Number of school buildings investigated: 12

Monitoring campaigns were conducted during the heating season of 2017/2018.

PL03 is located in the residential area of Lodz, close to the high traffic road. The school building was built from brick, concrete and wood, in the end of the fifties of the 20th century. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was benzene. The outdoor value for benzene concentration was slightly lower but on the similar level. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and was classified in the unhealthy range.

PL06 is located in the city centre of Lodz, in the area with a moderate traffic road. The school building was built from brick, in the second half of the 20th century. The indoor air quality was in the unhealthy category based on the indoor health index. The main indoor air pollutant was benzene. The benzene concentration was on similar level but slightly lower that in the indoor air. Considering the comfort parameters, should be noted that the CO2 concentration was in the unhealthy range; the CO2 concentration in the classroom was high.

PL13 is located in the residential area of Lodz, with a moderate traffic road nearby. The school building was built from brick, in the mid-fifties of the 20th century. The indoor air quality was in the moderate 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 also high (even slightly higher), thus the inappropriate indoor air quality was caused mainly by the outdoor air pollution. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and was classified in the unhealthy range.

PL19 is located in the suburban, residential area of Lodz, with a moderate traffic road nearby. The school building was built from brick and concrete, at the end of the eighties of the 20th century. The indoor air quality was in the unhealthy category based on the indoor health index. The main air pollutant was formaldehyde. It should be noted that the outdoor value for the formaldehyde concentration was low, thus the inappropriate indoor air quality was caused mainly by the indoor air pollution. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and was classified in the unhealthy range.

PL20 is located close to the city centre of Lodz, with a high traffic road nearby. The school building was built from brick, at the beginning of the 20th century. The indoor air quality was in the moderate category based on the indoor health index. The main indoor air pollutants were benzene and the PM2.5 mass concentration. It should be noted that the main outdoor air pollutant was the PM2.5 and also the benzene concentration was slightly higher than in the indoor air, thus the inappropriate indoor air quality was caused mainly by the outdoor air pollution. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and was classified in the moderate range.

PL21 is located is located in the residential area of Lodz, with a moderate traffic road nearby. The school building was built from brick, at the beginning of the 20th century. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was benzene. The outdoor value for benzene concentration was slightly lower but on the similar level. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and was classified in the unhealthy range.

PL22 is located close to the city centre of Lodz, with a very high traffic road nearby. The school building was built from brick, in the mid-fifties of the 20th century. The indoor air quality was in the moderate category based on the indoor health index. It should be noted that main outdoor air pollutant was benzene; however, it was present at similar concentration compared to the outdoor value. However, one of the comfort parameters was in the unhealthy range; the relative humidity in the classroom was low.

PL24 is located close to the city centre of Lodz, in the area with a low density of the traffic road. The school building was built from brick and concrete, in the end of the fifties of the 20th century. The indoor air quality was in the moderate category based on the indoor health index. The main air pollutant was benzene. The outdoor value for benzene concentration was slightly lower but on the similar level. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and was classified in the unhealthy range.

PL25 is located in the suburban area of Lodz, with a moderate traffic road nearby. The school building was built from brick, in the first half of the 20th century. The indoor air quality was in the moderate 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 lower, thus the inappropriate indoor air quality was caused mainly by the indoor air pollution. Considering the comfort parameters, should be noted that the relative humidity in the classroom was law and the CO2 concentration was high, thus the school was classified in the unhealthy range.

PL26 is located in the suburban area of Lodz, with a moderate traffic road nearby. The school building was built from brick, in the end of the fifties of the 20th century. The indoor air quality was in the healthy category based on the indoor health index (no data for the concentration of benzene indoors). The outdoor value for benzene concentration was high, thus potentially should be considered as the main source of the indoor air pollution. Considering the comfort parameters, should be noted that the CO2 concentration was high, thus the school was classified in the unhealthy range.

PL27 is located in the residential area of Lodz, with a moderate traffic road nearby. The school building was built from brick and concrete, at the end of the eighties of the 20th century. The main indoor air pollutant was PM2.5. It should be noted that the main outdoor air pollutant was the PM2.5 mass concentration but the outdoor PM2.5 mass concentration was slightly lower than in the indoor air. Considering the comfort parameters, should be noted that the relative humidity was law and the CO2 concentration was high, thus the school was classified in the moderate range.

PL28 is located in the residential area of Lodz, with a low traffic road nearby. The school building was built from brick, at the beginning of the sixties of the 20th century. The indoor air quality was in the healthy category based on the indoor health index. The outdoor value for the PM2.5 mass concentration was moderate and should be considered as the potential source of the indoor air pollution. Considering the comfort parameters, should be noted that the relative humidity was law and the CO2 concentration was high, thus the school was classified in the moderate range.