||National Bureau of Standards (NML), Gaithersburg, MD. Center for Analytical Chemistry. ;Global Geochemistry Corp., Canoga Park, CA.;Environmental Protection Agency, Research Triangle Park, NC. Atmospheric Sciences Research Lab.
During the past three years radiocarbon assay has emerged as a primary tool in the quantitative assignment of sources of urban and rural particulate pollution. Its use in several major field studies has come about because of its excellent (fossil/biogenic) discriminating power, because of advances in (14)C measurements of small samples, and because of the increased significance of carbonaceous particles in the atmosphere. The problem is especially important in the cities, where increased concentrations of fine particles lead to pollution episodes characterized by poor visibility and changes in the radiation balance (absorption, scattering), and immediate and possibly long-term health effects. Efforts in source apportionment in such affected areas have been based on emissions inventories, dispersion modeling, and receptor modeling, i.e., chemical and physical (and statistical) characterization of particles collected at designated receptor sites. It is in the last category that (14)C has become quite effective in helping to resolve particle sources. Results are presented for studies carried out in Los Angeles, Denver, and Houston which incorporated (14)C measurements, inorganic and organic chemical characterization, and receptor modeling. The (14)C data indicated wide ranging contributions of biogenic and fossil carbon sources -- e.g., <10% to 60% contemporary (biogenic) in Houston -- depending on meteorological, biological, and anthropological activity.