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°co(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).