Solid versus liquid particle sampling efficiency of three personal aerosol samplers when facing the wind

Abstract

The objective of this study was to examine the facing-the-wind sampling efficiency of three personal aerosol samplers as a function of particle phase (solid versus liquid). Samplers examined were the IOM, Button, and a prototype personal high-flow inhalable sampler head (PHISH). The prototype PHISH was designed to interface with the 37-mm closed-face cassette and provide an inhalable sample at 10 l min(-1) of flow. Increased flow rate increases the amount of mass collected during a typical work shift and helps to ensure that limits of detection are met, particularly for well-controlled but highly toxic species. Two PHISH prototypes were tested: one with a screened inlet and one with a single-pore open-face inlet. Personal aerosol samplers were tested on a bluff-body disc that was rotated along the facing-the-wind axis to reduce spatiotemporal variability associated with sampling supermicron aerosol in low-velocity wind tunnels. When compared to published data for facing-wind aspiration efficiency for a mouth-breathing mannequin, the IOM oversampled relative to mannequin facing-the-wind aspiration efficiency for all sizes and particle types (solid and liquid). The sampling efficiency of the Button sampler was closer to the mannequin facing-the-wind aspiration efficiency than the IOM for solid particles, but the screened inlet removed most liquid particles, resulting in a large underestimation compared to the mannequin facing-the-wind aspiration efficiency. The open-face PHISH results showed overestimation for solid particles and underestimation for liquid particles when compared to the mannequin facing-the-wind aspiration efficiency. Substantial (and statistically significant) differences in sampling efficiency were observed between liquid and solid particles, particularly for the Button and screened-PHISH, with a majority of aerosol mass depositing on the screened inlets of these samplers. Our results suggest that large droplets have low penetration efficiencies through screened inlets and that particle bounce, for solid particles, is an important determinant of aspiration and sampling efficiencies for samplers with screened inlets.

Fig. 1

(a) Photograph of constructed screened PHISH; (b) photograph of open-faced PHISH.

Fig. 2

Schematic of the wind tunnel showing aerosol inlet and location of the RBD.

Fig. 3

Facing-the-wind sampling efficiency for the IOM sampler as a function of particle size and phase. Filled symbols represent solid particles and open symbols represent liquid particles. Facing-the-wind mannequin aspiration efficiency at 0.4 m s⁻¹ is shown as a solid line, for comparison (Kennedy and Hinds, 2002).

Fig. 4

Facing-the-wind sampling efficiency for the Button sampler as a function of particle size and phase. Filled symbols represent solid particles and open symbols represent liquid particles. Facing-the-wind mannequin aspiration efficiency at 0.4 m s⁻¹ is shown as a solid line, for comparison (Kennedy and Hinds, 2002).

Fig. 5

Facing-the-wind sampling efficiency for the open-faced PHISH as a function of particle size and phase. Filled symbols represent solid particles and open symbols represent liquid particles. Facing-the-wind mannequin aspiration efficiency at 0.4 m s⁻¹ is shown as a solid line, for comparison (Kennedy and Hinds, 2002).

Fig. 6

IOM fractional collection efficiency defined as the concentration measured on each sampler component relative to the concentration measured by a sharp-edged isokinetic sampler as a function of particle size and type (solid particles versus droplets) at 0.4 m s⁻¹ wind speed. Black bars represent fractional collection efficiency for solid particles by gravimetry (i.e. the sampling efficiency). Gray bars represent the collection efficiency of the filter; white bars depict the collection efficiency of the sampler inlet/cassette as determined by fluorescence analysis.

Fig. 7

Button fractional collection efficiency defined as the concentration measured on each sampler component relative to the concentration measured by a sharp-edged isokinetic sampler as a function of particle size and type (solid particles versus droplets) at 0.4 m s⁻¹ wind speed. Black bars represent collection efficiency for solid particles by gravimetry (i.e. the sampling efficiency). Gray bars represent the collection efficiency of the filter (i.e. the sampling efficiency); white bars depict the collection efficiency of the sampler's screened inlet as determined by fluorescence analysis.

Fig. 8

Open-faced PHISH fractional collection efficiency defined as the concentration measured on each sampler component relative to the concentration measured by a sharp-edged isokinetic sampler as a function of particle size and type (solid particles versus droplets) at 0.4 m s⁻¹ wind speed. Black bars represent fractional collection efficiency for solid particles by gravimetry (i.e. the sampling efficiency). Gray bars represent the collection efficiency the filter (i.e. the sampling efficiency); white bars depict the collection efficiency of the cassette estimated by wiping the inside of the open-faced PHISH and cassette as determined by fluorescence analysis.