Distinguishing the flow of airborne microorganisms along with environmental conditions and their influence on historic heritage buildings.

The National Theater of Costa Rica is a national symbol of our country and an important architectural landmark. It was built in 1897 and is decorated with large-format paintings made by Italian artists. One of these painters was Paolo Serra, who was in charge of decorating three chambers, including the Management's Office (MO). A yearly volumetric air sampling was conducted in seven rooms of the theater, showing high levels of circulating fungal spores in the MO. Thus, further analysis was carried out in this venue. First, the environmental conditions (wind velocity, temperature, relative humidity, and particles) were monitored. Then, the air and particles' flow and the probability of particles concentration were simulated for different scenarios of natural ventilation using a Discrete Phase Model. This allowed us to identify areas where damage and microorganisms were probably more prevalent. The artworks in this chamber were analyzed to determine the types of damages identified: buckling, cracks, cuts, craquelure, holes, scratches, color gaps with exposed fabric or wall, insect debris, flaking, humidity stains, interventions of old restorations, opaque stains, whitish stains and total loss of the original image. As a complement, a microbiological sample was held in 34 sites of interest, resulting in the isolation and identification of five bacterial isolates and thirteen fungi. We identified the artist's main colour palette: madder lake, lead white, calcium carbonate, yellow ocher, natural ultramarine and natural barite. We can conclude that artworks under non-controlled environmental conditions may present a significant degree of deterioration, biodeterioration, and chromatic alteration.