This Strategic Workplan for Particulate Matter Research is designed to provide direction for the research on particulate matter (PM) being undertaken by and on behalf of the transportation community. It identifies a set of five research focus areas and describes the research projects necessary to most effectively develop needed information and tools and to target resources. Sponsored by the Federal Highway Administration (FHWA), this plan was developed by FHWA in cooperation with atmospheric scientists, air quality experts, environmental and transportation planners from state departments of transportation (DOTs), metropolitan planning organizations (MPOs), air quality agencies, industry, and academia.
PM is the term used to describe a complex mix of solid particles and liquid droplets found in the air. PM varies widely in terms of its physical and chemical properties and there are many sources that contribute to atmospheric concentrations. A primer on PM is provided in Appendix A.
Concern about the adverse health impacts of particulates first led to regulation of PM under the Clean Air Act (CAA) in 1971 when the United States Environmental Protection Agency (EPA) established a National Ambient Air Quality Standard (NAAQS) for PM. Since the early 1970s, a number of transportation agencies, primarily in Western States, have been involved in the development of air quality plans to reduce PM emissions and to reach attainment of the national standards.
More recently, numerous scientific studies have linked exposure to fine PM with significant human health problems across the United States. In response to these findings, the EPA established major changes to the NAAQS for PM in July 1997.1 The revised NAAQS are expected to have wide-ranging impacts on the transportation community.2 These impacts include:
An expected increase in the number of PM nonattainment areas, particularly in the Eastern United States, thus greatly expanding the number of state DOTs, MPOs, and local transportation agencies that are affected by PM regulations;
A focus on combustion processes (including vehicle engines), as a major source of PM, particularly in urban areas where combustion-related emissions are likely to compose a greater share of total emissions, thus increasing the likelihood of more widespread transportation-related control programs for PM;
An emerging recognition of PM as a regional problem, caused in part by secondary PM, that is formed and transported over great distances, thus redefining PM, in part, from a local to a regional-level issue and expanding the need for broader emission control programs.
Given an increase in the number of PM nonattainment areas, transportation agencies in many parts of the country will be required to participate in the development of transportation-related emission inventories and control strategies for inclusion in State Implementation Plans (SIPs) for PM. They will also potentially be faced with undertaking conformity analyses for PM.
In addition to these new requirements, transportation agencies also have an interest in PM because of the relationships between PM and other current and emerging atmospheric concerns. The interrelationship between PM and other air pollutants is summarized in Figure 1. Interactions between PM and ozone are an important concern since ozone's precursors, oxides of nitrogen (NOX) and volatile organic compounds (VOCs), also contribute to secondary formation of PM and for many locations meteorological conditions conducive to high ozone formation often lead to high levels of PM. High concentrations of PM also contribute to regional haze, which is a concern for visibility in urban and rural areas. In addition, PM indirectly affects global climate change by increasing light scattering and the number of particles available for cloud droplet formation. Some particulates are also toxic, such as diesel particulate exhaust and semi-volatile polycyclic aromatic hydrocarbons (PAH), therefore reductions in the mass of these particulates may also reduce toxic air contaminants.
Figure 1. Relationship of PM to Other Atmospheric Concerns
Despite continued challenges to meet existing PM standards, as well as the potential repercussions of the new PM NAAQS on the transportation community, and the relationship between PM and other air quality concerns, there are acknowledged major weaknesses in the basic analytic tools and data that are needed to develop appropriate policy responses. In particular, policymakers charged with responding to the new PM standards are challenged by factors such as a limited understanding of spatial and chemical trends in ambient PM emissions, inaccurate and incomplete emissions inventories, and inadequate emissions models. The large gaps in information necessitate targeted research focused specifically on the needs of the transportation community.
The FHWA's 1998 National Strategic Plan establishes the Agency's mission "to continually improve the quality of our Nation's highway system and its intermodal connections." It identifies five strategic goals for achieving this mission, one of which is to protect and enhance the natural environment and communities affected by highway transportation.
Building on the National Strategic Plan, FHWA established an environmental research program as a core component of the Agency's environmental stewardship responsibilities. The Agency's broad environmental research goals are identified in FHWA's 1998 Strategic Plan for Environmental Research. Air quality research, including investigation of PM-related issues, is one of eight program goals established in the Strategic Plan for Environmental Research.
This Strategic Workplan for PM Research draws on FHWA's previous strategic planning initiatives to provide direction and focus for the Agency's role in PM research. It establishes a two-fold vision for conducting research that establishes a transportation focus in PM research and ensures that research results are relevant to the needs of transportation policymakers.
