# Source-Based Size-Resolved Optical Properties of Carbonaceous Aerosols
## 4 Summary and Discussions  
In this study, the source-based optical properties of polydisperse carbonaceous aerosols were investigated based on the measurements of PM\({}_{2.5}\) concentrations at the GAW station, Anmyeon Island, on the western coast of Korea. The PM\({}_{2.5}\) samples were collected every six days from July 2015 to April 2016. The optical properties, such as the extinction and absorption coefficient, of carbonaceous aerosols were calculated using the WSOC, WISOC, HULIS, and EC contents. The source-identified mass extinction and absorption efficiencies and optical properties were obtained based on the source-based mass concentration from the PMF model. The results show that the source-based aerosol optical properties (MEE, MAE and SSA) depend on the size distribution and the refractive index of the absorbing aerosol, which is related to the chemical composition. Compared to MEE, MAE was higher for aerosols with small diameters because of the absorption properties of EC and HULIS. The biogenic source of aerosols with small diameters has a higher MAE than other sources. The MAE for biogenic sources at a \(d_{g0}\) of 0.01 is 0.89 m\({}^{2}\)/g, which is higher than 0.38 m\({}^{2}\)/g at a  
Figure 6: Comparison of the average source-based extinction coefficient for different geometric mean diameters. The background condition (\(d_{g0}\) of 0.5 \(\upmu\)m, IRI of 0.006) is compared with sources with different \(d_{g0}\) values (\(\sigma_{g}=1.5\)) (**a**) \(b_{ext}\) and mass concentration, (**b**) Contribution of \(b_{ext}\) and the mass (%). \(d_{g0}\) of 0.5 \(\upmu\)m (\(\sigma_{g}\) of 1.5, HULIS IRI of 0.006). On the contrary, MAE for large particles was relatively consistent regardless of the source. This study also shows that the source-based SSA (single scattering albedo) depends on the source-based size distribution and refractive index of HULIS under the condition of the same mass special concentration. The SSA for smaller biogenic source particles was lower than for other sources. The influence of the HULIS imaginary refractive index on SSA is greater at smaller particle sizes. This is because the MEE and MAE is more sensitive to small particles than large particles. Consequently, the source-based contribution of total extinction coefficient depends on the source-based mass concentration and corresponding MEE and size distribution. LBB aerosol, which has a mass concentration of 20%, for example, holds a 12.1-23.1% total extinction efficiency--depending on the size and refractive index--in the range of 0.1-0.5 \(\upmu\)m in \(d_{g0}\) and a HULIS IRI of 0.006-0.3. In conclusion, the aerosol optical properties depend on the physico-chemical characteristics of the aerosol source. These characteristics are important for estimating source-based optical properties and the related climate effects of aerosols. More combinations of different aerosol sources with different sizes and refractive indices for absorbing aerosols may result in a wider range of optical properties and related climate effects. In this study, we made the simple polydisperse aerosol assumption, which assumes that aerosols retain a lognormal size distribution. This assumption does not consider the aggregation of individual particles which can lead to discrepancies and error. Thus, alternative methods, such as the Rayleigh-Debye-Gans theory for aggregates [25] and the T-matrix method for non-spherical particles [26], should be utilized. However, most aerosol retrieval algorithms are based on the Mie theory, although there is sufficient theoretical evidence that the non-sphericity of dust particles can cause scattering properties different from those predicted by the Mie theory [27]. It should be also noted that, despite these deficiencies, the Mie theory usually calculates MEE with high accuracy based on the known mass-size distribution of chemical components [28,29].