###### Abstract
Concerning airborne suspended particles, already known in the scientific literature as Particulate Matters (PMs), their harmful effect on children's health could be important, especially for the smaller ones (PM\({}_{2.5}\) and PM\({}_{1}\), with the down index corresponding to the largest particle diameter of this class, in \(\upmu\)m), which could penetrate the inner parts of the pulmonary tissue after inhalation. Consequently, numerous studies have examined the sources of particulate matter (PM) in schools, whether they originate from indoors or outdoors, and if they are influenced by factors, such as the school location and local climate (e.g., the built environment). These studies have also explored the harmful effects of PM on students' health and proposed ventilation solutions to mitigate the concentration of PM in the classroom air [18; 19; 20; 21] A recent systematic literature review on the IAQ related to aerosol dispersion in indoor spaces with a high occupancy degree (schools included) showed the necessity to establish a robust optimization tool to assess the correlation between several influencing factors, such as ventilation, infection risk, people'sbehavior, and design comfort parameters [22]. The authors of this research concluded that such an optimized tool is lacking at present and should be clearly defined based on a more holistic approach. Regarding the influence of the traffic air pollution nearby the schools, [PERSON] et al. [23] showed the major impact of elevated PMs (notably PM\({}_{10}\) and PM\({}_{2.5}\)) and nitrogen oxide (NO\({}_{\text{x}}\)) outdoor concentrations on the corresponding indoor air concentrations, which directly affect the executive function and academic performance of primary-school-aged children. An important contribution to the ventilation strategies to be adopted for schools to reduce the risk of airborne viral infections was presented by [PERSON] et al. [24], which searched an optimal ventilation strategy to minimize the air transmission of biological pathogens in classrooms, with a particular focus of the SARS-CoV-2 virus, responsible for the COVID-19 infection [25]. In their study, the authors demonstrated that a 2 ACH (air changes per hour) ventilation rate, combined with a 2-meter physical distance between two persons in the class should be an optimal strategy to reduce the POI (Probability Of Infection) with SARS-CoV-2, at a decent energy cost. The increase in the ventilation rate above this value was found to be more effective than the increase in the social distance, in terms of a POI reduction, but with higher cooling energy costs. It appears obvious, as a result of numerous studies investigating the IAQ in schools, that ventilation is the main factor influencing the magnitude of indoor pollutant concentrations. Moreover, mechanical ventilation is much more appropriate to ensure a good IAQ (e.g., concentrations below threshold values given by reference regulations), because it does not depend on the variability of meteorological factors (wind and outdoor temperature) or on the occupants behavior (windows opening periods). Regarding the necessary ventilation airflow for the dilution of indoor pollutants, an interesting comparison between the values recommended by the American norm (ASHRAE standard 62.1 [26]) and European norm (EN standard 16798-1 [5]) was conducted by [PERSON] et al. [27]. The authors showed that, for a classroom with 10-12 years old pupils, the ventilation airflow recommended by the EN 16798-1, equal to 9.81/s\"person, is larger than the corresponding airflow recommended by ASHRAE 62.1 (e.g., 6.71 1/s\"person). Moreover, [PERSON] et al. [27], performed in this study, a meta-analysis judging the effect of ventilation on intellectual productivity in schools, based on a large survey with 3679 participants, by varying ventilation airflows. They demonstrated that an airflow of 10.7 1/s\"person would be an ideal choice for an optimum IAQ in classrooms, when searching for high intellectual productivity of pupils.