Source apportionment of black carbon aerosols by isotopes (14C and 13C) and Bayesian modeling from two remote islands in east Asian outflow region

Abstract

We report the results of source apportionment of combustion-derived black carbon (BC), in PM2.5 aerosols collected from the East Asian continental outflow region at two islands; Okinawa and Fukue during the period from October 2009 to May 2010. The 14C contents of BC from Okinawa (Cape Hedo) and Fukue islands (Fukue) varied from 24.4 to 34.2 pMC and from 18.1 to 43.0 pMC, respectively. Source apportionment of BC was conducted by using a simple 14C mass balance model and a dual-isotope Bayesian Markov chain Monte Carlo model. Biomass combustion contributions (e.g., wood fuel and crop residues) were 23–31 % (mean 27 ± 3 %) at Cape Hedo and 15–38 % (mean 27 ± 12 %) at Fukue. Both sites were equally affected by biomass combustion, whose levels are similar to those observed in the hotspot regions (megacities) in China. Fossil fuel contributions (e.g., oil, gasoline, and diesel) were 69–77 % (mean 74 ± 3 %) with 2–69 % from coal and 3–76 % from liquid fossil at Cape Hedo, and 55–85 % (mean 73 ± 12 %) at Fukue with 3 % from coal and 53–56 % from liquid fuel for the early winter. Those variations for both sites showed significantly different source region-specific trends and this trend was also consistent with the results of the air mass trajectory analysis with a higher contribution of coal-BC from North China including Beijing, and East China including Shanghai. In spring, we found a higher contribution of liquid fossil fuel combustion (e.g., traffic) over the East China Sea, including Pacific air masses, suggesting that the possible contribution of ship emissions was relatively high. Although our results for isotopes-based source apportionment of BC are preliminary, these findings suggest that long-term monitoring of BC aerosols, even in remote sites of Asian outflows, and source-specific descriptions of BC are important to improve climate models. We also recommend further measurements for implementing regionally tailored mitigation.