## 3 Results
### Univariate Analysis  
The results of the univariate analysis are shown in Table 2. The table shows the correlation coefficients for the relationship of PM2.5 and its ionic components with pbPEFR, pbPEFRm, pbPEFRe and the daily prevalence of each respiratory symptom.  
An interesting point is that in this study, some of the ions in PM2.5 worsened symptoms and PEFR, while others improved them.  
Figure 1 shows a scatter plot of the relationship between NO3\({}^{-}\) and pbPEFR, pbPEFm, pbPEFe, and the daily prevalence of respiratory symptoms as a typical example of the relationships.  
Vertical axes show the number of symptoms per day in the total number of participants, and horizontal axes show the daily ion concentration of NO3\({}^{-}\) in \(\upmu\)gm\({}^{-3}\).  
Numbers are logarithmic.  
pbPEFR, mean the ratio of daily Peak Expiratory Flow Rate (PEFR) to personal best PEFR in the study period, pbPEFRm, mean morning PEFR, pbPEFR mean evening PEFR, pbPEFR mean the daily average PEFR.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Unit** & **Mean** & **SD** & **Median** & **Min** & **Max** \\ \hline Air pollutants & & & & & & \\ \hline PM2.5 & \(\upmu\)g/m\({}^{3}\) & 14.9220 & 7.7530 & 13.5380 & 2.8630 & 45.5470 \\ CI\({}^{-}\) & \(\upmu\)g/m\({}^{3}\) & 0.0424 & 0.0688 & 0.0149 & \(-\)0.0004 & 0.3558 \\ NO3\({}^{-}\) & \(\upmu\)g/m\({}^{3}\) & 1.0020 & 1.0421 & 0.6922 & 0.0092 & 7.5198 \\ SO4\({}^{2-}\) & \(\upmu\)g/m\({}^{3}\) & 2.9016 & 2.0106 & 2.2711 & 0.5938 & 12.3098 \\ Na+ & \(\upmu\)g/m\({}^{3}\) & 0.4190 & 0.1960 & 0.3893 & 0.0576 & 0.9702 \\ NH4\({}^{+}\) & \(\upmu\)g/m\({}^{3}\) & 0.7520 & 0.8239 & 0.5192 & 0.0221 & 5.8882 \\ K+ & \(\upmu\)g/m\({}^{3}\) & 0.2733 & 0.1266 & 0.2583 & 0.0845 & 0.8990 \\ Mg2+ & \(\upmu\)g/m\({}^{3}\) & 0.3428 & 0.2776 & 0.2874 & 0.0906 & 2.8840 \\ \hline Symptoms & & & & & & \\ \hline Runny nose & (\%) (1/100) & 0.3946 & 0.1086 & 0.3784 & 0.1892 & 0.6486 \\ Stuff nose & (\%) (1/100) & 0.3609 & 0.1118 & 0.3514 & 0.1081 & 0.6486 \\ Sneezing & (\%) (1/100) & 0.1641 & 0.0828 & 0.1389 & 0.0000 & 0.3590 \\ Coughing & (\%) (1/100) & 0.2859 & 0.0936 & 0.2703 & 0.1282 & 0.7436 \\ pbPEFR (mean) & ratio & 0.8260 & 0.0131 & 0.8281 & 0.7832 & 0.8490 \\ pbPEFR (morning) & ratio & 0.8137 & 0.0139 & 0.8136 & 0.7703 & 0.8381 \\ pbPEFR (evening) & ratio & 0.8377 & 0.0149 & 0.8392 & 0.7954 & 0.8722 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of concentrations of air pollutants, daily prevalence of respiratory symptoms, and personal best peak expiratory flow rates (pbPEFR).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ion** & **Cough** & **Runny Nose** & **Stuffy Nose** & **Sneeze** & **pbPEFR** & **pbPEFRn** & **pbPEFRe** \\ \hline PM2.5 & 0.002 & 0.066 & 0.085 & 0.159 & 0.047 & 0.099 & 0.023 \\ CI\({}^{-}\) & 0.226 & 0.371 ** & 0.404 ** & 0.260 ** & \(-\)0.318 ** & \(-\)0.169 * & \(-\)0.379 ** \\ NO3\({}^{-}\) & 0.076 & 0.405 ** & 0.315 ** & 0.403 ** & \(-\)0.253 ** & \(-\)0.075 & \(-\)0.354 ** \\ SO4\({}^{-}\) & 0.062 & 0.058 & 0.065 & 0.017 & 0.004 & \(-\)0.026 & 0.061 \\ Na+ & \(-\)0.294 ** & \(-\)0.355 ** & \(-\)0.302 & \(-\)0.256 & 0.263 ** & 0.169 & 0.300 ** \\ K+ & \(-\)0.087 & \(-\)0.113 & \(-\)0.158 & 0.073 & 0.237 ** & 0.189 * & 0.257 ** \\ Mg2+ & 0.016 & 0.118 & 0.338 ** & 0.042 & \(-\)0.208 * & 0.132 & \(-\)0.222 * \\ \hline \hline \end{tabular}
\end{table}
Table 2: Correlation coefficients for the relationship of PM2.5 and ionic concentrations of PM2.5 with daily prevalence of respiratory symptoms and mean personal best peak expiratory flow rates.