APPENDIX D-Mobile Source Air Toxics: Background for FHWA Interim Policy
The EPA and the public health community are conducting research on a group of emissions called "air toxics" or "hazardous air pollutants." According to EPA, existing and newly promulgated rules will cause significant reduction in air toxics from mobile sources-in the range of 67 percent to 90 percent by 2020. This paper provides guidance on whether and how highway projects should be analyzed for air toxics through the NEPA process.
A. Background
The Clean Air Act identified 188 air toxics, also known as hazardous air pollutants. The EPA has assessed this expansive list of toxics and selected a group of 21 that it considers mobile source air toxics (Attachment A). More recently, the agency has extracted a subset of this list of 21 and developed what EPA now labels the six priority MSATs. These are benzene, formaldehyde, acetaldehyde, diesel particulate matter/diesel exhaust organic gases, acrolein, and 1,3-butadiene. While EPA has identified these as the more significant MSATs, the agency has not proposed to establish ambient standards for any of these pollutants.
The EPA issued a final rule on Control of Emissions of Hazardous Air Pollutants from Mobile Sources in March 2001 under provisions of the Clean Air Act requiring EPA to characterize, prioritize, and control these emissions as appropriate. In addition to highlighting the 21 MSATs, the final rule summarized the mobile sources contribution to national inventories of hazardous air pollutants. Since MSATs can be loosely defined as volatile organic compounds, nonvolatile organics, diesel particulate matter/diesel exhaust gases, or metals, so the linkage with transportation vehicles and fuels is direct.
In the March 2001 rule, the EPA projected that the reductions in mobile source air toxic emissions via several existing and new control programs and technology-oriented vehicle standards would be considerable. That same final rule highlighted a number of emissions projections, including a 67 to 76 percent drop in benzene, acetaldehyde, and 1,3-butadiene between 1990 and 2020. For highway-related diesel particulate matter, the agency projects a 90 percent reduction by 2020. The following chart, produced by FHWA, takes a closer look at these projected MSAT reductions from 2000 to 2020:
Projected MSAT Trends, 2000-2020
These steep drops expected for MSATs are slated against a backdrop of three decades of steady decreases in other highway emissions. Since 1970, the carbon monoxide from highway vehicles has dropped 43 percent. For hydrocarbons, on-road vehicle emissions fell just under 60 percent during the same period, while nitrogen oxides exclusively from passenger vehicles fell more than 30 percent since 1970.
Progressively tighter motor vehicle tailpipe standards have accounted for the lion's share of the mobile source emissions reductions occurring over the past 30 years. Other in-place or proposed programs are playing a strong role with further reductions in both the Clean Air Act criteria pollutants and MSATs expected in the next generation. Considerable air toxic emissions reductions are projected from these programs, which include:
- Reformulated Gasoline (RFG), a product of Clean Air Act legislation, targeting the nation's more acute ozone nonattainment areas
- National Low Emissions Vehicle (NLEV) standards
- Tier 2 motor vehicle emission standards and associated gasoline sulfur control requirements
- Heavy-duty engine standards and on-highway diesel sulfur control requirements, and
- Final rule for nonroad diesel engines, and proposals for marine and locomotive engines
- 2001 MSAT rule, toxic emissions performance standard
The EPA has committed to develop another rule to address mobile source air toxics. The agency has committed to propose this rule by February 28, 2006. While the long-term projections are impressive, the impacts of today's levels of mobile source air toxics have become a public health concern. Air toxics have been raised as an issue with several major highway projects around the country, resulting in lengthy deliberations and in some cases, litigation.
On a regional basis, the transportation conformity rule has been employed alongside the National Environmental Policy Act (NEPA) to provide the framework for analysis of mobile source emissions resulting from Federal-aid highway projects. However, the conformity process is applicable only to CAA nonattainment and maintenance areas-those areas designated by EPA due to violation of a National Ambient Air Quality Standard (NAAQS) for a criteria pollutant. Since EPA has not established ambient standards for air toxics, there are no nonattainment areas for air toxics. Also, for Federal programs such as those administered by FHWA, the USEPA has not yet developed national peer reviewed and approved guidance on how to conduct scientifically valid and reliable mobile source air toxics health assessments.
In the preamble to the March 2001 MSAT rule, EPA acknowledged significant gaps in its knowledge regarding exposure to toxics and the potential benefits of further reductions. It specifically stated that inclusion on the MSAT list is not itself a determination by EPA that emissions of the compound in fact present a risk to public health or welfare, or that it is appropriate to adopt controls to limit emissions. Rather, EPA identified the purpose of the MSAT list as providing "a screening tool that identifies those compounds emitted from motor vehicles or their fuels for which further evaluation of emissions controls is appropriate." See Control of Emissions of Hazardous Pollutants from Mobile Sources, 66 FR at 17234-35 (March 29, 2001).
