Jessica Slater

Because of increased interest in the marine and atmospheric sciences in elemental carbon, or black carbon or soot carbon, and because of the difficulties in analyzing or even defining this pervasive component of particulate carbon, it has become quite important to have appropriate reference materials for intercomparison and quality control. The NIST "urban dust" Standard Reference Material® SRM 1649a is useful in this respect, in part because it comprises a considerable array of inorganic and organic species, and because it exhibits a large degree of isotopic heterogeneity, with biomass carbon source contributions ranging from about 2 % to about 32 %. A primary purpose of this report is to provide documentation for the new isotopic and chemical particulate carbon data for the most recent SRM 1649a Certificate of Analysis. Supporting this is a critical review of underlying international intercomparison data and methodologies, provided by 18 teams of analytical experts from 11 institutions. Key results of the intercomparison are: a new, Certified Value for total carbon in SRM 1649a; 14C Reference Values for total carbon and a number of organic species, including for the first time 8 individual PAHs; and elemental carbon Information Values derived from 13 analytical methods applied to this component. Results for elemental carbon, which comprised a special focus of the intercomparison, were quite diverse, reflecting the confounding of methodological-matrix artifacts, and methods that tended to probe more or less refractory regions of this universal, but ill-defined product of incomplete combustion. Availability of both chemical and 14C speciation data for SRM 1649a holds great promise for improved analytical insight through comparative analysis, and through application of the principle of isotopic mass balance.