Primary Volatile Organic Compounds Research Articles

Comparison of seasonal phenol and p-cresol emissions from ground-level area sources in a dairy operation in central Texas

Although there are more than 200 odor-causing volatile organic compounds (VOCs), phenol and p-cresol are two prominent odor-causing VOCs found downwind from concentrated animal feeding operations (CAFOs). The VOC emissions from cattle and dairy production are difficult to quantify accurately because of their low concentrations, spatial variability, and limitations of available instruments. To quantify VOCs, a protocol following U.S. Environmental Protection Agency (EPA) Method TO-14A has been established based on the isolation flux chamber method and a portable gas chromatograph (GC) coupled with a purge-and-trap system. The general objective of this research was to quantify phenol and p-cresol emission rates (ERs) from different ground-level area sources (GLASs) in a free-stall dairy during summer and winter seasons using this protocol. Two-week-long sampling campaigns were conducted in a dairy operation in central Texas. Twenty-nine air samples were collected during winter and 37 samples were collected during summer from six specifically delineated GLASs (barn, loafing pen, lagoon, settling basin, silage pile, and walkway) at the free-stall dairy. Thirteen VOCs were identified during the sampling period and the GC was calibrated for phenol and p-cresol, the primary odorous VOCs identified. The overall calculated ERs for phenol and p-cresol were 2656 ± 728 and 763 ± 212 mg hd−1 day−1, respectively, during winter. Overall phenol and p-cresol ERs were calculated to be 1183 ± 361 and 551 ± 214 mg hd−1 day−1, respectively, during summer. In general, overall phenol and p-cresol ERs during winter were about 2.3 and 1.4 times, respectively, higher than those during summer. Implications: Concentrated animal feeding operations contribute a considerable amount of VOCs to the atmosphere. The phenol and p-cresol are two VOCs recognized as potential odor-causing compounds emitted from livestock operation. To develop effective strategies for mitigating livestock odorous VOC emissions, relative emissions from different GLAS in a livestock operation under different climate conditions should be quantified. It is also important to obtain direct estimates of VOC emissions from different GLAS in CAFOs to compile emission inventories. This research determined phenol and p-cresol emissions from different GLAS in a free-stall dairy and also identified areas in a dairy operations that have the highest phenol and p-cresol emissions.

A Study on Dynamic Volatile Organic Compound Emission Characterization of Water-Based Paints

ABSTRACT Volatile organic compounds (VOCs) emitted from surface coatings have caused growing public concern for air quality. Even the low-emitted VOC impact from water-based paints on indoor air quality in urban areas has caused concern. This paper presents experimental data using a mathematical model to simulate dynamic VOC emissions from water-based paints that is based on mass transfer and molecular diffusion theories. A series of field-analogous experiments were carried out to continuously measure the VOCs emitted from two typical water-based paints using a gas chromatography–flame-ionization detector monitor in an artificial wind tunnel system. In the study cases, the mass flux of VOCs emitted from the water-based paints was up to 50 μg/m2sec. It was found that the time needed to completely emit VOCs from water-based paints is just hundreds of seconds. However, the order of magnitude of the VOC emission rate from water-based paints is not lower than that from some dry building materials and solvent-based paints. The experimental data were used to produce a useful semiempirical correlation to estimate the VOC emission rates for water-based paints. This correlation is valid under appropriate conditions as suggested by this work with a statistical deviation of ±7.6%. With this correlation, it seems feasible to predict the dynamic emission rates for VOCs during a painting process. This correlation is applicable for assessing the hazardous air pollutant impact on indoor air quality or for environmental risk assessment. Associated with the dynamic VOC emission characterization, the air-exchange rate effect on the VOC emission rates is also discussed. IMPLICATIONS This paper presents experimental data using a mathematical model to simulate dynamic VOC emissions from water-based paints that is based on mass transfer and molecular diffusion theories. A semiempirical correlation is suggested to estimate the VOC emission rates for water-based paints. With this correlation, it is feasible to interpret and predict the dynamic emission rates for VOCs during a painting process. The results obtained in this work will be useful in evaluating the indoor air quality impact by primary VOCs or hazardous air pollutants emitted from water-based paints.

