Continuous measurements of PM2.5 OC and EC at Gosan superstation, Korea and their source identification

Semi-continuous measurements of atmospheric organic and elemental carbon (OC and EC) in PM2.5 were made from October 2009 to June 2010 at Gosan supersite on Jeju Island, Korea. OC and EC were analyzed hourly using Sunset Laboratory Model-4 Semi-Continuous OC/EC Field Analyzer with NIOSH 5040 thermal/optical transmittance protocol. The mean values of OC and EC for the whole measurements were 2.1 ± 1.4 μg/m^3 and 0.7 ± 0.6 μg/m^3, respectively. The ratio of OC to EC was 4.2 ± 6.9 and EC accounted 25 ± 2.1 % of total carbon (TC, TC=OC+EC). The PSCF receptor model was used to identify the spatial source distributions of OC, EC, PM2.5 and PM10 with 3-day backward trajectories arriving at Gosan supersite (33.17 N, 126.09 E) every hour (00:00~23:00, local time) using HYSPLIT model. Figure 1 indicates that concentrations of OC and EC at Gosan supersite were largely affected by long range transport from China. In general, OC and EC showed similar seasonal variations with higher concentrations in fall and summer and lower in spring. OC and EC were best correlated in winter. The ratio of OC to EC was the highest in summer which is likely due to the formation of secondary organic aerosol and biomass burning in China and Siberia. Air mass trajectories were classified into 5 groups, among which the air from northeastern China and from the Pacific Ocean were characterized by the highest and lowest carbonaceous concentrations (Figure 2).