Seasonal Characteristics of Organic Carbon and Elemental Carbon in PM2.5 in Daejeon

To investigate the seasonal variations of carbonaceous aerosol in Daejeon, OC (organic carbon), EC (elemental carbon) and WSOC (water soluble organic carbon) in PM2.5 samples collected from March 2012 to February 2013 were analyzed. PM2.5 concentrations were estimated by the sum of organic matter (1.6 x OC), EC, water-soluble ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, SO42-, NO3-). The estimated PM2.5 concentrations were relatively higher in winter (29.50 +/- 12.04 mu g/m(3)) than those in summer (13.72 +/- 6.92 mu g/m(3)). Carbonaceous aerosol (1.6xOC+EC) was a significant portion (34 similar to 47%) of PM2.5 in all season. The seasonally averaged OC and WSOC concentrations were relatively higher in winter (6.57 +/- 3.48 mu gC/m(3) and 4.07 +/- 2.53 mu gC/m(3) respectively), than those in summer (3.07 +/- 0.8 mu gC/m(3), 1.77 +/- 0.68 mu gC/m(3), respectively). OC was correlated well with WSOC in all season, indicating that they have similar emission sources or formation processes. In summer, both OC and WSOC were weakly correlated with EC and also poorly correlated with a well-known biomass burning tracer, levoglucosan, while WSOC is highly correlated with SOC (secondary organic carbon) and O-3. The results suggest that carbonaceous aerosol in summer was highly influenced by secondary formation rather than primary emissions. In contrast, both OC and WSOC in winter were strongly correlated with EC and levoglucosan, indicating that carbonaceous aerosol in winter was closely related to primary source such as biomass burning. The contribution of biomass burning to PM2.5 OC and EC, which was estimated using the levoglucosan to OC and EC ratios of potential biomass burning sources, was about 70 +/- 15% and 31 +/- 10%, respectively, in winter. Results from this study clearly show that PM2.5 OC has seasonally different chemical characteristics and origins.