On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols
Atmospheric Chemistry and Physics Discussions
Radiocarbon ( 14 C) measurements of elemental carbon (EC) and organic carbon (OC) separately (as opposed to only total carbon, TC) allow an unambiguous quantification of their non-fossil and fossil sources and represent an improvement in carbonaceous aerosol source apportionment. Isolation of OC and EC for accurate 14 C deter-of the non-fossil sources. Consequently, the optimal strategy for 14 C-based source apportionment of carbonaceous aerosols should follow an approach to subdivide TC into
... subdivide TC into different carbonaceous aerosol fractions for individual 14 C analyses, as these fractions differ in their origins. To obtain the comprehensive picture of the sources of carbonaceous aerosols, the Swiss 4S protocol is not only implemented to measure OC and EC 5 fractions, but also WINSOC as well as a continuum of refractory OC and non-refractory EC for 14 C source apportionment. In addition, WSOC can be determined by subtraction of the water-soluble fraction of TC from untreated TC. Last, we recommend that 14 C results of EC should in general be reported together with the EC recovery. separation between them, which is not trivial. Indeed, the distinction between OC and EC is based on a conceptual and operational definition and does not correspond in reality to a clear boundary. On the one hand, OC compounds become more chemically refractory and optically absorbing with increasing molecular weight. On the other hand, EC also presents a continuum (Elmquist et al., 2006), the least refractory part of which 5 may show a chemical and physical behaviour similar to high-molecular-weight OC compounds. Consequently, thermal separation of OC and EC may suffer from untimely EC removal (Andreae and Gelencser, 2006) described as the negative EC artefact. These losses are particularly enhanced for wood-burning-impacted samples because of the presence of inorganic combustion catalysts (Novakov and Corrigan, 1995) and of the 10 The previous two-step combustion method The THEODORE (T wo-step Heating system for the EC/OC Determination Of Radiocarbon in the Environment) system (Szidat et al., 2004a) is a set-up that was previously used for the combustion and the recovery of carbonaceous fractions for 5 14 C-based source apportionment. It consists of a quartz combustion tube where a filter Abstract ACPD Abstract ACPD Abstract ACPD Supplementary material related to this article is available online at: http://www.atmos-chem-phys-discuss.