Ambient air was sampled into two parallel streams(Fig.1).in the first stream, the sampled air was unaltered and therefore representative of ambient black carbon in the sampled air to 230°c (450°F)in a thermodenuder (TD) with residence time of about 23 s.Our TD was built to similar specifications described in a study by Huffman et ai (2008),where particle losses were experimentally determined to be comparable to the losses detailed in Wehner et al.(2002).The TD was heated by two 4_ft. 312 wall ,120 VAC Extreme-Temperature Heat Carbon (McMaster-Carr,Santa Fe springs CA) that were wrapped around a fabricated stainless steel pipe measuring 61 cm (24inches) in length with a 2.2 cm (0.875in.)inner diameter and 2.54cm (1inch) outer diameter.