Temporal Variations and Characteristics of the Carbonaceous Species in PM2.5 Measured at Anmyeon Island, a Background Site in Korea

Routine measurements of carbonaceous species in PM2.5 inculidng organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and humic-like-substance carbon (HULIS-C) in PM2.5 were performed at Anmyeon Island (AI) to clarify the seasonal variation and carbonaceous aerosol concentrations at a background site in Korea between 2015 and 2016. The annual average OC and EC concentrations were 4.52±3.25 μg/m3 and 0.46±0.28 μg/m3, respectively, and there were no clear seasonal variations in OC and EC concentrations. The average concentrations of WSOC and water-insoluble organic carbon (WISOC) were 2.56±1.95 μg/m3 and 1.96±1.45 μg/m3, respectively, and their composition in OC showed high temporal variations. A low correlation between WISOC and EC was observed, while WSOC concentrations were highly correlated with secondary organic carbon concentrations, which were estimated using the EC tracer method. The results indicate that the formation of secondary organic aerosols is a major factor for the determination of WSOC concentrations in this region. HULIS-C was the major component of WSOC, accounting for 39–99% of WSOC and the average concentration was 1.88±1.52 μg/m3. Two distinct periods with high carbonaceous speciess in PM2.5 were observed and characterized by their OC/EC ratios. The high concentration of OC with high ratio of OC/EC was due to the influence of a mixture of emissions from biomass burning and secondary formation transported from outside AI. While, the high concentrations of OC and EC with low OC/EC ratio were related to local vehicular emissions.