## 1 Introduction  
This study aims to expand the knowledge of the degradation behavior of painting materials used in modern and contemporary art under selected environmental pollutants. Paintings are usually preserved in museums, galleries, and deposits. However, one of the main problems of these locations is related to the presence of polluting gases and high relative humidity values, as reported in the European Standard EN 16798. In fact, various outdoor pollutants can enter a building through its natural ventilation or by the presence of a high number of visitors, posing a risk to the collections [1]. An example of this phenomenon was observed in the Refectory of Santa Maria delle Grazie (Milan, Italy), where the _Last Supper_ by [PERSON] was conserved [2]. Specifically, the results confirmed the correlation between the presence of tourists inside the museum and the variation in air pollutant values during visits and closure of the museum. Further problems arise from the fact that, although monitoring of environmental conditions is carried out in museums, the conservation parameters chosen are not always suitable for every artwork under examination. In other cases, it is often difficult to control these environmental parameters, especially for historic buildings, which usually are not insulated and for which implementation of building structures is not always allowed [3,4]. The major outdoor pollutants detected inside museums are sulfur dioxide (SO\({}_{2}\)); nitrogen dioxide (NO\({}_{2}\)); ozone (O\({}_{3}\)); and reduced sulfur gases, such as hydrogen sulfide (H\({}_{2}\)S) [1]. As is known, SO\({}_{2}\) is produced during the combustion of fossil fuels, the metal-refining process, and pulp and paper production. Comparing the SO\({}_{2}\) concentration values detected from the 1960s and 1980s to recent times in Europe, they have drastically decreased, but some areas in the Mediterranean and Asian countries, including Southern Italy, China, and India, still exceed the limits recommended by the World Health Organization (WHO) [5, 6, 7]. It is important to consider the impact of SO\({}_{2}\) in the artistic field because it can be catalytically converted to highly corrosive sulfuric acid (H\({}_{2}\)SO\({}_{4}\)) under high humidity conditions (from 60% of relative humidity onwards) [8], causing the chemical and physical degradation of a wide variety of materials, such as leather, parchments, stones, paper, textiles, and paintings--in this case, both the binder and the pigments present in the mixture [1,6]. A recent study by [PERSON] et al. [6] reported the precipitation of sulfate salts causing the whitening of the paint surfaces; it can be observed especially with acid-sensitive types of pigments, leading to color changes that are usually irreversible [1]. Thus, the study of the interaction of these environmental factors with the artworks is of crucial importance in developing suitable conservation strategies and mitigation policies for preventive conservation plans. In this study, the impact of SO\({}_{2}\) and high relative humidity on the degradation behavior of modern and contemporary paints mixed with manganese violet pigment (PV16, C.I 77742, and NH\({}_{4}\)MnP\({}_{2}\)O\({}_{7}\)) was investigated. The samples were artificially aged under a stream of SO\({}_{2}\) in 80% relative humidity for 168 h. These specific [PERSON] conditions were chosen to simulate accelerated aging in museum environments, where works of art are usually exhibited and where it is often difficult to monitor and keep environmental parameters below recommended limits. Although PV16 is a modern pigment not as widely used as titanium white or cobalt blue, it can be found in various fields, ranging from art to cosmetics, sensor technology, and construction [9,10].