Organic carbon (OC) and elemental carbon (EC) in PM 2.5 were measured using Sunset OC/EC Field Analyzer at Seoul Hwangsa Monitoring Center from March to April, 2016. The mean concentrations of OC and EC during the entire period were 4.4 ± 2.0 μgC m −3 and 1.4 ± 0.6 μgC m −3 , respectively. OC/EC ratio was 3.4 ± 1.0. The average concentrations of PM 10 and PM 2.5 were 57.4 ± 25.9 and 39.7 ± 19.8 μg m , respectively, which were detected by an optical particle counter. The OC and EC peaks were observed in the morning, which were impacted by vehicle emission, however, their diurnal variations were not noticeable. This is determined to be contributed by the long-range transported OC or secondary formation via photochemical reaction by volatile organic compounds at afternoon. A conditional probability function (CPF) model was used to identify the local source of pollution. High concentrations of PM 10 and PM 2.5 were observed from the westerly wind, regardless of wind speed. When wind velocity was high, a mixing plume of dust and pollution during long-range transport from China in spring was observed. In contrast, pollution in low wind velocity was from local source, regardless of direction. To know the effect of long-range transport on pollution, a concentration weighted trajectory (CWT) model was analyzed based on a potential source contribution function (PSCF) model in which 75 percentiles high concentration was picked out for CWT analysis. PM 10 , PM 2.5 , OC, and EC were dominantly contributed from China in spring, and EC results were similar in both PSCF and CWT. In conclusion, Seoul air quality in spring was mainly affected by a mixture of local pollution and anthropogenic pollutants originated in China than the Asian dust.

. 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, 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.

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<p>Organic carbon (OC) and elemental carbon (EC) in PM<sub>2.5 </sub>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<sup>-3</sup> and 0.7 μg m<sup>-3</sup>, 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 O<sub>3</sub>, CO, NOx, SO<sub>2</sub>, and CO<sub>2</sub> 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 O<sub>3</sub> clearly showed the influence of land-sea breeze, in which O<sub>3</sub> 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.</p><p> </p>