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Introduction

Emissions from mobile sources ranging in size from small, handheld gardening equipment to on-road passenger vehicles, heavy-duty trucks, and large construction equipment contribute significantly to air pollution in the United States. The federal Clean Air Act (CAA) mandates, with specific exceptions, that the U.S. Environmental Protection Agency (EPA) regulate mobile sources by uniform national emissions standards (CAA section 209(a)). An exception to federal preemption of these standards is granted to the state of California. California’s exemption was granted in the early years of mobile-source regulation because air pollution was more severe in California than in the rest of the nation, and the state had a long history of establishing its own emissions standards for on-road vehicles and other mobile sources (CAA sections 209(b) and 209(e)). Other states may choose to adopt California emissions standards as a mitigation strategy but may not establish their own standards.

California and the federal government have set mobile-source emissions standards and have tightened those standards over time. This evolution has led to important technological advances in emission-control systems and substantial reductions in mobile-source emissions. Several states, particularly in the Northeast region, have adopted California emissions standards in the past 2 decades as part of their plans to improve air quality and protect public health. Because mobile-source emissions still represent a substantial fraction of air pollutant emissions, mobile-source emissions reductions can still contribute substantially to improvements in air quality. The role of state versus federal government in establishing



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State and Federal Standards for Mobile-Source Emissions 1 Introduction Emissions from mobile sources ranging in size from small, handheld gardening equipment to on-road passenger vehicles, heavy-duty trucks, and large construction equipment contribute significantly to air pollution in the United States. The federal Clean Air Act (CAA) mandates, with specific exceptions, that the U.S. Environmental Protection Agency (EPA) regulate mobile sources by uniform national emissions standards (CAA section 209(a)). An exception to federal preemption of these standards is granted to the state of California. California’s exemption was granted in the early years of mobile-source regulation because air pollution was more severe in California than in the rest of the nation, and the state had a long history of establishing its own emissions standards for on-road vehicles and other mobile sources (CAA sections 209(b) and 209(e)). Other states may choose to adopt California emissions standards as a mitigation strategy but may not establish their own standards. California and the federal government have set mobile-source emissions standards and have tightened those standards over time. This evolution has led to important technological advances in emission-control systems and substantial reductions in mobile-source emissions. Several states, particularly in the Northeast region, have adopted California emissions standards in the past 2 decades as part of their plans to improve air quality and protect public health. Because mobile-source emissions still represent a substantial fraction of air pollutant emissions, mobile-source emissions reductions can still contribute substantially to improvements in air quality. The role of state versus federal government in establishing

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State and Federal Standards for Mobile-Source Emissions mobile-source emissions standards has been and remains an important environmental policy issue. ORIGIN OF STUDY AND COMMITTEE CHARGE In January 2003, a Senate omnibus bill included a provision directing EPA to “submit a report … on the practices and procedures by which States develop separate emission standards, including standards for nonroad engines or vehicles, as compared to the development by EPA of national emission standards under the Clean Air Act. This report shall include an assessment of the procedures, practices, standards and requirements used by States as opposed to those used by EPA, including how States and the EPA take into account technological feasibility, economic feasibility, impact on the economy, costs, safety, noise and energy factors associated in the development of these standards.” The provision was later modified, directing EPA to contract with the National Academy of Sciences to conduct the review and submit a report of its findings to the Committees on Appropriations. In response to EPA’s request, the National Research Council (NRC) established the Committee on State Practices in Setting Mobile Source Emissions Standards. The NRC study began in March 2004. The Statement of Task set forth to the committee is as follows: This committee will review and evaluate the scientific and technical practices used by states in setting emissions standards for mobile sources, including those for nonroad engines and vehicles. The committee will assess the scientific and technical procedures used by states to develop or adopt emissions standards separate from those set by EPA under the Clean Air Act and assess the factors that cause states to move to more stringent emissions standards. The committee will consider the scientific, technical, and economic rationale and methods used by the states in setting standards and how they compare with those used by EPA. In addition, the committee will take into consideration the direct and indirect impacts and benefits that state emissions standards have had on various factors, including compliance costs, energy consumption, air quality, and human health. Specifically, the committee will assess the following:

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State and Federal Standards for Mobile-Source Emissions How states assess their need for more stringent emissions standards. How California develops and other states adopt separate emissions standards. How states take into consideration technical and economic feasibility of compliance with separate emissions standards. How states take into account expected impacts on cost to consumers, employment, safety, noise, and energy as part of the standards-setting process. How expected emissions reductions and air quality benefits are accounted for in the state emissions standards-setting process, and how those benefits help states to meet their air quality attainment requirements. How the rationale and methods used by states compare with those used by EPA. How California emissions standards affect those set by EPA. The committee was also asked to consider the effects of over 30 years of experience by California in setting separate emissions standards, not only in terms of the impacts and benefits on such factors as compliance costs, energy use, air quality and human health but also in terms of the effects on the timing of federal emissions standards. The committee was also asked to examine the intersection of state emissions standards with fuel standards. THE COMMITTEE’S APPROACH TO THE CHARGE AND THE REPORT ORGANIZATION The committee began its work with a historical review of mobile-source regulation by California and the federal government. The review includes the significance of mobile-source emissions to air quality and health (Chapter 2), the history and status of mobile-source regulation in the United States (Chapter 3), and the evolution of technology to meet emissions standards (Chapter 4). The report continues with an analysis of the reasoning behind the current system of mobile-source regulation in the United States (Chapter 5). The committee then considers several case studies of mobile-source regulation (Chapters 6 and 7) to understand and explain the specific aspects of regulating the various sectors of mobile

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State and Federal Standards for Mobile-Source Emissions sources. The report concludes with a chapter of findings and recommendations (Chapter 8). The committee interpreted its charge to include any mobile-source emission standard that has been established as a rule by California. The committee did not consider emissions standards for federally preempted sources, such as aircraft, locomotives, commercial marine vessels, and certain other nonroad equipment. The committee limited its considerations to emissions standards for new mobile sources or engines and did not consider in-use emissions control programs, such as motor vehicle emissions inspection and maintenance programs (I/M). Furthermore, the committee did not consider fuel composition or refueling emissions standards. Historically, emissions standards set by California and the federal government have aimed to reduce ambient concentrations of criteria pollutants, including nitrogen dioxide (NO2), ground-level ozone (O3), carbon monoxide (CO), particulate matter (PM), and sulfur dioxide (SO2) (see “criteria air pollutants” in Glossary). Emissions standards have also been developed or proposed for hazardous air pollutants (also called air toxics) by EPA and California and for greenhouses gases by California. The committee’s assessment focuses on emissions standards for criteria pollutants. However, in Chapter 6, the committee also summarizes standards that have been recently set for greenhouse gas emissions, recognizing that no such standards have been established by the federal government. The committee did not perform an in-depth analysis of the recent greenhouse gas standards or develop findings and recommendations specific to these standards. The committee decided that it would be premature to consider the greenhouse gas emissions standards because these standards were passed into law by California after the committee had begun its analysis and because the legal standing of the standards was in question during this study. In the course of its work, the committee found that, historically, EPA and CARB have focused on the technical feasibility of proposed standards, the emissions benefits of the standards, and the monetary costs to manufacturers to comply with the standards. EPA has been required to assess and monetize the health benefits of its major regulations in recent years and utilizes air quality analysis as part of this process. With some exceptions, the impacts of emissions standards on employment, safety, noise, and energy are dealt with qualitatively or not at all. Therefore the main focus in this report is on the technical feasibility of proposed standards, the emissions and air quality benefits of those standards, and the monetary costs to manufacturers to comply with the standards.