## 3 Results
The median ratios of pollutants during window opening periods to the reference periods for NO\({}_{2}\) and PM\({}_{2.5}\) were 1.56 and 1.13, respectively with the maximum values up to 5.23 and 1.85 respectively (Table 3). The NO\({}_{2}\) and PM\({}_{2.5}\) levels during window opening periods were significantly higher than that of the reference periods, and the maximum increased values were 53.25 ppb and 44 ug/m\({}^{3}\), respectively. Table 4 shows the ratios of air pollutants during cooking periods to reference \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Area**} \\ \cline{2-4}  & **Traffic** & **Industry** & **General** \\ \hline Window opening & 68.75 & 66.67 & 87.50 \\ Occupants (>4 people) & 40.40 & 57.01 & 34.41 \\ Cooking & 87.50 & 83.33 & 95.83 \\ Air-conditioning use & 62.50 & 83.33 & 95.83 \\ Making tea & 31.25 & 30.00 & 0 \\ Smoker & 63.64 & 40.00 & 26.09 \\ Incense burning & 72.73 & 50.00 & 29.17 \\ Mosquito coil burning & 37.50 & 22.22 & 12.50 \\ Essential oil using & 31.25 & 33.33 & 25.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The percentage (%) of household characteristics in traffic, industry, and general areas. Figure 1: The 24-h average concentration of indoor air pollutants (**A**) CO, (**B**) CO\({}_{2}\), (**C**) NO\({}_{2}\), and (**D**) O\({}_{3}\) in the houses of traffic, industry, and general areas. \({}^{\star}\) Scheffe test \(p\) < 0.01.  
periods and the differences in air pollutants between window opening periods and reference periods. The median ratios of pollutants during cooking periods to the reference periods for CO, CO\({}_{2}\), NO\({}_{2}\), and PM\({}_{2.5}\) were 0.93, 1.06, 1.11, and 1.09, respectively. The concentrations of CO\({}_{2}\), NO\({}_{2}\), and PM\({}_{2.5}\) during the cooking periods were significantly higher than those of reference periods with increased concentrations of 26.17 ppm, 5.40 ppb, and 5 ug/m\({}^{3}\), respectively. However, the CO level during cooking periods was significantly lower than that of the reference periods with the decreased concentration of 0.25 ppm. Table 5 shows the association between air pollutants concentrations (24-h average concentration of air pollutants in each house as dependent variable), and household characteristics by using the generalized estimating equations model. This study revealed that CO concentrations were positively associated with the number of occupants, cleaning, smoking, incense burning, mosquito coil burning, and negatively correlated to cooking with a statistical significance. Indoor CO\({}_{2}\) concentrations were positively associated with the number of occupants, air-conditioning use, smoking, incense burning, and negatively correlated to mosquito coil burning with a statistical significance. In addition, significantly higher NO\({}_{2}\) levels were found in the homes with smokers than homes without smokers. There were significantly positive associations between indoor SO\({}_{2}\) concentrations and smoking and incense burning. In terms of O\({}_{3}\), indoor O\({}_{3}\) concentrations were positively associated with the window opening and negatively correlated to the number of occupants, incense burning, and essential oil use with a statistical significance. For PM\({}_{2.5}\), it was positively associated with cleaning and incense burning with a statistical significance.