Characterization of carbonaceous aerosols in Asian outflow in the spring of 2015: Importance of non-fossil fuel sources

The sources of elemental (EC) and organic carbon (OC) aerosols in Asian outflow were investigated in the spring of 2015 in terms of radiocarbon (14C) and molecular marker analyses. The contribution of fossil fuel (FF) sources to carbonaceous aerosols (TC) significantly increased in polluted air masses with enhancements in the concentrations of carbon monoxide. For EC, FF sources dominated in the polluted air masses. For OC, the contributions of non-FF sources other than biomass burning (BB) were found to be significant (comparable to or higher than those of FF sources), especially in air masses with higher values of the water-soluble fraction of OC (fWSOC) and 14C concentrations (F14C). Positive correlations between fWSOC and F14C indicate that the origins of TC (mainly OC) have great impacts on the water solubility variability and the subsequent cloud formation processes of OC during transport. We found the importance of natural sources as possible origins of OC in non-polluted (i.e., background) air. This study raises the need to further investigate the source apportionment of OC, especially its natural origins, for more accurately assessing the climatic impacts of EC and OC in East Asia.