Indoor air quality monitoring with stable carbon isotope ratio of CO2 in Museum Environments: study for the Leonardo da Vinci’s “Last Supper”

This work regarded the possible use of stable carbon isotopic ratio of CO2 to monitor the influence of visitors in the Refectory of Santa Maria delle Grazie (Milan, Italy) which houses one of the most important paintings of Leonardo da Vinci, the Last Supper. Indoor air quality is of utmost importance to guarantee the appropriate preservation condition of the painting since the exposure of artwork and materials to gaseous and particulate pollutants emitted from either indoor or outdoor sources contributes to their decay. The results showed a good correlation between the isotopic composition of CO2 and the tourists inside the museum during the visits and the closure of the museum. The variation of indoor atmospheric δ13C is related to the presence of visitors in the Refectory and follows their direction from the entrance to the exit. This new methodology can be used as a supplemental and non-invasive tool to help in calibrating microclimatic conditions through the ventilation rate of HVAC and air filtration systems in the museum and to manage the number of visitors per turn.