Fossil Sources of Ambient Aerosol Carbon Based on ¹⁴C Measurements
Special Issue of Aerosol Science and Technology on Findings from the Fine Particulate Matter Supersites Program

Abstract

Organic and elemental carbonaceous material constitute significant portions of PM₁₀ and PM_2.5 mass on a global basis and are typically 35% and 10%, respectively, in urban areas of the southeastern United States. The organic portion of this is a complex mixture of primary compounds and secondary materials formed in situ from primary emissions. These materials derive from a variety of sources that are dynamically changing in time and space, making difficult the quantitative characterization of their sources. Results of measurements of the ¹⁴C content of organic aerosol particles (PM₁₀ and TSP) sampled at Look Rock, TN are reported in this work with the aim of better estimating bounds to fossil and biogenic sources that contribute to PM mass concentrations. The fraction of fossil-derived carbon in these particles has been estimated as 1 minus the fraction of “modern” carbon, the latter by definition biologically synthesized in equilibrium with atmospheric, cosmic ray-derived ¹⁴CO₂. Fossil carbon fractions vary in a wide range from less than 10 to about 60% during spring, summer, and fall seasons at this ridge-top site near the Great Smoky Mountains National Park. The implications of these findings on control strategies for the organic carbon fraction of PM_2.5 mass are discussed.