In 1997, the U.S. Environmental Protection Agency (EPA) promulgated National Ambient Air Quality Standards (NAAQS) for PM2.5 (particles in air with a diameter of 2.5 microns or less). States in areas exceeding the Particulate Matter (PM) NAAQS are required to develop State Implementation Plans (SIP) that describe, with scientific justification, their approaches to reducing PM to below the level of the standards. In recognizing the need for improved information, Congress provided EPA with funds to support a major air quality program within the United States with one of its main objectives being to provide states and regional air quality organizations with additional scientific information for understanding the accumulation of PM on local and regional scales. Thus, EPA's PM Supersites Program was developed as a multi-year, multi-institutional, multi-million-dollar program of air quality methods development and evaluation, measurements, data analysis, and modeling with three main objectives: (1) characterize PM in air to better understand source-receptor relationships, (2) in support of the first objective to develop and evaluate methods, and (3) support health and exposure studies via air quality measurements performed in conjunction with the first objective. Additional information regarding the Supersites Program can be found at (http://www.epa.gov/ttn/amtic/supersites.html).
The major activities of the program included initial methods testing in two locations (Atlanta, GA and Fresno, CA) in 1999, followed by one to several years of methods development and evaluation and measurements in New York, New York; Baltimore, Maryland; Pittsburgh, Pennsylvania; St. Louis, Missouri; Houston, Texas; Fresno, California; and Los Angeles, California. These areas were selected based on different atmospheric pollution conditions resulting from differences in sources and meteorological conditions. Given the wealth of information coming from the Supersites Program, EPA initiated a synthesis and integration of findings around 17 science/policy relevant questions (Synthesis) to ensure the most useful information from the program is provided directly to key stakeholders in support of new NAAQS development, SIP efforts, and future PM planning activities in both government and private sector organizations. The scope of the Synthesis goes beyond the Supersites Program information and includes related studies conducted during the last half decade or so since the Supersites Program projects integrated with many other projects conducted at the same time.
To support the Synthesis, EPA in conjunction with the American Association for Aerosol Research organized an international specialty conference entitled “Particulate Matter (PM) Supersites Program and Related Studies,” in Atlanta, GA, February 7–11, 2005. The conference was chaired by Paul A. Solomon (US EPA/ORD, Las Vegas, NV). Participation included nearly 400 scientists, air quality managers, and policy makers from a wide range of groups interested in reducing uncertainties in our understanding of atmospheric PM accumulation in urban and regional environments. Meeting attendees came from 19 countries. The 340 presentations were split between platform (2/3) and posters (1/3). Additional information regarding the conference, including abstracts, can be found at http://www.aaar.org/archived_meetings.htm.
The scope of the presentations was broad, covering the fate of aerosols and related species from their sources, through the atmospheric environment, and to their eventual sampling and receptor locations. Presentations focused on dissemination of field data, data analysis and interpretation, three-dimensional chemical transport modeling, and investigation of the links between source contributions and observed concentrations at receptors. A major theme was the policy implications of these results, as well.
The overall goal of the conference was to bring together atmospheric scientists, air quality managers, and policy makers to allow for enhanced communications and exchange of information among these groups. Specific objectives of the conference were to:
-
Advance the science in the area of PM pollution and to widely disseminate that information to key stakeholders, and thus, support and provide guidance on policy planning and decisions for reducing PM concentrations in air;
-
Provide important information on methods, measurements, modeling, and data analysis in support of EPA's PM Supersites Program and Related Studies Key and Policy Relevant Findings Synthesis; and
-
Add significantly to the peer-reviewed literature by publishing research results presented at the conference in a variety of special issues of selected journals.
Four peer-reviewed special journal issues are resulting from this conference helping to meet the objectives described above. The four special journal issues include: Aerosol Science and Technology—the Journal of American Association for Aerosol Research; Journal of Geophysical Research—Atmospheres; Journal of the Air & Waste Management Association; and Atmospheric Environment. We estimate that nearly 80 papers will be published in these journals and all four will be published during the first half of 2006.
