Indoor to outdoor ratio of particle chemical components in an occupied residence

• IntroductionConsidering that on average in developed countries we spend about 65% of our time in private homes, understanding the exposures in homes is of outmost importance. Aerosol concentrations indoors come from indoor sources, infiltrate from outdoors and can be formed from precursors both of indoor and outdoor origin. Several characteristics and processes influence the properties of aerosols indoors, among them: active indoor sources (presence of occupants), outdoor aerosol characteristics, change of chemical composition upon infiltration (from outdoors to indoors), size dependant penetration from outdoors, ventilation, tightness of the building envelope and deposition (Morawska, et.al. 2013). In this study, we aimed to investigate the differences in chemical composition between aerosols indoors and outdoors. We report preliminary results for 6-days period, with the full duration of the campaign of 1 month.MethodsMeasurements were conducted indoors and outdoors in an occupied residence in Malmo, Sweden. The apartment was naturally ventilated, had four bedrooms and a total area of 117 m2. It was located in a three-store concrete building and enclosed from other areas by green zone. Time-of-Flight Aerosol Mass Spectrometer (AMS, DeCarlo, et al. 2006) was used to measure mass loadings and size-resolved mass distributions of indoor and outdoor organic, sulphate and nitrate particles. Two parallel sampling lines (indoor and outdoor) with automatically switching valve were used. The valve alternated the measurements between indoor and outdoor for 20 and 10 minutes, respectively. Both sampling lines were led to the basement where the aerosol was dried and measured by AMS. Calculated residence time of the particles in line was about 1.5 minutes. Indoor sampling line was heated and insulated, additional carrier flow was used to lower the residence time and ensure the same temperature. ConclusionsCalculated mean indoor/outdoor (I/O) ratios were 3.4 for organics, 0.1 for nitrate, 0.5 for sulphate, 0.2 for ammonium. High I/O ratio for organics was due to high contribution from indoor sources. Indoor activities/sources that contributed to high organics loadings inside comprised of cooking, using of the oven, and candle burning. The nitrate I/O ratio was the lowest because of its evaporation indoors i.e. dissociation of ammonium nitrate particles into gases (nitric acid and ammonia) due to higher temperature and lower relative humidity compared to outdoors. The differences between the indoor and outdoor temperature and RH during the measurements time: outdoor temperatures varied from -1.5 to 7.1 °C and RH from 72 to 100 %; indoors, T ranged from 20 to 26 °C with RH from 27 to 50 %. Low value I/O ratio for non-volatile sulphate can be explained by dominating outdoor sources and reflects reduced infiltration. As can be seen from the Figure 1, during non-occupancy period, mass concentration of organics was very low - a few µg/m3, while with the presence of indoor activities led to organics loadings up to 1 mg/m3. In general, the results confirm differences in chemical composition of particles found indoors and outdoors. Levels of organics in indoor environments was mainly influenced by indoor sources, thus theses should not be neglected when considering possible health effects. This work was financed by the Swedish Research Council FORMAS (Project Dnr 942-2015-1029)

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Annan samhällsbyggnadsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Other Civil Engineering (hsv//eng)

Nyckelord

chemical composition

I/O ratio

AMS

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