## 4 Conclusions  
In this study, the concentrations of PM10, PM2.5, and 19 components of PM2.5 (SO\({}_{4}\)\({}^{2-}\), NO\({}_{3}\)\({}^{-}\), Cl\({}^{-}\), Na\({}^{+}\), NH\({}_{4}\)\({}^{+}\), K\({}^{+}\), Mg\({}^{2+}\), Ca\({}^{2+}\), OC, EC, K, Ti, V, Mn, Fe, Ni, Zn, As, and Pb) were analyzed to investigate the effects of industrial complexes nearby the Ulsan Metropolitan City on the air quality. Although the annual PM2.5 concentration in the Ulsan Metropolitan City in 2017 improved over the previous years, it is still higher than the WHO's recommendation. Results showed that the concentrations of Ti, Mn, Ni, Zn, As, and Pb in PM2.5 increased because of industrial complexes and that OC and EC were affected more by traffic changes than by industrial complexes. To investigate the effects of industrial complexes in the Ulsan Metropolitan City on the air quality, the V component of PM2.5 was used as the tracer given that the change in the V concentration of PM2.5 depends on the wind direction. The result showed that among the weather variables of the SCs, the southeasterly wind direction (which is the direction of the two industrial complexes) mainly appeared at the monitoring station, and the frequency was high in summer due to the Northeast Asia monsoon. Furthermore, not only the concentrations of PM2.5, NO\({}_{3}\)\({}^{-}\) in PM2.5, and most heavy metals excluding K (a soil component) but also the correlations between V and Ni and between Mn and Fe/Zn were higher in SCs than in ALL. These cases can be considered to represent the effects of industrial complexes. When the temporal changes in the OC and EC concentrations were analyzed, the concentrations were higher during commuting hours, and the OC/EC ratio tended to decrease both in ALL and SCs. However, the changes over time and the correlation between OC and EC showed differences between all cases and SCs. The low correlation between OC and EC in SCs during the daytime than nighttime appeared to be due to the formation of SOCs that were not yet stabilized, considering the inverse correlation between OC/EC in SCs and the diurnal wind speed. Additionally, the concentrations of heavy metals, namely, Zn, Pb, As, Mn, and Fe, in SCs were divided into weekdays and holidays, and the temporal changes were analyzed to infer the cause of each heavy metal. Pb, As, and Zn were inferred to be emissions due to cold start, wherein equipment that obtains energy through fossil fuel combustion, such as engines, generates a large amount of pollutants because of the low efficiency of air pollution reduction or incomplete fuel combustion without rising to the proper temperature, usually observed when the engine starts, because they increased at 9:00, i.e., at the beginning of work hours. Furthermore, based on the changes over time of Mn and Fe, it is presumed that there are emission sources in Ulsan industrial complexes that generate Mn and Fe emissions at the ratio of 1:3.8. The above results show that the effect of the emissions from Ulsan industrial complexes on the air quality in the downtown area is greater in summer when the main wind direction  
Figure 13: Changes in iron (Fe) and manganese (Mn) concentrations over time. is southeasterly. The concentrations of PM2.5 were expected to be high due to the presence of various industries in the area, such as oil refineries; however, this was not the case. This may be due to the use of enhanced air pollutant reduction devices. However, because the PM2.5 concentrations of the SCs, which seem to be impacted by Ulsan industrial complexes at the observation site, were higher than the annual mean, strong activities to control air pollutants in Ulsan industrial complexes would be necessary to reduce the PM2.5 concentration in the Ulsan Metropolitan City. At the same time, the concentrations of carbons and heavy metals increased at low levels. The concentrations of carbons and heavy metals in PM2.5 were found to correspond to activity cycles such as commuting hours.