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Strategic Plan for Particulate Matter Research: 2005-2010

1. Introduction

1.1 Overview

This Strategic Plan for Particulate Matter Research identifies priority particulate matter (PM) research issues for the transportation community for the years 2005 through 2010. It updates and expands on a previous Federal Highway Administration (FHWA) strategic plan for PM research covering the 2000 through 2004 time period (Carr et al., 2002a) . This Strategic Plan is intended to define areas of research that have the greatest potential to yield insights directly applicable to state Departments of Transportation (DOTs) and regional Metropolitan Planning Organizations (MPOs) charged with developing and implementing transportation plans, programs, and projects. A key DOT and MPO concern is the ability to demonstrate that long-range regional transportation plans (RTPs), shorter-term transportation improvement programs (TIPs), and individual transportation projects meet federal transportation conformity and National Environmental Policy Act (NEPA) requirements. Thus, DOTs and MPOs are interested in research that yields new insights into quantifying and mitigating on-road transportation-related emissions of PM₁₀ and PM_2.5, the two size fractions of PM for which National Ambient Air Quality Standards (NAAQS) have been established. The timeframe for this strategic research plan extends to 2010 to correspond with PM_2.5 air quality plan preparation and implementation, as well as the timeframe identified by the National Research Council (NRC) for its long-range PM research portfolio (National Research Council, 1998).

1.2 What is Particulate Matter?

PM is the term used to describe a complex mix of solid and liquid particles in the air, regardless of chemical composition. The principal chemical components of PM mass are sulfate, nitrate, ammonium, elemental carbon (EC), organic carbon (OC), and geologic material (e.g., road dust). Other trace elements can be detected in PM but do not typically compose a significant fraction of the PM mass. A substantial fraction of ambient PM is not directly emitted as PM (primary emissions) but is instead formed in the atmosphere (secondary formation) through the reactions of gaseous precursors. For example, condensation or chemical transformation of volatile organic compounds (VOCs) results in the formation of secondary OC. On-road mobile sources emit all of these precursors and components to differing extents.

PM ranges in size from very small (a few nanometers) to large (100s of micrometers). Most particles by number are smaller than 0.1 μm (ultrafine), whereas most of the particle mass is contributed by particles larger than 0.1 μm. The current National Ambient Air Quality Standards (NAAQS) for PM regulate mass concentrations of two sizes of PM; particles with aerodynamic diameter smaller than 2.5 microns (PM_2.5 or the "fine" fraction) and those with aerodynamic diameter smaller than 10 microns (PM₁₀). The mass concentrations of PM_2.5 are always less than or equal to those of PM₁₀ because the PM_2.5 fraction is included in the measurement of PM₁₀. Most PM emitted from motor vehicle exhaust falls within these (the PM_2.5 and PM₁₀) size ranges. Health effects research suggests the number of particles may also be an important factor in health outcomes, which implicates the smallest particle sizes (ultrafine particles or PM_0.1). However, there are no current regulations for particle number or for size ranges smaller than PM_2.5.

1.3 Why is PM Important?

PM can adversely impact the environment and human health. PM is known to contribute to regional haze, global climate change, air toxics, and can also be important for acid rain (Figure 1). PM has also been linked to health outcomes such as asthma, strokes, and decreased life expectancy. For the transportation planning community, failure to attain the NAAQS for PM, or failure to demonstrate conformity to PM state implementation plans (SIPs), can result in loss of federal highway funding for local, regional, or state governments. The transportation community, therefore, has a vested interest in working with federal, state, and regional air quality agencies to assist in timely attainment of the PM NAAQS.

Figure 1. Example relationships among mobile source PM, its precursors, and other air quality issues, modified from Carr et al., 2002a.

1.3.1 Regulatory Framework

Federal regulations require that state and local governments and their transportation agencies participate in the air quality planning process. It is important that local and regional transportation agencies have the tools and knowledge necessary to create realistic emissions estimates, to identify achievable reductions in emissions, and to predict project-level air quality impacts. Near-term research recommendations should focus on issues that can help the transportation community meet the requirements within the current regulatory framework.

