## 3 Results
### Long-Distance Transport Using VOCs  
We then determined whether the 32 VOCs measured in this study could be used as an evaluation index for long-range transport. It is well known that VOCs are generally removed by the physical adsorption process of wet and dry deposition in the troposphere and transformed by photolysis and OH radical reactions [56]. Adsorption removal of VOCs in wet and dry environments is determined by temperature, humidity, and pressure in the troposphere. The change in VOCs is influenced by oxidation speed for OH radicals. This oxidation speed for OH radical is different in VOC compounds involved in the lifetime of VOCs [57]. According to a previous study, KOH values of m-xylene and p-xylene are 23.6 and 14.3, respectively. The lifetime of m-xylene and p-xylene in the air are 11.8 h and 19.4 h, respectively. KOH and the lifetime of ethylbenzene are 6.05 and 1.6 days, respectively [57]. These data were used as an evaluation index for long-range transport in this study using VOC lifetime in the air and components that increased during the event period. Table 3 indicates concentrations of VOCs in this study. The average VOC concentration during the total study period was 2.588 ppb, including 2.118 ppb during the event period and 2.682 ppb during other periods. The concentrations of VOCs were about 22% lower during the event period than during other periods. However, the concentrations were higher during the event period than during other periods for chloroform (Cf), 1,2-dichloroethane (12 Dice), tetrachloroethene (TcCE), and chlorobenzene (CB). For comparisons between the event and other periods, the concentrations of Cf, 12 Dice, TcCE, and CB were found to be 1.92 times, 3.74 times, 1.67 times, and 2.00 times higher, respectively, during the event period. Considering the four VOCs mentioned above, previous studies indicate that Cf, 12 Dice, TcCE, and CB have a lifetime in the air of 146 days, 90 days, 200 days, and 13 days, respectively [58; 59; 60]. In addition, the time for VOCs to arrive at the study area was 12-48 h based on the back-trajectory analysis. Thus, Cf, 12 Dice, TcCE, and CB might have been introduced into the study area by long-range transport based on the overall concentration increases, lifetime in the air, and arrival time calculated using the back-trajectory analysis during the event period. Cf, 12 Dice, TCCE, and CB transported into the study area by long-range transport can be released artificially or naturally [61]. It is particularly difficult to investigate natural and artificial sources of Cf. In addition, CB is an ingredient of pesticides [60; 61]. The study area was an orchard located in an agricultural region. Only comparing concentrations between events and other periods is not enough to evaluate external influxes due to the natural generation of VOCs and the frequent usage of pesticides. Therefore, concentrations of Cf, 12 Dice, TCCE, CB, and naphthalene (NaT) during the event period were determined in this study. The reason for selecting NaT is because NaT, in an artificial atmospheric environment, is evaluated as the most abundant component of PAHs and that gaseous NaT is eliminated in a short time [62]. A previous study indicated that its lifetime in the air is 48 min-9 h with the OH radical, according to specific circumstances [62]. Therefore, it is expected that NaT will disappear within 12 h, which is the minimum time for an external influx. As indicated in Table 3, the deviation in NaT concentration during other periods was very low at 0.014. This means that gaseous NaT was abundantly distributed in the atmospheric environment. It is a compound with a short lifetime and a relatively low deviation in the study area. Ratios of Cf, 12 Dice, TCCE, and CB to NaT were 2.047 times, 3.967 times, 2.005 times, and 1.974 times higher during the event period than during other periods, respectively. These results confirmed that concentrations of Cf, 12 Dice, TCCE, and CB were increased not by emission sources in the study area but by external influxes.