Numerous epidemiological studies have provided evidence of an association between elevated outdoor particulate air pollution and adverse health effects. Young children typically spend majority of time at home and indoors.

There is still limited knowledge on indoor particles sources and especially on their health effects.

Even insights into the influence of differently sized indoor particles on human health are extremely rare.

We studied these correlations for three year aged children. Information on possible particle sources (exposure to environmental tobacco smoke, type of heating, and traffic at place of residence as well as in front of the children’s room) and respiratory outcomes were obtained from questionnaires. Short-term measurements of particle mass and number concentrations within different particle size fractions were carried out in children’s rooms.

Indoor concentrations of these size fractions were correlated with possible sources of indoor particles and with respiratory health impacts. Daily smoking, smoking more than 5 cigarettes per day at home and traffic density in front of the window of children’s room were found to be related to indoor exposure by particles of different diameters.

High indoor particle exposures were associated with an increased risk for the development of obstructive bronchitis and in some extent of non-obstructive bronchitis.

The strongest impact was associated to mass concentration of particles < 1 μm and ...