Exposure to ultrafine particles in relation to indoor events and dwelling characteristics

Exposure to ultrafine particles (UFP) in homes is associated with health risks such as cardiovascular disease and/or respiratory problems. These risks are heightened by the long time that people spend indoors. Therefore reducing the particle concentration in homes leads to improved health among its occupants. The use of particle filtration units may be an effective way of reducing UFP indoors. The purpose of this study was to evaluate associations between UFP concentrations and dwelling characteristics, estimate UFP removal rates indoors and to assess the effectiveness of installed particle filtration units. In a randomised cross-over design in 27 homes, we ran the particle filtration units for two periods, each lasting two weeks with and without the inclusion of a HEPA filter. By using the particle filtration units in dwellings, we achieved a 57% reduction of the UFP concentration and the removal rate was increased from 0.33 h−1 to 1.94 h−1. We found human activities to be far more relevant to high UFP concentrations than dwelling characteristics. Window-opening habits reduce exposure to UFP during peaks caused by occupant behaviour and increase exposure to UFP during low indoor activity. Furthermore, the winter season was associated significantly with high UFP levels indoors. Results of our study also indicated that owning a pet, wood-type floors and floor levels close to the ground are associated with increased UFP levels.