Indoor-to-outdoor ratios of ultrafine particles in Swedish residences

A number of health effects have been linked to exposure to airborne particles, however the consequences of exposure to ultrafine particles is largely unknown. Ultrafine particles can be emitted from different indoor activities or be of the outdoor origin. This is further complicated by the fact that we are spending majority of the time indoors. The aim of this work was to assess the influence of renovations on indoor-to-outdoor (I/O) ratios of ultrafine particles (UFP) in 6 occupied Swedish residences. Simultaneous indoor and outdoor measurements were performed in 6 residences for seven consecutive days in urban area in southern Sweden. The apartments were mechanically ventilated and had volumes between 115-218 m3. The renovation activities included adjusting air exchange rates (AER) to meet Swedish standards (0.5 AER h-1) and installation of the new kitchen extraction fans. NanoTracers (Oxility Aerasense) were used to measure particle number concentrations and mean particle diameters (10 - 300 nm). Based on the averages of particle number concentrations (PNC) during occupancy period, indoor-to-outdoor ratios (I/O) were calculated for each home. AER have been increased in the apartments during renovations to 0.4-0.7 h-1 in comparison to values before the renovation 0.2-0.4 h-1. After renovation I/O ratios of PNC during occupancy periods varied between 0.2-3.8 and were lower in comparison to the values before renovations 1.0-11.9. This could indicate increased efficiency of particles removal after renovation but also can be influenced by lower amount of performed activities by occupants, which were 2-3 times lower after in comparison to before. Results have shown the positive changes of the renovation processes on AER and particle removal. Nevertheless, the frequency and type of indoor activities performed by residents at home influence the indoor concentrations. The Swedish Research Council FORMAS and the Swedish Energy Agency financed the project. (Less)