## 1 Introduction
[34] at a primary school in Australia, emphasized the influence of garden maintenance work on internal concentrations of PM\({}_{2.5}\). In addition, in Brazil, [PERSON] et al. [35] reported that a high proportion of soot was found in the measured suspended particles of two school buildings. Additionally, the research of [PERSON] et al. [36] in classrooms of the Niger Delta highlighted the impact of ambient air pollution on IAQ. In Greece, [PERSON] et al. [37] reported that internal concentrations of airborne particles in seven primary schools in Athens were strongly influenced by resuspension due to the activities of pupils. This research, along with the respective work of [PERSON] et al. [38], [PERSON] et al. [39] and [PERSON] et al. [40] comprised some of the first research efforts concerning IAQ within Greek schools. More recently, [PERSON] et al. [41] implemented IAQ measurements in nine naturally ventilated schools in various areas of Athens. They concluded that the levels of indoor PM\({}_{10}\) were extremely high and mainly originated from chalk. Additionally, by using scientific questionnaires, students associated low levels of IAQ with elevated temperature values, highlighting the importance of seasonality. Relevant publications such as [PERSON] et al. [42], [PERSON] et al. [43] and [PERSON] et al. [44] reported similar results about IAQ and energy savings in Greek classrooms. Referring to school buildings with a green roof system (GRS), [PERSON] et al. [45] and [PERSON] et al. [46] reported satisfactory indoor temperature levels and reduced CO\({}_{2}\) emissions in South Korean classrooms compared to conventional buildings. In Mediterranean climates, [PERSON] et al. [47] noted that the addition of a GRS improved thermal comfort conditions of an educational institution in Italy[PERSON] Nevertheless, the vegetation type also plays an important role in both energy savings (low water requirements) and reduction of gaseous pollutants, according to [PERSON] et al. [48][PERSON] Additionally, it should be noted that green roofs can lead to a reduction of ambient PM\({}_{10}\) (and other air pollutants) only if they are installed on several buildings in the same location. In particular, [PERSON] et al. [49] highlighted a PM\({}_{10}\) reduction of 14% after the installation of 170 green roofs in Chicago, USA, while a 10-20% GRS extension on buildings in Toronto led to significant improvement of air quality, as [PERSON] and [PERSON] [50] noted. More recently, the study of [PERSON] et al. [51] highlighted that some specific kinds of grass on roofs in Manchester could effectively remove airborne particulate matters. From all the above, it becomes obvious that from the large number of studies in different climatic zones, IAQ depends on occupancy, ventilation patterns, location and outdoor sources. However, few IAQ studies at schools to which an intervention for energy upgrade has been applied, such as the installation of a GRS, exist. To this direction, the present study aims to investigate the concentration levels, chemical composition and potential sources contributing to coarse particulate matter (PM\({}_{10}\)) in the indoor and outdoor environments of a primary school, which retains a GRS. As source apportionment studies inside classrooms are limited, this work will add information on the investigation of PM sources in the school microenvironment and, consequently, on the exposure of the child population.