Abstract  A wide variety of surface materials in buildings can release organic compounds. Examples include building materials, furnishings, maintenance materials, clothing, and paper products. These sources contribute substantially to the hundreds of organic compounds that have been measured in indoor air. Their emissions have been directly connected to complaints of odors or hyperreactivity and are presumed to contribute to the problems in many "sick buildings" where the cause of complaints is uncertain. Significant progress has been made in the past decade in developing procedures for measuring emissions from such materials, in controlled experiments where factors affecting emission rates can be determined and quantified. Emissions data are still limited but are being accumulated gradually by research groups in Europe and North America. It is clear from the recent data gathered in research and modeling studies that one of the most effective ways to limit indoor concentrations of organic compounds is to limit the content of volatile compounds in materials that are used in buildings. Limiting the original residual content of such compounds in the materials, or conditioning such materials prior to use in buildings, or (perhaps) conditioning such materials in place before occupancy of a new or renovated building, are most likely to prevent excessive indoor concentrations. If emissions testing and product certification procedures are available and there is sufficient market demand for low-emitting materials caused by indoor air quality concerns, significant reductions of indoor concentrations of vapor-phase organic compounds could be achieved within the next decade.

Abstract  Among the potential fates of indoor air pollutants are a variety of physical and chemical interactions with indoor surfaces. In deterministic mathematical models of indoor air quality, these interactions are usually represented as a first-order loss process, with the loss rate coefficient given as the product of the surface-to-volume ratio of the room times a deposition velocity. In this paper, the validity of this representation of surface-loss mechanisms is critically evaluated. From a theoretical perspective, the idea of a deposition velocity is consistent with the following representation of an indoor air environment. Pollutants are well-mixed throughout a core region which is separated from room surfaces by boundary layers. Pollutants migrate through the boundary layers by a combination of diffusion (random motion resulting from collisions with surrounding gas molecules), advection (transport by net motion of the fluid), and, in some cases, other transport mechanisms. The rate of pollutant loss to a surface is governed by a combination of the rate of transport through the boundary layer and the rate of reaction at the surface. The deposition velocity expresses the pollutant flux density (mass or moles deposited per area per time) to the surface divided by the pollutant concentration in the core region. This concept has substantial value to the extent that the flux density is proportional to core concentration. Empirically, the problem of human exposure to ozone in commercial buildings has been successfully modeled by using the deposition velocity to parameterize ozone removal onto indoor surfaces. The concept has also been applied in investigations of the indoor dynamics of other pollutant species. However, despite the successful application of this concept, caution is advised in using deposition velocity to characterize pollutant-surface interactions. Limitations that are explored in this paper include these: the presumption of uniform mixing throughout the core region may fail; deposition may vary strongly with position in an enclosure; certain classes of surface-pollutant reactions may not be represented adequately as a first-order loss process; transformation processes within the boundary layer may need to be considered in theoretical investigations; and transport rates through boundary layers may depend strongly on near-surface air flow conditions. Published results from experimental and modeling studies of fine particles, radon decay products, ozone, and nitrogen oxides are used as illustrations of both the strengths and weaknesses of deposition velocity as a parameter to indicate the rate of indoor air pollutant loss on surfaces.

Abstract  The objective of this study was to test the effectiveness of individual commercially available portable indoor air cleaning units in removing dust particulates, tobacco smoke particulate and vapor phase constituents (nicotine and vinylpyridine), viable and total fungal spores, pollen, and gaseous contaminants (carbon monoxide[CO], nitrogen dioxide [NO2], and formaldehyde [HCHO]), in a clean air test chamber. The air cleaner chamber results presented here represent initial-use results. In general, High Efficiency Particulate Air (HEPA) and electrostatic precipitator systems demonstrated the highest efficiencies with respect to particulate contaminants, followed closely by electret filter systems. Ionizers and ozone generators were least effective in particulate removal. Systems which included sufficient sorbent material (i.e. activated carbon or potassium permanganate) were marginally effective at gaseous contaminant removal. None of the systems tested were effective at carbon monoxide removal. Sensory testing was conducted to discern potential correlation between human perceptive response and measured air cleaner performance (with respect to tobacco smoke removal). An electret filter (EF) loaded with carbon sorbent received the best ratings with respect to odor strength, nasal irritation, eye irritation, and overall air acceptability

