Variation of OC and EC in PM2.5 at Mt. Taehwa

Abstract

Organic carbon (OC) and elemental carbon (EC) in PM2.5 were measured with Sunset OC/EC Field Analyzer at Taehwa Research Forest (TRF) near Seoul metropolitan area from May 2013 to April 2014. During the study period, the mean concentrations of OC and EC were 5.0+/-3.2 mu gC/m3 and 1.7+/-1.0 mu gC/m(3), respectively. They showed clear seasonality reaching their maximum in winter (6.5 mu gC/m(3) and 1.9 mu gC/m(3)) and minimum in wet summer (2.5 mu gC/m3 and 1.4 mu gC/m(3)). 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 similar to June, when 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/EC ratio implies the influence of non-local sources of OC at the Mt. Taehwa.