## 3 Results and Discussion
### Days of High Concentration and Transport Paths
There are many active volcanoes in the Japanese island, and the air quality in the Kyushu area including Fukuoka is often affected by volcano eruptions, which brought sulfate in PM\({}_{2.5}\). Emissions from ships account for less than 5% of all PM\({}_{2.5}\) emission sources in the Kyushu area, which is very low [24]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Date**} & \multicolumn{1}{c}{**PM\({}_{2.5}\)/ugm\({}^{-3}\)**} & \multicolumn{1}{c}{**N Nitrate/ugm\({}^{-3}\)**} & \multicolumn{1}{c}{**Su Sulfate/ugm\({}^{-3}\)**} & \multicolumn{1}{c}{**Total**} & \multicolumn{1}{c}{**Total**} & \multicolumn{1}{c}{**Total**} & \multicolumn{1}{c}{**O/ugm\({}^{-3}\)**} & \multicolumn{1}{c}{**EC/ugm\({}^{-3}\)**} & \multicolumn{1}{c}{**O/y/ppb**} \\ \hline
1 Feb & 13.8 & **2.81** & 4.21 & 9.90 & 0.97 & 1.72 & 3.05 &  
Figure 5: Backward trajectories of high concentration days for PM\({}_{2.5}\), sulfate, and total PAHs. (**a**) February 2–3, and 10–11. (**b**) March 26 and April 17. Closed triangle: Sakurajima, open triangle: Suwanosejima. (**c**) March 1–3 and 28–29. Typical examples of the days when only PAHs concentration were high were seen on 1-3, 28-29 March. In the case of 1-3 March, ozone showed a diurnal variation and the wind direction shows a sea-land breeze pattern [9,22,23]. The weather chart shows that the atmospheric pressure pattern was in the transient state, in which there were low-pressure systems around Japan on 1-2 March and a high-pressure system moved from the Asian continent on 3 March. This pattern showed the prevailing influences of local emission. On the other hand, on 28-29 March, ozone concentrations did not decrease at night and did not show a diurnal pattern. In addition, the winds remained mostly northerly and wind speeds were at 6 to 8 ms\({}^{-1}\). The weather chart shows that high-pressure systems remained around at the Shangdon peninsula and the East China Sea. This pattern is presumably the prevailing influence of transboundary air pollution [9]. The patterns of ozone, wind direction, wind speed and the atmospheric pressure system on 1-3 March are different from 28-29 March, suggesting that the periods of 1-3 March are under the local prevailing influence and those of 28-29 March are under the influence of the transboundary air pollution. However, there are common features for the periods of 1, 3, 28-29 March, which include that the backward trajectory reached Fukuoka from Sea of Japan via Shimane and Yamaguchi prefectures as shown in Figure 5c. This suggests that these periods are affected by the local emissions, including local industries in Fukuoka and Kitakyushu [15] and ship emissions [25,26]. High PAHs concentrations may be brought due to the influence of local emission sources. As shown above, some of chemical components, such as sulfate and PAHs, showed different concentration variations from PM\({}_{2.5}\) and other chemical components. This indicates that it is necessary to examine not only the health effects of PM\({}_{2.5}\), but also that of each chemical component. At the same time, it also indicates the need to study the source of each chemical component and its formation process in the atmosphere.