The microclimatic parameters (Ta, RH, E, and CO2) reflect the indoor quality of the environment. Their relationship, connected with the design of the building, can facilitate the growth of photo/heterotrophic organisms and therefore facilitate the increase of the relative CO2 production. Taking this into account, the impact of biological proliferation in a historical building is discussed for the Mithraeum of "Casa di Diana" in the archaeological site of Ostia Antica, which is subjected to guided tours. In this work, for the first time, we propose a study on biological monitoring to evaluate the contribution of bioactivity to air quality, with the objective to increase the comfort of visitors and to open the site for more than one day per week, suggesting possible tools providing a good compromise between building conservation and human comfort. In the sense, it has been possible to distinguish the contribution of the plants from the one deriving from humans: high values of carbon dioxide have been recorded during the night and its scarce removal during the day (air flow). The window present is not sufficient to eliminate the CO2, involving concentrations of CO2 relatively high in comparison to the proposed limits and guidelines defined by law. The obtained results strongly encouraged the elimination of flora in order to increase the comfort of visitors and to open the house for more than one day per week. Although, this process involves an important economic effort, the present study allows making an objective decision which has an important value in a cultural heritage management. Graphical Abstract CO2 contribute by bioactivity as damage to human health.
Keywords: Air flow; Air quality; Human comfort and well-being; Microclimatic parameters; Natural and artificial light; Roman masonry.