## 3 Results
### Time Series Results of Measured Concentrations
According to previous studies, an increase in EC could result from external influxes if no specific EC sources are available. A 68% increase in EC has been reported [40]. Our study location was an orchard located in an agricultural region without any residential houses, highways, or industrial duplexes discharging EC nearby. However, EC was found to be increased about 2.1 times when comparing its concentrations between the event period and other periods. This increase in EC during the event period might be due to external influxes associated with the geological features of the study location. The third reason for an external influx is that water-soluble ions were the main cause of increased PM\({}_{2.5}\). Previous studies have insisted that an increase in SOA is a big factor influencing long-range transport [40]. Generally, atmospheric SO\({}_{2}\) and NO\({}_{2}\) react with hydroxyl radicals and generate sulfuric acid and nitric acid. Then nano-particles such as (NH\({}_{4}\))\({}_{2}\)SO\({}_{4}\), (NH\({}_{4}\))HSO\({}_{4}\), and NH\({}_{4}\)NO\({}_{3}\) are produced by reactions between ammonia and sulfuric and nitric acids [41,42]. Additionally, if ammonia is available after NH\({}_{3}\) reacts with sulfuric acid first, it can react with nitric acid [31]. This study showed that the content of water-soluble ions within PM\({}_{2.5}\) was 60.27% during the event period and 40.64% during other periods. Thus, the event period had a higher content of water-soluble ions than other periods. Concentrations of SO\({}_{4}^{2-}\), NO\({}_{3}\)\({}^{-}\), and NH\({}_{4}\)\({}^{+}\) within PM\({}_{2.5}\) were increased about 2.9 times, 7.2 times, and  
Figure 2: Time-series concentrations of PM\({}_{2.5}\), CO, CO\({}_{2}\), EC, eBC, and ionic compounds. 4.7 times, respectively, during the event period compared with those during other periods. On the other hand, atmospheric concentrations of SO\({}_{2}\), NO, and NO\({}_{2}\) (factors to generate SOA such as SO\({}_{4}\)\({}^{2-}\) and NO\({}_{3}\)\({}^{-}\)) in PM\({}_{2.5}\) were increased by 0.97 times, 1.06 times, and 1.4 times, respectively. Their increases were much lower than the increases in water-soluble ions in PM\({}_{2.5}\). Along with ammonium-rich SOA due to NO\({}_{3}\)\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), and NH\({}_{4}\)\({}^{+}\), the mole ratio of NH\({}_{4}\)\({}^{+}\)/SO\({}_{4}\)\({}^{2-}\) was 3.8 during other periods and 6.14 during the event period, indicating a stronger condition for SOA during the event period than during other periods. Based on the mole ratio of NO\({}_{3}\)\({}^{-}\)/SO\({}_{4}\)\({}^{2-}\), the contribution of NO\({}_{3}\)\({}^{-}\) to PM\({}_{2.5}\) was also higher during the event period, which was 4.5 compared with 1.83 during other periods. Atmospheric NH\({}_{3}\), a dominant factor for generating SOA by NO\({}_{3}\)\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), and NH\({}_{4}\)\({}^{+}\), displayed about a 2.7 times difference between the event period and other periods. There were small differences in concentrations of SO\({}_{2}\), NO, and NO\({}_{2}\) during each period. Even without increasing concentrations of SO\({}_{2}\), NO, and NO\({}_{2}\) in the atmosphere, these materials could be caused by external influxes such as an increase in water-soluble ions like NO\({}_{3}\)\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), and NH\({}_{4}\)\({}^{+}\) in PM\({}_{2.5}\), ammonium-rich status increase during the event period, and increased contributions of NO\({}_{3}\)\({}^{-}\) and gaseous NH\({}_{3}\). That is, types of water-soluble ion compounds were increased during the event period. After sufficient NH\({}_{3}\) in the process of SOA formation reacted with sulfuric and nitric acids, the remaining NH\({}_{3}\) might affect the study area. Some previous studies have suggested that an increase in NH\({}_{3}\) is due to external influxes and that SOA compositions in PM\({}_{2.5}\) and NH\({}_{3}\) can be increased by long-range transport.