Areas that do not attain the NAAQS (nonattainment areas) or that previously have been designated as nonattainment (maintenance areas) are required to develop SIPs that document how the NAAQS will be met or maintained. These SIPs include regional emissions budgets for PM and PM precursors from transportation sources (conformity budgets) and demonstrate how emissions reductions from all sources will result in attainment of the NAAQS. In nonattainment and maintenance areas, MPOs and DOTs are required to demonstrate that transportation plans and programs conform to SIPs and that projects do not create or exacerbate violations of NAAQS (transportation conformity). Conformity is demonstrated by using emissions models to show that regional emissions are within budgets, and by using dispersion models to show that emissions from individual projects do not cause or contribute to NAAQS-related air quality problems (e.g., "hot-spots" or "localized" problems near roadways). In some cases, such as areas that have yet to develop SIPs and emissions budgets, DOTs and MPOs in nonattainment and maintenance areas are required to compare emissions from future "build" and "no-build" scenarios. Project-level air quality analyses can also be required under the National Environmental Policy Act (NEPA).

As part of meeting designated emissions budgets, local MPOs and DOTs are sometimes required to consider emission control strategies at the regional or project level. These control strategies work in concert with federal PM regulations promulgated by the U.S. Environmental Protection Agency (EPA) and regional PM control programs adopted by state and local air quality management agencies. Given the complexity of air quality problems, it is possible that control strategies may decrease the effects of one air quality issue (e.g., ozone, air toxics, haze, global warming, or acid rain) at the expense of increasing the effects of another, or they may conflict with other transportation-related objectives (e.g., mobility and safety). Therefore, a key challenge for the transportation and air quality planning communities is to work across disciplines to develop effective and complementary control strategies.

1.3.2 Potential Regulatory Issues

Pollutant emissions from mobile sources can contribute to high concentrations near roadways, and recent research has identified various potential health hazards linked with proximity to roads with high traffic volumes. Although the chemical or physical mechanisms responsible for these potential health effects are not well-understood, it is possible some combination of ultrafine particles, reentrained road dust (dust resuspended by a vehicle as it drives), diesel particulate matter (DPM), or PM from gasoline vehicles may be responsible. As a result of recent findings linking road proximity and potential health effects, there is growing consideration of restricting certain activities from taking place near high-volume traffic corridors. California, for example, requires that proponents of proposed school sites within 500 feet of busy traffic corridors conduct dispersion modeling and make a determination that exposure does not pose a significant health risk to pupils.

The EPA has identified components of diesel exhaust as a mobile source air toxic (MSAT) (U.S. Environmental Protection Agency, 2001). The state of California has identified DPM as a Toxic Air Contaminant (TAC) and has quantified estimated excess cancer risks associated with DPM exposure (California Air Resources Board and California Office of Environmental Health Hazard Assessment (OEHHA), 1998). A southern California assessment showed that the cancer risk associated with DPM was larger than that of all other air toxics investigated in the study combined (South Coast Air Quality Management District, 2000). DPM can be a component of PM_2.5 or PM₁₀, but conformity regulations do not address components of PM (or other MSATs). However, requests for localized and/or regional assessments of MSAT impacts have been made, and at least one lawsuit sought to impact whether such assessments will be required for roadways (Shrouds, 2003) .

By law, the EPA must periodically review and, as appropriate, adjust the NAAQS. As of mid-2005, the EPA was proceeding under court order to review the PM NAAQS. The EPA is expected to propose a rulemaking action December 2005, and to issue a final rule in September 2006, regarding its PM NAAQS review. If, over time, sufficient scientific evidence accrues suggesting alternative PM NAAQS are appropriate, for example to address concerns related to ultrafine particles, the EPA will change or augment the PM NAAQS.

Existing conformity requirements include qualitative PM hot-spot analyses for primary emissions. As of mid-2005, the EPA was developing updated transportation conformity regulatory requirements for PM_2.5 and PM₁₀ project-level hotspot analyses (U.S. Environmental Protection Agency, 2004c). Depending upon the final rulemaking, transportation agencies may be responsible for completing various qualitative or quantitative project-level PM_2.5 and PM₁₀ assessments.

Finally, upcoming implementation of regulations on low-sulfur fuels (2006) and introduction of cleaner heavy-duty diesel vehicles (2007-2010) are expected to have a major impact on PM emissions from diesel vehicles over a period of several decades. Although substantial PM emission reductions are forecast due to the implementation of the new fuel and tailpipe standards, there have yet to be any real-world data collected to document the emission reduction benefits that will accrue from these programs. Research will be needed to confirm the real-world results of these programs and to compare real-world experience to modeled expectations.

1.4 Research Coordination

Multiple organizations sponsor and coordinate PM research, interagency research planning, and transportation-related PM research. Different agencies and organizations have different responsibilities and focus areas.

