Relationship between carbonaceous components and aerosol light absorption during winter at an urban site of Gwangju, Korea

To examine the relationship between the chemical composition of light-absorbing organic aerosols and the absorption properties of the aerosols, daily PM2.5 samples were collected during winter at an urban site of Gwangju, Korea, and analyzed for organic carbon and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), humic-like substances (HULIS), and water-soluble inorganic substances. The real-time black carbon (BC) concentration in PM2.5 was also measured using a dual-spot aethalometer. During the study period, average WSOC/OC and HULIS-C/WSOC ratios were 0.53 and 0.52, respectively. K+/EC and K+/OC ratios indicate that bio-mass burning (BB) emissions are a possible source of the observed carbonaceous aerosols and K+. Moderate-to-strong correlations of HULIS with NO3-, oxalate, SO42-, K+, CO, and Delta BC (=BC@370nm- BC@880 (nm)) suggest that in addition to the primary BB emissions, secondary processing is another important contributor to the formation of HULIS in winter at the site. The average absorption Angstrom exponent (a) of fine aerosols for the wavelengths of 370-950 nm and 590950 nm was 1.29 and 1.18, respectively, but the aerosol a value was higher in the near UV wavelength range (370-520 nm), with an average of 1.51 (0.76-2.36), indicating that aerosol absorption characteristics during winter were influenced by BB aerosol sources, as well as by traffic emissions. Over the study period, the alpha(370-520) (nm) value during the highest EC, highest OC, and Asian dust events was 1.42 +/- 0.10 (1.26-1.59), 1.44 +/- 0.15 (1.16-1.68), and 1.90 +/- 0.28 (1.54-2.36), respectively. Higher alpha(370-520) (nm) values during the Asian dust event were attributed to the influence of dust particles. In addition, the light absorption coefficients of aerosols at 370 nm were strongly correlated with OC (R-2 = 0.76), water-insoluble OC (R-2 = 0.70), and water-soluble HULIS (R-2 = 0.64). These tight correlations suggest that water-insoluble fractions of OC, as well as the water-soluble brown carbon, could be important contributors to aerosol light absorption. This study demonstrates that a newly-developed dual-spot aethalometer could be utilized to characterize light absorption properties of organic aerosols and dust particles. (C) 2016 Elsevier B.V. All rights reserved.