# The Interplay between Air Quality and Energy Efficiency in Museums, a Review
## 3 Results and Discussion
### IAQ in Museums
Works of art have been and continue to be threatened as a result of a variety of indoor and outdoor pollutant sources [81]. Museums are typically located in congested, central areas with significant outdoor air pollution, which can be transported indoors via windows, ventilation systems, or by visitors (for example road dust from their shoes) [82]. Indoor sources, on the other hand, are unambiguous in museums. Visitors are an obvious and significant source of indoor air pollution. People emit particulate matter, including bioacerosols, through their skin and clothing, and by speaking and breathing, and they also cause PM resuspension [83; 84; 85]. Other chemical compounds, such as VOCs, are also emitted by people through their breath and personal care products, as well as from building and construction materials [50; 86; 87]. Vacuuming and cleaning the rooms can release a variety of gaseous and particulate pollutants into the atmosphere [49; 88]. A sophisticated HVAC system with appropriate air filtration is the most commonly recommended intervention to reduce indoor air pollutants [89]. Without air filters, the HVAC system cannot adequately protect the artworks housed [90]. [PERSON] et al. [69] measured indoor air pollutants above the recommended levels in five museums (three of which had HVAC systems but no filtration) (Table 2). [PERSON] and [PERSON] [64; 91] monitored the IAQ in museums in California, USA; these authors measured indoor and outdoor concentrations of O\({}_{3}\), NO\({}_{2}\), SO\({}_{2}\), H\({}_{2}\)S, total reduced sulfur (TRS), peroxyacetyl nitrate (PAN), methyl chloroform, and tetrachloroethylene in three of the 12 examined museums. In the remaining nine museums, they monitored NO\({}_{2}\), PAN, nitrate, methylchloroform, tetrachloroethylene, and nitric acid. They concluded that the chlorinated hydrocarbon I/O concentration ratios were greater than unity in all locations, indicating indoor sources. Many consumer and industrial products, such as cleaning products, contain chlorinated hydrocarbons [64; 92]. [PERSON] and [PERSON] [64; 91] observed that the influx of outdoor air diluted the chlorinated hydrocarbons and reduced their I/O ratio. On the contrary, because pollutants like PAN originate outside, the influx of outdoor air increased their I/O ratio. Except for two museums, the authors reported that PAN indoor concentrations were close to outdoor levels in all of them. They observed that, in museums without an HVAC system, indoor air pollutant concentrations were very close to outdoor levels. They found a modest removal of NO\({}_{2}\), PAN, and chlorinated hydrocarbons in museums with HVAC systems. Only one of the three museums equipped with HVAC and chemical filtration achieved low I/O air pollutant concentration ratios [64]. [PERSON] et al. [60] monitored airborne particles indoors and outdoors of museums in California, USA: a historical museum, an archaeological museum, and three art museums. In the historical museum, the Sepulveda House, the indoor fine-particle concentrations were nearly identical to those outdoors. However, the coarse particle concentrations were much lower than outdoors. The indoor particle concentrations at the three museums with sophisticated HVAC systems and particle filtration were significantly lower than those measured outdoors. In particular, the lowest indoor particle concentrations were found at the Norton Simon Museum. In this museum, with a high air recirculation rate, the infiltrated air from outdoors and the recirculated air passed through a series of air filters. Thus, among all the museums studied, its indoor PM levels were the lowest [60]. [PERSON] et al. [90] found that the Oscar Niemeyer Museum (MON) in Curitiba, Brazil has satisfactory air quality, which may be favoring the conservation of its art collection. The quantity of bulk particles in the MON was lower than outdoors. However, air filters with a higher efficiency were suggested for use in the HVAC system of the MON, particularly to capture fine particles.