Role of Aerosols in Enhancing SVOC Flux between Air and Indoor Surfaces and its Influence on Exposure

Abstract

Indoor surfaces play an important role in the transport of, and exposure to, semi-volatile organic compounds (SVOCs) in buildings. in this study, we develop a model that accounts for SVOC transport mediated by particles and find that, due to large gas-particle partition coefficients along with large differences in Brownian and gas diffusivities, SVOC transport across concentration boundary layers is significantly enhanced in the presence of particles. Two important dimensionless parameters, Bi m,g and Bi m,g/Bi m,p, were identified: Bi m,g is the ratio of 1) the characteristic time for the SVOC to transport across the concentration boundary layer to 2) the characteristic time for boundary layer to either be " swept" of SVOCs by particles or " saturated" by release of SVOCs from particles. This parameter can be regarded as a dimensionless mass transfer coefficient. Bi m,g/Bi m,p characterizes the SVOC mass associated with particles, relative to SVOCs in the gas-phase. Analysis on monodisperse particles shows that flux can be enhanced by as much as a factor of 5 over transport in the absence of particles, for a large particle/gas partition coefficient (log K part = 13), small particles (d p ~ 0.1 μm) and a small free stream velocity (U ∞ = 0.01 m s -1). as particle diameter decreases, flux enhancement tends to increase. However, as particles become very small (e.g., d p < 0.05 μm), flux enhancement for SVOCs with log K part = 13 decreases slightly. Particles larger than 2 μm do not significantly influence the flux. an exponential correlation is found to fit the results for polydisperse particles associated with typical indoor environments, cooking and smoking. Two illustrative examples are used to show that, 1) the timescale for di(2-ethylhexyl) phthalate (DEHP) to approach equilibrium between the gas and a surface is shortened from 3.0 years to 0.45 years; and 2) in the presence of particles, the gas-phase DEHP concentration and emission rate are predicted to be as much as 4 times higher by our model than that by prior model estimates. Particle mediated gas-phase transport of SVOCs can result an increase in occupant exposure by a factor of 4-10. © 2012 .

Department(s)

Civil, Architectural and Environmental Engineering

Comments

National Natural Science Foundation of China, Grant 51076079

Keywords and Phrases

Dermal; Indoor air quality; Mass transfer; Particles; Phthalate

International Standard Serial Number (ISSN)

1873-2844; 1352-2310

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 Elsevier, All rights reserved.

Publication Date

01 Aug 2012

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