suspicious but unproved adverse impacts. The committee recommends that suspicious chemicals emitted above a certain threshold concentration be tracked through a listing process and that a system for further addressing such chemicals be explored (see Box 7-4).

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Air Quality Management in the United States BOX 7-3 Example of a Potential Classification Scheme for Hazardous Pollutants A number of schemes could be used to aid in setting resource priorities for HAPs on the basis of the relative risks posed to human health and welfare by these pollutants. One example would be a system with three tiers, applied on a national basis or, if a more effective allocation of resources is allowed, on a multistate airshed basis. Tier 1 would most likely contain a few HAPs that, because of their diverse sources, ubiquitous presence in the atmosphere, and exceptionally high risk to human health and welfare, merited treatment similar (although not necessarily identical) to the treatment for criteria pollutants (for example, benzene). These HAPs would probably be drawn from the high-priority list identified in EPA’s urban air toxics strategy (EPA 2000b) and be those identified as posing the highest population risk in such assessments as EPA’s national air toxics assessment (EPA 2000b). In a small number of cases, these pollutants might be proposed for formal criteria pollutant status. In most cases, however, the Tier 1 HAPs not assigned NAAQS, as is done for criteria pollutants, might reasonably be incorporated into national monitoring programs and required or recommended for inclusion in an AQMP. As is the case for all HAPs, Tier 1 HAPs would be regulated through nationally mandated emission controls. Tier 2 HAPs, perhaps initially drawn from the remainder of the list of high-priority urban toxics identified by EPA in its urban air toxics strategy, would receive increased resources for monitoring and research, so that the risk they pose to human health and welfare could be assessed more accurately. In addition to nationally mandated emission controls, incentive programs could be implemented to encourage Tier 2 HAP inclusion in multipollutant AQMPs. Tier 3 HAPs, presumably initially drawn from the list of remaining HAPs, would be given the lowest priority for research and monitoring but would still be subject to nationally mandated emission controls. Beyond these tiers, the committee recommends that a list of potential air toxicants be established and that these toxicants be subject to some minimal level of regulatory review and consideration (see Box 7-4). Possible regulatory approaches include the development of exposure triggers (for example, emission concentrations, volume of use, or high exposures to some urban populations) for suspicious chemicals with sparse test data; some degree of testing and control would be required when the trigger measure was exceeded. Testing might include a minimal battery of tests, such as an expanded version of the current high-production-volume testing program instituted by EPA and the chemical industry. Inclusion on such a list of potential air toxicants might encourage the development of substitutes for those that exhibit initial indications of toxicity. However, a dynamic review of all pollutants, including those not on the current list,

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Air Quality Management in the United States BOX 7-4 Identifying New Toxicants A well-funded periodic review of air pollutants and their classification as HAPs and criteria pollutants should include an effort to identify new toxicants that pose a threat to human health and welfare. Some newly identified toxicants should be added to the HAPs list, and others should be listed for low-level regulatory oversight, as discussed below. Identifying New HAPs To conserve resources in reviewing the numerous unregulated air pollutants for potential placement on the HAPs list, an EPA-based program could be established that relied on existing hazard evaluations from other agencies and institutions, as well as new hazard evaluations for chemicals that have not received prior adequate evaluation. Special attention should be given to the implementation of these evaluation processes to ensure that they do not become too protracted or resource intensive and that output of chemical evaluations is sufficient. Candidates could be screened by emission concentrations, and screening-level exposure analyses could be performed. New hazard evaluations should focus on those air pollutants that have not been assessed adequately by other institutions and that have a current or future potential for large exposures, such as chemical substitutes for listed HAPs. The evidentiary threshold for listing a chemical as a HAP is that it can be identified as reasonably anticipated to cause toxicity. The number of chemicals undergoing traditional toxicity testing in traditional toxicity studies is diminishing as methods for toxicity screening are evolving. Beyond traditional toxicity tests, EPA should explore adding chemicals to the HAPs list with the use of the full range of analyses. Persistent, bioaccumulative toxins released into the air in relatively small volumes may pose substantial toxic risks (Lunder et al. 2004) and are important candidates for evaluation using non-traditional approaches. With regard to the use of hazard evaluations from other institutions, there are several possible sources for use in identifying HAPs candidates. Examples are chemicals required for reporting in the Toxics Release Inventory Program; chemicals classified in categories 2B, 2A, or 1 by the International Agency for Research on Cancer; chemicals identified as reproductive toxicants of concern by the National Toxicology Program’s Center for Evaluation of Reproductive Health Risks and listed on California’s Proposition 65 list of chemicals known to cause cancer or reproductive toxicity; chemicals identified by EPA as known or likely to cause cancer (old B2 category and above); chemicals regulated on the basis of adverse health effects by the Occupational Safety and Health Administration; chemicals identified as toxic by the National Institute for Occupational Safety and Health; and chemicals described as emitted into the air with a toxicological profile published by the Agency for Toxic Substances and Disease Registry. A screening analysis for addition of chemicals to the HAPs list has recently been provided (Lunder et al. 2004). Identifying Chemicals for Regulatory Oversight There is a vast array of unregulated emitted substances with sparse or no toxicological data to assess hazard potential adequately, and thus they cannot be placed on the HAPs list. Nevertheless, some attempt should be made to identify those chemicals that have sparse toxicological data but have structural similarities

