## 1 Introduction
As the incidence of COVID decreased, schools relaxed their preventive measures and ventilation protocols, and intermediate solutions--which could differ between climate zones--were taken. This provided a new opportunity to analyse the measures implemented in the different climate zones in order to ascertain whether air quality and comfort can be guaranteed simultaneously, without the prevalence of either of them. In northern Spain, [PERSON] et al. [17] conducted a large on-site measurement campaign in primary and secondary schools, detecting widespread natural cross-ventilation and compliance with the minimum IAQ requirement but poor thermal comfort, mainly in summer. [PERSON] et al. [18] monitored secondary schools located in southern Spain, identifying more hours of discomfort (in summer) than bad IAQ. Similarly, [PERSON] et al. [19] explored the relationship between thermal comfort and IAQ in 26 classrooms in central Italy. They found overall adequate average levels of CO\({}_{2}\) but quite high indoor maximum temperatures even in winter. However, despite the above-mentioned studies, in general, few published works address this combined approach of analysing thermal comfort and IAQ, taking into consideration different European climates [20]. Regarding current regulations, the Spanish requirements on the ventilation of educational spaces [21] establish the mandatory implementation of mechanical ventilation systems in non-residential buildings constructed after 2007 (a system not usually found in schools built earlier). For the purposes of this study, focus is placed on two IAQ categories defined in this regulation: IDA 1 (optimal air quality, not mandatory in schools), specifying a minimum outdoor air ventilation rate of 20 1/s per person or a maximum CO\({}_{2}\) concentration of 350 ppm above outdoor level, and IDA 2 (good air quality, mandatory for classrooms), specifying 12.51/s per person or 500 ppm above outdoor level CO\({}_{2}\) concentration. According to the Spanish Ministry of Health indications during the COVID-19 pandemic, concentrations above 800 ppm measured over outdoor levels indicate poor air quality [22]. In Italy, the first regulation related to IAQ in school buildings was introduced with DM 1975 [23], which requires air exchange to be ensured according to the grade of the classroom (3.5 ACH for middle schools, and 5 ACH for high schools). During the COVID-19 pandemic, [23] was the only legislative reference in Italy. Since the pandemic, the Italian government has made the installation of mechanical ventilation systems mandatory for public school building renovations and energy requalification [24]. Ventilation system designs must now comply with UNI 10339:1995 [25] or EN 16798-1:2019 [7]. In the case of the former, minimum outdoor air ventilation rates of 6 1/s per person and 71/s per person are required for middle schools and high schools, respectively. In the European reference, Category II is defined with specifications of a minimum outdoor air ventilation rate of 7 1/s per person or a maximum CO\({}_{2}\) concentration of 800 ppm above the outdoor level. Nevertheless, regulations are focused on IAQ or thermal comfort, and there is a lack of proposals using combined standards [26]. This, coupled with the gap detected in the literature on recent combined studies in the Mediterranean context, induced us to focus the aim of this work on providing a characterisation of different natural ventilation protocols that are being applied post-pandemic (influenced by local climate adaptations factors), analysing their influence on air quality and thermal comfort. A comparison was carried out on the on-site measurements of environmental and air quality conditions in eight characteristic classrooms located in the Mediterranean region, specifically in southern Spain and northern Italy. These locations were selected as representative of different heating and natural ventilation patterns, applied post-pandemic, within the Mediterranean climatic context of southern Europe.