# Estimation of the Human Extrathoracic Deposition Fraction of Inhaled Particles Using a Polyurethane Foam Collection Substrate in an IOM Sampler

^{1}

^{2}

^{*}

## Abstract

**:**

_{1}) and the posterior nasal and oral passages (ET

_{2}). For this study, polyurethane foam was used as a collection substrate inside an inhalable aerosol sampler to provide an estimate of extrathoracic particle deposition. Aerosols of fused aluminum oxide (five sizes, 4.9 µm–44.3 µm) were used as a test dust in a low speed (0.2 m/s) wind tunnel. Samplers were placed on a rotating mannequin inside the wind tunnel to simulate orientation-averaged personal sampling. Collection efficiency data for the foam insert matched well to the extrathoracic deposition convention for the particle sizes tested. The concept of using a foam insert to match a particle deposition sampling convention was explored in this study and shows promise for future use as a sampling device.

## 1. Introduction

_{1}for the anterior nasal passages and ET

_{2}for the posterior nasal passages and oral passages), tracheobronchial (BB and bb), and alveolar fractions, with different conventions for particles in the aerodynamic (>0.5 µm) and thermodynamic (<0.5 µm) size ranges.

_{1}(Equation (1)) and ET

_{2}(Equation (2)), described for the aerodynamic size range (>0.5 µm) by the following cumulative lognormal functions, with d

_{ae}being the particle aerodynamic diameter (in µm):

_{2}(Equation (2)) is dependent on ET

_{1}(Equation (1)). In fact, the total ET deposition efficiency (Equation (3)) can be obtained by replacing the constant “0.325” with “1.000,” which is then given simply by:

_{1}and ET

_{2}. This function reflects the fact that at large d

_{ae}all aerosol particles that enter into the nose and/or mouth deposit in the extrathoracic region. Curves for ET

_{1}and ET

_{2}are shown in Figure 1, with the anatomical descriptions of these two conventions shown in Figure 2.

_{ae}) is the inhalable aerosol fraction as a function of aerodynamic particle size (in µm) for low wind speed environments [17] given by the following equation:

## 2. Materials and Methods

#### 2.1. Sampler Design

_{f}is the foam equivalent fiber diameter. St is the Stokes number, Ng is the gravitational settling number and Pe is the Peclet number, which taken together describe how a particle behaves in air. They are determined by the following equations:

_{0}is the density of water, d

_{ae}is the particle aerodynamic diameter, U is the air velocity through the foam, C

_{c}is the Cunningham slip correction factor, η is the viscosity of air, g is the acceleration due to gravity, d

_{th}is the particle thermodynamic equivalent diameter, k is Boltzmann’s constant, and T is temperature (Kelvin). It should be noted that the primary difference between this model and a previous one developed by Kenny et al. [26] is the addition of the Peclet number, which describes the tendency of a particle to move via diffusion.

#### 2.2. Wind Tunnel

#### 2.3. Aerosol Characterization

#### 2.4. Aerosol Generation

#### 2.5. Sampling Methods

#### 2.6. Data Analysis

## 3. Results

## 4. Discussion

#### Future Work

## 5. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## Abbreviations

ICP-MS | Inductively-Coupled Plasma – Mass Spectroscopy |

ISO | International Organization for Standardization |

ET | Extrathoracic |

ET_{1} | Anterior Nasal Passage |

ET_{2} | Posterior Nasal and Oral Passages |

ICRP | International Committee for Radiological Protection |

BB and bb | Tracheobronchial |

PUF | Polyurethane Foam |

PPI | Pores Per Inch |

MMAD | Mass Median Aerodynamic Diameter |

GSD | Geometric Standard Deviation |

PAS | Portable Aerosol Spectrometer |

APS | Aerodynamic Particle Sizer |

HEPA | High-Efficiency Particulate Air |

SD | Standard Deviation |

RH | Relative Humidity |

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**Figure 1.**International Organization for Standardization (ISO) sampling conventions for extrathoracic (ET) deposition of particles in the human respiratory tract [16]. ET

_{1}(solid line) represents deposition in the anterior nasal passages, ET

_{2}(dashed line) represents deposition in the posterior nasal passages and oral passages.

