## 3 Results and Discussion
### Characteristics of Carbonaceous Components  
As shown in Table 1 and Figure 4, the OC concentration was higher in the winter than in the summer at both sites due to the increased consumption of fossil fuels for domestic heating and increased BB emissions. Slightly higher OC concentrations were observed at the BKO site, which is closer to the roadway, during both the summer and winter. However, comparable OC levels were observed at both the sites during winter. For the EC concentration, there was also little difference between the BKO and CNU sites during both seasons. Our measurements showed no notable increases in the concentrations of carbonaceous components strongly associated with traffic emissions at the  
Figure 6: Temporal profiles of (**a**) CO and (**b**) NO\({}_{2}\), and (**c**) the relationship between the 24 h averaged NO\({}_{2}\) and NO\({}_{3}\)– concentrations during winter at the CNU site. site that was closer to the roadway. During the summer, the contribution of OM (organic mass, 1.8\(\times\)OC) to the PM\({}_{2.5}\) was approximately 6.0% higher at the BKO site (41.3%, 18.3-70.0%) than at the CNU site (34.5%, 14.1-66.7%), but EC had similar contributions at both sites (6.8% at CNU vs. 6.7% at BKO). The OM contributions during winter decreased due to an increased contribution of \(\sum\)SIS concentrations, especially NO\({}_{3}\)\({}^{-}\). The average contributions of the OM concentration to the PM\({}_{2.5}\) during the winter were 26.1% (16.6-37.3%) at CNU, and 28.3% (16.1-43.0%) at BKO. In this study, the OM concentration was calculated by multiplying the OC concentration by 1.8 in both the summer and winter. Generally, a conversion factor of 1.6 is applied in urban atmospheres [56]. However, an OM factor of 1.8 was used in this study to reflect the impact of the photochemistry in summer and the BB emissions in winter. The influence of the BB emissions on the chemical composition of aerosol particles is discussed below. Figure 7 shows the relationships between the OC and EC concentrations at both sites during the summer and winter. During the summer, a regression analysis showed slopes of 3.3 and 2.4 and R\({}^{2}\) values of 0.60 and 0.59 at the BKO and CNU sites, respectively. High R\({}^{2}\) values (0.59-0.60) indicate that the OC and EC levels at both sites were associated with common sources--e.g., traffic emissions. It is not entirely clear, but the higher OC/EC slope at the BKO site was likely attributable to more enhanced SOA formation rather than additional primary sources of OC. During the winter, there were two distinct regression slopes between the OC and EC, but little difference in their slopes was found between the two sites. The winter period, representing the lower OC/EC slope, was classified as the case I period, and the higher slope was designated the case II period. For the case I period, lower slopes of 3.0-3.2 likely indicate the influence of traffic emissions on the OC and EC concentrations. On the other hand, the higher slopes of 6.6-6.7 for case II suggest the additional influence of BB emissions (e.g., wood burning) as well as traffic emissions and fossil fuel emissions for heating. In addition to traffic emissions, the influence of the other combustion emissions supports the comparable OC concentrations measured during the winter at the CNU and BKO sites. To estimate the primary and secondary OC (POC and SOC) during the summer and winter, the primary EC tracer method was applied in this study. Many previous studies have used the minimum OC/EC ratio to estimate the contribution of the POC and SOC to the OC [2; 6; 10; 11; 57]. The OC/EC ratio was generally used to identify the sources of carbonaceous components [2; 6; 10; 58; 59]. A low OC/EC ratio of less than 2-3 [6] represents the predominance of sources from fossil fuels and vehicle emissions, while a high OC/EC ratio, as seen in this study during the winter, suggests the impact of other sources (e.g., BB and SOA formation) as well as primary traffic emissions.