Investigation of the Treatability of the Primary Indoor Volatile Organic Compounds on Activated Carbon Fiber Cloths at Typical Indoor Concentrations

Volatile organic compounds (VOCs) are a major concern for indoor air pollution because of the impacts on human health. In recent years, interest has increased in the development and design of activated carbon filters for removing VOCs from indoor air. Although extensive information is available on sources, concentrations, and types of indoor VOCs, there is little or no information on the performance of indoor air adsorption systems for removing low concentrations of primary VOCs. Filter designs need to consider various factors such as empty bed contact time, humidity effects, competitive adsorption, and feed concentration variations, whereas adsorption capacities of the indoor VOCs at the indoor concentration levels are important parameters for filter design. A preliminary assessment of the feasibility of using adsorption filters to remove low concentrations of primary VOCs can be performed. This work relates the information (including VOC classes in indoor air, the typical indoor concentrations, and the adsorption isotherms) with the design of a particular adsorbent/adsorbates system. As groundwork for filter design and development, this study selects the primary VOCs in indoor air of residences, schools, and offices in different geographical areas (North America, Europe, and Asia) on the basis of occurrence, concentrations, and health effects. Activated carbon fiber cloths (ACFCs) are chosen as the adsorbents of interest. It is demonstrated that the isotherm of a VOC (e.g., toluene on the ACFC) at typical indoor concentrations—parts per billion by volume (ppbv) level—is different than the isotherm at parts per million by volume (ppmv) levels reported in the publications. The isotherms at the typical indoor concentrations for the selected primary VOCs are estimated using the Dubinin–Radushkevitch equation. The maximum specific throughput for an indoor VOC removal system to remove benzene is calculated as a worst-case scenario. It is shown that VOC adsorption capacity is an important indicator of a filter’s lifetime and needs to be studied at the appropriate concentration range. Future work requires better understanding of the realistic VOC concentrations and isotherms in indoor environments to efficiently utilize adsorbents.

VOC reactivity in central California: comparing an air quality model to ground-based measurements

Abstract. Volatile organic compound (VOC) reactivity in central California is examined using a photochemical air quality model (the Community Multiscale Air Quality model; CMAQ) and ground-based measurements to evaluate the contribution of VOC to photochemical activity. We classify VOC into four categories: anthropogenic, biogenic, aldehyde, and other oxygenated VOC. Anthropogenic and biogenic VOC consist of primary emissions, while aldehydes and other oxygenated VOC include both primary anthropogenic emissions and secondary products from primary VOC oxidation. To evaluate the model treatment of VOC chemistry, we compare calculated and modeled OH and VOC reactivities using the following metrics: 1) cumulative distribution functions of NOx concentration and VOC reactivity (ROH,VOC), 2) the relationship between ROH,VOC and NOx, 3) total OH reactivity (ROH,total) and speciated contributions, and 4) the relationship between speciated ROH,VOC and NOx. We find that the model predicts ROH,total to within 25–40% at three sites representing urban (Sacramento), suburban (Granite Bay) and rural (Blodgett Forest) chemistry. However in the urban area of Fresno, the model under predicts NOx and VOC emissions by a factor of 2–3. At all locations the model is consistent with observations of the relative contributions of total VOC. In urban areas, anthropogenic and biogenic ROH,VOC are predicted fairly well over a range of NOx conditions. In suburban and rural locations, anthropogenic and other oxygenated ROH,VOC relationships are reproduced, but calculated biogenic and aldehyde ROH,VOC are often poorly characterized by measurements, making evaluation of the model with available data unreliable. In central California, 30–50% of the modeled urban VOC reactivity is due to aldehydes and other oxygenated species, and the total oxygenated ROH,VOC is nearly equivalent to anthropogenic VOC reactivity. In rural vegetated regions, biogenic and aldehyde reactivity dominates. This indicates that more attention needs to be paid to the accuracy of models and measurements of both primary emissions of oxygenated VOC and secondary production of oxygenates, especially formaldehyde and other aldehydes, and that a more comprehensive set of oxygenated VOC measurements is required to include all of the important contributions to atmospheric reactivity.

The use of positive matrix factorization with conditional probability functions in air quality studies: An application to hydrocarbon emissions in Houston, Texas

In this paper, we describe two advanced statistical techniques suited to address the following questions: which source categories of emissions affect given areas and where do these source categories come from? A source category is defined as a combination of volatile organic compounds (VOCs) associated with a specific industrial process. A discussion of the positive matrix factorization (PMF) multivariate receptor model is presented, and this PMF technique applied to hourly average concentrations of VOCs measured at five Photochemical Assessment Monitoring Stations (PAMS) located near the emission-rich Houston Ship Channel region in Texas. The observations were made between June and October 2003, and the PMF analysis was limited to nighttime measurements (21:00–06:00 CDT) to remove the complexity of photochemical processing and associated changes in the concentrations of primary and secondary VOCs. Six to eight VOCs source categories were identified for the five Ship Channel sites. Specific geographic areas associated with each source category were identified through the use of conditional probability functions that identify source regions when superimposed on maps of VOC emissions.