Bringing a Transportation Focus to Study of PM Issues.Despite significant concern about the health impacts of PM and increasing evidence that the transportation sector may be a significant contributor to ambient PM concentrations, substantial research gaps remain in terms of understanding the formation, characteristics, source apportionment, and modeling of PM, particularly in relation to transportation sources.
Critical uncertainties in the research include a lack of knowledge about the chemical composition of PM and relative source contributions, as well as the extent of secondary PM formation in the atmosphere. Developing better information about the characteristics and source apportionment of PM is a critical step for the development of emissions models and inventories that can be used for policy development and planning. As a result, a program of transportation-focused research is needed both to develop the information and tools needed to shape future policies and programs.
Developing Applied Research Products that Respond to Needs of Transportation and Air Quality Planning Practitioners. Transportation-focused PM research must be targeted to the policy and program needs of the transportation community, and integrating these needs with ongoing and future research initiatives in a timely and cost-effective manner. In this regard, the Workplan is designed to:
This Strategic Workplan for PM Research was developed with input from transportation and air quality experts throughout the country, as shown in Figure 2. It draws extensively on information gathered in a detailed literature review of PM research, and on the results of a one-day symposium with transportation and air quality experts held in January 2000.
PM Literature Review. A comprehensive review of recent literature was conducted to gather information about current PM research in five broad topic areas:
One-Day PM Symposium. To more fully incorporate the perspectives of the transportation community, a one-day symposium was held in Charleston, South Carolina, during January 2000. A range of academic and applied researchers, as well as air quality and transportation planners from federal, state, and local agencies were invited to the symposium. Attendees participated in a series of breakout sessions designed to gather expert input on key research topics. The breakout sessions matched the topics used for the literature review. Together, the results of the literature review and the symposium were used to provide insights during development of this Workplan. The results of the symposium are summarized in Appendix B.
Figure 2. Workplan Development Process
The final output of this Workplan is a set of priority research projects. The projects are intended to fill PM research gaps that are most critical to the transportation community. Within the Workplan, the priority projects are categorized according to five broad research focus areas and according to how they address four key transportation policy questions. By linking research focus areas to resolution of key transportation policy questions, implementation of the Workplan will facilitate development of information, tools, and approaches that transportation agencies can use to handle emerging issues related to the new PM standards.
The research community and transportation professionals who participated in the FHWA PM Research Symposium identified five key research focus areas for inclusion in the Workplan:
Monitoring - Research to incorporate transportation source concerns into PM monitoring approaches;
Characterization - Research that addresses the spatial, temporal, and chemical variations in ambient PM;
Transportation Sources - Research that addresses sources of PM from transportation;
Modeling - Research concerned with improving transportation source PM emission factor models and travel data inputs; and,
Control Strategies - Research to identify and evaluate transportation source PM control strategies.
Each of these topics represents a distinct area of research that is also linked to resolution of a key transportation policy question.
Transportation agencies will face a number of important policy challenges in regard to PM over the coming years. Transportation agencies in PM2.5 and PM10 non-attainment areas may be required to assist air quality agencies in developing transportation control strategies for State Implementation Plans (SIPs). Transportation agencies will also need to demonstrate conformity of their transportation plans in PM nonattainment and maintenance areas. Gaps in knowledge and lack of tools, however, currently constrain the ability to effectively carry out these activities. Addressing these and other issues will require resolution of four important policy questions.
What areas are expected to be in nonattainment?
EPA will designate PM2.5 nonattainment areas over the period 2002-05, and transportation agencies need to know early on whether they may be faced with a nonattainment designation. Early knowledge will allow transportation agencies to develop the capacity to address PM nonattainment issues and participate with air quality agencies in the development of nonattainment area designations and SIPs, and in the completion of the conformity process.
What kind of problem is PM: local, regional, or both?
This question addresses two issues: 1) To what extent are PM2.5 problems associated with local sources versus transported from other regions? and 2) To what extent are atmospheric concentrations of PM affected by direct PM emissions versus secondary formation? Transportation and air quality agencies need to be able to answer these questions in order to identify the appropriate level and target for control strategies.
What is the transportation contribution to PM?
The contribution of transportation sources determines the extent to which the SIP may focus on these sources. Transportation agencies need to understand the contributions of different transportation sources and how roadway characteristics and transportation system performance affect transportation emissions.
What are the most cost-effective control strategies for transportation sources?
Transportation agencies need to understand the costs and effectiveness of potential strategies, and the other implications of these strategies, to select and implement the most appropriate control strategies.
