Optical and thermal characteristics of carbonaceous aerosols measured at an urban site in Gwangju, Korea, in the winter of 2011

Abstract

Carbonaceous components (organic carbon [OC] and elemental carbon [EC]) and optical properties (light absorption and scattering) of fine particulate matter (aerodynamic diameter <2.5 mu m; PM2.5) were simultaneously measured at an urban site in Gwangju, Korea, during the winter of 2011. OC was further classified into OC1, OC2, OC3, and OC4, based on a temperature protocol using a Sunset OC/EC analyzer. The average OC and EC concentrations were 5.0 +/- 2.5 and 1.7 +/- 0.9 mu g C m(-3), respectively. The average single-scattering albedo (SSA) at a wavelength of 550 nm was 0.58 +/- 0.11, suggesting that the aerosols observed in the winter of 2011 had a local warming effect in this area. During the whole sampling period, "stagnant PM" and " long-range transport PM" events were identified. The light absorption coefficient (b(abs)) was higher during the stagnant PM event than during the long-range transport PM event due to the existence of abundant lightabsorbing OC during the stagnant PM event. In particular, the OC2 and OC3 concentrations were higher during the stagnant PM event than those during the long-range transport event, suggesting that OC2 and OC3 might be more related to the light-absorbing OC. The light scattering coefficient (b(scat)) was similar between the events. On average, the mass absorption efficiency attributed to EC (sigma(EC)) was 9.6 m(2) g(-1), whereas the efficiency attributed to OC (sigma(OC)) was 1.8 m(2) g(-1) at lambda = 550 nm. Furthermore, the sigma(EC) is comparable among the PM event days, but the sigma(OC) for the stagnant PM event was significantly higher than that for the long-range transport PM event (1.7 vs. 0.5).