Chemically-resolved particle mass composition in a Swedish residence assessed by a Time-of-Flight Aerosol Mass Spectrometer

• A number of deleterious health effects have been identified from exposure to outdoor airborne particulate matter. Given that in developed countries we spend majority of our time indoors, in private homes about 65 % (Brashe et al., 2005), the understanding of this exposure is important, yet knowledge is sparse. Particle levels indoors are affected by indoor sources, infiltration from outdoors or particle mass forms through reactions of gas-phase precursors emitted both indoors and outdoors (Morawska et al., 2013). The aim of this work was to characterize a chemical composition of particle mass indoors, and to gain a better understanding about major contributors to the observed indoor levels with Aerosol Mass Spectrometer. We aimed to identify mass spectral signatures of specific indoor sources. This is preliminary results of measurements for a 1-month period.Indoor and outdoor measurements were performed in an occupied residence in Malmö, Sweden. It was a naturally ventilated four-room apartment (292 m3), located in a three-store concrete building surrounded by a green zone. A Time-of-Flight Aerosol Mass Spectrometer (DeCarlo et al., 2006) was used to measure particle mass loadings and size-resolved mass distributions (50-500 nm) of indoor and outdoor chemical species. An automatic switching valve alternated between indoor and outdoor lines with a time interval of 20 and 10 minutes, respectively. Both sampling lines were mounted at the ground floor level and led to the basement where the aerosols were dried and measured by AMS. Our results showed higher total average mass concentration indoors (12.9 μg/m3) compared to outdoors (5.4 μg/m3) over the entire measuring period. Indoor to outdoor (I/O) ratio for organics was 6.7, for sulphate 0.5, for nitrate 0.3, for ammonium 0.2 and for chloride 0.2. The dominant species indoors was organic matter, accounting for most of the total particle mass (92 %) due to contribution from indoor sources and from outdoor infiltration. Non-volatile sulphate showed reduced infiltration from outdoors. From comparison of outdoor and indoor concentrations of ammonium nitrate and ammonium chloride, which are sensitive to temperature and RH (Lunden et al., 2004), a clear reduction due to phase change was observed upon outdoor-to-indoor transport. We investigated different organic mass spectra for indoor events as recorded in the logbooks. The main events analysed comprised from various types of cooking and candle burning. They showed to emit different proportions of hydrocarbons and oxygenated organic species, which yield CxHy+, CxHyO+, CxHyOz+ ion classes. The relative intensity of CxHy+ ion class out of the total organic signal during frying was 65-68 %, deep-frying ~ 68 %, baking 60-70 %, other forms of cooking 60-68 %, candle burning 60-70%. For CxHyO+ ion class: frying 25-30 %, deep-frying 24-25 %, baking 27-32 %, cooking 25-31 %, candle burning 20-30 %. For CxHyOz+ ion family: frying 7-8%, deep-frying 7-8 %, cooking and baking 6-9 %, candle burning 6-8 %. The observed variability in organic mass spectral signature for different indoor sources should allow us to apply Positive Matrix Factorization for source apportionment and processes occurring in indoor air. This will help us to gain a better understanding about main contributors to the observed loading indoors.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Annan teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies (hsv//eng)

Nyckelord

Indoor sources

Particle mass concentration

Outdoor-to-indoor transport

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