## 2 Materials and Methods
### Investigation Strategy
Subsequently, the collected air volume was analyzed in an external laboratory through quantitative and qualitative VOCs analysis performed according to the gas chromatography-mass spectrometry (GC/MS) method [36]. The cut-off value for VOCs was set equal to 1% of the air sample [37]. Both active and passive methods were used in the biological analysis to sample TBL and molds. Active sampling involved the collection of air flow with a surface air system impactor (sampling rate of 100 L/min). However, the sampling rate and, thus, the total air volume varied from 0.3 to 1 m\({}^{3}\), according to the different occupational patterns of the monitored museum room, assuming a potentially higher pollutant concentration in relation to a greater presence of visitors. Passive sampling was used to gather information about the microbial load, using Petri dishes positioned next to the microclimatic station (\(\Phi\) = 90 mm, plate count agar for microbial growth and Sabouraud dextrose agar for mold growth). The microbial load naturally falls on the plate as an effect of the movement of air (due to both the passage of people and to the air flows from the HVAC systems). Using this method, the total biological pollution was measured for 2 h. At the end of the sampling period, the dishes from the active and passive methods were analyzed in an external laboratory where they were incubated at the required temperature-time range (three days at 30 \({}^{\circ}\)C for TBL and five days at 25 \({}^{\circ}\)C for molds). Thereafter, the samples were analyzed to determine the CFU for both bacteria and molds according to the ISS Report [28]. During phase (iv) all the sampled and monitored data were post-processed and organized in tables and graphs summarizing the minimum, maximum, and average values of the parameters. The parameters were analyzed for each selected room. For the organic, inorganic, and biological pollutants, the collected data were compared with reference values reported in the analyzed literature and, for the VOCs, also with cut-off values. Similarly, the measured air temperature and relative humidity values were compared with reference values for artwork conservation [30] and for occupants' well-being [20; 21]. In phase (v), the results of the data collection were critically analyzed. The correlation of the level of pollutants (i.e., CO\({}_{2}\), VOCs, TBL and molds) with various influencing \begin{table}
\begin{tabular}{c c} \hline \hline  & \(\blacksquare\)**Psychrometer** \\ \hline Sensor & Pt100 (1/3 DIN) \\  & 0.10 \({}^{\circ}\)C (0 \({}^{\circ}\)C); 0.13 \({}^{\circ}\)C (20 \({}^{\circ}\)C) \\ Accuracy & 2\% (15 \(\div\) 40\%); 1\% (40 \(\div\) 70\%); \\  & 0.5\% (70 \(\div\) 98\%) \\ Response time & 90\({}^{\prime\prime}\) (operating fan) \\ Measurement range & t\({}_{\text{db}}\) * 25 \(\div\) 150 \({}^{\circ}\)C; \(t_{\text{wb}}\) **: 0 \(\div\) 60 \({}^{\circ}\)C \\  & RH: 0 \(\div\) 100\% \\ \hline \multicolumn{2}{c}{**CO\({}_{2}\) Probe**} \\ \hline Sensor & Absorption infra-red cell \\ Accuracy & 3\% measure range \\ Response time & \textless{}30\({}^{\prime\prime}\) \\ Measurement range & 0 \(\div\) 3000 ppm \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Main features of the microclimate station. variables, including the type of HVAC system, the maintenance procedures, the cleaning procedures, etc., were investigated. In particular, the total bacterial load and total colony forming units (CFUs) in the bioaerosol were assessed. Finally, the outcomes of phase v) were utilized in phase (vi) to propose strategies and guidelines for the improvement of IAQ in museums.