Odour can be regarded as a 'pollutant' or as an indicator of the presence of pollutant. Sometimes it may alert the occupant to a potential health risk, although this need not always be reliable since some highly toxic pollutants, such as radon and carbon monoxide, are odourless. More generally, odour causes discomfort, especially in sedentary environments such as the office or home. A difficulty with odour analysis is that many odours cannot be measured by instrumentation.

The severity of climate influences the degree of heating or cooling that is necessary to condition the incoming air. Greater potential exists for the use of complex ventilation strategies combined with heat recovery when ventilation heating or cooling loads are high. A system that may be cost effective in one climatic zone may not be appropriate in another.

Outdoor air may be ‘cleaned’ by filtration. This is a method by which particulates and, sometimes, gaseous pollutants are removed from the air. Pollutants are intercepted by a filter while allowing clean air to pass through. This method of air cleaning is especially necessary when high concentrations of particulates are present or when the source of pollutant is derived from outside the building. Potential benefits can include improved air quality, reduced dependence on ventilation and improved energy efficiency.

Measurements are needed to verify the performance of ventilation systems and to test the air-tightness of the building shell. They are essential for commissioning, diagnostic analysis, design evaluation and research.