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Organic carbon(OC)and elemental carbon(EC)in PM2.5 were measured with Sunset OC/EC Field Analyzer at Taehwa Research Forest(37°30′N,127°32′E)near Seoul metropolitan area from May 2013 to April 2014.It employs TOT(Thermal-Optical-Transmittance)method.For the entire period,the mean concentrations of OC and EC were 5.0 ± 3.2 μgC/m3 and 1.7 ± 1.0 μgC/m3,respectively.Their seasonal mean concentrations were 4.8 μgC/m3 and 1.8 μgC/m3 in May~June,2.5 μgC/m3 and 1.4 μgC/m3 in Aug.~Sep.,3.3 μgC/m3 and 1.4 μgC/m3 in Oct.~Nov.,6.5 μgC/m3 and 1.9 μgC/m3 in Dec.~Feb.,and 6.1 μgC/m3 and 1.8 μgC/m3 in Mar.~Apr.,repsectively.While OC showed greater seasonal variation,the diurnal variation was more noticeable for EC through all seasons with a clear maximum in the morning,which reveals the influence of vehicle emissions.In contrast,OC exhibited a broad second peak in the afternoon during May~June,during which biological activities were the highest.Using the morning peaks of EC and OC,primary OC/EC ratio was assessed,which was assumed to be anthropogenic origin.It was the greatest in winter followed by spring and the lowest in wet summer.The seasonal difference in primary OC/E ratio implies the influence of non-local sources of OC at the Mt.Taehwa Research Forest.