Be Aware of the Indoor Air. Physicochemical Characterization of Airborne Fine Particles in Occupied Homes : Physicochemical Characterization of Airborne Fine Particles in Occupied Homes

Negative health effects of exposure to particles of outdoor origin have been confirmed by epidemiological studies. In developed countries, we spend on average 65% of our time in our homes. Thus, the properties of airborne particles indoors need to be understood. The aim of this PhD thesis was to investigate the differences in physicochemical and toxicological characteristics of fine particles (PM2.5) inside and outside occupied homes, as well as to understand the contribution of indoor sources to exposure indoors. The effects of energy renovation and of the occupants' activities on indoor concentrations were assessed.Indoor and outdoor differences in physicochemical and toxicological characteristics of PM2.5 were studied in 15 homes in urban and rural areas of southern Sweden. PM2.5 characterization was performed with online state-of-the-art techniques, simpler portable instruments, and with offline methods. The occupants’ self-reported activities were used to identify the contribution of indoor sources and for interpretation of the results. Measurements in homes were supported by a laboratory study focused on the characterization of particle emissions from candles under stressed burning conditions. An in-vivo toxicity study in mice was performed to assess the differences in toxicological properties of PM2.5 collected indoors and outdoors by evaluating inflammation in bronchoalveolar lavage cells. To understand if the energy renovation affect particle concentrations, measurements were performed inside and outside of seven occupied apartments over three consecutive years, before renovation, after renovation and at a follow-up. High number of ultrafine particles (UFP) were observed mainly due to the presence of indoor sources such as cooking, and candle burning in homes. Some of the indoor sources additionally contributed to elevated PM2.5 and black carbon (eBC) mass concentrations. In one apartment, a detailed online characterization using a mass spectrometric technique showed that PM1 emissions from indoor sources (e.g., cooking, e-cigarette vaping) were dominated by organic matter (86% of the total mass). Positive Matrix Factorization (PMF) source apportionment of the organic particle fraction showed that the largest contributors to indoor PM1 were e-cigarettes (50%), followed by cooking (40%), and outdoor infiltration was a minor contributor (10%). Candle burning, under stressed burn conditions in the laboratory experiments, emitted large amounts of UFP number concentration, PM2.5 mass and eBC mass concentrations. The wax and wick composition influenced emissions of eBC, PM2.5 and particle-phase polycyclic aromatic hydrocarbons (PAHs). In homes, candle burning also contributed to elevated levels of UFP, PM2.5 and eBC mass concentrations.In 15 homes, the chemical composition of particles indoors and outdoors was different regarding metals, PAHs and endotoxins. Higher concentration of metals such as Fe, Cr, Al, Zn and Mg were found in particles collected indoors compared to outdoors. This was most probably due to cooking, candle and incense burning. Indoor particles collected in 15 homes showed higher toxicity compared to those collected outdoors. This was most likely linked to higher levels of metals, polycyclic aromatic hydrocarbons (PAHs) and endotoxins in particles collected in all homes indoors in comparison to outdoors.After energy renovation, the UFP concentrations did not decrease and the observed concentrations were mainly affected by the occupants' activities. In order to reduce exposure to UFP particles, more stringent building regulations for kitchen extraction hoods should be considered. The indoor PM2.5 mass concentration had decreased at the follow-up. This could be a result of a lower amount of PM2.5 generated from indoor activities at the follow-up compared to before renovation, and of decreased infiltration of outdoor particles due to the renovation.The knowledge obtained in this thesis can be used for developing appropriate strategies to minimize exposure to particles indoors. A combination of methods is needed to effectively remove particles generated indoors and to prevent outdoor infiltration. Additionally, the data presented here can be included in mapping of real-life indoor concentrations and in development of indoor air quality models for exposure assessmen