The FHWA's 1998 National Strategic Plan established the Administration's mission "to continually improve the quality of our Nation's highway system and its intermodal connections." (Federal Highway Administration, 1998). It identified five strategic goals for achieving this mission, one of which was to protect and enhance the natural environment and communities affected by highway transportation. Air quality research, including investigation of PM, was one of the eight program goals established in the Strategic Plan. The document established two criteria for conducting PM-related research: first, to bring a transportation focus to the study of PM issues, and second, to develop applied research products that respond to the needs of transportation and air quality planning practitioners.

While FHWA is most interested in applied research addressing on-road mobile source PM pollution, some of the research priorities identified in this Strategic Plan address fundamental questions about sources, characterization, and monitoring of PM that must be understood to assess the impact of on-road mobile sources. Therefore, some of the research priorities identified in this Strategic Plan may be funded either wholly or partially by organizations or agencies other than FHWA or the transportation community. Some of these organizations are listed here:

• The FHWA, EPA, and other federal agencies are members of an Air Quality Research Subcommittee (AQRS) of the Committee on Environment and Natural Resources (CENR) of the National Science and Technology Council, under the Office of Science and Technology Policy. The AQRS formed a separate public/private air quality research partnership for North America (including Canada and Mexico) known as NARSTO.
• For research specific to transportation, the Transportation Research Board (TRB), which is a division of the National Research Council (NRC), administers the National Cooperative Highway Research Program (NCHRP). NCHRP is sponsored by individual state DOTs belonging to the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with FHWA.
• The Coordinating Research Council (CRC) is a non-profit organization supported by associations and companies in the automotive and petroleum industries, and by government agencies such as the EPA and the California Air Resources Board (CARB). CRC directs engineering and environmental studies on the interaction between automotive equipment and petroleum products. CRC is also a member of NARSTO.

One of the objectives of this Strategic Plan is to create an information resource that FHWA can use in consultation with its partner agencies and stakeholders to prioritize and support research across the many organizations involved with transportation-related PM. The PM research efforts that FHWA will fund directly will likely be a function of the various research efforts taking place within the broader PM research community. Many of these agencies and organizations have also prepared strategic research plans or reviews of the existing literature; these plans and reviews were among the resources consulted during this study. A short list of documents is provided here for readers interested in more detailed information:

• Research Priorities for Particulate Matter: I-IV by the National Research Council (National Research Council, 2004, 2001, 1999, 1998) .
• Particulate Matter Science for Policy Makers (NARSTO, 2004) .
• Strategic Plan for Particulate Matter prepared by the PM Research Coordination Working Group of the AQRS of the CENR (Particulate Matter Research Coordination Working Group, 2002) .
• The EPA Particulate Matter Research Program: five years of progress (U.S. Environmental Protection Agency, 2004a).
• Air quality criteria for PM (U.S. Environmental Protection Agency, 2004b).
• Transportation and Particulate Matter: Assessment of Recent Literature and Ongoing Research (Tamura et al., 2005)

1.5 Developing a Strategic Research Plan for PM

This Strategic Plan for PM is the third of three steps FHWA has taken as part of its current process to identify and prioritize PM research issues for the transportation community. The first step involved completion of an assessment of recent and ongoing PM research (Tamura et al., 2005) . Table 1 provides a summary of the major research issues identified during the literature assessment step. The second step involved an FHWA-sponsored one-day workshop where atmospheric scientists; air quality experts; industry experts; members of the academic community; and environmental and transportation planners from state and regional DOTs, MPOs, and air quality agencies discussed and prioritized the key research topics facing the transportation community (McCarthy et al., 2005) . Appendix A includes a list of the workshop participants. The third step (this report) involved synthesizing the results of the assessment document and the workshop into a cohesive Strategic Plan. Figure 2 shows this process.

The first step, the literature assessment (Tamura et al., 2005) , was the review of past research plans, a survey of current PM and transportation literature, and a description of ongoing PM research initiatives. Research topics were organized in five broad categories, which are discussed in Section 2. These five research focus areas were first identified in the 2000 to 2004 Strategic Research Plan. Briefly, these five focus areas are

• Monitoring - Ambient measurements of PM and precursors at outdoor locations
• Characterization - The use of air quality or receptor models to tie emissions sources to ambient concentrations
• Emissions Measurements - Quantification of vehicle emissions via data collection for in‑use vehicles
• Emissions and Hot-spot Models - Models used to calculate emissions or impact of emissions on ambient air concentrations near roadways
• Control Strategies - Measures used to reduce emissions with the intended consequence of improving air quality

Monitoring, characterization, and emissions measurements topic areas are considered basic research by the transportation community. Emissions models, hot-spot models, and control strategies are considered applied research areas by the transportation community.