These four questions provide a logical sequence to undertake the priority projects in the Workplan. Answers to the first two questions need development to provide state and local transportation agencies with an understanding of whether PM is a problem in their regions and where the problem is originating. The last two questions are most critical to transportation agencies and relate directly to transportation sources and the effectiveness of transportation control strategies.
Figure 3 summarizes how the five research focus areas and the key transportation policy questions are interrelated. This diagram is the "blueprint" for the Workplan and it identifies how each priority project helps to answer one or more of the transportation community's critical policy questions.
As this figure shows, a number of research projects help answer more than one of the research questions. Most emphasis, however, has been placed on research to help understand the contribution of transportation sources to PM, because this is a critical research gap of primary importance to the transportation community. The blueprint shows how the research priorities in this plan form a research path that integrates findings across focus areas to answer the transportation community's critical research questions.
Currently, many research initiatives are being conducted on PM. Most projects focus on health effects of PM. However, agencies within EPA, other Federal and State agencies and industry also are sponsoring studies examining the relationships between PM and source contribution, as well as the local and regional nature of PM. In identifying the key transportation related projects for this workplan as shown in Figure 3, extensive literature was reviewed that included published peer reviewed papers, conference proceedings and reports prepared for commercial and government agencies.
Two important Web sites currently contain a broad array of information on studies related to PM research. These sites are maintained and updated frequently and provide the latest information on current and planned PM research efforts. The first is an EPA site (http://www.epa.gov/ttnamti1/files/ambient/pm25/casac/amticpm.html). This site maintains: 1) current and ongoing information on the EPA sponsored PM Supersites; 2) the latest from the Clean Air Scientific Advisory Committee (CASAC) on PM; and 3) EPA guidance on PM network design, data management, speciation, and policy. The second site is the Particulate Matter Research Activities (PMRA) Web site (http://www.pmra.org). That site keeps and sorts current, ongoing and future PM research. The site is operated and maintained by the Health Effects Institute in collaboration with EPA. The PMRA Web site broadly covers all aspects of PM research; and identifies a project's title, principal investigator, sponsor, schedule (time period), funding level, and an overview of the study.
Based on a review of these Web sites, at least one relevant project was found within each of the five research focus areas discussed in the "Research Focus Areas, Goals, and Priority Projects" section of this Workplan. Below, current ongoing research projects, relevant to projects identified in Figure 3 are identified. Note that recommended project numbers are used in the discussion (e.g., Project P3) to facilitate the cross-referencing of Figure 3 with the details of the topic areas and projects outlined below.
Recommended Project P3 identifies the need for examining state-of-the-art techniques for measuring semi-volatiles. Three current research projects are ongoing, or have been recently completed, in this area. First, Gundel and Stockburger, sponsored by EPA's National Exposure Research Laboratory (NERL), are investigating the development of a PM2.5 semi-volatile organic compounds (SVOC) sampler -- since in areas of the country where organics are a main component of the fine particle mass, this will result in a significant negative bias in the mass measurement. The earliest sampling of ambient organic aerosol consisted of collecting particles on quartz filters and analyzing them for compounds of interest. With the recognition that positive and negative artifacts were possible, a sorbent bed of an acrylic polymer (PUF or XAD) was added following the filter to collect SVOCs that were vaporized from the filter or were present in the gas phase of the incoming air stream. To account for compounds that are in both gaseous and particulate phases (and thus increase accuracy), current thinking is that SVOCs require a denuder to be placed upstream of the filter.
Second, Koutrakis et al., sponsored by Electric Power Research Institute (EPRI), are investigating fine particulate mass measurements in field studies with the specific intent of 1) measuring the particle mass artifacts due to losses or gains of semi-volatile compounds, and 2) comparing measurements obtained from a variety of integrated and continuous particle mass measurement techniques.
The third study, sponsored by Tennessee Valley Authority (TVA) is using a sampler which incorporates the state-of-the-art collection techniques for semi-volatile aerosol particles. The sampler is operated in the field along with one of the FRM monitors in the TVA network. Data collected will help in determining the contribution of semi-volatile aerosols to fine particulate matter loadings.
Project P4 identifies the need for updated source profile information for PM speciation analysis. Three current research projects are ongoing, or have been recently completed, in this area.
First, under sponsorship by the Health Effects Institute (HEI), Gertler is investigating ambient sampling of diesel PM. The study is obtaining chemically speciated diesel profiles that will be used to source apportion diesel versus other ambient constituents in the air. The particle number and the chemically speciated, size-segregated, particle distributions are being measured. These results will be compared to measurements from 25 years ago to determine the change in diesel exhaust particle mass in ambient air. Particulate emissions from light-duty gasoline vehicles are also being measured to compare their contribution to those from diesel vehicles.