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Air Quality Management in the United States to known HAPs and thus are likely to have adverse impacts. If chemicals so identified are also emitted in large amounts and have the potential for relatively high hot-spot exposures, they should be listed by EPA for enhanced monitoring and effects research and perhaps some low level of regulatory oversight. Because of the interrelated nature of environmental media (air, soil, water, and biota [see Box 7-1]), new chemicals suspected of being toxic or causing exposure but with few data on environmental fate and effects should be examined for inclusion on the HAPs list based on their production and use qualities and their likelihood of release into the air. followed by decision-making on controlling exposures to those compounds that pose the most significant risks, is essential to incorporating the as-yet-unlisted chemicals in future AQM strategies. Institute a Dynamic Review of Pollutant Classification EPA, as mandated in the CAA, must undertake a periodic review of the classifications given to pollutants. For example, successful mitigation of some criteria pollutants could logically result in their reclassification as HAPs to address remaining exposure and risk issues, and the proliferation of new technologies and products might require that some HAPs be reclassified as criteria pollutants. As new scientific information becomes available, the tier assigned a given HAP might need to be changed. Especially important is the need to identify and regulate pollutants that pose significant risks to human health and welfare but that are not yet listed as HAPs. Classifying and setting priorities for air toxicants would be facilitated by the development of benchmark air concentrations. The process for developing such values within EPA is resource intensive and protracted, and benchmark concentrations (for example, a reference air concentration of a pollutant likely to cause a harmful effect in humans) are not available for a number of substances on the HAPs list that have sufficient data for guidance level derivations. A tiered system could be adopted for the development of guidance values. The first tier would be the de novo resource-intensive derivations of guidance values. The second tier would be the adoption of values derived by other EPA programs or federal or state agencies. The third tier would be the development of guidance values by expedited techniques. Different levels of review would apply to each of the tiers.

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Air Quality Management in the United States Address Multiple Pollutants in the NAAQS Review and Standard-Setting Process In current practice, EPA interprets the CAA and its amendments as requiring it to set NAAQS for each criteria pollutant independently from one another. Although the committee does not believe that the science has evolved to a sufficient extent to permit development of multipollutant NAAQS, it would be scientifically prudent to begin to review and develop NAAQS for related pollutants in parallel and simultaneously. Such a practice would facilitate the assessment of the commonality of sources, exposures, and effects among the pollutants, as well as the development of multipollutant AQMPs as recommended in Recommendation Three. Although such a change will require a transition period to be accomplished, it is not unprecedented and should be implemented expeditiously. (Earlier criteria documents address PM and SO2 at the same time, for example.) Thus, we recommend the following: The criteria document and staff paper processes should be modified so that a simultaneous review of multiple interrelated pollutants could be developed in these documents. The interrelated NAAQS could then be considered in concert. Coordinated recommendations should be made to the EPA administrator with respect to modifications of the existing NAAQS so that new or modified NAAQS could be simultaneously promulgated. The implementation plans and attainment deadlines to address these NAAQS should be developed in a coordinated fashion to enable the development of multipollutant AQMPs. Enhance Assessment of Residual Risk In the current program to reduce emissions of HAPs from stationary sources, EPA is directed to undertake an assessment of residual risk following implementation of MACT and, on the basis of that assessment, decide whether additional controls are necessary. This program is getting under way somewhat slowly, the first completed assessment (on coke oven emissions) is expected in 2004. There are two key ways in which this process can be enhanced: The assessment of residual risk is challenging and time consuming. Nevertheless, given the importance of these assessments, EPA should move to accelerate this process to address an increased number of assessments in the years to come. To the extent that EPA is challenged to enhance resources to support risk assessments, residual risk assessments should be enhanced.

