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Five portable air cleaning technologies including one new technology were evaluated to find their effectiveness in removing ultrafine particles. Measurements were carried out both in a duct and in a test room. The results showed that the technologies that use/create ozone to clean air can increase the ozone level significantly in the room. Moreover, they can cause generation of ultrafine particles and consequently increase ultrafine particle concentration in the room. The study suggests using a mechanical filter with low pressure drop as a recommended air cleaning technology in order to remove ultrafine particles efficiently from the indoor environment.

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An emerging issue in Denmark is passive smoking in residential buildings where non-smokers are exposed to smoke from their neighbours. There are various ways that smoke is transferred from one flat to another. The air transfer rate between two flats in a multi-storey building depends on its construction, tightness and age. This paper presents results of a study on the transfer of ultrafine particles and tracer gas in an older multi-storey building in Copenhagen. The aim of the study was to quantify the transfer of ultrafine particles and gases from one flat to another flat before and after sealing the floor. A new floor-sealing method was applied to seal the floor between the two flats. The sealing method was developed by a firm specialising in sealing. Indoor ultrafine particle concentrations and tracer gas were measured continuously in the two flats during the measuring periods. In the unoccupied flat, the gas source was N 2 O and the particle source was burning cigarettes. Reduction of the concentration of ultrafine particles and tracer gas by sealing the floor with polyethylene and joint filler made of bitumen was studied. It was evaluated how the sealing performed with regard to decreasing the amount of ultrafine particles and a tracer gas transferred between two flats separated by a floor. When the floor between the flats was not sealed, the results showed that about 4% of the ultrafine particles and 14% of the tracer gas were transferred. After sealing, the amount transferred was reduced to 1.6% and 5%, respectively.