In the March 2001 rule, it also concluded that preexisting vehicle-based emission controls already offer the "greatest degree of toxics control achievable at this time considering existing standards, the availability and cost of the technology and noise, energy, safety factors and lead time." 66 FR 17230. It further noted that the technology to reduce one type of pollutant reduces the other types as well. 66 FR at 17239-41.
Finally, in conjunction with the rule, EPA established a Technical Analysis Plan in which the agency committed to obtaining more data in critical areas and to improve its ability to estimate exposures. Specifically, it stated:
To improve our ability to characterize [mobile toxic] exposures to highly exposed subpopulations requires better information regarding ambient concentrations of [mobile toxics] in hot spot areas and appropriate microenvironmental factor values for high-exposure microenvironments. The EPA is developing local-scale emissions and dispersion models for mobility sources to better inform the Agency and the public about potential hot spots. In addition, EPA is conducting spatially refined urban area modeling (including mobile sources). 66 FR at 17259.
Work on these models is still in progress.
B. Research on Air Toxics
This is an emerging area of research. While much has been completed to estimate the overall health risk of the major mobile source toxics, there is a knowledge gap in our ability to apply accurate dose-response relationships to many of the pollutants. Consequently, the transportation community is confronted with the challenge of assessing the impacts of these emissions without the benefit of standards similar to those set for the six criteria pollutants defined in the Clean Air Act. While past research has focused on waterborne toxic pollutants and on widely known carcinogens, such as benzene, today's research agenda is considerably more expansive and focuses much more attention on air toxics suspected to cause cancer or other serious health effects. A number of recent studies have centered on EPA's short list of 21 MSATs, including the FHWA research summarized in Attachment B.
C. Relevant Legal Requirements
The National Environmental Policy Act (NEPA) requires all Federal agencies to prepare an environmental impact statement for every major action significantly affecting the quality of the human environment. Implementing regulations from the Council on Environmental Quality (40 CFR 1500) and FHWA (23 CFR 771) specify how these responsibilities are to be carried out and how to handle actions that do not require the preparation of an EIS. These regulations stress the importance of evaluating issues that are relevant to agency decision-making and avoiding studies and analyses that are not relevant. Specifically, the CEQ regulations call for a scoping process to help determine which issues are significant in the preparation of an EIS and to eliminate from detailed study issues which are not significant.
In assessing environmental impacts for highway projects, FHWA has analyzed air quality at the project level. This is particularly true in nonattainment and maintenance areas where the concern about violating the National Ambient Air Quality Standards (NAAQS) is a significant issue. These assessments at the project level have centered, largely, on carbon monoxide and PM-10 "hotspots," a common term for confined, local area impacts where there is a concern about exceeding the NAAQS. However, given that national ambient air quality standards have not been established for MSATs and the evolving state of the science, there are no established criteria for determining when MSAT emissions should be considered a significant issue.
Regulations under the Council on Environmental Quality (CEQ) recognize that there will be situations encountered in the NEPA process for EISs in which very little or no information exists to allow a reasonably thorough analysis of cause and effect, impact, or potential environmental harm. When addressing potential MSAT impacts, these CEQ provisions must be met (see Attachment C). A description of the uncertainties of both the analytical processes and the interpretation of results should be included in addition to a clear explanation of how the analysis meets the CEQ requirements in 40 CFR 1502.22 covering incomplete or unavailable information. This latter discussion should detail why the information cannot be obtained - due either to exorbitant costs or unknown means to obtain it - and should cover all the elements outlined in 40 CFR 1502.22. It is critical that the decisions made regarding the type of analysis, its results and interpretation be clearly described in the environmental document (EIS or EA).
Attachment A--List of Mobile Source Air Toxics
(Priority MSATs in bold)
Acetaldehyde
Acrolein
Benzene
1,3-Butadiene
Diesel Particulate Matter & Diesel Exhaust Organic Gases
Formaldehyde
Arsenic Compounds
Chromium Compounds
Dioxin/Furans
Ethylbenzene
n-Hexane
Lead Compounds
Manganese Compounds
Mercury Compounds
Methyl Tertiary Butyl Ether (MTBE)
Naphthalene
Nickel Compounds
POM
Styrene
Toluene
Xylene
Attachment B - FHWA Scientific Research on Air Toxics
Human epidemiology and animal toxicology experiments indicate that many chemicals or mixtures termed air toxics have the potential to impact human health. As toxicology, epidemiology and air contaminant measurement techniques have improved over the decades, scientists and regulators have increased their focus on the levels of each chemical or material in the air in an effort to link potential exposures with potential health effects. The USEPA's list of 21 mobile source toxics represents their prioritization of these chemicals or materials for further study and evaluation. The EPA's strategy for evaluating air toxic compounds effect is focused on both national trends and local impacts. The FHWA has embarked on an air toxics research program with the intent of understanding the mobile source contribution and its impact on local and national air quality. Several of the studies most relevant to the highway community either initiated or supported by FHWA are described below.
