Investigation of PM2.5 Pollution Episodes in Gwangju

24-hr integrated PM2.5 measurements were performed between December 2013 and October 2014 at an urban site in Gwangju and the collected samples were analyzed for organic carbon (OC), elemental carbon (EC), ionic species, and elemental species. Objectives of this study were to identify PM2.5 pollution episodes, to characterize their chemical components, and to examine their probable origins. Over the course of the study period, average PM2.5 concentration was 37.7 +/- 23.6 (6.0 similar to 121.5) mu g/m(3). Concentrations of secondary ionic species; NH4+, NO3-, and SO42- was on average 5.54 mu g/m(3) (0.28 similar to 20.86), 7.60 mu g/m(3)(0.45 similar to 33.53), and 9.05 mu g/m(3) (0.50 similar to 34.98), accounting for 13.7% (4.6 similar to 22.7), 18.6% (2.9 similar to 44.8), and 22.9% (4.9 similar to 55.1) of the PM2.5 concentration, respectively. Average OC and EC concentrations were 5.22 mu gC/m(3) and 1.54 mu gC/m(3), taking possession of 4.6 and 22.2% (as organic mass) of the PM2.5, respectively. Frequencies at which 24-hr averaged PM2.5 exceeded a 24-hr averaged Korean PM2.5 standard of 50 mu g/m(3) (termed as an "episode" in this study) were 30, accounting for 21.3% of total 141 measurements. These pollution episodes were mostly associated with haze phenomenon and weak surface wind speed. It is suggested that secondary formation of aerosol was one important formation mechanism of the episodes. The episodes were associated with enhancements of organic mass, NO3- and SO42- in winter, of NO3- and SO42- in spring, and of SO42- in summer. Potential source contribution function results indicate also that PM2.5 episodes were likely attributed to local and regional haze pollution transported from northeastern China in winter, to atmospheric processing of local emissions rather than long-range transport of air pollutants in spring, and to the SO42- driven by photochemistry of SO2 in summer.