The U.S.
Environmental Protection Agency (EPA) has recently proposed new regulations for
fine airborne particulate matter (PM), specifically the fraction of PM less than
2.5 microns in diameter (PM2.5). PM2.5
is a complex mixture of ammonium
sulfate, ammonium nitrate, carbon (both inorganic and organic), and inorganic
constituents. At the present time, there is considerable uncertainty regarding
two critical problems:
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Assigning different components of PM2.5 to specific sources (source apportionment).
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Identifying specific components of PM2.5 that may be important for testing toxicological hypotheses regarding the effects of PM2.5 on human health.
Most studies of source attribution and assessments of the relationship between health effects and particle concentrations have not taken advantage of the advances in analytical tools for measuring the detailed molecular structure and microstructure of particles and of the knowledge of particle formation mechanisms in combustion systems. The team that has been assembled for this investigation will use a variety of analytical techniques that can provide both structural and compositional information. These include:
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x-ray absorption fine structure (XAFS) spectroscopy,
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Mössbauer spectroscopy,
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high resolution inductively coupled plasma mass spectrometry (ICP-MS),
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x-ray fluorescence (XRF),
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instrumental neutron activation analysis (INAA),
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and C-13 nuclear magnetic resonance (NMR).
The samples are derived from several sources:
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large-scale combustion systems at the EPA;
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ambient sampling of airborne particulates;
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small-scale laboratory combustion systems.
These investigations will provide analysis of the molecular structure (specific chemical phases, valence states, etc.) and microstructure (particle size distributions, composition ranges of different phases, particle morphologies) of PM2.5 derived from the major fossil energy sources of airborne particulate matter - coal and oil. This will furnish a new dimension for source apportionment studies and provide health researchers with much needed detailed chemical characterization of particles. The focus on combustion- generated particles is motivated by the dominant contribution of combustion sources to the primary emission of fine particles.