Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity

Abstract

The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50%, and 70% RH). The "green" materials contained recycled materials and were friendly to environment. A dynamic dual-chamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for two kinds of wallboards and carpet. The carpet was also found to be very permeable resulting in an effective diffusion coefficient at the same order of magnitude with the formaldehyde diffusion coefficient in air. The partition coefficient (K(ma)) of formaldehyde in conventional wallboard was 1.52 times larger at 50% RH than at 20% RH, whereas it decreased slightly from 50% to 70% RH, presumably due to the combined effects of water solubility of formaldehyde and micro-pore blocking by condensed moisture at the high RH level. The partition coefficient of formaldehyde increased slightly with the increase of relative humidity in "green" wallboard and "green" carpet. At the same relative humidity level, the "green" wallboard had larger partition coefficient and effective diffusion coefficient than the conventional wallboard, presumably due to the micro-pore structure differences between the two materials. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings.

Assessment of steady state diffusion of volatile organic compounds in unsaturated building materials based on fractal diffusion model

“…Furthermore, the ranking of predicted effective diffusion coefficients of some of VOCs shown in Fig. 9 corresponds to the one reported by Xu et al and Luo et al from experiments (Formaldehyde > toluene > p-Xylene z Ethylbenzene) [12,17].…”

“…Compound Test method/condition Effective diffusion coefficients (m 2 /s) Conventional gypsum wallboard [17] Formaldehyde (CH 2 O) A dynamic dual-chamber, 50% RH 6.34 Â 10 À8 "Green" gypsum wallboard [17] Formaldehyde (CH 2 O) A dynamic dual-chamber, 50% RH 2.24 Â 10 À8 Calcium silicate [16] Formaldehyde (CH 2 O) A dynamic dual-chamber, 50%RH 3.28 Â 10 À6 Medium density fireboard [15] Formaldehyde (CH 2 O) C-history method in closed chamber,50%RH 8.15 Â 10 À8 Painted drywall [11] Ethylbenzene (C 6 H 5 CH 2 CH 3 ) Environmental chamber,50%RH 2.68 Â 10 À8 Cement slab [12] Ethylbenzene (C 6 H 5 CH 2 CH 3 ) Field and laboratory emission cell,25 1.72 Â 10 À10 Cement slab [12] p-Xylene (C 6 H 4 (CH 3 ) 2 ) Field and laboratory emission cell,25 1.77 Â 10 À10 Cement slab [12] Toluene (C 6 H 5 CH 3 ) Field and laboratory emission cell,25 1.47 Â 10 À10 Saturated inactive clay [10] Benzene (C 6 H 6 ) A double-reservoir glass diffusion cell test (1.5e5.0) Â 10 À10…”

“…9. It was considered that scattered results of effective diffusion coefficients of different VOCs from previous literatures may be preliminarily interpreted by various water solubility: Formaldehyde and methanol are known as the water-soluble substances and thus have superior diffusible abilities [17,47]; conversely, non-soluble property of benzene and its derivations as well as Xylene isomers is responsible for the low value of effective diffusion coefficients [16]. However, from the fractal model and Fig.…”

“…This may be attributed to two factors [7]: 1) the reliable diffusion values of building materials are still unknown until now, it is thus lack of critical value for comparing the results among various laboratory measurements; and 2) different building materials/VOCs/test methods/conditions used in various laboratories may be one of sources of scattered data [10e18]. In particular, some studies considered that either chamber testing approaches or other cup methods may be inappropriate for some porous materials [14,17]. On the other hand, theoretically, several researchers have attempted to model the diffusion-driven emission of VOCs based on fluid dynamics in completely dry or wet building materials [6,19,20].…”

Study on the air pollution in typical transportation microenvironment: Characteristics and health risks

“…Based on the investigation of human activities by the U.S. Environmental Protection Agency (EPA), the time of human activities spent on these three environmental parts were at rates of 85%, 7%, and 8%, respectively (EPA, 1989). Nowadays, the pollution of indoor air has received high attention (Baez et al, 2003;Khoder et al, 2006;Golden et al, 2011;Abdel-Salam et al, 2013); in China, the pollution of indoor air has received some attention (Xu et al, 2012;Cheng et al, 2014), but the air pollution of transportation microenvironment has not received enough attention to match with the popularization of cars, whereas the pollution of air by transportation microenvironment in foreign countries has been received high attention (Johnson et al, 2014).…”