This work reports the results of a survey carried out on a hall in a historic building in Palermo (Italy) with the aim of assessing the air quality by means of objective measurement of carbon dioxide (CO2) concentration and its subjective evaluation through a questionnaire. The measured values of CO2 concentration were compared with those evaluated using the Meckler equation under steady-state conditions, having verified necessary parameters such as the constancy of the indoor and outdoor CO2 levels and the uniformity of the CO2 generation rate for all the occupants. The positive correspondence between measured and calculated results allowed us to utilise, under differing circum- stances, the values of the natural ventilation rates achieved in steady-state conditions. By using measured and calculated data, an experimental assessment of the relationships between the CO2 concentration levels and the number of occupants and their level of satisfaction was performed. The indoor air quality level in the hall, evaluated by means of the experimental data, was compared with the subjective responses expressed through a specific multiple choice questionnaire handed out to the occupants. A comparison between the calculated ventilation rates and those required by the main American and European standards shows that natural ventilation in the hall is often insufficient according to these standards which have regard for the minimum requirements for air acceptability. In addition, some general observations on the thermal condition of the hall have been drawn from a compar- ison between microclimate parameters and the sub- jective opinions provided by the occupants
