## 2 Materials and Methods  
### Investigation Strategy  
This research builds upon a previous study [35] in which a general investigation strategy for the assessment of the indoor air quality of museums was defined. In the present study, this approach is presented and applied in a case study of a specific museum building. This methodology is based on the following phases:  
1. collection of general data;
2. definition of monitoring strategies;
3. sampling of indoor parameters;
4. analysis of data and comparison between measured and recommended values;
5. IAQ parameter critical analysis and their correlation with possible pollution sources;
6. definition of guidelines and strategies for the improvement of IAQ conditions in museums. During phase (i), combined with site inspections, primary information about the museum was collected, such as documents and drawings, the characteristics of rooms and the equipment held, the typical presence of visitors in each room, the presence and typology of the HVAC system, the characteristics of the building materials, the characteristics of the objects exposed and their conservation requirements, and the methods of cleaning the environment and the detergents used. Moreover, interviews with technical staff were carried out to identify possible concerns regarding management of the indoor air quality conditions in the museum environment. During phases (ii) and (iii), the monitoring strategies (instruments used, time of sampling, duration and frequency of sampling, etc.) for the evaluation of indoor air quality were defined, consistent with the research objectives. Moreover, based on the outcomes of phase (i), the reference rooms of the museum to be analyzed and the sampling location inside each room were defined. The analyzed rooms were selected based on various considerations related to the conservation of the artworks, i.e., their importance and the potential critical issues for their preservation, user factors, i.e., the number of visitors and occupants' well-being related to indoor air quality, and the characteristics of the air conditioning system. In each room selected, the monitoring systems were placed in the best location with the purpose of collecting representative data (at a height of 1.5 m from the floor), while limiting visitors' interaction with them, to ensure the proper and undisturbed functioning of the rooms  
Since the museum is visited by many people every day, parameters characterizing air pollution in the rooms of the museum were collected for the selected representative rooms. Furthermore, the principal indoor parameters defining environmental and air quality conditions were collected, such as air temperature, relative humidity, organic (VOCs) and inorganic (CO\({}_{2}\)) pollutants, and bacteria aerosols (bacteria and molds). Measurements were carried out both during the opening hours and the closing hours of the museum. The latter measurements were used as reference values for the conditions without occupants. In this case, monitoring was carried out during a day when the museum was closed to the public and a day when the museum was open to the public (opening hours8:15 to 18:50), corresponding to a greater number of visitors. The monitoring was carried out before the maintenance of the HVAC systems to assess the most critical conditions. To monitor the indoor air temperature, relative humidity and CO\({}_{2}\) concentration, a datalogger connected with a psychrometer (air temperature [\({}^{\circ}\)C] and relative humidity [%]), and a CO\({}_{2}\) probe [ppm] were used. This microclimate station measured the parameters every minute for 30 min in sequence in each room analyzed. Table 6 summarizes the main features of the microclimate station [35]. Organic pollutant and bacteria aerosol sampling were carried near the microclimate station [35]. The VOCs were monitored through active sampling of a 5 L air volume in nalophan bags.