Number of school buildings investigated: 12
Monitoring campaigns were conducted during the heating season of 2017/2018.

SI01 is located near city center of Ljubljana, close to a busy road. The main industrial point source is heating plant. The school building was built from brick and concrete at the end of the 18^th century (1976). It was renovated in 2006 (windows) and 2008 (roof renovation). Air conditioning and mechanical ventilation is only in some parts of the building: kitchen. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants were benzene, formaldehyde and particulate matter (PM_2.5). It should be noted that the outdoor values for benzene and PM_2.5 mass concentration were similar; however, the formaldehyde concentration was considerably higher indoors than outdoors. Furthermore, all the comfort parameters were in the healthy range except for the concentration of carbon dioxide

SI02 is located near the city center of Ljubljana in residential area, close to busy road, parking lot and agriculture fields. The main industrial point source is heating plant. The school building was built from concrete at the end of the 18^th century (1981). It has not been renovated yet. Air conditioning and mechanical ventilation is only in some parts of the building: kitchen. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants were benzene and PM_2.5. Furthermore, two of the comfort parameters were in the unhealthy range; the relative humidity was low in the classroom and the concentration of carbon dioxide was high.

SI03 is located in the city center of Ljubljana, close to busy road. The school building was built from brick at the end of the 19^th century (1884) and extended in 20^th century (1950). It was renovated in 1963 (roof renovation and some other partial renovations like electrical cables, classrooms). Mechanical ventilation is only in some parts of the building: kitchen, gym, and offices. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants were benzene, formaldehyde and PM_2.5. It should be noted that the outdoor values for the concentration of benzene and PM_2.5 mass were also at the same levels, thus the inappropriate indoor air quality was mainly caused by the outdoor air pollution. However, the concentration of formaldehyde was considerably higher indoors than outdoors. Furthermore, two of the comfort parameters were in the moderate range; the relative humidity was low in the classroom and the concentration of carbon dioxide was high.

SI04 is located in the city center of Ljubljana, close to busy road and railway. The school building was built from brick and wood at the beginning of the 20^th century (1908) and extended at the end of the 20^th century (1976). It was renovated in 1988 (roof) and in 1992 (façade). Mechanical ventilation is only in some parts of the building: kitchen, and computer room. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutant is benzene. It should be noted that the outdoor value for the benzene mass concentration was slightly lower than indoor (indoor 5.7 µg/m³; outdoor 4.5 µg/m³); however, the inappropriate indoor air quality was mainly caused by the outdoor air pollution. Furthermore, one of the comfort parameters was in the unhealthy range; the relative humidity was low in the classroom.

SI05 is located in the suburban area, close to the main road, light industry and agriculture fields. The school building was built from brick and concrete at the beginning of the 21^st century (2000). It has not been renovated yet. Mechanical ventilation is only in some parts of the building: kitchen. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant is formaldehyde (12.4 µg/m³). Furthermore, all comfort parameters were in the healthy range.

SI06 is located in the city center of Logatec, close to the main road, light industry, agriculture fields and waste storage site. Nearby were noted also a lot of individual heating devices. The school building was built from brick, concrete and stone at the end of the 19^th century (1883) and extended at the end of the 20^th century (1976). It was renovated in 1994 (roof) and in 1996 (façade). Mechanical ventilation is only in some parts of the building: kitchen, dining room, and school hall. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants are benzene, formaldehyde and PM_2.5. It should be noted that the formaldehyde concentration was higher indoors than outdoors, while benzene and PM_2.5 showed similar pattern indoors compared to outdoors. Furthermore, one of the comfort parameters was in the moderate range; the relative humidity was low in the classroom.

SI07 is located in the suburban area, close to the main road and main railway node, light industry, and agriculture fields. Nearby were noted also a lot of individual heating devices. The school building was built from concrete at the end of the 20^th century (1995) and extended at the beginning of the 21^st century (2010). It was renovated in 2010 (roof and façade). Mechanical ventilation is only in some parts of the building: kitchen, office, and in four classrooms. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant is benzene. It should be noted that the outdoor value for the benzene concentration was similar to that measured indoors (indoor 2.2 µg/m³; outdoor 2.1 µg/m³), thus the inappropriate indoor air quality was probably mainly caused by the outdoor air pollution. Furthermore, one of the comfort parameters was in the moderate range; the relative humidity was low in the classroom.

SI08 is located in the village, close to the main road, medium industry, and agriculture fields. The school building was built from brick, concrete and iron at the end of the 20^th century (1975). It was renovated in 2013 (partial renovation: windows, insulation – façade, new mechanical ventilation). Mechanical ventilation is in the whole building. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants are benzene, formaldehyde and PM_2.5. It should be noted that only the concentration of formaldehyde was higher indoors than outdoors. Furthermore, two of the comfort parameters were in the moderate range; the relative humidity was low in the classroom and the concentration of carbon dioxide was high.

SI09 is located in a town, close to the main road, and agriculture fields. The school building was built from brick, and concrete at the end of the 20^th century (1974) and extended at the beginning of the 21^st century (2006). It was renovated in 2006 (partial renovation: roof and façade). Mechanical ventilation is only in some parts of the building: kitchen, and school hall. The indoor air quality was in the moderate category based on the indoor health index. Furthermore, one of the comfort parameters was in the unhealthy range; the relative humidity was low in the classroom.

SI10 is located in the town, close to the main road, medium industry and agriculture fields. The school building was built from brick, and concrete at the end of the 20^th century (1967). It was partial renovated: electric cables, water system, and flooring in the classrooms. Mechanical ventilation is only in some parts of the building: kitchen, and office. The indoor air quality was in the dangerous category based on the indoor health index. The main air pollutant is benzene. It should be noted that the outdoor value for the benzene mass concentration was lower than indoor (indoor 11.1 µg/m³; outdoor 6.2 µg/m³), thus the inappropriate indoor air quality was probably mainly caused by the indoor air pollution. Furthermore, two of the comfort parameters were in the moderate range; the relative humidity waslow and the carbon dioxide concentration was high in the classroom.

SI11 is located in the town, close to the busy road, parking lot, medium industry and agriculture fields. The school building was built from brick, and concrete at the end of the 20^th century (1972). It was partial renovated in 2016: electric cables, lighting, water system, classrooms, windows and insulation. Mechanical ventilation is only in some parts of the building: kitchen. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutant was benzene. It should be noted that the outdoor value for the benzene concentration was similar to the indoor (indoor 5.5 µg/m³; outdoor 5.5 µg/m³), thus the inappropriate indoor air quality was probably caused by the outdoor air pollution. Furthermore, all comfort parameters were in the healthy range except for carbon dioxide concentration.

SI12 is located in a village, close to the road, parking lot, medium industry and agriculture fields. Nearby were noted also a lot of individual heating devices. The school building was built from concreteat the end of the 20^th century (1978) and extended at the beginning of the 21^st century (2006). It has not been renovated yet. Mechanical ventilation is only in some parts of the building: kitchen and two classrooms. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants are benzene, formaldehyde, and particulate matter (PM_2.5). . It should be noted that only the concentration of formaldehyde was higher indoors than outdoors. Furthermore, one of the comfort parameters was in the moderate range; the relative humidity was low in the classroom.

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