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Air Quality Management in the United States Although the CAA enables EPA to consider the full range of sources of a particular set of emissions in considering residual risk, in practice, EPA has focused primarily on the emissions from the source categories that were the subject of MACT. To better address the full range of pollutant exposures in all settings (especially in hot spots and in areas surrounding major stationary sources), EPA should attempt to include other major sources of the same chemicals as much as possible, so that the contribution of the MACT-regulated source is assessed in the context of its contribution to broader exposures. That assessment might take the form of creating hot-spot scenarios for estimating risk, drawn from actual locations of some of the regulated stationary sources. Targeted monitoring in areas in which relevant industrial activity is heavily concentrated could be useful in this attempt. Recommendation Five Enhance protection of ecosystems and other aspects of public welfare. Findings The CAA was established to protect both human health and welfare, and in one key aspect, the setting of NAAQS, the CAA mandates the establishment of both primary standards to protect public health and secondary standards to protect welfare (including sensitive ecosystems, forests, crops, materials, historical monuments, visibility, and other resources). Indeed, ecosystems provide invaluable services, such as the supply of high-quality water, soils that support the structure and function of ecosystems, forest and crop production, diverse aquatic habitat, and maintenance of fisheries. A loss or limitation of these services as a result of air pollution can therefore have significant consequences on the economy and quality of life. However, programs and actions undertaken thus far in response to the CAA have largely focused on the protection of human health, neglecting efforts to protect environmental quality with secondary standards or to take actions to address air pollution impacts on ecosystems and crops. The current practice of using the primary standard to serve as the secondary standard for most criteria pollutants does not appear to be sufficiently protective of sensitive crops and unmanaged ecosystems (see Chapter 2), although in one case EPA did recommend a separate secondary standard that was never implemented (EPA 1996b). Concentration-based standards are inappropriate for some resources at risk, such as soils, groundwater, forests, surface water, and coastal eco-

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Air Quality Management in the United States systems from air pollutants, such as sulfur, nitrogen, or mercury. For such resources, a deposition-based standard would be more appropriate (see Chapter 2). EPA should undertake a comprehensive review of the need and use of standards to protect public welfare. The nation’s AQM system has not been able to build a cohesive program capable of reliably reporting the status and trends in exposure and ecosystem conditions across regions and the nation (see Chapter 6). Proposed Actions Specific activities are recommended that will help EPA to establish measures and actions to more effectively protect public welfare: Develop and implement networks for comprehensive ecosystem monitoring. Networks for monitoring terrestrial and aquatic ecosystem structure and function are needed to quantify the exposure of natural and managed resources to air pollution and the effects of air pollutants on ecosystems. Establish acceptable exposure levels for natural and managed ecosystems. On an ongoing basis, EPA should evaluate current research on the effects of air pollutants on ecosystems as a means to establish acceptable exposure levels for both natural and managed resources. In setting these acceptable exposure levels, EPA should consider the relevant geographic dimensions and sensitivity of the various resources to determine if acceptable exposure levels vary regionally. The adequacy of resource-specific acceptable exposure levels should be reviewed and revised, if necessary, at least every 10 years. Promulgate secondary standards. From the improved understanding gained from the above two actions, secondary standards should be promulgated where appropriate. In some cases, deposition-based secondary standards may be preferable to concentration-based standards. If acceptable exposure levels vary significantly from one region of the nation to another, consideration should be given to the promulgation of regionally distinct secondary standards.9 Design and implement controls. Within the context of EPA’s recommended enhanced responsibility and authority for addressing multistate air 9   A move to regional secondary standards may require an amendment of the CAA. The courts have held that the primary NAAQS must be met on a nationwide basis. It is possible, however, that a court would find that a standard designed to protect the public welfare did not have to be uniform throughout the country, even though a standard designed to protect public health must be uniform. See Lead Industries Ass’n v. EPA, 647 F.2d 1130 (D.C. Cir. 1980).

