# System for Indoor Comfort and Health Monitoring Tested in Office Building Environment
## 2 Indoor Comfort
Volatile organic compounds are organic substances that evaporate very easily. About 150 such substances have been identified, with the most harmful and frequently found within indoor spaces being formaldehyde, acetaldehyde, benzene and toluene. The main sources of TVOCs are cleaning substances, processed wood furniture and paint, including those for textile and plastic products [37]. The recommended TVOC values are max. 100 ppb. Dust includes all suspended particulate matter of various sizes and origins. Particulate matter is classified into two significant size categories: PM 10 (particles with a maximum size of 10 micrometres) and PM 2.5 (particles with a maximum size of 2.5 micrometres). High concentrations of suspended particles are found in urban agglomerations, with the sources of PM 10 being represented by construction sites or road dust raised by traffic and wind, while PM 2.5 particles come from combustion processes [37]. The recommended maximum values of suspended particles are suggested in Table 3.  
* _Thermal comfort_ is closely related to the air quality index and has a strong impact on workplace satisfaction. However, the studies reported in [36; 37] show that work productivity can be improved even with reduced levels of control achieved by the \begin{table}
\begin{tabular}{c c} \hline \hline Clean outdoor air & 250-350 ppm \\ \hline Polulted outdoor air & 400–500 ppm \\ \hline Vertilated room & 500–1000 ppm \\ \hline Unventilated room, closed-air feeling & 1000–2000 ppm \\ \hline Unventilated room, drowsiness, inability to & 2000–5000 ppm \\ concentrate & \\ \hline \end{tabular}
\end{table} 
Table 1: Recommended CO\({}_{2}\) concentration values [36]. \begin{table}
\begin{tabular}{c c} \hline \hline Wintertime & At least 30\% \\ \hline Summertime & Max. 60\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Recommended values of humidity [36]. occupants. Air temperature is the main parameter that influences the occupants' thermal comfort. Usually, this is the only parameter that is taken into account, but it is not the only one that influences the hot or cold sensations [37]. Table 4 indicates the recommended temperature values. According to the California Department of Public Health [39], the permissible exposure limit (PEL) for formaldehyde is 0.75 parts of formaldehyde per million parts of air (0.75 parts per million, or 0.75 ppm). Legally, the exposure may be above the PEL at times, but the average exposure for any 8 h period has to fall under 0.7 ppm. Also, in July 2023, the European Union established specific limits for both formaldehyde and formaldehyde-releasing substances in different products, like furniture and wood-based items [40]. Taking into account that these regulations must be implemented by July 2026, there is a need to develop accessible IoT systems for formaldehyde monitoring. The requirements specify that the maximum values should fall under 0.062 mg/m\({}^{3}\) (0.05 ppm) for formaldehyde are released by furniture and wood-based articles [41]. Radon measurements were also considered because this radioactive gas has a significant impact on people's health. According to the World Health Organization (WHO), radon is the second leading cause of lung cancer in the general population after smoking. It emanates from rocks and soils and tends to concentrate in enclosed spaces like underground mines or residential spaces. Soil gas infiltration is recognized as the most important source of residential radon. This pollutant is a major contributor to the ionizing radiation dose received by the general population [42]. Regarding the permissible values of radon, the European Environment and Health Information System (ENHIS) recommends action levels between 200 Bq/m\({}^{3}\) and 400 Bq/m\({}^{3}\).