Radiocarbon measurement of the biogenic contribution to summertime PM-2.5 ambient aerosol in Nashville, TN

Radiocarbon (C-14) measurements performed on PM-2.5 samples collected near Nashville, TN from June 21 to July 133 1999, showed high levels of modern carbon, ranging from 56% to 80% of the total carbon in the samples. Radiocarbon measurements performed on dichloromethane extracts of a subset of the samples showed modern carbon levels that were on average only 9% smaller than those for total carbon. A new approach based on the Chapman-Richards model of tree growth was used to define the quantitative relationship between measurements of 'percent modern carbon' and inferred 'percent biogenic carbon'. The results of this study contribute to a growing body of evidence (including measurements of radiocarbon, organic carbon to elemental carbon ratios and organic tracer species, as well as results from chemical mass balance and air quality simulation modeling) in support of the importance of biogenic secondary organic aerosol in the Southeastern US during summer. (C) 2004 Elsevier Ltd. All rights reserved.