## 3 Materials and Methods
### Experimental Setup for 222 nm far-UVC Exposition  
For this study, a far-UVC exposition chamber (Figure 2) was specially designed and constructed to simulate the long-term effects of 222 nm far-UVC light on various materials. It consisted of two Quantadose B-Series DF28B-B3 20-watt filtered excimer 222 nm far-UVC lamp modules, which were equipped with 222 nm bandpass filters and special enclosures to cool and to protect the lamps from damage. The lamps were powered by a special 40 W input high voltage power excimer lamp electronic power supply. The use of bandpass filters in the lamp modules ensured that only the desired wavelength of UV light was emitted, further enhancing the precision and accuracy of the far-UVC exposition chamber. These modules were installed in a specially designed box, which helped to minimize the amount of ambient light entering the chamber, further enhancing the accuracy of the far-UVC exposition process. The exposure of the far-UVC light could be varied by adjusting the distance between the material sample and the far-UVC light source. The distance could be varied in 13 mm increments, from 18 mm to 330 mm, corresponding to an irradiance from 0.93 mW/cm\({}^{2}\) to 0.27 mW/cm\({}^{2}\). This allowed for a detailed study of the effects of different levels of far-UVC exposure on the materials under test and simulation of different far-UVC exposure and disinfection scenarios, for public transport environments. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample No.** & **Material** & **Example of a Piece of Material** & **Location** & **Properties Under Investigation** & **Properties of Unaged Material** \\ \hline \multirow{8}{*}{1.} & Fiber-reinforced composite (E-glass fiber with epoxy resin) & & & Tensile strength, 0 \(\circ\)/ 90\(\arcmin\) & 292.67 \\  & & Wall cladding trim elements, constructional wall material & Tensile strength, 0 \(\pm\) 45\(\arcmin\) & 171.30 \\  & & & wall material & Elastic modulus, 0 \(\circ\)/ 90\(\arcmin\) & 36.8 \\  & & & fiber orientation, GPa & \\  & & & Elastic modulus, 0 \(\pm\) 45\(\arcmin\) & 20.70 \\  & & & fiber orientation, GPa & \\  & & & Elongation at break, \(\pm\) 9\(\arcmin\)/ 90\(\arcmin\) & 0.57 \\  & & & fiber orientation, \(\%\) & \\
2. & Floor covering-PVC & Floor covering of public transport/city bus & Tensile strength, MPa & 7.79 \\  & & & Elastic modulus, MPa & 149.29 \\  & & & Elongation at break, \(\%\) & 73 \\
3. & Velour fabric of seats & Fabric covering of passenger seats & Not applicable & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Samples of bus interior materials. The spectra of the lamps used in the far-UVC exposition chamber were measured using an AvaSpec ULS2048 CL spectroscope manufactured by Avantes. The spectrogram of the direct light from the lamps is shown in Figure 3. As can be seen from the graph, the lamps emit light primarily at a wavelength of 222 nm. Radiant exposure was measured using a Gigahertz Optik, X1-5 optometer with a 222 nm calibrated sensor. In this study, far-UVC radiant exposure is conducted in 3 iterations, every 50 h. Radiant exposure values are shown in Table 2 for each exposition iteration. According to [PERSON] et al. [34], it is sufficient to expose surfaces for 2.0 mJ/cm\({}^{2}\) under far-UVC 222 nm irradiation to deactivate the COVID-19 virus; for other pathogens, such as influenza, it should be almost 4.0 mJ/cm\({}^{2}\), and to deactivate most widespread biological pathogens, up to 8.0 mJ/cm\({}^{2}\) exposure is necessary. It takes approximately 1 h for a regular \begin{table}
\begin{tabular}{c c} \hline
**Time, h** & **Radiant Exposure, J/cm\({}^{2}\)** \\ \hline
50 & 96.714 \\
100 & 193.428 \\
150 & 290.142 \\ \hline \end{tabular}
\end{table} 
Table 2: Radiant exposure values for each far-UVC exposition iteration. Figure 3: Spectrogram of the light from the used far-UVC lamps.