## 3 Results and Discussion
### Atmospheric Concentrations of PAHs and OH-PAHs
These differences may reflect differences in the sampling locations between this study (roadside) and the previous study (rooftop of a building on a university campus). To the best of our knowledge, this is the first report on annual seasonal variations of multiple OH-PAHs in the atmosphere in Japan. Figure 1: Daily atmospheric concentrations of PAHs in April, August, and November 2017, and February and April 2018 in Kanazawa. The ratio of total PAHs/total OH-PAHs did not show significant differences among the seasons (ratio: 11.5-14.4, \(p\) = 0.67-0.99 by Tukey's test), though these were weak differences between warmer seasons (spring and summer: 15.8-17.8) and colder seasons (autumn and winter: 13.4-13.7). These results are not consistent with those of [PERSON] et al. [22], who reported clear seasonal differences with ratios of 33.3 in the warmer seasons (April-October) and 14.2 in the colder seasons (November-March) in Beijing, China. The samples in the present study were collected near a main road, and the major emission source was traffic. Additionally, compared with China, coal and biomass burning are rarely conducted in cities in Japan. Therefore, this inconsistency probably reflects differences in the emission sources of OH-PAHs. The total PAH and total OH-PAH concentrations were significantly correlated (Figure 3, \(p\) < 0.01, \(r\) = 0.885). Additionally, there were significant correlations between Pyr and 1 OH-Pyr (\(p\) < 0.01, \(r\) = 0.920) and BaA + Chr and OH-BaA + OH-Chrs (\(p\) < 0.01, \(r\) = 0.937). These results indicate that these two groups of chemicals have common emission sources. The OH-PAHs primarily originate as oxidized derivatives of PAHs through the combustion of organic matter, including fossil oil [17,21,25]. They can also form from PAHs after photochemical reactions in the atmosphere [26,27,28,29]. Both pathways likely caused the significant correlations between PAHs and OH-PAHs. Unlike the other PAHs and OH-PAHs, 3 OH-BaP was not detected in any of the samples, even though BaP was detected in all analyzed samples (0.04 \(\pm\) 0.02 ng/m\({}^{3}\)). This indicated that 3 OH-BaP was not contained in the emission source of BaP and/or was unlikely to form from BaP in the atmosphere. To group and estimate emission sources, principal component analysis (PCA) and diagnostic ratio analysis were conducted. The results of the PCA for PAHs and OH-PAHs found some seasonal differences. For PAHs, spring, summer, autumn 2017 and spring 2018 formed a related group and winter 2018 was relatively separated (Figure S3). Similarly, for OH-PAHs 4 seasons formed a related group and the winter of 2018 was relatively separated (Figure S4). In both cases, winter 2018 was separated from summer, autumn 2017 and spring 2018, and spring 2017 was located between winter 2018 and other 3 seasons. These results likely indicate that these three seasons had similar contamination sources that differed from the winter 2018 samples. In addition, it may be that some abrupt event occurred in spring 2017, especially 29-30 April, such as the long-range transport from China [2]. The PAH diagnostic ratio analysis indicates clear seasonal differences, as well (Figure S5). The ratio of IDP and IDP+BgPe (IDP/(IDP+BgPe)) was used to assess the contribution difference between diesel vehicles and gasoline vehicles [34], and no clear difference was found with the five periods. However, combustion source estimation using the ratio of Flt  
Figure 2: Daily atmospheric concentrations of OH-PAHs in April, August, and November 2017, and February and April 2018 in Kanazawa. and Flt+Pyr (Flt/Flt+Pyr) [44] showed a remarkable difference, indicating that fossil fuel combustion was the dominant source in the spring and autumn, while petrogenic sources were dominant in the summer and organic matter combustion was the dominant source in the winter. In Japan, grass, wood, and related organic matter combustion (open burning) has been regulated [45].