Second, under sponsorship of EPA's National Risk Management Research Laboratory (NRMRL), Smith and Wasson are developing PM source signatures. The project will provide updated and augmented data on the chemical composition and size distribution of fine particulate matter (PM), smaller than 2.5 microns, from a variety of source types. Particular emphasis will be placed on acquiring detailed PM organic speciation data in order to allow greater differentiation of sources in source apportionment than is possible when source profiles are limited to PM elemental compositions. The extended profiles will be made available for inclusion in the Office of Air Quality Planning and Standards (OAQPS) SPECIATE database for use by EPA Regional Offices and State environmental agencies in apportioning ambient fine PM to emission sources.
The TVA project is a study on mobile source contribution to fine particulate mass. The study uses two continuous PM mass monitors; one collocated with a routine fine PM monitor and one located in the same community adjacent to a major interstate highway. The contribution of mobile sources will be inferred from the difference in PM mass and chemistry at the two monitors that capture the same community sources. This will provide information on mobile source contribution that is currently lacking in the Tennessee Valley. A chemical mass balance (CMB) modeling technique will be applied to historical and recently-collected chemically-speciated samples of PM2.5 to determine source attribution for PM2.5 in the Tennessee Valley.
Project P6 recommends that engine testing be conducted on a representative fleet of diesel fueled engines to generate better data on the contribution of diesel fueled vehicles to PM pollution. An ongoing project, under sponsorship of EPA/NRMRL, has developed an integrated on-road sampling system to test gaseous emissions from heavy-duty diesel tractors as they operate on highways. This system has demonstrated the transient nature of exhaust emission levels even for "steady state" operations and is being modified to include particle size and mass measurements. The measurement systems available to define the particle size distribution of these emissions are laboratory grade units with relatively long sample processing times. The development of a suitable sampling system that provides a sample which is cooled and diluted as the actual exhaust pipe discharges, and preserves the sample for a sufficient period to allow the analytical instruments to complete their cycles, is the focus of this effort.
Project P11 recommends the development of a modeling procedure for assessing ammonia emissions from transportation sources. A current research project being sponsored by the Coordinating Research Council (CRC) involves the determination of ammonia emission rates from in-use light and heavy-duty vehicles. The objective of this study is to sample the rate of ammonia and ammonium ion emission levels from on-highway vehicles while traveling in a tunnel. Samples are to be taken during an existing tunnel study in the Tuscarora Mountain Tunnel. The contribution of ammonia from mobile sources represented by this on-highway fleet will be estimated and compared to other estimates.
Project P12 seeks to determine the cost and effectiveness of existing transportation source PM control strategies. As part of EPA's Supersite program, the New York State DOT is assessing the effectiveness of new emission control technologies, for example, Compressed Natural Gas (CNG) bus deployment and Continuously Regenerating Technology (CRT) introduced in New York City and their impact on ambient air quality, using remote open path roadside, mobile platform, and fixed site measurements of carbon dioxide, carbon monoxide, nitric oxide, nitrous acid, and formaldehyde and aerosol chemical composition. At the conclusion of this study, sufficient information will be available to assess both the cost and effectiveness of these new engine control technologies on PM and PM precursors.
Likewise, Project P14 seeks to expand the understanding between ozone and PM control strategies. An ongoing research study is being conducted by Cass et al., under the sponsorship of EPA's National Center for Environmental Research and Quality Assurance (NCERQA), to investigate the effects of emissions controls on ozone and fine particle air quality in both California and the Northeast region of the United States. By simultaneously accounting for ozone and fine particle formation and transport, improved methods will be developed to greatly increase the computational speed of PM air quality models. The models developed will be applied both in Southern California and in the Northeastern United States, and formal evaluations of model performance will be conducted. The completed models will be used to evaluate the effects of emissions controls on ozone and fine particle air quality in both California and the Northeast.
1 On May 14, 1999, the U.S. Court of Appeals for the District of Columbia Circuit issued an opinion on the national ambient air quality standards for ozone and PM that EPA issued in July 1997. On June 28, 1999, the federal government filed a petition for rehearing key aspects of the case in the U.S. Court of Appeals for the D.C. Circuit. The U.S. Supreme Court ruled on February 27, 2001, in favor of EPA's revised standards although implementation of the requirements is pending.
2 In the context of this Workplan, the terms "transportation," "transportation sector," and "transportation community" are considered to include on-road mobile sources, including passenger and commercial vehicles and bus transit service, as well as sources like road dust associated with mobile sources. Rail and non-surface transportation modes are not considered as part of the Workplan, although they may contribute to total transportation sector PM emissions.