Indoor environments contribute significantly to total human exposure to air pollutants, as people spend most of their time indoors. Indoor air quality is influenced by: penetrating outdoor air; specific indoor pollution sources; interactions between building system/construction techniques; and occupants. Some pollutants may be 2–5-fold more concentrated inside than outside buildings. Indoor pollutants may have an important biological impact even at low concentrations over long exposure periods. Indoor exposure occurs mainly at home and in schools, but also in day-care centres, social recreation settings or microenvironments, such as cars, buses, trains, subways and aeroplanes. Workplace indoor exposure is conventionally treated separately as ‘occupational exposure’ (see chapter 7).
The European Union (EU)-funded Towards Healthy Air in Dwellings in Europe (THADE) project showed that air pollution in dwellings is an important health problem across Europe. An EU-funded European Federation of Allergy and Airways Diseases Patients’ Associations (EFA) project, Indoor Air Pollution in Schools, pointed out that the right to breathe good air at school is largely ignored in many countries, where high levels of common indoor pollutants are frequent because of poor building construction and maintenance, poor cleaning and poor ventilation. Indoor air quality is particularly important for vulnerable subpopulations, such as children (their defence mechanisms are still evolving, and they inhale a higher volume of air per bodyweight than adults), elderly people, subjects with cardiac and respiratory diseases and those with socioeconomic deprivation.