## 1 Introduction
### State-of-the-Art Indoor Air Quality Measurement Systems
Frequently, carbon dioxide is used as an indicator of IAQ, although it does not have such a negative effect on the health of residents in the concentrations in which it is usually found in buildings. In our opinion, CO\({}_{2}\) is rather a marker of human bioeffluents. Examples of different understandings of the set of typical pollutants in an indoor environment are shown in Table 1[4]. This table provides recommended values from the results of the European project HealthVent [5], which aimed to develop health-based ventilation guidelines. Table 1 also includes recommendations provided by the Word Health Organization (WHO) on the acceptable levels of pollutant concentrations [6; 7], as well as recommendations from other organizations, such as China's IAQ standard values [8]. Different approaches to the IAQ issue mean that the exposure limits assumed in the various source materials differ. Figure 1: Overview of the physical and chemical processes of potential pollution sources in the indoor environment of a building. (VOCs—Volatile Organic Compounds,SVOCs—semi Volatile Organic Compounds). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Pollutant**} & **WHO Guidelines for** & **HealthVent Project [5,9]** & **EN 16798-12019 [10]** & **IAQ Standards for China** & **IAQ Certification Hong Kong [13]** \\  & **IAQ with Updates [6,7]** & & & & \\ \hline \multirow{2}{*}{CO\({}_{2}\)} & & & \(<\)50 ppm beyond & & \(<\)1000 ppmv \\  & & & outdoor level & & 1800 mg/m\({}^{3}\) (8 h) \\ \hline \multirow{4}{*}{CO} & 100 mg/m\({}^{3}\) (15) & & 100 mg/m\({}^{3}\) (15) & & \\  & 35 mg/m\({}^{3}\) (1 h) & 19 mg/m\({}^{3}\) (8 h) & 35 mg/m\({}^{3}\) (1 h) & 1 mg/m\({}^{3}\) & 10 mg/m\({}^{3}\) \\  & 10 mg/m\({}^{3}\) (8 h) & 7 mg/m\({}^{3}\) (24 h) & & 7000 ug/m\({}^{3}\) (8 h) \\ \hline Formaldehyde & 0.1 mg/m\({}^{3}\) (307) & 0.03 mg/m\({}^{3}\) (307) & 0.1 mg/m\({}^{3}\) (307) & 10 ug/m\({}^{3}\) & \(<\)0.1 mg/m\({}^{3}\) (8 h) \\ \hline Benzene & \(>\)0.17 mg/m\({}^{3}\) & \(<\)outdoor concentra & No safe level can be determined & 0.11 mg/m\({}^{3}\) & 17 ug/m\({}^{3}\) \\ \hline \multirow{2}{*}{NO\({}_{2}\)} & 40 ug/m\({}^{3}\) (1 year) & 40 ug/m\({}^{3}\) & 40 ug/m\({}^{3}\) & \multirow{2}{*}{10} \\  & 200 ug/m\({}^{3}\) (1 h) & (1 week) & (1 year) & & \\  & & 200 ug/m\({}^{3}\) (1 h) & & 200 ug/m\({}^{3}\) (24 h) & \\ \hline SO\({}_{2}\) & 20 ug/m\({}^{3}\) (24 h) & & 20 ug/m\({}^{3}\) (24 h) & 20 ug/m\({}^{3}\) (24 h) & \\ \hline Naphthalene & 0.01 mg/m\({}^{3}\) & 0.01 mg/m\({}^{3}\) & 0.01 mg/m\({}^{3}\) & & \\  & 0.02 (1 year) & (1 year) & (1 year) & & 0.01 mg/m\({}^{3}\) (8 h) \\ \hline Trichorethene & \(>\)2.3 ug/m\({}^{3}\) & & & & 230 ug/m\({}^{3}\) (8 h) \\ \hline Tetrachloroethene & 0.25 mg/m\({}^{3}\) & 0.25 mg/m\({}^{3}\) & 0.25 mg/m\({}^{3}\) & & 0.25 mg/m\({}^{3}\) (8 h) \\  & (1 year) & (1 year) & (1 year) & & 0.25 mg/m\({}^{3}\) (1 year) \\ \hline Respirable particulate matter & 10.0 ug/m\({}^{3}\) & & 10 ug/m\({}^{3}\) & 15 ug/m\({}^{3}\) (1 year) & \\  & (1 year) & (1 year) & 35 ug/m\({}^{3}\) (24 h) & 100 ug/m\({}^{3}\) (8 h) \\ \hline PAH \({}^{*}\) & \(>\)0.012 ng/m\({}^{3}\) & & No safe level can be determined & 1.2 ng/m\({}^{3}\) (8 h) \\ \hline TVOC ** & & & & \\ \hline \end{tabular}  
* PAH Para-Aminobutyric Acid\(-\)cyclic aromatic hydrocarbons; ** TVOC fetal Volatile Organic Compounds; Reference [13] provides additional TVOC certification tests for new office building by determining (at the ppb level) the content of carbon tetrachloride, chloroform, 1,2- and 1,4-dichlorobenzene, ethylbenzene, toluene, and \(\diamond\), m\(-\)and, p-value.  
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