Zhishi Guo

Penetration of Ambient Fine Particles into the Indoor Environment

Several recent studies have indicated significant health risks associated with exposure to fine particles as measured outdoors. However, much of the exposure is believed to have occurred indoors. Consequently, there is considerable interest in the relationship between indoor and outdoor fine particles. This paper describes some results from a study in which the processes of particle removal from infiltrating air by building envelopes are simulated in a chamber. The chamber consists of two compartments, each having a volume of 19 m3. Particles with aerodynamic diameters in the range of 0.05 to 5

Polynuclear aromatic hydrocarbon degradation by heterogeneous reactions with N2O5 on atmospheric particles

Abstract The degradation of particulate polynuclear aromatic hydrocarbons (PAH) on atmospheric soot particles in the presence of gas phase dinitrogen pentoxide (N2O5) was explored. Dilute diesel and wood soot particles containing PAH were reacted with∼10ppm of N2O5 in a 200 l continuous stirred tank reactor (CSTR). To provide a stable source of particles for reaction in the CSTR, diesel or wood soot particles were injected at night into a 25 m3 Teflon outdoor chamber. The large chamber served as a reservoir for the feed aerosol, and the aerosol could then be introduced at a constant flow rate into the CSTR. PAH-N2O5 heterogeneous rate constants for wood soot at 15°C ranged from2 × 10−18to5 × 10−18 cm3 molecules−1 s−1. For diesel soot the rate constants at 16°C were higher and ranged from5 × 10−18to30 × 10−18 cm3 molecules−1 s−1. Comparisons with other studies suggest that sunlight is the most important factor which influences PAH decay. This is followed by ozone, NO2, N2O5 and nitric acid. The rate constants of nitro-PAH formation from a parent PAH and N2O5 were of the order of1 × 10−19−1 × 10−18 molecules−1s−1. The uncertainty associated with all of these rate constants is± a factor of 3. Given, however, the small magnitude of the rate constants and the low levels of N2O5 present in the atmosphere, we concluded that PAH heterogeneous reactions with gas phase N2O5 degrade particle-bound PAH or to form nitro-PAH from PAH arenot very important. (Direct application of the specific rate constants derived in this study to ambient atmospheres should not be undertaken unless the ambient particle size distributions and chemical composition of the particles are similar to the ones reported in this study.)

The effect of ventilation on emission rates of wood finishing materials

Abstract The rate of emission of organic compounds from building materials varies according to: type of material, material loading (area of material/volume of room), compound emitted, temperature, humidity, and ventilation rate. For some compounds and materials (e.g., formaldehyde from particleboard), the relationship between emission rate and these variables is well established. For most materials and compounds, however, such relationships are unavailable. Research, using small test chambers, is being conducted by the U.S. Environmental Protection Agency (EPA) to develop data on emission rates from a variety of building materials. This paper presents selected results from the EPA studies. Emphasis is placed on the effect of ventilation (air changes/h) and material loading on the emission rate for selected organics and total measured organics. Test data for three wood finishing materials (i.e., stain, polyurethane, and wax) are presented. The data are analyzed to show the effect of ventilation on the emission characteristics of each material.

Predicting the emissions of individual VOCs from petroleum-based indoor coatings

The indoor use of petroleum-based coating materials may cause elevated volatile organic compound (VOC) concentrations. This paper presents a newly developed mass transfer model for estimating the emissions of individual VOCs from freshly coated surfaces. Results of a four-step validation show that the predicted individual VOC emissions are in good agreement with experimental data generated in small chambers and an indoor air quality test house. The values of the parameters introduced in this model are all easily obtained, and thus its utilization can provide indoor air quality professionals with emission rate estimates for individual VOCs without having to conduct costly dynamic chamber testing.

Emissions of perchloroethylene from dry cleaned fabrics

Abstract A study was conducted to evaluate the emissions of perchloroethylene (tetrachloroethylene) from dry cleaned fabrics to determine: (a) how the introduction of fresh dry cleaning into a home affects the indoor concentration of perchloroethylene, and (b) the effectiveness of ‘airing out’ dry cleaned clothes in reducing perchloroethylene emissions. Small chamber tests were conducted to determine perchloroethylene emission characteristics for three fabrics at several air exchange rates. Test house studies were conducted to determine the indoor concentration of perchloroethylene due to the placement of dry cleaned clothing in the house. Based on the study results, and assuming that test conditions were representative of normal dry cleaning and consumer practices, the following conclusions were reached. (1) Emissions from freshly dry cleaned clothing cause elevated levels of perchloroethylene in residences. (2) For the three fabrics tested, ‘airing out’ of dry cleaned clothing by consumers for short time periods (4–8 h) will not be effective in reducing perchloroethylene emissions. (3) Adsorptive surfaces (i.e. sinks) in residences may have a major impact on consumer exposure to perchloroethylene. It is emphasized that these conclusions are based on the results of the study reported. Significant variations in dry cleaning practices and/or in the mix of fabrics and clothing being cleaned could provide different results and conclusions.

