Radiocarbon analysis of BC and OC in PM13 aerosols at Cape Hedo, Okinawa, Japan, during long-range transport events from East Asian countries

We determined the C-14/C-12 ratio and concentrations of black carbon (BC) and organic carbon (OC) in airborne particulate matter (APM) with diameter <10 mu m (PM10) collected in Okinawa, Japan, between March and June 2008. During Asian dust events in March and April, APM and DC concentrations in PM10 aerosols were approximately threefold and twofold higher than those during the non-Asian-dust period in June. Refractory BC concentrations (i.e., because of refraction, <100% of BC was likely recovered) were also higher during Asian dust events than during the non-Asian-dust period. The percentages of modern carbon (pMC) in BC and OC were much smaller for PM10 aerosols collected during the Asian dust events (mean = 41.5% and 62.3%, respectively) than for those collected in the non-Asian-dust period (mean = 67.2% and 93.8%, respectively), indicating a strong influence of fossil-fuel-derived carbon during Asian dust events. One sample showed high OC concentration but relatively low BC concentration, suggesting formation during the long-range transport of biogenic organic compounds. The results suggest that not only fossil-fuel-derived air pollutants but also organic compounds derived from biomass in Asia should be considered to better characterize long-range transported aerosols. (C) 2009 Elsevier B.V. All rights reserved.