The Estimation of Resuspension Rates of Fine
Particulate Matter in an Environmental Chamber
Valerie Bauza1 and Andrea Ferro2
Department of Civil and Environmental Engineering
A great deal of research has been conducted to study outdoor air quality, resulting in state and
federal regulations that are enforced to protect the health and welfare of the general public. Indoor
air quality, on the other hand, is not regulated, with the exception of the workplace. Indoor
environments account for a significant portion of human exposure to hazardous particles, as
Americans spend an average of 87% of their time indoors (Ott et al. 2007, Thatcher 2002). As a
result of both infiltration and track-in, many toxic chemicals are brought into homes and become
existent in common household dust, some at high concentrations. Pollutants of concern
commonly found in household dust include allergens, heavy metals, pesticides, polycyclic
aromatic hydrocarbons (PAHs), plus several endocrine disruptors and carcinogenic compounds
(Tong 2000, Rudel 2003, Ott et al. 2007). Normal human activities, preformed throughout the
house, cause dust to become resuspended in the air, resulting in exposure to elevated levels of
particulate matter. Small children, who spend a lot of time close to the floor, are especially at risk
for health problems due to indoor dust and resuspension (Ott et al. 2007). Short term exposure to
elevated levels of particulate matter has been associated with asthma symptoms, chronic
obstructive pulmonary disease (COPD), and decreased heart rate variability (Delfino et al. 1998,
Morgan et al. 1998, Gold et al. 2000).
Since walking is a common activity responsible for dust resuspension, it has been used to model
resuspension rates of dust and human exposure due to resuspension. In 2005, Jing Qian
conducted 54 experiments within a controlled environmental chamber to investigate the
resuspension rate of particulate matter. For these experiments, flooring samples were seeded with
ultrafine Arizona Test Dust (ATD) that has a distribution of particles in the size range of 0.1-10
μm. Participants then performed walking and sitting activities for a specified amount of time in
the chamber, while the particle concentration and size distribution was measured using optical
particle counters (OPCs). Over the course of these 54 experiments, particle concentrations were
1
Class of 2008, Civil and Environmental Engineering, University of Wisconsin-Madison, REU
2
Assistant Professor, Department of Civil and Environmental Engineering, Clarkson University
measured in relation to several factors including flooring type, ventilation type, particle loading,
and person-to-person variability. Experiments were preformed using hard floor, new carpet, old
carpet, mixing ventilation, displacement ventilation, and different walking styles to see how these
factors affected the resuspension rates of particles. Following the experiments, resuspension rates
were calculated for particles in the size ranges 0.8-1.0 μm, 1.0-2.0 μm, 2.0-5.0 μm, and 5.0-10.0
μm. The estimated particle resuspension rates from the experiments varied from 10-5 to 10-2 hr-1.
These experiments showed that person-to-person variability in walking style accounted for the
largest variance in resuspension rates among experiments with a “heavy and fast” walking style
resuspending more particles being than walking styles that involve less activity. Furthermore, it
was observed that for the size range 0.8-10 μm, larger particles have larger resuspension rates
(Qian 2007).
Although the experiments performed in the environmental chamber used particle monitors that
recorded airborne particle concentration in the range of 0.4-0.8 μm, these data points were not
included in the overall analysis. This range was not included because the distribution of particles
within this size range was not specified in the manufacturer’s specifications of the ATD test dust,
and this distribution is needed in order to calculate floor particle loading. This range of particles
is part of the accumulation mode of fine particles (0.1-1.0 μm) which are less affected by removal
mechanisms and thus stay airborne longer than other sizes of particles. This size range of
particles can also penetrate further into the lungs than larger particles, as they are less likely to be
removed my interception or gravitational settling (Ott et al. 2007). My contribution to this study
was to investigate the distribution of ATD within the size range 0.4-0.8 μm, and use this data to
calculate resuspension rates within this size range and compare them to resuspension rates for
larger size ranges. The size distribution was obtained using two methods: running a particle
pulsing experiment with OPCs measuring the count distribution in the chamber, and using a
previously published paper that had measured the size distribution using OPCs. After the size
distribution was estimated, continuous floor loading was calculated using Eqn.1 and resuspension
rates were calculated using Eqn.2 and the concentration time series measured during previously
preformed experiments.
Eqn.1
Where L(t) represents the floor concentration at time t, L(0) is the initial floor loading, V is the
indoor air volume, A is the floor area, Ci(t) is the indoor concentration at time t, Ci(0) is the initial
indoor concentration, and a is the air exchange rate.
Eqn.2
Where r is the resuspension rate, Ar is the seeded floor area, k is the deposition rate, and all other
variables are defined above. Equations 1 and 2 are derived from a two-compartment materials
balance model which assumes instantaneously well-mixed compartments.
Preliminary results show that resuspension rates in the size range of 0.4-0.8 μm are lower than
larger size ranges, following the overall trend of resuspension rates increasing with increasing
diameter. However, contradictory to previous work (e.g., Thatcher and Layton 1995), this study
demonstrates that particles in the 0.4-0.8 μm size range are resuspendable by normal human
activity, and walking across residential flooring results in substantial submicron airborne particle
concentrations.
References
Delfino, R.J., Zeiger, R.S., Seitzer, J.M., Street, D.H. “Symptoms in pediatric asthmatics and air
pollution: differences in effects by symptom severity, anti-inflammatory medication use
and particulate averaging time.” Environ Health Perspect, 106:751-761: 1998.
Gold, D.R., Litonjua, A., Schwartz, J., Lovett, E., Larson, A, Nearing, B., Allen, G., Verrier, M.,
Cherry, R., Verrier, R. Ambient pollution and heart rate variability. Circulation,
101:1267-1273: 2000.
Morgan, G., Corbett, S., Wlodarczyk, J. Air pollution and hospital admissions in Sydney,
Australia, 1990 to 1994. Amer J Pub Health, 88:1761-1766: 1998.
Ott, Wayne R., Steinemann, Anne C., Wallace, Lance A. Exposure Analysis. “Chapter
1: Exposure Analysis: A Receptor-Oriented Science”, “Chapter 8: Exposure to Particles”,
“Chapter 14: Exposure to Pollutants from House Dust.” Taylor & Francis Group: Boca
Raton, FL: 2007.
Qian, Jing. “Particle Resuspension via Human Activity Indoors: A Research Dissertation
for the Degree of Doctor of Philosophy.” June 5, 2007.
Rudel, Ruthann A., Camann, David E., Spengler, et al. “Phthalates, Alkylphenols,
Pesticides, Polybrominated Diphenyl Ethers, and Other Endocrine-Disrupting
Compounds in Indoor Air and Dust.” Environmental Science & Technology 37:20. June
18, 2003.
Thatcher, Tracy L., Lai, Alvin C. K., Moreno-Jackson, Rosa, et al. “Effects of room
furnishing and air speed on particle deposition rates indoors.” Atmospheric Environment
36(2002): 1811-1819. Jan. 15, 2002.
Thatcher, T.L., and Layton, D.W. “Deposition, resuspension, and penetration of particles within
a residence.” Atmospheric Environment 29(13): 1487-1497. 1995.
Tong, Susanna T.Y., Lam, Kin Che. “Home sweet home? A case study of household dust
contamination in Hong Kong”. The Science of the Total Environment 256(2002): 115123. March 4, 2000