**Figure 2.**Diagram showing the various locations of potential extrathoracic particle deposition in humans [18].

**Figure 3.**The Institute of Occupational Medicine (IOM) Multidust foam deposition efficiency modeled using Equation (6), for a sampler flow rate of 2 L/min (dotted line), compared to the extrathoracic (ET) convention (solid line) (Equation (4)), both normalized with the low-wind inhalability convention.

**Figure 4.**Estimated sampling bias (%) for the modeled IOM Multidust foam insert (Equation (6)) relative to the normalized extrathoracic (ET) deposition convention (Equation (4)) for a range of particle size distributions (mass median aerodynamic diameters up to 30 µm and geometric standard deviations between 2 and 4).

**Figure 6.**Foam insert sampling efficiency (circles, n = 45, with many circles overlapping due to tight reproducibility) compared to the normalized extrathoracic (ET) deposition sampling convention (solid line). The dotted line is the foam deposition efficiency as modeled by Clark et al. [24].

**Figure 7.**Estimated sampling bias (%) for the modeled foam insert operated at 5 L/min (using Equation (6)) relative to the normalized extrathoracic (ET) deposition convention (Equation (4)) for a range of particle size distributions (MMAD up to 50 µm and GSD between 2 and 4).

Mass Median Aerodynamic Diameter (µm) | Geometric Standard Deviation | No. of Samples (n) | Mean Inhalable Collection Efficiency ^{c} (Standard Deviation) | Mean Foam Collection Efficiency ^{d} (Standard Deviation) | Normalized Foam Collection Efficiency ^{e} (Standard Deviation) | Reference Extrathoracic Deposition Efficiency ^{f} |
---|---|---|---|---|---|---|

4.9 ^{a} | 1.73 ^{a} | 5 | 0.79 (0.01) | 0.53 (0.01) | 0.68 (0.01) | 0.73 |

9.5 ^{b} | 1.32 ^{b} | 10 | 0.59 (0.06) | 0.56 (0.05) | 0.94 (0.01) | 0.88 |

12.8 ^{b} | 1.47 ^{b} | 10 | 0.89 (0.07) | 0.86 (0.07) | 0.97 (0.02) | 0.96 |

32.7 ^{b} | 1.71 ^{b} | 10 | 0.83 (0.21) | 0.80 (0.20) | 0.97 (0.01) | 0.87 |

44.3 ^{b} | 1.59 ^{b} | 10 | 0.78 (0.16) | 0.74 (0.16) | 0.95 (0.03) | 0.83 |

^{a}Determined using a Portable Aerosol Spectrometer (GRIMM Technologies model 1.109, Douglasville, GA, USA);

^{b}Obtained from Schmees et al. (2008) [28];

^{c}Calculated as inhalable mass concentration measured by the IOM sampler divided by the reference concentration;

^{d}Calculated as mass concentration measured by the foam divided by the reference concentration;

^{e}Normalized foam efficiency is the foam collection efficiency divided by the inhalable collection efficiency;

^{f}Calculated using Equation (4).

© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Sleeth, D.K.; Balthaser, S.A.; Collingwood, S.; Larson, R.R.
Estimation of the Human Extrathoracic Deposition Fraction of Inhaled Particles Using a Polyurethane Foam Collection Substrate in an IOM Sampler. *Int. J. Environ. Res. Public Health* **2016**, *13*, 292.
https://doi.org/10.3390/ijerph13030292

**AMA Style**

Sleeth DK, Balthaser SA, Collingwood S, Larson RR.
Estimation of the Human Extrathoracic Deposition Fraction of Inhaled Particles Using a Polyurethane Foam Collection Substrate in an IOM Sampler. *International Journal of Environmental Research and Public Health*. 2016; 13(3):292.
https://doi.org/10.3390/ijerph13030292

**Chicago/Turabian Style**

Sleeth, Darrah K., Susan A. Balthaser, Scott Collingwood, and Rodney R. Larson.
2016. "Estimation of the Human Extrathoracic Deposition Fraction of Inhaled Particles Using a Polyurethane Foam Collection Substrate in an IOM Sampler" *International Journal of Environmental Research and Public Health* 13, no. 3: 292.
https://doi.org/10.3390/ijerph13030292