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Air Quality Management in the United States pollution problems (see Recommendation 2), the agency should develop regulatory programs and mitigation actions to attain the standards. Track progress toward attainment of secondary standards. The aforementioned monitoring of ecosystem exposure and function should be used to track progress toward attainment of standards and to determine whether the progress results in the expected improvement in ecosystem function. CONCLUSION In an advanced technological society such as the United States, air is a resource whose quality must be managed through the control of pollutant emissions. However, these controls can be implemented without abandoning technology or dismantling the economy. Experience over the past three decades of air pollution control in the United States has shown that effective AQM can often be accomplished best by encouraging and embracing new technologies as well as by using market forces within a vibrant economy to control emissions. AQM is also more effective when science and engineering have a central role in identifying critical problems, helping to optimize strategies for mitigation, designing systems to implement these strategies, and finally, tracking the success of these systems. The nation’s AQM system has had major successes over the past 30 years, but it must work to complete the task already before it (for example, attainment of the NAAQS for PM and O3) and to face substantial new challenges in the future. In the committee’s view, the AQM system should strive to Target the most significant exposures, risks, and uncertainties. Take an integrated multipollutant approach. Be a performance-oriented system. Take an airshed-based approach. In this chapter, the committee has proposed a set of five broad and interrelated recommendations for moving the AQM system in the above direction over the next decade or so. Because the nation’s AQM system has been effective in many areas over the past decades, much of the system is good and bears retaining. Thus, the recommendations proposed here are intended to evolve the AQM system incrementally rather than to transform it radically. The recommendations are also not intended to deter the current, on-going AQM activities aimed at improving air quality. Indeed, even as these recommendations are implemented, there can be little doubt that important decisions to safeguard public health and welfare must continue to be made, at times in the face of scientific uncer-

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Air Quality Management in the United States tainty. Moreover, new opportunities and approaches for managing air quality will appear. Even today, looking forward, we can identify several such areas: First, the challenge of moving beyond “one atmosphere” to “one environment” (see Box 7-1). The effects of air pollutants in water and soil (as well as air) and the multimedia implications of control strategies for all media have already been demonstrated (for example, air pollutant emissions from wastewater-treatment and site-remediation facilities and impacts on water from fuel additives for enhanced combustion). The remaining challenging task is to develop multimedia approaches and strategies, a task that was beyond the scope of this committee’s endeavors but one that will require attention in the years ahead. Second, the opportunities presented by rapidly developing and increasingly sophisticated science and technology (Box 7-5). New advances in biotechnology, enhanced analytical and monitoring technologies, and many more such innovations are just beginning to have a part in AQM. These advances offer the prospect of even more targeted and effective air quality strategies in the decades ahead. Third, the enhancement of the AQM system by the public and private sectors. Over a longer time horizon, the nation’s AQM system would be significantly enhanced by empowering the public and private sectors to undertake pollution prevention activities on their own accord rather than by merely controlling air pollutants after they have been produced. Although specific recommendations for incorporating these new approaches into the nation’s AQM system are not advanced here, the enhancements to the system—with its greater emphasis on performance and its encouragement of innovation—should facilitate their appropriate use in AQM over time. Implementing this integrated set of recommendations will require the development of a detailed plan and a schedule of steps to be undertaken. Although the committee expects that many of the recommendations can be accomplished within the current CAA, some may require legislative action. A comprehensive analysis will be required to identify recommendations that can be implemented within the existing statutory framework and those that require legislative action—an analysis beyond the charge and expertise of this committee. To ensure timely implementation, the committee urges EPA to convene an implementation task force of experts from the key parties—the states; tribal and local agencies; environmental, industrial, and other stakeholders; and the scientific and technical community—to prepare a detailed implementation plan and an analysis of which, if any, statutory changes may be necessary.

