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Strategic Plan for Particulate Matter Research: 2005-2010

Table of Contents



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

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

  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.

  4. Mobile particle instrumentation unit from the UCLA-based Southern California Particle Center Supersite. Photo courtesy of the Southern California Particle Center Supersite.

  5. Predicted downwind pollutant concentrations as a function of wind speed and distance from the roadway from the EPA's CAL3QHC model, not including background concentrations. Reprinted from Tamura and Eisinger (2003).

  6. Attenuation of PM10 and PM2.5 mass concentrations with time and vertical mixing volume. (Reprinted from Countess et al., 2001 with permission.)

  7. PM emissions as a function of speed from the MOBILE6.2 emissions model. Figure reprinted with permission from Granell et al., (2004).

  8. Collage of control measure situations. High occupancy vehicle lanes in Denver (left-courtesy of The Regional Transit District-Denver, CO), bike lane in San Francisco (center-stock photo courtesy of San Francisco Metropolitan Transportation Commission), and fugitive dust in Nevada (right-photo courtesy of Business Environmental Program of Nevada).


ES-1. High priority research issues

ES-2 Prioritized research issues categorized within research topic areas

  1. Research gaps identified during the transportation and particulate matter literature assessment

  2. Participant votes from FHWA workshop, topics discussed by all participants

  3. Participant votes from FHWA workshop, new topics identified during small-group forums.

  4. Prioritized research issues categorized within research topic areas

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

  6. High priority research issues

  7. Medium-priority research issues

  8. Low priority research issues

Executive Summary

ES.1 Overview

This Strategic Plan for Particulate Matter Research (Strategic Plan) 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 identifies 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. The timeframe for this Strategic Plan extends to 2010 to correspond with PM2.5 attainment planning and the timeframe used by the National Research Council (NRC) for its long-range PM research portfolio (National Research Council, 1998).

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 FHWA's 1998 National 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.

Multiple organizations sponsor and coordinate PM research. This Strategic Plan was developed to define areas of research that will ultimately assist state DOTs and MPOs, regardless of whether this research is funded by FHWA or other organizations. While FHWA is most interested in applied research addressing 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 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. In addition, the research priorities identified in this Strategic Plan reflect, as of 2005, the consensus view of experts from various geographic regions and institutional affiliations. These priorities will undoubtedly change as new scientific information becomes available. Thus, readers should review the report findings presented in this Strategic Plan as a tool to assist in identifying and prioritizing research, but not as an absolute guide.

ES.2 Background

PM is the term used to describe a complex mix of solid and liquid particles in the air that can adversely impact the environment and human health. PM is known to contribute to regional haze, global climate change, and acid rain and has also been linked to health outcomes such as asthma, strokes, and decreased life expectancy. On-road mobile sources (i.e., motor vehicles) can directly emit PM in exhaust, or contribute to PM in the air from tire wear, brake wear, and road dust. In addition, mobile sources emit gases that can react or condense in the air to form secondary PM.

National Ambient Air Quality Standards (NAAQS) for PM regulate concentrations of two sizes of PM; particles with aerodynamic diameter smaller than 2.5 microns (PM2.5 or the "fine" fraction) and those with aerodynamic diameter smaller than 10 microns (PM10; note that PM2.5 is also a subset of PM10). Most PM emitted from motor vehicle exhaust is within the PM2.5 and PM10 size categories. Failure to attain the NAAQS for PM, or to meet progress milestones while working towards attainment, can result in loss of federal highway funding for local, regional, or state governments.

Federal "transportation conformity" regulations require that state and local governments and their transportation agencies participate in and contribute to the air quality planning process. Areas that do not attain the NAAQS (nonattainment areas)-and areas that attain, but were previously designated as nonattainment (maintenance areas)-are required to develop State Implementation Plans (SIPs). The SIPs must include regional conformity emissions budgets, meaning caps on allowable emissions, for PM and PM precursors from on-road transportation sources. The SIPs must also demonstrate how emission reductions from mobile sources and other sources will result in attainment and maintenance of the NAAQS. The deadline for states to submit PM2.5 SIPs to the U.S. Environmental Protection Agency (EPA)is 2008.

In the nonattainment and maintenance areas, MPOs and DOTs are also required by the conformity process to demonstrate that transportation plans and programs conform to SIPs and that projects do not create or exacerbate violations of the NAAQS. Conformity is demonstrated by using models to show regional emissions are within allowable budgets and to demonstrate emissions from individual projects do not cause or contribute to NAAQS-related air quality problems (e.g., hotspots near roadways). Project-level air quality analyses can also be required under the National Environmental Policy Act (NEPA).

ES.3 Research Recommendations


This 2005 to 2010 PM Strategic Plan for PM research 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 and research plans (Tamura et al., 2005) . 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) . The third step involved synthesizing the results of the assessment document and the workshop into a Strategic Plan for PM Research (this report).