The correlation between photocatalytic oxidation performance and chemical/physical properties of indoor volatile organic compounds

In this study, six species of volatile organic compounds (VOCs), n-hexane, iso-butanol, toluene, p-xylene, m-xylene, and mesitylene, were selected as the target pollutants to investigate how the photocatalytic oxidation (PCO) performance is related to their physical/chemical properties. The PCO kinetics were well fit by a Langmuir–Hinshelwood (L–H) model for bimolecular surface reaction and competitive adsorption at gas flow rate above 1000 mL min −1 (reaction-controlling region), where the gas-phase mass transfer effect was negligible. The rate constants of PCO for toluene, p-xylene, m-xylene, and mesitylene ranged from 1.22 to 4.00 μmol m −2 s −1, and were proportional to VOC-hydroxyl radical rate constant ( k OH). The Langmuir adsorption constants of the four aromatic VOCs investigated and water ranged from 0.95 to 1.35 ppm −1 and from 5.61×10 −3 to 1.44×10 −3 ppm −1, respectively. A strongly linear positive relationship was found between the reciprocal of the Langmuir adsorption constants of the four aromatic VOCs investigated and Henry's Law constants. Conversely, the reciprocal of Langmuir adsorption constants of water showed a strong negative relationship with Henry's Law constants (in units kPa m 3 mol −1) of the four aromatic VOCs investigated. The relationships noted above were not found between different classes of VOCs ( n-hexane, iso-butanol, and aromatic VOCs investigated). The percentage of residual intermediates (partially oxidized and incompletely mineralized organic compound from the primary VOCs) decreased as the inlet VOCs concentration decreased.

Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002

An extensive set of volatile organic compounds (VOCs) and particulate organic matter (POM) was measured in polluted air during the New England Air Quality Study in 2002. Using VOC ratios, the photochemical age of the sampled air masses was estimated. This approach was validated (1) by comparing the observed rates at which VOCs were removed from the atmosphere with the rates expected from OH oxidation, (2) by comparing the VOC emission ratios inferred from the data with the average composition of urban air, and (3) by the ability to describe the increase of an alkyl nitrate with time in terms of the chemical kinetics. A large part of the variability observed for oxygenated VOCs (OVOCs) and POM could be explained by a description that includes the removal of the primary anthropogenic emissions, the formation and removal of secondary anthropogenic species, and a biogenic contribution parameterized by the emissions of isoprene. The OVOC sources determined from the data are compared with the available literature, and a satisfactory agreement is obtained. The observed sub‐μm POM was highly correlated with secondary anthropogenic gas‐phase species, strongly suggesting that the POM was from secondary anthropogenic sources. The results are used to describe the speciation and total mass of gas‐ and particle‐phase organic carbon as a function of the photochemical age of an urban air mass. Shortly after emission the organic carbon mass is dominated by primary VOCs, while after two days the dominant contribution is from OVOCs and sub‐μm POM. The total measured organic carbon mass decreased by about 40% over the course of two days. The increase in sub‐μm POM could not be explained by the removal of aromatic precursors alone, suggesting that other species must have contributed and/or that the mechanism for POM formation is more efficient than previously assumed.

A study on VOC source and sink behavior in porous building materials - analytical model development and assessment