Abstract  The filtration efficiency of ventilation air cleaners is highly particle-size dependent over the 0.01 to 3 mu m diameter size range. Current standardized test methods, which determine only overall efficiencies for ambient aerosol or other test aerosols, provide data of limited utility. Because particles in this range are respirable and can remain airborne for prolonged time periods, measurement of air cleaner fractional efficiency is required for application to indoor air quality issues. The objectives of this work have been to 1) develop a test apparatus and procedure to quantify the the fractional filtration efficiency of air cleaners over the 0.01 to 3 mu m diameter size range and 2) quantify the fractional efficiency of several induct air cleaners typical of those used in residential and office ventilation systems. Results show that efficiency is highly dependent on particle size, flow rate, and dust load present on the air cleaner. A minimum in efficiency was often observed in the 0.1 to 0.5 mu m diameter size range. The presence of a dust load frequently increased an air cleaner's efficiency; however, some air cleaners showed little change or a decrease in efficiency with dust loading. The common furnace filter had fractional efficiency values of less than 10% over much of the measurement size range.

Abstract  Eleven portable air cleaning devices have been evaluated for control of indoor concentrations of respirable particles and radon progeny. Following injection of cigarette smoke and radon in a room-size chamber, decay rates for particles and radon progeny concentrations were measured with and without air cleaner operation. Particle concentrations were obtained for total number concentration and for number concentration by particle size. In tests with no air cleaner the natural decay rate for cigarette smoke was observed to be 0.2 hr/sup -1/. Air cleaning rates for particles were found to be negligible for several small panel-filters, a residential ion-generator, and a pair of mixing fans. The electrostatic precipitators and extended surface filters tested had significant particle removal rates, and a HEPA-type filter was the most efficient air cleaner. The evaluation of radon progeny control produced similar results; the air cleaners which were effective in removing particles were also effective in removing radon progeny. At low particle concentrations plateout of the unattached radon progeny is an important removal mechanism. Based on data from these tests, the plateout rate for unattached progeny was found to be 15 hr/sup -1/. The unattached fraction and the overall removal rate due to deposition of attached and unattached nuclides have been estimated for each radon decay product as a function of particle concentration. While air cleaning can be effective in reducing total radon progeny, concentrations of unattached radon progeny can increase with increasing air cleaning.

Abstract  Residents of a western Pennsylvania community have been using a public groundwater supply known to be contaminated with trichloroethylene (TCE) at concentrations as high as 260 micro-g/L. Volatilization studies were conducted in several homes in this community to assess inhalation exposures received while showering. A newly developed indoor air quality model, MAVRIQ, was used to apply our volatilization models to these measurements. Calibration of MAVRIQ showed that air-exchange rates between the shower stalls and bathrooms are higher than often assumed. Consistent with predictions from our laboratory studies, the inhalation exposures from a six-minute shower in these homes were estimated to be about twice that from direct ingestion of one-liter of contaminated water.

Abstract  The 2003 Commercial Buildings Energy Consumption Survey (CBECS) was administered as a computer-assisted personal interview (CAPI) that was programmed using Blaise software. The interview involved many complex skip patterns, driven by different variables such as the type of structure and the building activity.

Abstract  Tracer gas techniques can be used to measure air infiltration rates in buildings, but it is expensive and time-consuming to obtain a complete characterization of airtightness through these methods. Instead, there are models that predict air infiltration rates from pressurization test results and weather conditions. Other models predict air infiltration without the input of a pressurization test. In order to study the predictive accuracies of these models, a group of identical homes in Freehold, NJ was subjected to both pressurization and tracer gas measurements of infiltration. The infiltration and pressurization test results are compared. Four air infiltration models are used to predict the infiltration rates in the houses, and these predictions are compared with the measured rates. The predictions are made using several, different values of the inputs required for the models, and the effects of varying these inputs are studied. Use of identical houses eliminates variability in the pressurization-infiltration relation due to house style and vintage. Simultaneous measurements of infiltration in all the houses enable analysis of each night's data without the confounding effects of weather.

Abstract  Sixteen particleboard products manufactured in the USA in 1986 and 1987 were tested for formaldehyde emission repeatedly over a period of time (up to just over 500 days) by the FTM-2 large chamber method. Data were generated from 4 different large chamber locations and represented a large cross section of the US particleboard industry. Formaldehyde emission decay curves were plotted from test results and these were used to calculate the three-quarter life and half-life of emissions. Initial measurements of formaldehyde emissions varied from 0.41 p.p.m. to 0.10 p.p.m.; the overall average initial emission level was 0.21 p.p.m. The overall three-quarter and half-lives were 38 and 216 days, respectively. The rate at which emissions decreased was not constant but decreased with time. In general, emissions decreased linearly with respect to the natural logarithm of time.

