## 3 Results and Discussion
However, biomass burning sources (D, TBB, and LBB) showed discrepancies at a d\({}_{\rm g}\) value of 1.5 \(\upmu\)m, which indicates that the HULIS imaginary refractive index had a stronger influence on these sources than on other sources. Figure 6 shows the trends of the source-resolved total extinction coefficient (\(b_{ext}\)) and their contributions. The d\({}_{\rm g}\) values of 0.1 and 0.5 \(\upmu\)m were compared, with a GSD of 1.5 during the sampling period. The source-resolved mass concentration is also displayed in Figure 6[14]. In general, the trends of the source-based optical property were similar to those of the source-based mass concentrations [14] (see also contribution of mass in Supplementary Figure S3). However, the specific contributions to \(b_{ext}\) and mass were different according to the sources. Total \(b_{ext}\) values were generally high during winter and spring and low during summer. In the source-based analysis, the \(b_{ext}\) associated with some sources such as G and LBB did not show significant seasonal variation. The contributions of G and LBB were relatively consistent regardless of the season. However, the contributions of transported sources (TS and TBB) showed relatively distinct seasonal characteristics: they were high during winter and low during summer. For LN, the contribution increased during winter and spring but remained low in summer. The contribution of LS was great in summer and low in winter. Figure 6 also shows that \(b_{ext}\) increased as d\({}_{\rm g}\) increased from 0.1 to 0.5 \(\upmu\)m. This was due to the MEE with a GSD of 1.5, which increased as d\({}_{\rm g}\) increased from 0.1 to 0.5 \(\upmu\)m (except for EC), as shown in Figure 3. Although there were differences in the \(b_{ext}\) values, the contributions of each source were similar. Table 3 shows the source-based extinction coefficients across the whole sampling period with different geometric mean diameters (GSD = 1.5). The \(b_{ext}\) will have different values for different GSDs. As Table 3 clearly shows, size distributions can influence source-based \(b_{ext}\) values. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**d\({}_{\rm g}\) (\(\upmu\)m)** & **TS** & **LS** & **LN** & **G** & **D** & **TBB** & **LBB** & **FSD** \\ \hline
0.1 & 9.3 & 10.0 & 12.7 & 4.6 & 16.2 & 11.1 & 5.2 & 2.4 \\
0.2 & 26.6 & 24.0 & 34.5 & 9.7 & 26.5 & 26.4 & 11.0 & 4.8 \\
0.3 & 34.7 & 30.7 & 44.1 & 10.7 & 25.7 & 30.8 & 12.6 & 5.2 \\
0.4 & 34.7 & 30.8 & 43.5 & 9.5 & 21.2 & 28.3 & 11.6 & 4.6 \\
0.5 & 30.9 & 27.9 & 38.4 & 7.8 & 16.7 & 23.7 & 9.8 & 3.8 \\
0.6 & 26.1 & 23.9 & 32.4 & 6.3 & 13.3 & 19.2 & 8.0 & 3.1 \\
0.7 & 21.7 & 20.2 & 26.9 & 5.1 & 10.9 & 15.6 & 6.6 & 2.5 \\
0.8 & 18.1 & 17.0 & 22.5 & 4.3 & 9.3 & 13.0 & 5.5 & 2.1 \\
0.9 & 15.3 & 14.5 & 19.0 & 3.6 & 8.0 & 11.0 & 4.7 & 1.8 \\
1.0 & 13.2 & 12.5 & 16.4 & 3.2 & 7.1 & 9.6 & 4.1 & 1.6 \\ \hline \hline \end{tabular}  
* TS, transported secondary sources; LS, local secondary sulfates; LN, local secondary nitrates; G, gasoline; D, diesel; TBB, transported biomass burning; LBB, local biomass burning; FSD, fugtitive soil dust.  
\end{table} 
Table 3: Source-based extinction coefficients (\(b_{ext}\), Mm\({}^{-1}\)) for different geometric mean diameters (geometric standard deviation = 1.5). Figure 7 compares the source-based mass contributions with the source-based \(b_{ext}\) contributions for different d\({}_{\text{g}}\) values. The average values were based on the whole sampling period. In this study, several size distributions with geometric mean diameters of 0.1, 0.3, 0.5, and 1.0 \(\upmu\)m for a GSD of 1.5 were considered. Supplementary Figure S3 shows detailed mass concentrations and their contributions based on chemical compounds and sources. Figure 5: Composition-based mass extinction efficiency as a function of the geometric mean diameter for different humic-like carbon substance (HULIS) imaginary refractive indices (GSD = 1.5) for (**a**) TS, (**b**) LS, (**c**) LN, (**d**) G, (**e**) D, (**f**) TBB, (**g**) LBB, and (**h**) FSD.