Poor air quality can be caused by inadequate ventilation and heating systems, or the lack of such systems. However, the stuffiness of enclosed spaces can also depend on our bad habits.
Even in the absence of other pollutants, indoor air quality becomes progressively worse the more people there are in a room over a long period of time. Stuffy air (mostly due to high concentrations of carbon dioxide) can cause headaches, difficulty in concentration and drowsiness, thus impairing learning performance. Each person in a room uses oxygen and produces carbon dioxide, heat, odours and water vapour (40 people will produce around 300 grams of steam per hour, depending on physical activity).
The more overcrowded the classroom, the sooner the air becomes stuffy and unpleasant as the oxygen is consumed and the carbon dioxide fills the classroom space. The quality of the air in the school building and in the individual classrooms varies greatly, depending on the level of air exchange or ventilation.