Papers published in these journals have been subject to the normal peer-review process of their respective journals. Papers in this special issue of Aerosol Science and Technology are categorized as follows: instrument development and evaluation, measurement methods, PM characterization, and modeling and source apportionment. Three papers relate to instrument development and evaluation. Middha and Wexler describe the design of a nanoparticle virtual impactor for concentrating ultrafine particles while the other two papers present instrument evaluations done as part of the New York Supersite. Schwab et al. evaluated a Sulfate Particulate Analyzer that shows promise for sulfate monitoring in the Eastern United States, and Hogrefe et al. discuss performance of a new Scanning Mobility Particle Sizer that contains a differential mobility analyzer and particle counter in one cabinet.
Five papers discuss measurement methods of ambient aerosols. Subramanian et al. investigated the effect of temperature protocol employed in thermal-optical analysis on elemental carbon. Larsen et al. measured levoglucosan concentrations, a marker for biomass combustion, in NIST standard PM reference materials and compared them to those in ambient PM samples. Four semi-continuous monitors measuring carbonaceous aerosol were compared by Venkatachari et al. while Grover et al. report a comparison of two instruments that quantify both the semi-volatile and nonvolatile fractions of PM2.5. Lastly, Chow et al. describe a large-scale comparison of twenty samplers, including Federal Reference Methods, for PM10 and PM2.5 measurement.
PM characterization includes studies on PM2.5 mass and chemistry as well as single-particle characteristics. Herner et al. discuss the effects of atmospheric chemical mechanisms on particle size and composition in central California. Semi-continuous measurements are presented from the Baltimore and Pittsburgh Supersites. Park et al. present PM2.5 episodes that correspond to particular upwind sources while Polidori et al. show the estimates of local and regional secondary organic aerosol. Real-time single particle chemistry was used to investigate short-term PM events by Tolocka et al.
The final section of this special issue concerns the use of air quality models to apportion PM to specific sources. Park et al. traced sulfur dioxide and PM bound metals back to small coal-fired boilers in Pittsburgh and estimated emission rates from those sources using a new model formulation, the Pseudo-Deterministic Receptor Model. Zhao and Hopke used PMF to resolve PM2.5 sources in Indianapolis. Both Pekney et al. and Eatough et al. employed the PMF and UNMIX models in Pittsburgh, while Grover et al. applied UNMIX in Lindon, Utah. Pekney et al. searched for major source categories of PM2.5 while Eatough et al. apportioned PM2.5 into primary and secondary pollutants. Grover et al. apportioned PM2.5 into primary and secondary and then primary into additional sources categories. Lastly, Pekney et al. applied two probabilistic functions to PMF-modeled sources to determine more precise locations for them.
The American Association for Aerosol Research was the primary professional society sponsoring the AAAR PM Supersites Meeting with co-sponsorship by the Air and Waste Management Association. The primary financial sponsor was the U.S. Environmental Protection Agency. Other sponsors included: American Petroleum Institute; California Air Resources Board; Southern Company; Department of Energy, National Energy Technology Laboratory; EPRI; Mid-Atlantic Regional Air Management Association; NARSTO; National Oceanic and Atmospheric Administration; National Science Foundation, Atmospheric Chemistry Program; New York State Energy Research and Development Authority; and Pacific Northwest National Laboratory. The sizable financial sponsorship allowed for a reduced general registration fee and even more so for students, numerous regular and student travel grants, as well as enhancing the overall character of the meeting.
The guest editors of this special issue of Aerosol Science and Technology are grateful to all of the authors and attendees, the conference organizers, and to those who submitted and revised manuscripts.
The conference special issue guest editors hope that the papers in this special issue provide Aerosol Science and Technology readers with useful information that they can use today and that will still be beneficial for years to come. These articles provide a sample of the hard work and effort invested by the Supersites Program investigators and related study participants, as well as all of the conference participants.
Disclaimer: The United States Environmental Protection Agency through its Office of Research and Development partially funded and collaborated in the development of the preface and special issue described here and within under funding to the American Association for Aerosol Research. It has been subjected to Agency review and approved for publication.