Indoor air quality in a high school classroom in Rijeka, Croatia (sick classrooms caused by rising CO2 levels)

School’s indoor air quality (IAQ) is very important as it can affect student’s learning abilities and lead to health issues. Therefore, indoor air quality, and in particular the CO2 concentration, was monitored on a daily basis from mid-November till the end of December 2017, by using several low-cost instruments. The measuring was performed in the physics classroom of a grammar school in Rijeka, Croatia. Detailed CO2 generation rates, air exchange rates, and ventilation rates are calculated and reported in this work, from the experimentally obtained data. Very high concentrations of over 4.000 ppm were recorded, indicating that ventilation rates are far below 5 Ls-1 per person, which is the lowest recommended value of ventilation rate according to the European standard EN 13779. The experimentally obtained data are compared with the theoretical models and a strong correlation are achieved. This is one of the first comprehensive studies of this kind in Croatia; therefore, we hope that it will stimulate interest between health workers, scientists, and school management to implement indoor air quality monitoring practices and perhaps introduce automated ventilation systems in classrooms for the benefit of students’ health and their learning abilities.