## 3 Results and Discussion
### Backward Trajectory  
The individual PAH concentrations significantly differed between non-AD and AD days in Kanazawa (\(p\) < 0.001), while the difference was not significant in Fukuoka (Table 3). Backward trajectories from Fukuoka and Kanazawa were compared for AD and LRT-PAHs (Figure 3). AD is transformed from Northwest and Central China or Mongolia deserts. It travels more than 6000 km to arrive in Japan. On the other hand, large amounts of PAHs are emitted from industrial and city areas near or on the east coast of China, which are less than 2000 km away from Japan. LRT-PAHs in Kanazawa mostly came from northeastern China areas above 35\({}^{\circ}\) N latitude, while it was from above and below 35\({}^{\circ}\) N latitude in Fukuoka. The northeast China areas above 35\({}^{\circ}\) N latitude include the Manchurian industrial region with the steel industry, coal, lubricating oil, chemicals, machinery, tools production, mills and shipyards, and Bohai Economic Rim with coal, steel and machinery production. On  
Figure 2: The concentrations of total PAH (ng m\({}^{-3}\)) and TSP (ug m\({}^{-3}\)) from March to May in 2020 and 2021 in Fukuoka and Kanazawa. the other hand, LRT-PAHs in Fukuoka come from the northeast China areas below 35\({}^{\circ}\) N latitude are the Yangtze River Delta with shipyards, oil refineries, flour mills, steel plants, metal works, and light industries. Differences in emission sources and concentration in those areas might result in different PAH concentrations at sampling sites. Further studies on their effect should be conducted. To find the reason for the lesser relationship between Fukuoka and Kanazawa for the PAH variation than for the TSP variation, we divided transporting routes of air mass into four patterns illustrated in Figure S2. During AD days, the TSP concentration is high because AD is from West and Central China to the sampling site. The PAH concentrations are high because the sampling site in Japan is on the LRT-PAH route (Figure S2a). On the other hand, the LRT-PAH route from Northeast China is narrower and shorter than AD. In this case, the PAH concentrations are low because the sampling site in Japan is not on the LRT-PAH route (Figure S2b). During non-AD days, TSP is low. However, the PAH concentrations are high when LRT-PAHs arrived at the sampling site in Japan (Figure S2c). The last pattern is that domestic sources only affect the PAH concentrations (Figure S2d). \begin{table}
\begin{tabular}{c c c c} \hline
**Place** & **Time** & **Total PAHs (ng m\({}^{-3}\))** & **TSP (\(\mu\)g m\({}^{-3}\))** \\ \hline \multirow{8}{*}{Fukuoka} & Mar 2020 & 0.89 \(\pm\) 0.72 & 15.0 \(\pm\) 5.9 \\  & Apr 2020 & 0.58 \(\pm\) 0.26 & 16.7 \(\pm\) 7.0 \\  & May 2020 & 0.45 \(\pm\) 0.40 & 15.2 \(\pm\) 8.1 \\  & Avg of 2020 & 0.64 \(\pm\) 0.53 & 15.6 \(\pm\) 7.0 \\ \cline{2-4}  & Mar 2021 & 1.17 \(\pm\) 1.11 & 23.7 \(\pm\) 27.3 \\  & Apr 2021 & 1.07 \(\pm\) 0.89 & 18.3 \(\pm\) 9.3 \\  & May 2021 & 0.53 \(\pm\) 0.68 & 15.5 \(\pm\) 12.5 \\  & Ave of 2021 & 0.92 \(\pm\) 0.94 & 19.2 \(\pm\) 18.3 \\ \cline{2-4}  & Avg of total & 0.78 \(\pm\) 0.77 & 17.4 \(\pm\) 14.0 \\ \hline \multirow{8}{*}{Kanazawa} & Mar 2020 & 0.37 \(\pm\) 0.16 & 22.6 \(\pm\) 10.2 \\  & Apr 2020 & 0.28 \(\pm\) 0.14 & 22.4 \(\pm\) 9.9 \\ \cline{1-1}  & May 2020 & 0.25 \(\pm\) 0.15 & 23.6 \(\pm\) 14.5 \\ \cline{1-1}  & Avg of 2020 & 0.30 \(\pm\) 0.16 & 22.9 \(\pm\) 11.6 \\ \cline{1-1} \cline{2-4}  & Mar 2021 & 0.42 \(\pm\) 0.15 & 39.6 \(\pm\) 54.8 \\ \cline{1-1}  & Apr 2021 & 0.30 \(\pm\) 0.16 & 26.7 \(\pm\) 17.7 \\ \cline{1-1}  & May 2021 & 0.21 \(\pm\) 0.14 & 24.0 \(\pm\) 18.3 \\ \cline{1-1}  & Avg of 2021 & 0.31 \(\pm\) 0.17 & 30.1 \(\pm\) 35.5 \\ \cline{1-1} \cline{2-4}  & Avg of total & 0.30 \(\pm\) 0.16 & 26.5 \(\pm\) 26.5 \\ \hline \end{tabular} SD: standard deviation.  
\end{table} 
Table 1: Total PAHs (ng m\({}^{-3}\)) and TSP (\(\mu\)g m\({}^{-3}\)) in Fukuoka and Kanazawa from March to May 2020 and 2021 (Mean \(\pm\) SD).