Abstract  Contaminated water can lead to the volatilization of chemicals to residential indoor air. However, previous research has focused on one source, namely showers. In addition, research has been limited to chemicals in which gas-phase resistance to mass transfer is of marginal significance. As a result, attempts to extrapolate chemical emissions from highly volatility chemical to lower volatility chemicals, or to source other than showers, have been difficult or impossible. This report presents the results of a series of experiments conducted to determine emissions from four sources of water use in a household (showers, bathtubs, washing machines, and dishwashers). Mass transfer coefficients and chemical stripping efficiencies were determined using these four sources and five tracer chemicals (acetone, ethyl acetate, toluene, ethylbenzene, and cyclohexane). The report presents a protocol for estimating emission rates for chemical other than those used in the experiments using a series of mass balance models.

Abstract  A Microsoft Windows-based indoor air quality (IAQ) simulation software package is presented. Named Simulation Tool Kit for Indoor Air Quality and Inhalation Exposure, or IAQX for short, this package complements and supplements existing IAQ simulation programs and is designed mainly for advanced users. IAQX version 1.0 consists of five stand-alone simulation programs. A general-purpose simulation program performs multi-zone, multipollutant simulations and allows gas-phase chemical reactions. The other four programs implement fundamentally based models, which are often excluded in the existing IAQ simulation programs. In addition to performing conventional IAQ simulations, which compute the time concentration profile and inhalation exposure, IAQX can estimate the adequate ventilation rate when certain air quality criteria are provided by the user, a unique feature useful for product stewardship and risk management. IAQX will be developed in a cumulative manner and more special-purpose simulation programs will be added to the package in the future.

Abstract  This User's Guide provides documentation for the Industrial Source Complex (ISC3) models, referred to hereafter as the Short Term (ISCST3) and Long Term (ISCLT3) models. This volume provides user instructions for the ISCST3 and ISCLT3 models, including the new area source and dry deposition algorithms, both of which are a part of Supplement C to the Guideline on Air Quality Models (Revised). This volume also includes user instructions for the following algorithms that are not included in Supplement C: pit retention (ISCST3 and ISCLT3), wet deposition (ISCST3 only), and COMPLEX1 (ISCST3 only). The pit retention and wet deposition algorithms have not undergone extensive evaluation at this time, and their use is optional. COMPLEX1 is incorporated to provide a means for conducting screening estimates in complex terrain. EPA guidance on complex terrain screening procedures is provided in Section 5.2.1 of the Guideline on Air Quality Models (Revised). Volume II of the ISC3 User's Guide provides the technical description of the ISC3 algorithms.

Abstract  A critical aspect of air pollution exposure models is the estimation of the air exchange rate (AER) of individual homes, where people spend most of their time. The AER, which is the airflow into and out of a building, is a primary mechanism for entry of outdoor air pollutants and removal of indoor source emissions. The mechanistic Lawrence Berkeley Laboratory (LBL) AER model was linked to a leakage area model to predict AER from questionnaires and meteorology. The LBL model was also extended to include natural ventilation (LBLX). Using literature-reported parameter values, AER predictions from LBL and LBLX models were compared to data from 642 daily AER measurements across 31 detached homes in central North Carolina, with corresponding questionnaires and meteorological observations. Data was collected on seven consecutive days during each of four consecutive seasons. For the individual model-predicted and measured AER, the median absolute difference was 43% (0.17 h(-1)) and 40% (0.17 h(-1)) for the LBL and LBLX models, respectively. Additionally, a literature-reported empirical scale factor (SF) AER model was evaluated, which showed a median absolute difference of 50% (0.25 h(-1)). The capability of the LBL, LBLX, and SF models could help reduce the AER uncertainty in air pollution exposure models used to develop exposure metrics for health studies.

