## 3 Results and Discussion  
### Overview of Results from February to April in 2020  
The results for ozone and meteorological data for February-April in 2020 are shown in Figure 2. The ozone and solar radiation data in Figure 2a shows a gradual seasonal progression from February to April. As solar radiation increase, ozone concentration (mole mixing ratio) also increases. In particular, ozone concentration exceeded the EQSs of oxidant, which is 60 ppb, on some days in the latter half of April, presumably because photochemical reactions became more active with the increase in solar radiation in spring. Figure 2b shows the wind speed and direction. Due to the topography of the Fukuoka area, northwesterly sea breezes prevail during the daytime and southeasterly land breezes prevail during the nighttime [22; 23]. The results from the Fukuoka Meteorological Observatory are daily averages and do not show sea and land breezes clearly during the day and night, but they do indicate that winds from the west-north, and southeast are dominant as the main wind directions. We plot hourly data of ozone, wind speed and wind direction data in Figure 2c. From the afternoon of 16 to the afternoon of 18 February, northerly winds were dominant, with wind speeds stronger than 3 ms\({}^{-1}\). At the same period, ozone concentration, especially at night, hardly dropped and showed no diurnal variations. In this case, we think that transboundary air pollution is dominant [9]. On the other hand, from 19 to 20 February, the ozone showed diurnal variations with southeasterly winds in the morning and evening and northerly winds in the afternoon, showing typical sea-land breeze in Fukuoka, as mentioned above. In this case, we think that local influence is relatively strong [9; 22; 23]. Thus, it is useful to refer to the diurnal variation data of ozone and wind direction when examining the influence of either transboundary air pollution or local pollution.  
Note that the daily average of ozone is about 33-39 ppb from 16 to 18 February, but less than 30 ppb on 19 and 20 February. On average, the ozone concentration tends to be relatively higher when transboundary air pollution continues [9].  
Figure 3 shows the results of concentrations of PM\({}_{2.5}\) and major chemical components. Figure 3a shows PM\({}_{2.5}\), total ionic components, and total metal components. The variations in PM\({}_{2.5}\) and total ionic components seem to be similar. The variations in total metals had a similar trend with PM\({}_{2.5}\) in February and March, but their concentrations remained low from the end of March to the first half of April, unlike the variations in PM\({}_{2.5}\) and total ionic component. Figure 3b shows the variations in EC, OC, and PAHs. All three are carbon-containing compounds, but their variations are different from time to time. This indicates that there are cases of external mixing, where each chemical component is transported from different sources and not contained in the same particle. The results from monitoring in Figure 3 show that there are days when the concentration of all substances is high, but there are also days when the concentration of each component is specifically high, suggesting that some of chemical components are transported from different sources.  
Figure 2: Time series of ozone, and meteorological data in spring 2020. (**a**) Ozone (O\({}_{3}\)), temperature, and solar radiation. (**b**) Wind speed and wind direction. (**c**) Data from 16 to 21 February for ozone, wind speed, and wind direction.