# Real-Time Monitoring of Indoor Air Quality with Internet of Things-Based E-Nose
## 4 Results and Discussion  
For air quality analysis with IoT-based e-nose, data were collected in a residence for 4 days at one-minute intervals. The housing area where air quality measurements were taken is 150 m\({}^{2}\). The room in which the measurements were made is 25 m\({}^{2}\) and the measurements were taken from a height of 1.5 m. The five-person house is heated by a central heating system. Although there were changes in the number of inhabitants during the day, there were always at least two people in the household. There was no air cleaning system in the house and the ventilation of the environment was done by manually opening the windows. The doors in the household were not closed during the measurement and thus the air was homogeneous throughout the house. Ventilation was carried out once a day for a duration of one hour. Ventilation started at 11:30 on the first day and at 07:30 on the other days. Figure 4 displays 4-day measurement graphs showing the relationships between humidity-CO\({}_{2}\), CO-CO\({}_{2}\), CO-CO\({}_{2}\)-NO\({}_{2}\), CO-NO\({}_{2}\), PM\({}_{10}\)-CO and PM\({}_{10}\)-NO\({}_{2}\). Figure 5 displays PM\({}_{10}\), CO\({}_{2}\), CO and NO\({}_{2}\) measurements over 4 days. When the graph is examined, it shows that the indoor PM\({}_{10}\), CO, NO\({}_{2}\) and CO\({}_{2}\) PM and gas concentrations vary depending on the number of household inhabitants and individual activities. It is seen that natural ventilation in the morning hours caused a decrease in CO, NO\({}_{2}\) and CO\({}_{2}\) gas concentrations. In addition, an increase in PM\({}_{10}\) is observed in the morning as a result of increased activity in the household. These increased rates at the PM\({}_{10}\) level are 27.1%, 32.2%, 14.4% and 12.5%, respectively. Figure 6 displays the daily changes of temperature, humidity, PM\({}_{10}\), CO, CO\({}_{2}\) and NO\({}_{2}\) values. One-day time, period 1 (00:00-07:30), period 2 (07:30-16:30) and period 3 (16:30-00:00) are divided into three parts; period 1 sleeping of household inhabitants, period 2 during which the daily activities (cooking, cleaning, etc.) of the individuals in the household are performed, and the period 3 of eating and resting of the household inhabitants. The PM\({}_{10}\) value seen in Figure 6a is in the order of 28.18 \(\mu\)g m\({}^{-3}\), 29.93 \(\mu\)g m\({}^{-3}\) and 28.40 \(\mu\)g m\({}^{-3}\) for periods 1-3, respectively. It can be seen that PM\({}_{10}\) has the lowest value in period 1 when the household is asleep. The CO\({}_{2}\) values in the periods are as follows: period 1, 565 \(\mu\)g m\({}^{-3}\); period 2, 317 \(\mu\)g m\({}^{-3}\); and period 3 has a mean value of 297 \(\mu\)g m\({}^{-3}\). The value of CO\({}_{2}\) reaches the highest value in period 1 when the household inhabitants are asleep. Figure 4: Relationship between gases during four-day measurement, (**a**) Humidity- CO\({}_{2}\), (**b**) CO-CO\({}_{2}\), (**c**) CO\({}_{2}\)- NO\({}_{2}\), (**d**) CO-NO\({}_{2}\), (**e**) PM\({}_{10}\)-CO, (**f**) CO-NO\({}_{2}\). When Figure 6b is examined, it is seen that NO\({}_{2}\) concentration has average values of 53.15 \(\upmu\)g m\({}^{-3}\) for period 1, 41.59 \(\upmu\)g m\({}^{-3}\) for period 2 and 42.22 \(\upmu\)g m\({}^{-3}\) for period 3. It is seen that the NO\({}_{2}\) concentration value reached the highest value in the period 1, similar to CO\({}_{2}\). The CO concentration has an average of 5.48 mg m\({}^{-3}\) in the period 1, 1.38 mg m\({}^{-3}\) in the period 2 and 1.09 mg m\({}^{-3}\) in the period 3. The CO value, and also CO\({}_{2}\) and NO\({}_{2}\) values, are observed to be highest in the period 1 while the household is asleep. Also, natural ventilation by opening the windows in the morning results in a significant reduction of CO, CO\({}_{2}\) and NO\({}_{2}\) concentrations.