Table 1. Research gaps identified during the transportation and particulate matter literature assessment (Tamura et al., 2005) . LA‑# indicates the number of the issue from the literature assessment document.

^a The characterization topic area includes references to air quality or receptor models, tools that are typically used by air quality management agencies, rather than by MPOs or DOTs.

Figure 2. Process used to determine transportation community research priorities for this Strategic Plan.

Individual research recommendations were classified under one of these five broad research focus areas. The interrelationship of these research areas is shown in Figure 3. Twenty key research recommendations were identified in the literature assessment as shown in Table 1. These research recommendations provided an initial set of topics for discussion at the one-day workshop.

Figure 3. Relationship among broad research topic areas and transportation policy issues. Broad research categories are colored by research topic area (the color scheme is consistent with Table 4 and Figure C-1). Air quality agency tasks are shown in green, and transportation agency tasks are shown in gray. Applied research topics are more likely to be funded by FHWA.

The second step of the process was a one-day multidisciplinary workshop conducted on April 7, 2005 (McCarthy et al., 2005) . Approximately 50 members of the academic, government, industry, and consulting communities (10 of whom represented the MPO-DOT community) attended the workshop and discussed the 20 research priorities suggested in the literature assessment (Table 1). In addition, participants were asked to suggest additional research issues that may have been omitted from the literature assessment. Following small-group forums where participants had the opportunity to discuss key research issues, each participant voted to help establish the highest priority research needs. Table 2 provides a numerical summary of the voting results from the one-day workshop.

During the workshop, some small-group forums identified and prioritized research needs not included in the literature assessment. Table 3 summarizes the participant voting results for these "newly identified" issues. Two of the new issues discussed were sufficiently similar to combine as one research priority for this document. The two new issues were to disaggregate uncertainty in vehicle activity data and estimate uncertainty in the planning, emissions, and air quality planning process. These were combined under the title "estimate uncertainty in the planning, emissions, and air quality planning process" for the final product.

This Strategic Plan is the third step in the FHWA PM research plan process. The Strategic Plan identifies high-, medium-, and low-priority PM research issues, based on the one-day workshop results. Priorities were assigned using the following criteria:

• Number of workshop votes from all participants.
• Number of workshop votes from MPO-DOT participants.
• Number of votes from individual discussion groups, where groups voted on newly introduced research topics not discussed by all workshop participants.

During the workshop, there was broad agreement between the MPO-DOT participants and the research and government participants on four high-priority and eight low-priority research issues. In other words, for the four top-ranked and the eight lowest-ranked research recommendations, there was widespread agreement among workshop participants independent of their organizational affiliation. This Strategic Plan identifies high- and low-priority research issues based on the broad consensus reached during the workshop. In addition, there were several research issues that were identified as medium-priority by at least one subset of workshop participants, but as either low- or high-priority by other subsets of workshop participants. Topics that were voted as medium-priority by any of the workshop groups (all participants, MPO-DOT participants, or individual groups discussing new topics) are identified in this research plan as medium-priority research issues. Table 4 summarizes the priorities of the participants of the FHWA workshop for all research issues by category.

Participant votes from FHWA workshop, topics discussed by all participants. Priorities are rated high, medium, or low for all participants (right) and for MPO-DOT participants only (left).

Research issues LA-7, LA-10, and LA -15 received no votes.

a Individual participants were given a maximum of 10 votes to allocate among the various research issues, with the stipulation that no more than 5 votes be linked to any one research need. There were approximately 50 total workshop participants, 10 of whom were from the MPO-DOT community. Small-group forums included about 12‑25 participants, depending on the group. Some individuals chose not to vote or to vote only a portion of their 10 votes.

Participant votes from FHWA workshop, new topics identified during small-group forums. Priorities are rated high, medium, or low for all participants (right) and for MPO-DOT participants only (left).

^a These issues, identified during individual breakout group discussions, were not discussed by all workshop participants; hence, the vote totals and rankings for these topics reflect only the prioritization by the workshop participants and MPO/DOT attendees who discussed these research issues.

^b Individual participants were given a maximum of 10 votes to allocate among the various research issues, with the stipulation that no more than 5 votes be linked to any one research need. There were approximately 50 total workshop participants, 10 of whom were from the MPO-DOT community. Small-group forums included about 12‑25 participants, depending on the group. Some individuals chose not to vote or to vote only a portion of their 10 votes.

1.6 Caveats Concerning Potential Funding

Sections 3, 4, and 5 address the high-, medium-, and low-priority research needs. Although, in general, FHWA and other members of the transportation planning community will likely look to fund higher-priority research needs over lower-priority research needs, several caveats are important to mention.

