This work investigates the possibility of implementing a nature-based solution (NBS) based on the photosynthetic process of Laurus nobilis L. (common laurel), for reducing peak CO2 concentrations in an air-tight museum environment, namely the Refectory of the Santa Maria delle Grazie Church (Milan, Italy), home of Leonardo da Vinci's painting "Last Supper". The phytoremediation potential of laurel plants was evaluated at CO2 ≅ 1000 ppm under controlled environmental conditions. Furthermore, light-saturated net assimilation (Pnmax) was measured at two CO2 concentrations (380 and 1000 ppm) during the growing season. Steady-state gas exchanges were not affected by elevated CO2 in the short-term, while Pnmax was significantly increased, also showing higher values in spring and autumn, and a reduction during summer. Our estimated CO2 removal rates indicate that, in order to control visitors' respiratory CO2 emissions in view of an increase in visitor numbers in the Refectory, a possible NBS in the form of an external greenhouse, connected to the HVAC system of the museum, should allocate from 58 to 112 young laurel plants, depending on their seasonal phytoremediation capacity. These results, although preliminary, allow to hypothesize the possibility of controlling CO2 indoors through a combination of traditional air-cleaning systems and a properly designed NBS, thus increasing the sustainability of air-tight museum environments. © 2020 by the authors.

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