Abstract  Sorption of semivolatile organic compounds (SVOCs) onto interior surfaces, often referred to as the "sink effect", and their subsequent re-emission significantly affect the fate and transport of indoor SVOCs and the resulting human exposure. Unfortunately, experimental challenges and the large number of SVOC/surface combinations have impeded progress in understanding sorption of SVOCs on indoor surfaces. An experimental approach based on a diffusion model was thus developed to determine the surface/air partition coefficient K of di-2-ethylhexyl phthalate (DEHP) on typical impervious surfaces including aluminum, steel, glass, and acrylic. The results indicate that surface roughness plays an important role in the adsorption process. Although larger data sets are needed, the ability to predict K could be greatly improved by establishing the nature of the relationship between surface roughness and K for clean indoor surfaces. Furthermore, different surfaces exhibit nearly identical K values after being exposed to kitchen grime with values that are close to those reported for the octanol/air partition coefficient. This strongly supports the idea that interactions between gas-phase DEHP and soiled surfaces have been reduced to interactions with an organic film. Collectively, the results provide an improved understanding of equilibrium partitioning of SVOCs on impervious surfaces.

Abstract  Organic farming and improvements to agricultural sustainability are often seen as synonymous. However, an extensive European review demonstrated that in practice this is not always true. This study aims to compare the status of soil and water properties between separate fields managed in either an organic or a conventional manner. Soil samples were collected from 16 pairs of farms, throughout England, with both arable and grass fields within each pair on similar soil type. Chemical (nutrients, pesticides, herbicides) and physical (aggregate stability, field capacity, shear strength, soil organic matter, infiltration rates) soil properties were measured in four main soil texture classes in organic and conventional fields. The physical soil properties varied significantly between the different classes of texture and land use. The heavier textured soils have significantly higher soil organic carbon (SOC), aggregate stability and shear strength. The coarse-textured soils have significantly lower field capacity moisture contents. The grassland has a significantly higher level of SOC, field capacity moisture content, aggregate stability and soil shear strength. However, there were no significant differences between organic and conventional treatments for any of the soil physical properties measured. There were fewer traces of agrochemicals in the soil water from the organic fields compared with the conventionally managed fields. The conventional arable fields had higher levels of total inorganic nitrogen than the other land uses and treatments. There was evidence to show that infiltration rates were significantly higher on organically managed grassland soils (7.6 mm/h) than conventionally managed grassland (2.5 mm/h) with lower stocking rates. The results suggest that improved grassland management, whether organic or conventional, could reduce predicted runoff by 28%.

Abstract  This report presents data from the American Housing Survey (AHS). The survey is sponsored by the Department of Housing and Urban Development (HUD) and conducted by the U.S. Census Bureau. The AHS is the most comprehensive national housing survey in the United States. It provides data on a wide range of housing subjects, including single-family homes, apartments, manufactured housing, vacant units, family composition, income, housing and neighborhood quality, housing costs, equipment, fuel type, and recent moves. National data are collected every 2 years from a sample of housing units. The national survey, which began in 1973, has sampled the same units since 1985; it also samples new construction to ensure continuity and timeliness of the data.

Abstract  The NO, NO2, and CO emissions from residential gas combustion appliances contribute to indoor air pollution. The work described investigated the impact of various unvented gas appliances designs and/or operational factors on pollutant emission rates. All experiments were performed in a 1150 ft3 (32.56 m3) all aluminum chamber under controlled conditions. Results are presented for the effect of the following factors on emission rates: 1) appliance type and/or design, 2) primary aeration level, 3) firing rate (fuel input rate), 4) chamber humidity, and 5) time dependence of emission rates. It is concluded that primary aeration level has the largest impact on pollutant emission rates of range-top burners, followed in turn by firing rate, appliance type, chamber humidity, and time dependence of emission rate.

Abstract  The emission charaaaistics of four organic compounds (non‐ane, decam, undecane, and 1, 2, 4‐trimethylbenzene)from wood stain have been measured in an environmental chamber It was found that the emission patterns of the four organic compounds can be described by a two‐phase model. Phase 1 represents the period when the wood stain is relatively wet. Phase 2 is when the wood stain becomes relatively dry. The changes of emission mechanisms between the two phases were reflcted by the significantly different emission rate canstants measured during the two periods and the relationship between the relative rate constant, the relative vapor pressure, and the relative diffusivity. A double‐exponential model was established that can be used to predict the relative emission rates of the four organic compounds fiom the wood stain.

