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

CZ01 is located in the residential area of the northwest quadrant of the city center of Prague. The road is characterized by moderate traffic density close to the school. The school building type is panel and it was built in the middle of the 20^th century. The building's electrical wirings, lightings and windows have been reconstructed in the past five years. The capacity of the school is 660 pupils. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was also high, thus the inappropriate indoor air quality was mainly caused by the outdoor air pollution. Furthermore, one of the comfort parameters was in the moderate range; the carbon dioxide concentration was relatively high in the classroom.

CZ02 is located in the residential area of the northwest quadrant of the city center of Prague, close to a relatively high traffic road. The school building was built from brick at the beginning of the 20^th century. The whole building was reconstructed in 2000. The building's insulations, windows and water mains have been reconstructed in the past five years. The capacity of the school is 450 pupils. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). Furthermore, one of the comfort parameters was in the unhealthy range; the relative humidity was low in the classroom.

CZ03 is located in the residential area of the northwest quadrant of the city center of Prague, close to a relatively high traffic road. The school building type is panel and it was built in the middle of the 20^th century. The whole building was reconstructed in 2001-2002. The capacity of the school is 600 pupils. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was considerably lower, thus the inappropriate indoor air quality was mainly caused by the indoor air pollutant source. Furthermore, one of the comfort parameters was in the unhealthy range; the relative humidity was low in the classroom.

CZ04 is located in the dense residential area of the northwest quadrant of the city center of Prague, close to a relatively high traffic area. The school building was built from brick at the beginning of the 20^th century. The whole building has been gradually reconstructed since 2010 and the reconstruction of electrical wiring, lighting and windows has taken place over the past five years. The capacity of the school is 618 pupils. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was lower, thus the inappropriate indoor air quality was mainly caused by the indoor air pollutant source. Furthermore, two comfort parameters were in the unhealthy range; the relative humidity was low in the classroom and the average temperature was relatively high.

CZ05 is located in the residential area of the northwest quadrant of the city center of Prague. The road is characterized by moderate traffic density close to the school. The school building was built from brick in the middle of the 20^th century. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutants were the benzene and the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was considerably lower, thus the inappropriate indoor air quality was mainly caused by the indoor air pollutant source. The benzene concentration was also high in the outdoor air. Furthermore, one of the comfort parameters was also in the unhealthy range; the relative humidity was low in the classroom.

CZ06 is located in the residential area of eastern Jihlava. The road is characterized by moderate traffic density close to the school. The school building type is panel and it was built in the third quarter of the 20^th century. The building's windows and insulation have been reconstructed in the past five years. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants were the formaldehyde and the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was also high; however, the formaldehyde concentration was lower outdoors, thus the inappropriate indoor air quality was caused by both outdoor and indoor sources. Furthermore, two comfort parameters were also in the moderate range; the relative humidity was low in the classroom and the carbon dioxide concentration was relatively high in the classroom.

CZ07 is located in the densely residential area of the northwest quadrant of the city center of Prague. The road is characterized by moderate traffic density close to the school. The school building was built from brick and concrete in the middle of the 20th century. The whole building was completely renovated in 2008. The capacity of the school is 461 pupils. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutants were the benzene and the particulate matter (PM_2.5). It should be noted that the outdoor values for the benzene and PM_2.5 mass concentration were also high, thus the inappropriate indoor air quality was mainly caused by the outdoor air pollution. Furthermore, two comfort parameters were also in the moderate range; the relative humidity was low in the classroom and the carbon dioxide concentration was relatively high.

CZ08 is located in the densely populated residential area of the northwest quadrant of the city center of Prague, close to a relatively high traffic area. The school building was built from brick at the beginning of the 20th century. Over the past five years, classrooms, electricity cables, lighting and water pipes have been partially reconstructed. There are 572 pupils at the school. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutants were the benzene and the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration and benzene concentration were also high, thus 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.

CZ09 is located in the suburb area of the Čelákovice. The road is characterized by moderate traffic density close to the school. The school building type is panel and it was built in the third quarter of the 20th century. It was reconstructed in the period of 1999-2002. Over the last five years, classrooms, electricity cables and lighting have been partially renovated. There are 676 pupils at the school. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was considerably lower, thus the inappropriate indoor air quality was mainly caused by the indoor air pollutant source. Furthermore, one of the comfort parameters was also in the unhealthy range; the relative humidity was low in the classroom.

CZ10 is located in the middle of the residential area of Mělnik, close to a relatively high traffic area. The school building was built from brick and concrete in the third quarter of the 20th century. Over the past five years, the lighting, classrooms, insulation and windows have been reconstructed or changed. There are 600 pupils at the school. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutants were benzene and the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was lower, thus the inappropriate indoor air quality was mainly caused by the indoor air pollutant source. Furthermore, one of the comfort parameters was in the unhealthy range; the relative humidity was low in the classroom.

CZ11 is located in the residential area of the northwest quadrant of the city center. The road characterized by moderate traffic density close to the school. The school building was built from brick in the first quarter of the 20th century, and it was extended in 1952. The building was reconstructed in 2005. There are 632 pupils at the school. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was also high, thus 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.

CZ12 is located in the residential area of the northwest quadrant of the city center of Prague. The road is characterized by moderate traffic density close to the school. The school building was built from brick, concrete and wood in the first quarter of the 20th century. In 2004, the school was partially renovated. Over the past five years, windows and insulation have been reconstructed. There are 270 pupils at school. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was the particulate matter (PM_2.5). It should be noted that the outdoor value for the PM_2.5 mass concentration was also high, thus 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.