# Development of an Automatic Low-Cost Air Quality Control System: A Radon Application
## 3 Results and Discussion
The 10 min and 2 h windows provide the best results, but the ones provided by the 2 h interpolation window are less dispersed. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Interpolation Window** & **Minimum Radon Concentration (Bg/m\({}^{3}\))** & **Mean Radon Concentration (Bg/m\({}^{3}\))** & **Maximum Radon Concentration (Bg/m\({}^{3}\))** & **Time with Air Flow System on (h)** & **Time Above Limit (h)** \\ \hline
10 min & 27 & **208** & 525 & **48.02** & 41.69 \\
30 min & 23 & 231 & 579 & 59.93 & 41.01 \\
1 h & 93 & 273 & 527 & 81 & 51.50 \\
2 h & 31 & 209 & **463** & 56.48 & **17.67** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Statistics for the different interpolation time window tested during a week each The air quality metric used for all the tests is based on the radon concentration. This metric is critical due to high radon concentrations being a direct health risk that has a more immediate impact than other environmental measures such as temperature or humidity. Despite this, it is interesting to evaluate the evolution of temperature and humidity during the tests due to the effect these variables have on energy efficiency, thermal comfort, noise pollution, and indoor environmental quality. Figure 7 shows the temperature and humidity evolution for each interpolation time window tested for a week. Figure 6: Comparison between the natural radon concentration and the concentration during the test for each interpolation time window (each test lasted one week, and the natural concentration was measured during one week). Figure 7: Evolution of temperature and humidity during a week for the tested interpolation time windows: (**a**) 10 min; (**b**) 30 min; (**c**) 1 h; (**d**) 2 h.  
When interpreting these results, we need to consider that the air quality control system did not try to control the temperature and humidity during the test, and also that the ventilation system moves air from the outside of the building to the room, making the temperature and humidity dependent on the weather conditions during the test. We can see that the one-hour and two-hour interpolation windows provide the most stable temperature levels. Still, the two-hour interpolation window kept the temperature at a more comfortable level. The humidity also suffered fewer fluctuations during the tests for the one-hour and two-hour interpolation windows. As previously explained, when exposed to radon, the risk increment is assumed to be linear with respect to radon concentration ((i.e., the risk is ten times higher at 1000 Bq/m\({}^{3}\) compared to 100 Bq/m\({}^{3}\)). The risk increment is also linear with respect to the time one is exposed to high radon concentrations, as shown in [13]. The time one is exposed to high radon concentrations is an essential metric because the WHO handbook and the European regulation establish the limits for safe annual continuous radon levels, not temporary ones [12; 37]. The air quality control system uses this limit (300 Bq/m\({}^{3}\)) as a threshold for activating the ventilation system when it predicts a radon concentration above the threshold. To reduce health risks from indoor radon exposure, we need to consider both radon concentrations and exposure time to high radon concentrations. Therefore, to select the interpolation window that offers the best results, we also need to consider both metrics. The results show that the ten minutes and two hours interpolation windows provide the lowest mean radon concentration. The two-hour interpolation window provides the lowest Maximum radon concentration. The results also show that using a two-hour interpolation window gives the best results regarding the total time it keeps the radon below the limit during the test (lowest exposure time). The radon concentration using the two-hour interpolation windows also shows less dispersion (less variability), so the radon concentrations are more stable. Considering these results, the two-hour interpolation window provides the best results among all the interpolation windows tested.