Building materials can strongly affect indoor air quality. Porous building materials are not only sources of indoor air pollutants such as volatile organic compounds (VOC) but they are also strong sinks of these pollutants. The knowledge of VOC transfer mechanisms in these materials is an important step for controlling the indoor VOC concentration levels, and for determining the optimum ventilation requirements for acceptable IAQ. This study provides a theoretical investigation of primary and secondary VOC source and sink behavior of porous building materials. A new analytical model was developed based on the fundamental theories of mass transfer mechanisms in porous materials. The proposed model considers both primary and secondary source/sink behavior for the first time. The former refers to the transfer of gas-phase and/or physically adsorbed VOC, while the latter refers to the generation or elimination of VOC within the solid because of chemical reactions like oxidation, hydrolysis, chemical adsorption, etc. The proposed model was assessed with experimental data, namely emission tests of carpets and sorption tests of wood chipboard. It was demonstrated that, unlike the existing analytical models, the proposed analytical model could simultaneously account for the effect of air velocity on both VOC source as well as sink behavior. Case studies were then carried out for secondary VOC source behavior. Due to the lack of experimental studies on mechanisms of secondary behavior, hypothetical generation functions were implemented. It was demonstrated that the proposed analytical model is suitable for describing various mechanisms involved in the secondary behavior due to the little limitations imposed on the generation/elimination term. When VOC generation takes place at the material-air interface, the simulation shows that although the primary emission is not affected by air velocity, the secondary emission, however, is clearly affected. This behavior agrees with the available experimental findings on secondary emissions. PRACTICAL IMPLICATION: The analytical model presented in this paper can predict both primary and secondary VOC source (emission) or sink (sorption) behavior of porous building materials. Since the model considers diffusion and adsorption/desorption within the material, and convection over the material surface, the simulation using the model can readily provide the effects of material properties and airflow properties on the primary and/or the secondary behavior, hence, it can provide a better understanding on the mechanisms. This will enable us to keep the indoor VOC concentration within a desirable level.

Contaminated site remedial investigation and feasibility removal of chlorinated volatile organic compounds from groundwater by activated carbon fiber adsorption

Groundwater contaminated by dense, non-aqueous phase liquids (DNAPLs) such as chlorinated solvents has become a serious problem in some regions of Taiwan. The sources of these contaminants are due to industrial discharges. These chlorinated volatile organic compounds (VOCs) have been proven to be carcinogenic to humans. The groundwater is used for domestic drinking water supply in some cities of Taiwan and the severely contaminated groundwater has to be treated in order to meet the requirement of drinking water standards. This study covers two areas of work. In the first part, polluted groundwater samples were collected from the contaminated site and analytical results indicated measurable concentrations of 12 representative chlorinated VOCs in water samples. The primary VOCs detected included trichloroethene (TCE), tetrachloroethene (PCE), 1,1,2-trichloroethane (1,1,2-TCA), and 1,1-dichloroethene (1,1-DCE). Second, to remove VOCs groundwater was treated using adsorption on activated carbon fiber (ACF). This involved pumping groundwater through vessels containing ACF. Most VOCs, including TCE, PCE, 1,1,2-TCA, and DCE, were readily adsorbed onto ACF and are removed from the water stream. Our study showed that the technology was able to significantly reduce chlorinated VOCs concentrations in groundwater.

Evaluation of Total Volatile Organic Compound Emissions from Adhesives Based on Chamber Tests

ABSTRACT In 1997, Homeswest in western Australia and Murdoch University developed a project to construct low-allergen houses (LAHs) in a newly developed suburb. Before the construction of LAHs, all potential volatile organic compound (VOC) emission materials used in LAHs are required to be measured to ensure that they are low total VOC (TVOC) emission materials. This program was developed based on this purpose. In recent times, the number of complaints about indoor air pollution caused by VOCs has increased. A number of surveys of indoor VOCs have indicated that many indoor materials contribute to indoor air pollution. Although some studies have been conducted on the characteristics of VOC emissions from adhesives, most of them were focused on VOC emissions from floor adhesives. Few measurements of VOC emissions from adhesives used for wood, fabrics, and leather are available. Furthermore, most research on VOC emissions from adhesives has been done in countries with cool climates, where ventilation rates in the indoor environment are lower than those in Mediterranean climates, due to energy conservation. VOCs emitted from adhesives have not been sufficiently researched to prepare an emission inventory to predict indoor air quality and to determine both exposure levels for the Australian population and the most appropriate strategies to reduce exposure. An environmental test chamber with controlled temperature, relative humidity, and airflow rate was used to evaluate emissions of TVOCs from three adhesives used frequently in Australia. The quantity of TVOC emissions was measured by a gas chromatography/flame ionization detector. The primary VOCs emitted from each adhesive were detected by gas chromatography/mass spectrometry. The temporal change of TVOC concentrations emitted from each adhesive was tested. A double-exponential equation was then developed to evaluate the characteristics of TVOC emissions from these three adhesives. With this double-exponential model, the physical processes of TVOC emissions can be explained, and a variety of emission parameters can be calculated. These emission parameters could be used to estimate real indoor TVOC concentrations in Mediterranean climates.

