## 3 Results
### OC Characteristics of PM\({}_{2.5}\) in Orchard Areas

Table 1: Concentration of volatile organic compounds in the agricultural chemicals used in orchards. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**PM (\(\mu\)g/m\({}^{3}\))** & \multicolumn{2}{c}{**Total**} & \multicolumn{2}{c}{**Rain**} & \multicolumn{2}{c}{**Non Rain**} \\ \hline rePM\({}_{2.5}\)\({}^{(1)}\) & 8.2723 & \(\pm\) & 6.0531 & 2.5619 & \(\pm\) & 0.7222 & 10.3168 & \(\pm\) & 5.8066 \\ OC & 3.9634 & \(\pm\) & 1.9814 & 2.0100 & \(\pm\) & 0.4346 & 4.6628 & \(\pm\) & 1.8463 \\ WSOC & 3.7688 & \(\pm\) & 1.6488 & 2.0465 & \(\pm\) & 0.3266 & 4.3854 & \(\pm\) & 1.4871 \\ WSOCnbb & 3.5953 & \(\pm\) & 1.5271 & 2.0016 & \(\pm\) & 0.3199 & 4.1659 & \(\pm\) & 1.3767 \\ EC & 0.3202 & \(\pm\) & 0.1625 & 0.150 & \(\pm\) & 0.0703 & 0.3829 & \(\pm\) & 0.1385 \\ eBC & 0.3260 & \(\pm\) & 0.2181 & 0.0930 & \(\pm\) & 0.0890 & 0.3982 & \(\pm\) & 0.1944 \\ NH\({}_{4}\)\({}^{*}\) & 0.7293 & \(\pm\) & 1.1345 & 0.0027 & \(\pm\) & 0.0090 & 0.9895 & \(\pm\) & 1.2212 \\ NO\({}_{3}\)\({}^{-}\) & 1.0661 & \(\pm\) & 1.6935 & 0.1139 & \(\pm\) & 0.1513 & 1.4071 & \(\pm\) & 1.8563 \\ SO\({}_{4}\)\({}^{2-}\) & 1.7783 & \(\pm\) & 1.7839 & 0.1466 & \(\pm\) & 0.1989 & 2.3625 & \(\pm\) & 1.7358 \\ Metals & 0.4149 & \(\pm\) & 0.2924 & 0.1437 & \(\pm\) & 0.0443 & 0.5120 & \(\pm\) & 0.2822 \\ Levoglucasan & 0.0136 & \(\pm\) & 0.0075 & 0.0075 & \(\pm\) & 0.0018 & 0.0158 & \(\pm\) & 0.0076 \\ \hline
**Gas (ppb)** & \multicolumn{2}{c}{**Total**} & \multicolumn{2}{c}{**Rain**} & \multicolumn{2}{c}{**Non Rain**} \\ \hline NH\({}_{3}\) & 16.0542 & \(\pm\) & 9.4465 & 7.7276 & \(\pm\) & 3.0311 & 20.2175 & \(\pm\) & 8.7898 \\ NO & 1.0505 & \(\pm\) & 0.4948 & 0.9234 & \(\pm\) & 0.5462 & 1.1227 & \(\pm\) & 0.4473 \\ NO\({}_{2}\) & 2.2635 & \(\pm\) & 1.0315 & 2.0730 & \(\pm\) & 0.5638 & 2.3718 & \(\pm\) & 1.2066 \\ \hline \hline \end{tabular} \({}^{(1)}\) Total of the concentrations of OC, EC, water-soluble ions, and heavy metals.  
\end{table} 
Table 2: Analysis result of PM\({}_{2.5}\) chemical concentration in orchard area. WSOC can be described in two forms. One is WSOC (biomass-burning, WSOCbb) by biomass combustion, while the other is WSOC (non-biomass-burning, WSOCnbb) by secondary organic compounds. In this study, WSOCnbb was calculated by referring to the calculation method from previous studies to determine the source of WSOC [43]. Briefly, WSOCnbb is determined by differences between total WSOC and biomass burning WSOC calculated from the ratio of levoglucosan to OC. As a result, WSOCnbb accounted for 90.71 and 95.40% of OC and WSOC, respectively. Therefore, it was suggested that the WSOC in the study area originated in secondary organic compounds, rather than in the primary biomass burning, from the results of levoglucosan analyzed in this study. Levoglucosan is a substance that can be produced only by the decomposition of cellulose and hemicellulose when the combustion temperature is higher than 300 \({}^{\circ}\)C [44,45]. Therefore, levoglucosan is used as one of the indicators of PM\({}_{2.5}\) from biocompustion, and the ratio of levoglucosan to OC (L/OC) is mainly used to track biomass burning combustion using water-soluble model [46, 47, 48]. Since the L/OC ratio has lots of variables, such as the type of biomass to be burned, and the combustion conditions, an absolute value in standard does not exist [49]. However, it was suggested that the maximum contribution of BB to OC was about 33%, and the minimum contribution was 4% [48]. Based on this, the L/OC of this study was 3.43%, confirming that the contribution of BB to OC was almost zero. In conclusion, OC, which takes a large portion of the PM\({}_{2.5}\) composition in the study area, did not originate from the combustion of biomass burning. As discussed, previous studies maintained that the secondary organic carbon (SOC) can be represented by WSOC without the effect of biomass combustion [50]. In other words, it was determined that most of the OC in PM\({}_{2.5}\) in the study area was formed by SOC.