## 3 Results
### OC Characteristics of PM\({}_{2.5}\) in Orchard Areas
In general, m,p-xylene and ethylbenzene originate by the same source of emission, though the theory that the decomposition rate by OH radicals in the air varies is applied, because the rate of oxidation is different [65]. That means that the K\({}_{\text{OH}}\) of m-xylene and p-xylene is 23.6 and 14.3, and the lifetimes in the air are 11.8 and 19.4 h, respectively. However, the K\({}_{\text{OH}}\) of ethylbenzene is 6.05, and the lifetime in the air is about 1.6 days [65]. Therefore, when m,p-xylene and ethylbenzene are emitted from the same source, the ratio of X/E decreases as the photochemical reaction time goes by. Additionally, based on this, the higher the ratio of X/E, the higher the influence of local occurrences, and the lower the ratio of X/E, the larger the radius of influence from external inflows and VOCs from the source [66]. The average X/E measured during the study period was 1.86. The range of X/E for major cities confirmed by previous studies is relatively constant, ranging (2.8 to 4.6) in the absence of strong emission sources in particular [65]. In addition, the X/E ratio of the suburbs of Colorado, USA, confirmed in the previous study, was 2.0, while the urban background concentration of Italy was 1.55, and these areas were found to be affected by the urban area [67; 68]. Additionally, the X/E ratio of the four agricultural chemicals analyzed in this study for pesticides, germicides, herbicides, and vapor deposition agents was 14.68, 0.78, 1.26 and 1.20, respectively, with an average of 4.48. Considering that the study period was summer, and the cultivated crop was the apple, it was assumed that the use of pesticides was high. Therefore, it can be concluded that after VOCs are emitted from the emission source, the ratio of X/E measured in the study area, which is 1.86, shows relatively long-term photochemical time change. The T/B of this study ranged from 1.89 to 33.05, with an average of 10.05, and 101 out of 106 observed T/B showed 4.0 or higher. T/B is used as data for estimating emission sources. Generally, biomass combustion has T/B of 1 or less, 0.1-5 for coal combustion, 0.5-10 for combustion by vehicles such as gasoline and diesel, and 1 or more for emissions from industrial processes and solvents, which in previous studies showed up to 10,000 [69]. The mean value of T/B in this study is 10.05, and as Figure 6 shows, a ratio of 10 or higher represents more than 40% of the entire observed values. In addition, the research area is the center of the orchard, and there is no industrial area within a radius of 1 km of the  
Figure 6: VOCs cross-plots for the ratio of toluene vs. benzene and m,p-xylene vs. ethylbenzene. observation point. In other words, considering the observed value of T/B in the study area and the surrounding environment, the source of VOCs in the study area is assumed to be solvents, and that seems to be due to the agricultural chemicals used in the orchard area. In this study, it was suggested that the agricultural chemicals used in agricultural activities are the source of VOCs in agricultural areas. In addition, it was confirmed that the measured VOCs had a photochemical time change for a long time after emission. Therefore, to confirm the process of VOCs emission into the air after agricultural chemicals are applied, the correlation between toluene/ethylbenzene (T/E) was investigated. According to previous studies, toluene and ethylbenzene originate from the same emission source, and the lifetime in the air is close to (1.9 and 1.6) days, respectively, which are quite similar to each other [65]. On the other hand, the boiling points of toluene and ethylbenzene differ by 110 and 136 \({}^{\circ}\)C, respectively. Therefore, in the previous study, the emission type was estimated based on the correlation of T/E. When toluene and ethylbenzene were emitted by combustion, such as automobiles and heating, a high correlation of 0.9 or higher was observed.