Volatile organic compound emission rates from mixed deciduous and coniferous forests in Northern Wisconsin, USA

Biogenic emissions of volatile organic compounds (VOC) from forests play an important role in regulating the atmospheric trace gas composition including global tropospheric ozone concentrations. However, more information is needed on VOC emission rates from different forest regions of the world to understand regional and global impacts and to implement possible mitigation strategies. The mixed deciduous and coniferous forests of northern Wisconsin, USA, were predicted to have significant VOC emission rates because they are comprised of many genera (i.e. Picea, Populus, Quercus, Salix) known to be high VOC emitters. In July 1993, a study was conducted on the Chequamegon National Forest near Rhinelander, WI, to identify and quantify VOC emitted from major trees, shrubs, and understory herbs in the mixed northern forests of this region. Emission rates were measured at various scales – at the leaf level with cuvettes, the branch level with branch enclosures, the canopy level with a tower based system, and the landscape level with a tethered balloon air sampling system. Area-average emission rates were estimated by scaling, using biomass densities and species composition along transects representative of the study site. Isoprene (C 5H 8) was the primary VOC emitted, although significant quantities of monoterpenes (C 10H 16) were also emitted. The highest emission rates of isoprene (at 30°C and photosynthetically active radiation of 1000 μmol m -2 s -1) were from northern red oak ( Quercus rubra, >110 μg(C) g -1 h -1); aspen ( Populus tremuloides, >77); willow ( Salix spp., >54); and black spruce ( Picea mariana, >10). Emission rates of hybrid poplar clones ranged from 40 to 90 μg(C) g -1 h -1 at 25°C; those of Picea provenances were generally <10, and emission rates of a hybrid between North American and European spruces were intermediate to parental rates. More than 30 species of plants were surveyed from the sites, including several from previously unstudied genera such as Alnus, Chamaedaphne, Ledum, Tilia, Rubus, and Sphagnum. Based on the measured isoprene concentrations in the daytime atmospheric surface layer and mixed layer, area-averaged fluxes of isoprene were estimated to be about 1 mg(C) m -2 h -1. This estimate agrees reasonably well with model predictions. Our results indicate that mixed forests in the Lake States region of the USA are a significant source of reactive VOC to the atmosphere. Accurate estimates of these emissions are required for determining appropriate regulatory air pollution control strategies. Future studies are needed to extrapolate these estimates to other landscapes and to better understand the factors controlling observed variations in VOC emissions.

Sensory and chemical characterization of VOC emissions from building products: impact of concentration and air velocity

The emissions from five commonly used building products were studied in small-scale test chambers over a period of 50 days. The odor intensity was assessed by a sensory panel and the concentrations of selected volatile organic compounds (VOCs) of concern for the indoor air quality were measured. The building products were three floor coverings: PVC, floor varnish on beechwood parquet and nylon carpet on a latex foam backing; an acrylic sealant, and a waterborne wall paint on gypsum board. The impacts of the VOC concentration in the air and the air velocity over the building products on the odor intensity and on the emission rate of VOCs were studied. The emission from each building product was studied under two or three different area-specific ventilation rates, i.e. different ratios of ventilation rate of the test chamber and building product area in the test chamber. The air velocity over the building product samples was adjusted to different levels between 0.1 and 0.3 m s -1. The origin of the emitted VOCs was assessed in order to distinguish between primary and secondary emissions. The results show that it is reasonable after an initial period of up to 14 days to consider the emission rate of VOCs of primary origin from most building products as being independent of the concentration and of the air velocity. However, if the building product surface is sensitive to oxidative degradation, increased air velocity may result in increased secondary emissions. The odor intensity of the emissions from the building products only decayed modestly over time. Consequently, it is recommended to use building products which have a low impact on the perceived air quality from the moment they are applied. The odor indices (i.e. concentration divided by odor threshold) of primary VOCs decayed markedly faster than the corresponding odor intensities. This indicates that the secondary emissions rather than the primary emissions, are likely to affect the perceived air quality in the long run. Some of the building products continued to affect the perceived air quality despite the concentrations of the selected VOCs resulted in odor indices less than 0.1. Therefore, odor indices less than 0.1 as an accept criterion cannot guarantee that a building product has no impact on the perceived air quality.