Air toxics emissions from mobile source have the potential to impact human health and often represent a regulatory agency concern. The FHWA has responded to this concern by developing an integrated research program to answer the most important transportation community questions related to air toxics, human health, and the NEPA process. To this end, FHWA has performed or is currently managing several research projects. Many of these projects are based on an Air Toxics Research Workplan that provides a roadmap for agency research efforts. These efforts include:
- Air Toxics Supersite Study (Traffic and Ambient Concentration Study). This study is designed to determine whether the contribution of vehicle-emitted air toxic compound concentrations to ambient air concentrations can be measured. The study is being conducted in conjunction with a particulate matter study to determine whether air toxic compounds (and PM) are local air quality impacts or regional concerns.
- Air Toxics Monitoring and Modeling Study. This study is designed to determine the reliability of emission models in predicting ambient measured air toxic concentrations. This is an important component of air toxics research since models are typically used for developing emission inventories and the resulting mitigation programs designed to limit emissions. Accurate forecasting of future emissions is essential to programs implemented to reduce toxic emissions.
- Kansas City Study. This study is designed to determine the distribution of PM emissions in a randomly selected fleet as well as identify the percent of high emitters in the fleet. The Kansas City Study was initiated by EPA to conduct exhaust emissions testing on 480 light-duty, gasoline vehicles in the Kansas City Metropolitan Area (KCMA). This project will also characterize gaseous and PM toxics exhaust emissions from a portion of these light-duty vehicles. Data obtained from this program will be used to evaluate and update emission models, evaluate existing emission inventories, and assess the representativeness of previous emissions studies.
- Multiple Air Toxics Exposure Study Science and Uncertainty Review (MATES-II). This study is designed to evaluate the scientific techniques of this influential Southern California study to determine whether these techniques would be appropriate for use today, and the scientific uncertainties associated with the 1998 study. There are two phases to the study. The first examines the transportation side (activity, emissions and concentrations), while the second looks at the toxicity and exposure assessments conducted as part of MATES-II. The FHWA wants to better understand how the results were obtained and how relevant they are to transportation planning.
- Knowledge Gaps and Research Needs in Linking Mobile Source Air Toxics To Potential Public Health Risks. This study, to be conducted by the independent Health Effects Institute (HEI), is designed to better understand the fundamental science and relationships between transportation vehicle emissions, potential and actual human health impacts, determine the technical strength of published studies, and identify data quality gaps and data gaps. The final study report will summarize concentration and dose-response relationships, toxic effects, and their relation to actual human health impacts that could result from real-world exposures to the extent possible. Researchers will be asked to evaluate the quality of study findings for use in risk assessments and the quality of such data on risk assessment numerical findings. Research cooperators can then synthesize their technical findings to identify knowledge gaps and research needed to determine the strength of linkages between mobile source air toxics, potential public health risks as expressed in epidemiology or risk assessment studies, and frank health effects with clearly definable cause and effect relationships. Research cooperators will be asked to chemical and physical composition of MSAT, identify variability in MSAT, and identify the strength of relationships between MSAT related pollutants and their potential health effects.
Attachment C - CEQ Provisions Covering Incomplete or Unavailable Information (40 CFR 1502.22)
Sec. 1502.22 Incomplete or unavailable information.
When an agency is evaluating reasonably foreseeable significant adverse effects on the human environment in an environmental impact statement and there is incomplete or unavailable information, the agency shall always make clear that such information is lacking.
(a) If the incomplete information relevant to reasonably foreseeable significant adverse impacts is essential to a reasoned choice among alternatives and the overall costs of obtaining it are not exorbitant, the agency shall include the information in the environmental impact statement.
- (b) If the information relevant to reasonably foreseeable significant adverse impacts cannot be obtained because the overall costs of obtaining it are exorbitant or the means to obtain it are not known, the agency shall include within the environmental impact statement:
- A statement that such information is incomplete or unavailable;
- a statement of the relevance of the incomplete or unavailable information to evaluating reasonably foreseeable significant adverse impacts on the human environment;
- a summary of existing credible scientific evidence which is relevant to evaluating the reasonably foreseeable significant adverse impacts on the human environment, and
- the agency's evaluation of such impacts based upon theoretical approaches or research methods generally accepted in the scientific community. For the purposes of this section, "reasonably foreseeable" includes impacts that have catastrophic consequences, even if their probability of occurrence is low, provided that the analysis of the impacts is supported by credible scientific evidence, is not based on pure conjecture, and is within the rule of reason.
(c) The amended regulation will be applicable to all environmental impact statements for which a Notice to Intent (40 CFR 1508.22) is published in the Federal Register on or after May 27, 1986. For environmental impact statements in progress, agencies may choose to comply with the requirements of either the original or amended regulation.