Abstract  The mixing rate of pollutants emitted from indoor sources influences the effectiveness of pollutant removal by building ventilation and the potential variability of exposure for a given release scenario. Quantitative information is scant on the mixing rate and the factors that govern it. We present mixing data for an instantaneously released tracer gas, carbon monoxide, in a sealed, unoccupied room under a range of forced airflow conditions, in which the flow is induced by blowers. The resulting mixing times, from 2 to 42 minutes, are related to the mechanical power of the air jets produced by the blowers. Mixing times are found to correlate well with the inverse of the cube root of power, in accordance with theoretical predictions and experimental observations for mixing in chemical reactors. The exposure index, defined as the time-averaged concentration at a point relative to the time-averaged concentration for the room as a whole, is presented for three experimental conditions, yielding quantitative information on the appropriateness of the well-mixed hypothesis under various flow conditions. In general, the exposure period following instantaneous release of a point-source pollutant must be much greater than the mixing time for the assumption of uniform mixing to hold. The correlation between mixing time and power input is used to predict the mixing time from the mixing action of a supply air jet for a typical ventilation scenario. The predicted mixing time, tau(mix) similar to 7 min, is substantially lower than the time scale for removal by ventilation, tau(vent) similar to 48 min. Under these conditions, complete mixing of an instantaneous release, point-source pollutant would be approximately attained within the interior space well before the pollutant would be thoroughly removed by ventilation.

Abstract  We report approximately 500 indoor-outdoor air exchange rate (AER) calculations based on measurements conducted in residences in three US metropolitan areas in 1999-2001: Elizabeth, New Jersey; Houston, Texas; and Los Angeles County, California. Overall, a median AER across these urban areas and seasons was 0.71 air changes per hour (ACH, or per hour; n = 509) while median AERs measured in California (n = 182), New Jersey (n = 163), and Texas (n = 164) were 0.87, 0.88, and 0.47 ACH, respectively. In Texas, the measured AERs were lower in the summer cooling season (median = 0.37 ACH) than in the winter heating season (median = 0.63 ACH), likely because of the reported use of room air conditioners as Houston is typically hot and humid during the summer. The measured AERs in California were higher in summer (median = 1.13 ACH) than in winter (median = 0.61 ACH). Because the summer cooling season in Los Angeles County is less humid than in New Jersey or Texas, natural ventilation through open windows and screened doors likely increased measured AER in California study homes. In New Jersey, AER were similar across heating and cooling seasons, although the median AER was relatively lower during the spring. PRACTICAL IMPLICATIONS: Adequate ventilation or air exchange rate (AER) for an indoor environment is important for human health and comfort, and relevant to building design and energy conservation and efficiency considerations. However, residential AER data, especially measured by more accurate non-toxic tracer gas methodologies, are at present quite limited worldwide, and are insufficient to represent the variations across regions and seasons within and between homes, including apartments and condominiums in more densely populated urban areas. The present paper presents quantitative and qualitative data to characterize residential AERs in three US urban areas with different climate attributes.

Abstract  Contaminated tap water may be a source of volatile organic compounds (VOCs) in residential indoor air. To better understand the extent and impact of chemical emissions from this source, a two-phase mass balance model was developed based on mass transfer kinetics between each phase. Twenty-nine experiments were completed using a residential dishwasher to determine model parameters. During each experiment, inflow water was spiked with a cocktail of chemical tracers with a wide range of physicochemical properties. In each case, the effects of water temperature, detergent, and dish-loading pattern on chemical stripping efficiencies and mass transfer coefficients were determined. Dishwasher headspace ventilation rates were also measured using an isobutylene tracer gas. Chemical stripping efficiencies for a single cycle ranged from 18% to 55% for acetone, from 96% to 98% for toluene, and from 97% to 98% for ethylbenzene and were consistently 100% for cyclohexane. Experimental results indicate that dishwashers have a relatively low but continuous ventilation rate (∼5.7 L/min) that results in significant chemical storage within the headspace of the dishwasher. In conjunction with relatively high mass transfer coefficients, low ventilation rates generally lead to emissions that are limited by equilibrium conditions after approximately 1−2 min of dishwasher operation.

Abstract  An element-assembly formulation of multi-zone contaminant dispersal theory that is not limited to the well-mixed zone idealization is described. In this approach flow systems are idealized as assemblages of elements that model specific instances of contaminant mass transport within a system. A general form and specific examples of element equations are presented. The process of assembling these element equations to form system equations and the qualitative character of the resulting system equations is discussed. Solutions options are outlined, examples of application are presented, and one implementation of the theory, the CONTAM family of programs developed at NBS, is briefly described.