Oxidation of Diesel-Generated Volatile Organic Compounds in the Selective Catalytic Reduction Process

The main part of the VOCs (volatile organic compounds) contained in diesel exhaust (≈80%) is oxidized to CO and CO2 over an SCR (selective catalytic reduction) catalyst. CO is the major product of this oxidation, representing about 50−70% of the formed products (CO + CO2). This preferential formation of CO leads to a pronounced increase of CO emissions when an SCR process is added to a diesel engine. A small fraction of the VOCs is selectively oxidized to carboxylic acids over the SCR catalyst. This selectivity is due to the acidic properties of the catalyst causing the preferential desorption at the oxidation state of the acid. The main products of these oxidation reactions are the lower monocarboxylic acids and some dicarboxylic acids forming stable anhydrides, especially maleic and phthalic acid. The highest emissions of these acids are found at low temperatures; they decrease at higher temperatures. Formic acid is preferentially decomposed into carbon monoxide and water. It must therefore be assumed that the strong increase of CO mentioned above is due to a mechanism involving the thermal decomposition of formic acid formed from various primary VOCs.

Effect of Volatile Reduction on Growth and Development in Closed Atmospheric Chambers

Plants produce and respond to a broad spectrum of volatile chemical compounds. The concentration and duration of volatile exposure during long-duration space missions will be higher than typically experienced by plants. The effects of using filters to reduce volatile organic compound (VOC) exposure on growth and development of several species has been studied in the Biomass Production Chamber (BPC) at Kennedy Space Center. The VOC composition of the BPC was determined weekly using a modification of EPA Method TO-14 with mass spectrometry. Ethylene concentration was monitored every 8 h using FID gas chromatography. Experiment durations were 84 days for wheat, 105 days for potato, 104 days for rice, and 90 days for tomato. In all cases, non-biological sources including siloxanes, Freon's, solvents and hydrocarbons were the primary VOC constituents. The primary biogeneic compounds detected include ethylene, acetaldehyde, pinene, isoprene, and carbon disulfide. Species-specific compounds detected included various terpenes, esters, furans, alcohols, aldehydes, and ethers. Filtering the atmosphere through activated carbon filters typically reduced the overall VOC concentration by at least 50%. Filtering the atmosphere through potassium permanganate pellets generally maintained ethylene concentrations &lt;25 ppb. Concentration difference between filtered and unfiltered treatments varied according to species, stage of development and specific compound. By reducing the overall VOC exposure, several species-specific morphological and development changes were observed, including: an increase in internode length of wheat, potato and rice, delayed anthesis of wheat and tomato, delayed tuber initiation in potato, delayed ripening of tomato, earlier anthesis of rice, and larger leaf area in potato. No phytotoxicity per se was noted during these experiments.

Forecast distributions of species and their atmospheric reactivities for the U.K. VOC emission inventory

The planned reductions of volatile organic compound (VOC) emissions in the U.K. will have an influence on both the total mass and species distribution of emissions. Different organic compound species vary in their ability to react and produce ground level ozone and reactivity scales can be used to link primary VOC pollutant species quantitatively with ground level ozone formation. This report examines the changes in emission inventory species distributions based on sector-specific reduction forecasts and compares the reactivities of these distributions using photochemical ozone creating potentials (POCP). Despite the variability in compound distributions and planned reductions from different sectors, reductions are forecast to change the fractional distributions of species and their reactivities for the overall U.K. emission inventory only slightly by the end of the century. The distribution of national emissions based on an atmospheric reactivity scale remains relatively stable because the largest mass reductions are made from sectors with distributions estimated to be similar to the overall distribution. There is also a balancing effect of making simultaneous reductions from source sectors with average ozone creating potentials which are higher and lower than that for the current national distribution.

The National Exposure Registry: procedures for establishing a registry of persons environmentally exposed to hazardous substances.

The Agency for Toxic Substances and Disease Registry has, as mandated in Superfund legislation, established the National Exposure Registry (NER). The purpose of the NER is to assess and evaluate the potential relationship between adverse health effects and environmental exposure for an exposed population, particularly the relationship between chronic health effects and long-term, low-level chemical exposures. The NER's primary goal is to facilitate epidemiology research by establishing multiple data bases (subregistries) that contain demographic, environmental, and health information on large populations exposed to selected chemicals. The Registry data mainly serve the purpose of being hypothesis-generating rather than hypothesis-testing. The NER is currently composed of subregistries of: (1) persons exposed to volatile organic compounds (VOCs)--a subset of registrants in whom trichloroethylene (TCE) is the primary VOC exposure, but others are present (N = 4,832), a subset in whom benzene is the primary VOC exposure (N = 1,142), and a subset in whom trichloroethane (TCA) and TCE are the highest VOC exposures (N = 3,666); and (2) persons with dioxin exposure (N = 250). Chromium and radioactive substances subregistries are planned.