Characterization of emissions of volatile organic compounds from interior alkyd paint

Alkyd paint continues to be used indoors for application to wood trim, cabinet surfaces, and some kitchen and bathroom walls. Alkyd paint may represent a significant source of volatile organic compounds (VOCs) indoors because of the frequency of use and amount of surface painted. The U.S. Environmental Protection Agency (EPA) is conducting research to characterize VOC emissions from paint and to develop source emission models that can be used for exposure assessment and risk management. The technical approach for this research involves both analysis of the liquid paint to identify and quantify the VOC contents and dynamic small chamber emissions tests to characterize the VOC emissions after application. The predominant constituents of the primer and two alkyd paints selected for testing were straight-chain alkanes (C9-C12); C8-C9 aromatics were minor constituents. Branched chain alkanes were the predominant VOCs in a third paint. A series of tests were performed to evaluate factors that may affect emissions following application of the coatings. The type of substrate (glass, wallboard, or pine board) did not have a substantial impact on the emissions with respect to peak concentrations, the emissions profile, or the amount of VOC mass emitted from the paint. Peak concentrations of total volatile organic compounds (TVOCs) as high as 10,000 mg/m3 were measured during small chamber emissions tests at 0.5 air exchanges per hour (ACH). Over 90% of the VOCs were emitted from the primer and paints during the first 10 hr following application. Emissions were similar from paint applied to bare pine board, a primed board, or a board previously painted with the same paint. The impact of other variables, including film thickness, air velocity at the surface, and air-exchange rate (AER) were consistent with theoretical predictions for gas-phase, mass transfer-controlled emissions. In addition to the alkanes and aromatics, aldehydes were detected in the emissions during paint drying. Hexanal, the predominant aldehyde in the emissions, was not detected in the liquid paint and was apparently an oxidation product formed during drying. This paper summarizes the results of the product analyses and a series of small chamber emissions tests. It also describes the use of a mass balance approach to evaluate the impact of test variables and to assess the quality of the emissions data.

Modeling of the fast organic emissions from a wood-finishing product—Floor wax

Abstract Environmental chamber and full-scale residential house tests were conducted to evaluate the fast organic emissions from a wood-finishing product—floor wax. For the environmental chamber tests, a very small amount of ( −2 ) of the wax was applied to an aluminum plate. It was found that the chamber exit organic concentrations can be estimated by a model with an initial condition of instant organic emissions. The model was applied to the house data to interpret the octane and nonane emissions. Significant sink effects were found in the house that prolonged the elevated octane and nonane concentrations for more than 2 days.

Evaluation of sink effects on VOCs from a latex paint.

The sink strength of two common indoor materials, a carpet and a gypsum board, was evaluated by environmental chamber tests with four volatile organic compounds (VOCs): propylene glycol, ethylene glycol, 2-(2-butoxyethoxy)ethanol (BEE), and Texanol. These oxygenated compounds represent the major VOCs emitted from a latex paint. Each chamber test included two phases. Phase 1 was the dosing/sorption period during which sink materials (pieces of carpet and gypsum board samples) were exposed to the four VOCs. The sink strength of each material tested was characterized by the amount of the VOCs adsorbed or absorbed. Phase 2 was the purging/de-sorption period during which the chambers with the dosed sink materials were flushed with purified air. The reemission rates of the adsorbed VOCs from the sinks were reflected by the amount of the VOCs being flushed. Phase 1 results indicated that the sink strength for the four target compounds is more than 1 order of magnitude higher than that for other VOCs previously tested by the U.S. Environmental Protection Agency (EPA). The high sink strength reflected the unusually high sorption capacity of common indoor materials for the four VOCs. Phase 2 results showed that reemission was an extremely slow process. If all the VOCs adsorbed were reemittable, it would take more than a year to completely flush out the VOCs from the sink materials tested. The long reemission process can result in chronic and low-level exposure to the VOCs after painting interior walls and surfaces.

Toxicological and chemical evaluation of emissions from carpet samples

This study investigated findings that the off-gassing of certain carpets caused sensory and pulmonary irritation, changes in neurobehavioral signs, and death in exposed mice. Two standard test method measures--one for estimating sensory irritancy (ASTM-E981-84), the other for evaluating the neurotoxic potential of chemicals (functional observational battery)--were coupled with a postmortem assessment to ascertain the mechanism of toxicity. The postmortem evaluation included measurements of hemoglobin, serum clinical chemistries, blood and lung lavage white cell counts and differential, organ weights, and a gross necropsy with a microscopic evaluation of all major organs. The study evaluated three treatment groups composed of two preheated carpet emission exposures and one preheated air-control exposure. No toxic effects were associated with exposure to the off-gassing of the two tested carpets. Clinical chemistry and histopathological alterations were observed with exposure to either filter-air or carpet when compared to nonexposed unrestrained control mice, indicating that the exposure procedure caused significant effects unrelated to carpet emissions. A detailed chemical and microbial evaluation of the carpets and carpet emissions showed volatile organic compounds, pesticide residues, and microbiological flora, but at insufficient quantities to result in acute toxicity. Based on this assessment, there was no indication that exposure to emissions from these two carpets poses a serious health risk.

VOC Sink Behaviour on Building Materials – Model Evaluation

The event of 11 September 2001 underscored the need to study the vulnerability of buildings to weapons of mass destruction, including chemical, biological, physical and radiological agents. Should these agents be released inside a building, they would interact with interior surfaces, building materials and furnishings, and could remain for a long period in an indoor environment. This study provides insights into the sink effect and absorption mechanisms of volatile organic compounds (VOCs) in indoor environments. In this study, the sink effect was investigated with building materials (e.g. painted gypsum wallboard, vinyl flooring, carpet and mortar) and VOCs, ethylbenzene, 1-butanol, decane and dodecane, which were used as surrogates of toxic chemicals. Vinyl flooring has the strongest sink for ethylbenzene and dodecane. The sink experimental data were employed to evaluate the Langmuir-isotherm and diffusion sink models. Test data were also compared to a no-sink model. The sorption and desorption rate constants for the Langmuir-isotherm model were obtained. Mass balance was analysed. There were strong correlations between equilibrium partition coefficients from the Langmuir-isotherm model and equilibrium partition coefficients and the effective diffusion coefficients from the sink diffusion model.