# Nanomaterials in Photocatalysis: An In-Depth Analysis of Their Role in Enhancing Indoor Air Quality
## 3 Common Volatile Organic Compounds  
Volatile Organic Compounds (VOCs) constitute a broad category of organic chemicals distinguished by their high volatility, making them predominantly present in the gaseous state at room temperature [36]. Common VOCs identified in indoor environments include carbonyl compounds (e.g., formaldehyde, acetaldehyde, acetone), aliphatic hydrocarbons (e.g., hexane, cyclohexane, isoprene), aromatics (e.g., benzene, toluene, xylene), and alcohols (e.g., ethanol, methanol, isopropanol). These compounds represent the primary pollutants in indoor settings and originate from a variety of sources both indoors and outdoors. Key sources of these pollutants include combustion processes, furniture, building materials, paints, and cleaning products, although specific sources may vary depending on the compound. Indoor concentrations of VOCs are generally higher than those outdoors, particularly during colder seasons when heating use increases, and ventilation decreases [37].  
Exposure to VOCs in indoor environments (Table 2) poses significant health risks, especially given that individuals spend a substantial portion of their time indoors. Research has established that VOCs can exert a profound impact on human health, causing symptoms ranging from eye and throat irritation, headaches, and nausea to more severe effects such as respiratory issues and cancer [38].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Key Points** & **Ref.** \\ \hline \multirow{6}{*}{
\begin{tabular}{c} Publication \\ transportation \\ \end{tabular} } & IAQ in public transport depends on factors like vehicle type (e.g., buses, trains, subways), ventilation, passenger density, and outdoor pollution exposure. \\ \cline{2-3}  & Pollutants: PM, CO\({}_{2}\), VOCs, NOx, and biological contaminants. \\ \cline{2-3}  & Subways in particular have higher levels of PM due to friction from brakes, wheels, and rails. \\ \cline{2-3}  & Buses and trains are exposed to outdoor pollution often allow infiltration \\ \cline{2-3}  & of vehicle emissions. \\ \cline{2-3}  & Crowded conditions increase bioaerosol concentrations (e.g., bacteria, viruses). \\ \cline{2-3}  & Solutions include effective ventilation, air purification systems, \\ \cline{2-3}  & and regular cleaning. \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Substance** & **Found in** & **Effects** & **References** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Benzene \\ \end{tabular} } & Cigarette smoke, cleaning products, building materials, furniture, heating systems & Headaches, insomnia, nausea, fatigue, acute & \\  & & & myeloid leukemia and genotoxic effects. Chronic & [39; 40; 41] \\ \cline{2-3}  & & & exposure can be fatal & \\ \hline \multirow{3}{*}{\begin{tabular}{c} Ethylene glycol \\ \end{tabular} } & Antifreeze and de-icing solutions, paints, cleaning agents & Headaches, dizziness, metabolic acidosis, kidney & \\  & & & damage. Chronic exposure can lead to respiratory issues and central nervous & [42; 43; 44] \\ \cline{2-3}  & & & system effects & \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Formaldehyde \\ \end{tabular} } & Combustion, wooden furniture, textiles, insulating materials, paints, wallpapers, and adhesives & Headaches, dizziness, nausea, eye and skin & [45; 46; 47] \\ \cline{2-3}  & & & irritation, nasal tumors, chronic bronchitis & \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Acetaldehyde \\ \end{tabular} } & silvering of mirrors, chemical in the paper industry, fuel mixtures, glue production and denaturant for alcohol & Irritation of eyes, nose, throat and respiratory tract, drunkenness, chronic respiratory irritation, upper respiratory tract cancer, chemical burns & [48; 49; 50] \\ \cline{1-1} \cline{2-3}  & & & \\ \cline{1-1} \cline{2-3}  & & & \\ \cline{1-1} \cline{2-3}  & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: List of common VOCs that can be found in indoor environments, along with their most common known effects on health.