• First, FHWA and other transportation agencies have a stronger interest in applied research than in basic research. As identified in Figure 3, of the five research topics covered in this effort, three topics (monitoring, characterization, and emissions measurements) typically involve basic research, while two topics (emissions and hot-spot modeling and control measures) typically involve applied research. Thus, notwithstanding high-, medium-, and low-priority rankings, there will likely be a general interest among transportation planning agencies to fund emissions and hot-spot modeling and control measure assessment research.
• Second, FHWA and other transportation agencies may have opportunities to leverage their existing research funds by extending research projects supported by other organizations. Thus, for example, an opportunity may emerge to fund, at modest expense, a medium-priority research topic even though other high-priority research needs have yet to be fully addressed. In such a situation, FHWA or other agencies may well take advantage of the opportunity to obtain useful data and information that might otherwise be more expensive to obtain at a later date.
• Third, the high-, medium-, and low-priority characterizations identified in this report reflect input from stakeholders representing various geographic areas throughout the United States and Canada. Priorities in any specific geographic area may vary. FHWA and other agencies may find it important to fund research that assists specific regions with their unique problems.
• Fourth, the high-, medium-, and low-priority needs discussed in this report represent an assessment as of 2005. As new information becomes available, research needs will change.

Thus, readers should view the high-, medium-, and low-priority rankings as a tool to assist in identifying and prioritizing research, but not as an absolute guide. The rankings need to be weighed in the context of emerging scientific knowledge, in consideration of information about ongoing research efforts being carried out by other members of the research community, and with an appreciation for the unique needs of specific geographic regions.

1.7 Research Priorities Organized By Completion Time

Individual research topics have different timeframes in which results applicable to the transportation community can be expected. Some of the research topics are short- or near-term research goals that can be completed in the next few years. These research issues can aid the transportation community in the near-term, particularly as states develop PM_2.5 SIPs (due 2008 for submission to the EPA) and complete initial rounds of PM_2.5 conformity analyses. Other research topics are high-priority items but may not produce useful results for the transportation community for several years (i.e., long-term). Finally, there are some research issues that may have both short- and long-term components. FHWA may consider giving more weight to those research topics where significant progress could be expected in the next few years. A list of the estimated timeframe for various research issues is shown in Table 5. Based on FHWA experience implementing the 2000 to 2004 research plan, FHWA may have the ability to fund only a subset of the research issues identified in this report; therefore, the discussion that follows focuses more attention on the higher priority research needs.

4. Prioritized research issues categorized within research topic areas. Each issue is numbered in the order of its relative priority ranking (e.g., M1 is the highest medium priority; M10 is the lowest medium priority). Rankings are based on participant feedback derived from an FHWA-sponsored PM research workshop held April 7, 2005.

^a Priority was rated low by MPO and DOT participants.

^b Priority was rated high by MPO and DOT participants.

^c The characterization topic area includes references to air quality or receptor models, tools that are typically used by air quality management agencies, rather than by MPOs or DOTs.

The research timeframes listed in Table 5 were designated using several criteria. First, projects based on analyses of existing data and literature were assumed to be appropriate for near-term completion (i.e., in one to two years). Second, projects that required field work, other primary data collection, or model development efforts were generally expected to take at least three years to complete. Third, projects that involved development of new modeling tools based on data that had not yet been collected were assumed to take six or more years. Most research could span an array of options depending on the funding available and the depth of data collection and analysis anticipated; in many cases, Table 5 identifies a time range (e.g., short to medium) to reflect the range of research options available. It should be noted that some topics, such as monitoring near roadways or measuring emissions profiles from gross-emitters, cannot be fully resolved while vehicle and fuel technologies continue to change substantially (e.g., diesel emissions after 2007).

During the workshop, it became clear that the MPO-DOT workshop participants were especially interested in identifying those research issues that could be completed relatively quickly to aid them in addressing near-term conformity requirements. As shown in Table 5, short-term research topics (medium or high-priority) include

• Compile a compendium of control strategy information.
• Create short-term "fixes" applicable to MOBILE6.2 (fixes refer to improvements that could correct important PM-related deficiencies, such as the lack of speed-corrected heavy-duty vehicle PM emissions).
• Create a data repository or information archive (web site) for MPOs and DOTs.

Priority and timeframe for medium- and high-priority research topics.

^a Short-term projects are assumed to provide needed information in approximately one or two years, medium-term projects in approximately three to five years, and long-term projects beyond five years; see text for additional detail.