PM2.5 organic carbon (OC) and elemental carbon (EC) of summer monsoon season observed at the Anmyeondo Global Atmosphere Watch (GAW) Regional Station, South Korea

Organic carbon (OC) and elemental carbon (EC) in PM_2.5 were measured with Sunset Laboratory Model-5 Semi-Continuous OC/EC Field Analyzer at Anmyeondo Global Atmosphere Watch (GAW) Regional Station (37°32´N, 127°19´E) in July and August, 2017. It employs TOT (Thermal-Optical-Transmittance) method. The mean values of OC and EC were 3.7 μg m^-3 and 0.7 μg m^-3, respectively. During the study period, the concentrations of reactive gases and aerosol species were evidently lower than those of other seasons. It is mostly due to meteorological setting of the northeast Asia, where the influence of continental outflow is at its minimum during this season under southwesterly wind. While the diurnal variation of OC and EC were not clear, the concentrations of O₃, CO, NOx, SO₂, and CO₂ were evidently enhanced under easterly wind at night from 20:00 to 8:00. However, the high concentration of EC was observed concurrently with CO and NOx under northerly wind during 20:00 ~ 24:00. It indicates the influence of thermal power plant and industrial facilities, which was recognized as a major emission source during KORUS-AQ campaign. The diurnal variation of O₃ clearly showed the influence of land-sea breeze, in which O₃ concentration was enhanced with OC in sea-breeze. OC concentration was relatively high, compared to those Seoul. This study suggests that in general, Anmyeondo station serves well as a background monitoring station. However, the variation in meteorological condition is so dynamic that it is primary factor to determine the concentrations of secondary species as well as primary pollutants at Anmyeondo station.