Elemental Carbon Observed at a Peri-Urban Forest Site near the Seoul Metropolitan Area as a Tracer of Seasonal Haze Occurrence

Abstract

In order to identify the seasonal variability and source of carbonaceous aerosols in relation to haze occurrence, organic carbon (OC) and elemental carbon (EC) were continuously measured at the Taehwa Research Forest (TRF) near the Seoul metropolitan area from May 2013 to April 2014. For the entire experiment, the mean OC (5.1 µgC/m3) and EC (1.7 µgC/m3) concentrations of TRF were comparable to those of Seoul, with noticeably higher concentrations in winter and spring than in other seasons, and during haze days (6.6 ± 3.2 and 2.1 ± 1.0 μgC/m3) than during non-haze days (3.5 ± 2.2 and 1.3 ± 0.8 μgC/m3). The seasonal characteristics of OC and EC reveal the various sources of haze, including biomass combustion haze either transported for long distances or, in spring, from domestic regions, the greatest contribution of secondary organic carbon (SOC) in summer, and fossil fuel combustion in winter and fall. In addition, the seasonal OC/EC ratios between haze and non-haze days highlights that the increase in EC was more distinct than that of OC during haze episodes, thus suggesting that EC observed at a peri-urban forest site serves as a useful indicator for seasonally varying source types of haze aerosols in the study region.