## 3 Results and Discussion
### Possible Sources of Secondary Inorganic Species
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sampling Site**} & \multicolumn{6}{c}{**CNU Site**} & \multicolumn{6}{c}{**BKO Site**} \\ \cline{2-10}  & \multicolumn{3}{c}{**Summer**} & \multicolumn{3}{c}{**Winter**} & \multicolumn{3}{c}{**Summer**} & \multicolumn{3}{c}{**Winter**} \\ \hline \multirow{2}{*}{**Parameters**} & **Range** & **Mean** & **Range** & **Mean** & **Range** & **Mean** & **Range** & **Mean** & **Range** & **Mean** \\  & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** & **(ug/m3)** \\ \hline PM\({}_{2.5}\) & 8.8-61.9 & 24.2 & 11.0–93.7 & 34.6 & 9.8-62.6 & 26.3 & 9.5–91.1 & 34.9 \\ \hline OC & 2.0-6.8 & 4.1 & 1.4-12.2 & 5.0 & 3.1-8.8 & 5.4 & 1.2–12.2 & 5.5 \\ EC & 0.7–2.6 & 1.5 & 0.4-2.0 & 1.0 & 0.9–2.3 & 1.6 & 0.4–1.8 & 1.1 \\ WSOC & 1.0–2.7 & 1.9 & 1.0–6.0 & 2.5 & 1.8–4.2 & 2.8 & 0.8–6.2 & 2.6 \\ OC/EC & 2.1–4.3 & 2.8 & 2.4-9.1 & 5.1 & 2.6–4.9 & 3.4 & 2.7–9.5 & 5.2 \\ WSOC/CC & 0.22-0.46 & 0.38 & 0.32–0.82 & 0.54 & 0.24–0.59 & 0.42 & 0.31–0.70 & 0.49 \\ WSOC/EC & 0.80–2.25 & 1.36 & 1.0–4.88 & 2.67 & 1.39–2.44 & 1.82 & 1.13–4.57 & 2.46 \\ \hline NH\({}_{4}\)\({}^{+}\) & 0.1–11.1 & 2.4 & 1.0–13.4 & 4.2 & 0.2–9.3 & 2.4 & 0.8–12.9 & 4.0 \\ K\({}^{+}\) & 0.03–0.61 & 0.15 & 0.07–0.68 & 0.24 & 0.03–0.60 & 0.14 & 0.08–0.71 & 0.25 \\ Cl\({}^{-}\) & 0.01–0.30 & 0.05 & 0.28–2.05 & 0.60 & 0.01–0.25 & 0.05 & 0.22–1.82 & 0.55 \\ NO\({}_{3}\)\({}^{-}\) & 0.2–10.3 & 1.8 & 1.2–27.7 & 8.8 & 0.5–8.8 & 2.0 & 1.2–26.2 & 8.4 \\ SO\({}_{4}\)\({}^{2}\) & 0.6–24.6 & 8.1 & 1.4–22.9 & 6.0 & 0.7–29.4 & 7.8 & 1.2–22.3 & 6.2 \\ Ocalate & N.D–0.26 & 0.14 & N.D–0.40 & 0.13 & N.D–0.42 & 0.19 & N.D–0.37 & 0.14 \\ NSS K\({}^{+}\) & 0.01–0.58 & 0.12 & 0.07–0.66 & 0.23 & 0.03–0.55 & 0.13 & 0.07–0.70 & 0.24 \\ ZSIS\({}^{(1)}\) & 1.2–45.8 & 12.2 & 3.6–64.0 & 19.0 & 1.3–4.25 & 12.3 & 3.5–61.4 & 18.5 \\ NO\({}_{3}\)–SO\({}_{4}\)\({}^{2-}\) & 0.05–0.79 & 0.29 & 0.57–4.06 & 1.55 & 0.06–1.09 & 0.38 & 0.51–4.0 & 1.47 \\ \hline \end{tabular} \({}^{(1)}\)SIS represents the total concentration of secondary ions, including NH\({}_{4}^{+}\), NO\({}_{3}\)\({}^{-}\), and SO\({}_{3}\)\({}^{2-}\).  
\end{table} 
Table 1: Summary of fine particulate matter (PM\({}_{2.5}\)) and its carbonaceous and water-soluble ionic species during the summer and winter at the two sampling sites. Unlike the low ratio seen in the summer, the high NO3-/SO42- ratios at both sites in the winter demonstrate the important role of vehicles in the secondary formation of particulate NO3- from gaseous NO2. Even though the photochemical activity accelerated in the summer, low NO3- concentrations occurred because most NO3- particles were found in the gas phase as nitric acid due to the higher temperature. In order to examine the influence of the local production of NO3- from gaseous NO2 from traffic emissions during winter, the relationship of NO2 with NO3- at the CNU site was investigated; the results are presented in Figure 6c. The temporal profiles of CO and NO2 are also plotted in Figure 6a,b, respectively. The hourly CO and NO2 concentrations were observed at an urban air monitoring station approximately 2.0 km from the sampling site. Since there was a great deal of missing data on NO2 at the station during summer, we did not perform a regression analysis between the summertime NO2 and NO3-. The hourly CO was strongly correlated with NO2, with a correlation coefficient of 0.88, implying that both arose from traffic emissions. During the winter, the particulate NO3- observed at the CNU site showed a good correlation with the gaseous NO2 (R2 = 0.38, \(p<0.01\)) (Figure 6c), indicating that locally produced NO2 played a role in the formation of secondary NO3- particles. A positive correlation between the 24 h average NO2 (at an air pollution monitoring station) and NO3- at the CNU site, high RH, and low WS during winter suggest that heterogeneous reactions were an important process of the wintertime particulate NO3- formation.