Optimizing isolation protocol of organic carbon and elemental carbon for 14C analysis using fine particulate samples

Radiocarbon (C-14) analysis is a unique tool that can be used to directly apportion organic carbon (OC) and elemental carbon (EC) into fossil and non-fossil fractions. In this study, a coupled carbon analyzer and high-vacuum setup was established to collect atmospheric OC and EC. We thoroughly investigated the correlations between C-14 levels and mass recoveries of OC and EC using urban PM2.5 samples collected from a city in central China and found that: (1) the C-14 signal of the OC fraction collected in the helium phase of the EUSSAR_2 protocol (200 degrees C for 120 s, 300 degrees C for 150 s, 450 degrees C for 180 s, and 650 degrees C for 180 s) was representative of the entire OC fraction, with a relative error of approximately 6%, and (2) after thermal treatments of 120 s at 200 degrees C, 150 s at 300 degrees C, and 180 s at 475 degrees C in an oxidative atmosphere (10% oxygen, 90% helium) and 180 s at 650 degrees C in helium, the remaining EC fraction sufficiently represented the C-14 level of the entire EC, with a relative error of <10%. The average recovery of the OC and EC fractions for C-14 analysis was 64 +/- 7% (n = 5) and 87 +/- 5% (n = 5), respectively. The fraction of modern carbon in the OC and EC of reference material (RM) 8785 was 0.564 +/- 0.013 and 0.238 +/- 0.006, respectively. Analysis of C-14 levels in four selected PM2.5 samples in Xinxiang, China revealed that the relative contribution of fossil sources in OC and EC in the PM2.5 samples were 50.5 +/- 5.8% and 81.4 +/- 2.6%, respectively, which are comparable to findings in previous studies conducted in other Chinese cities. We confirmed that most urban EC derives from fossil fuel combustion processes, whereas both fossil and non-fossil sources have comparable and important impacts on OC Our results suggested that water-soluble organic carbon (WSOC) and its pyrolytic carbon can be completely removed before EC collection via the method employed in this study. (C) 2017 Elsevier Ltd. All rights reserved.