Respiratory tract deposition of fine particles in candle smoke

Candles are common sources of both ultrafine and fine particles in indoor environments (Zai et al., 2006). Pagels et al. (2007) have shown that ultrafine candle smoke particles grow by absorption of water in a humid environment. As the relative humidity (RH) in the respiratory tract is high, this would alter the deposition from that of the models, which often only include insoluble particles (Londahl et al. 2007). There are few or none published measurements of respiratory tract deposition of any indoor particle source apart from tobacco smoke. This work presents preliminary results from measurements of respiratory tract deposition fraction (DF) of particles emitted from tea light candles. Three tea light candles were lit in a 0.5 m box. In order to establish an increased and “controlled” generation of soot, the candle flames were cooled by a plate of stainless steel. A fan was used to mix and dilute the aerosol. Number concentrations ranged from 6000-30000 cm and the size-distribution basically had two modes; the first with a geometric mean diameter (GMD) around 50 nm and the second with a GMD around 300 nm. An instrument, incorporating a scanning mobility particle sizer (SMPS), has previously been developed to measure the respiratory tract deposition of polydisperse aerosols (RESPI, Londahl et al. 2006). In this experiment it was used to determine the size-resolved DF in the range 20-400 nm on 2 healthy, non-smoking male subjects breathing spontaneously. The size shift of the particles at an RH > 90% was measured with a tandem differential mobility setup.

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