3.2. Effect of the airing strategy on particle and CO2concentrations in classroomsResults of tests performed in the classroom B-3 for prescribed airing periods are here reported. InTable 5window and door opening times for the different tests carried out are summarized. As expected from the scheduled airing procedure, the door opening time was negligible for the tests performed with a prescribed manual airing time since the door was just used for quick openings to allow people entering and exiting the classroom. Actually, during the“5-min window opening time”test teachers/students asked for an extra door opening period (about 22 min) due to the perceived discomfort in terms of air quality.On the contrary, no extra opening periods for windows were recognized. Concerning the two tests performed with“no indication”(i.e. tests during which classroom occupants were not asked to open door and windows on the basis of a scheduled procedure), measurements performed through the magnetic contacts showed that classroom occupants preferred using the door to improve the indoor air quality.