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Air Quality Management in the United States BOX 7-5 Advances in Environmental Instrumentation Resource constraints have resulted in an undersampling of the environment—temporally, spatially, and with regard to chemical speciation. New developments in biotechnology, engineering, nanotechnology, and information technology provide promise for the development of monitoring networks that will overcome some of these deficits (Steinfeld et al. 2001). Advances in instrumentation that could contribute to the enhancement of the AQM system include the following: Advances in solid-state tunable diodes that will enable the translation of powerful optical diagnostic techniques from the research laboratory to the field. Methods that provide capability of real-time measurements and remote sensing are differential absorption LIDAR (DIAL), correlation spectroscopy, and Fourier transform spectroscopy (Steinfeld et al. 2002). These laser diagnostics can be used to monitor fluxes (Shorter et al. 1996), in addition to mapping horizontal and vertical concentration distributions of pollutants (Tittel 1998; NASA 2003). Reduction in the size of diagnostic and data acquisition systems that will permit the use of accurate and fast response instruments on mobile platforms (vehicular or airborne) capable of mapping concentration profiles for model testing and quantifying area sources and for identifying hot spots, leaks, and upset conditions. Miniaturization will also facilitate the development of personal exposure monitors of increased sophistication to monitor vital health-related statistics. Miniaturized near-real-time instruments are already available for many gaseous pollutants and are becoming available for particles through the use of field-deployable desorption gas chromatography and mass spectrometry techniques (Jeon et al., 2001) and aerosol time-of-flight mass spectrometers (Noble and Prather 1996; Bhave et al. 2002; Jayne et al. 2000). The development of distributed networks of microsensors to monitor HAPs and biotoxins may become feasible as a result of recent developments of “laboratory-on-a-chip” technology initially driven by concerns with homeland security (Frye-Mason et al. 2001; Lindner 2001). Perhaps the largest potential impact on the current approaches to monitoring will be the development of methods in biotechnology to rapidly screen for impacts of individual chemicals and mixtures. One example of the developments that will be important for the AQM system is that of DNA microarrays that show the potential of differentiating between exposures to different classes of toxicants and different toxicological outcomes (Bartosiewicz et al 2001). Problems exist in the transitions of these technologies from research tools to commercial products that meet the needs of robustness, ease of use, cost, and equivalence to federal reference methods, problems that have only been partly alleviated by the Environmental Technology Verification Program. Use of instruments or procedures that do not satisfy a rigorous vetting process should be encouraged when valuable new insight is provided. For example, visual plume opacity readings have proved to be of great value, even though they do not provide the mass or composition of any specific pollutant, and cross-road sensors (Stedman et al. 1997; Jiminez et al. 2000) have proved their value in identifying high-emitting vehicles, even though their use for regulatory purposes is problematic. Some of the new methods might be introduced in the AQM system for specialized purposes, such as identifying hot spots, processing upset conditions for stationary sources, identifying breakdown in the emission control for mobile sources, and mapping spatially and temporally concentration distributions for ambient pollutants.

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Air Quality Management in the United States Implementation of the recommendations will also require additional resources. Although these resources are not insignificant, they should not be overwhelming. Even a doubling of the current EPA commitment to air pollution monitoring and research would be only about 1% of the costs incurred annually to comply with the CAA. Such resources are even smaller when compared with the costs imposed by the deleterious effects of air pollution on human health and welfare (see discussion in Chapter 1). Fundamental changes will also be needed in aspects of the nation’s AQM system to shift the focus to tracking progress. Such a transition will be difficult, but as noted above, it is imperative that actions to further reduce emissions continue even as this transition takes place. Finally, implementation of these recommendations and meeting the challenges of AQM in the decades to come will require a major commitment from the research and development and scientific communities to provide the human resources and technologies needed to underpin an enhanced AQM system and to achieve clean air in the most expeditious and effective way possible. The committee believes that these communities are ready to respond.