Prioritized research topics are organized into one of five research categories: monitoring, characterization, emissions measurements, emissions and hot-spot (or localized) modeling, and control strategies. Each of the five research categories corresponds to research areas defined by the FHWA during the development of its first PM research plan (Carr et al., 2002a) .

This Strategic Plan identifies high-, medium-, and low-priority research issues. During the one-day workshop, a voting process was used to quantify the level of interest among workshop participants for specific research opportunities. The votes, categorized by all workshop participants and by the subset of participants representing the MPO-DOT community, clearly identified high priority research needs; these were used as a guide to develop the priority ranking presented here. Table ES-1 provides a description and illustration of each of the high priority research issues. Table ES-2 lists the high, medium, and low research priorities resulting from the literature assessment and workshop processes. The Table ES-2 color scheme was chosen to reflect that used in the 2000 to 2004 Strategic Plan.

The main contribution from FHWA's work efforts has been to achieve broad consensus across a wide range of stakeholder groups that four transportation-related PM research issues are of highest priority for the 2005 to 2010 time period. The highest priority research issues are:

FHWA intends to work with its partner agencies and with other stakeholders to provide funding or other forms of support for research efforts. Completion of research efforts will advance understanding about the relationship between on-road mobile sources and PM problems, provide improved analysis tools for SIP and conformity analyses, and facilitate identification and implementation of effective PM control strategies.

Table ES-1. High-priority research issues.

Illustration Issue

Example of a monitoring unit deployed near roadways by the UCLA-based Southern California Particle Center.

H1. Near roadway monitoring is needed to evaluate hot-spot modeling tools, determine concentration gradients of PM and precursors near roadways, and to support health effects research. Current United States monitoring networks do not monitor near roadways. The illustration is an example monitoring unit deployed near roadways by the UCLA-based Southern California Particle Center.


H2. "Hot-spot," or localized, PM models need to be evaluated. Although conformity requirements for PM have not yet been finalized, the EPA has announced that hot-spot models may be applicable to "hot-spot" PM evaluations. The ability of new and existing models to predict PM emissions and concentrations at the micro-scale needs to be evaluated for a wide variety of roadway types and travel conditions. The illustration is CAL3QHC model output showing downwind pollutant concentration decay as the distance from the roadway increases.


H3. Research is needed to correct known deficiencies in MOBILE6.2 and resuspended road dust emissions models. Important examples related to PM include a lack of speed correction factors, the inability to model effects of traffic signal changes, and the inability to model varying travel conditions that affect acceleration changes. Model results need to be evaluated using emissions test data and real-world measurements. The illustration, from an FHWA study, shows that certain MOBILE6.2-based estimates of vehicle PM exhaust emissions are insensitive to changes in travel speed.


H4. The efficacy and costs of control strategy programs need to be evaluated. In particular, it is important to test if real-world emission reductions are consistent with predicted reductions. In addition, cost-benefit and off-model analysis techniques should be improved to more accurately credit PM control opportunities. The illustration shows high occupancy vehicle lane implementation in Denver, Colorado. Photo courtesy of the Denver Regional Transportation District (RTD).

Table ES-2. 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.

Basic Research Applied Research



Emissions Measurements

Emissions and Hot-Spot Models

Control Strategies


H1. Monitor

near roadways


H2. Evaluate hot-spot models.

H3. Develop and evaluate PM emissions models.

H4. Evaluate control strategy programs.


M7. Improve PM measurements.a

M8. Increase the spatial extent and temporal resolution of PM measurements.a


M1. Collect information on fugitive dust emissions.b

M5. Evaluate roadway project effects on emissions.

M9. Collect exhaust emissions from gross-emitters.a

M3. Create short-term MOBILE6.2 fixes.

M6. Improve information for MOBILE6.2 users regarding default assumptions.a

M10. Estimate uncertainty in the emissions/planning/air quality process.a

M2. Compile a compendium of control strategy information.

M4. Create a data information repository for MPOs/DOTs.



L1. Support model evaluation and improvements.

L4. Determine contribution of mobile sources to ambient PM concentrations.

L6. Provide adequate data to support air quality model evaluation.

L2. Improve information on ultrafine particles in exhaust.

L7. Collect exhaust emissions for non-gross-emitters.

L7. Evaluate dilution issues for condensable mass.

L5. Develop models for ultrafine particles.

L7. Ensure that hot-spot and air quality models start where emissions models end.

L3. Develop guidance for weighing offsetting air quality and transportation goals (ozone, PM, air toxics, safety, and mobility).

a Priority was rated low by MPO and DOT workshop participants, although workshop participants as a whole rated this topic a medium priority.

b Priority was rated high by MPO and DOT workshop participants, although workshop participants as a whole rated this topic a medium priority.

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.

Updated: 07/06/2011
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