Tracking sources and behaviors of water-soluble organic carbon in fine particulate matter measured at an urban site in Korea

PM2.5 water-soluble organic carbon (WSOC) was measured over 24-h periods with organic carbon and elemental carbon (OC and EC) at an urban site in Gwangju, Korea, during summer (1 June–22 August 2008) and winter (26 November 2008–27 February 2009). The average mass concentrations of OC and WSOC were 5.0 ± 2.9 μg C m−3 and 2.8 ± 1.6 μg C m−3 during summer, respectively, and 8.4 ± 4.6 μg C m−3 and 3.7 ± 2.5 μg C m−3 during winter, respectively. The WSOC/EC and WSOC/OC ratios were 1.74 ± 0.60 and 0.55 ± 0.10 in summer, and 1.30 ± 0.70 and 0.43 ± 0.11 in winter, respectively. According to the results of air mass backward trajectory analysis, high fractions of WSOC to OC in the study region, compared to those reported in many other urban sites, could be explained by the atmospheric transport of water-soluble organic species from upwind regions, i.e., large-scale Steel Works and national industrial complexes located in the southeastern and eastern directions of the sampling site and northeastern regions (Beijing, Shenyang, and Shanghai) of China in the summer, and the northeastern regions of China in the winter. The secondary OC concentrations, estimated using the EC-tracer method, accounted for 26.9 ± 19.1% (0.0–65.0%) and 24.3 ± 19.5% (0.0–73.5%) of the measured OC in summer and winter, respectively. Higher correlation between secondary OC and WSOC was found in the summer (R2 = 0.78) than in the winter (R2 = 0.34), reflecting a high fraction of secondary WSOC in the summer. The entire winter sampling period was separated into two periods, i.e., winter periods “A” (Nov 26 2008–Jan 8 2009) and “B” (Jan 19–Feb 27 2009), due to the existence of open burning activities around the sampling site. Highly enriched behaviors of potassium ion (K+) and WSOC concentrations during the winter “A” period are in accordance with the fact that open burning of wood and vegetation debris at a construction working place near the sampling site was occasionally observed. The moderate correlations between water- soluble K+ and WSOC concentrations suggest that some of the WSOC observed during summer and winter could be attributed to the impact of biomass burning.