Reducing Indoor Air Formaldehyde Concentrations

Urea-formaldehyde resin bonded partlcleboard, medium density fiberboard and plywood paneling are used as flooring, wall paneling, for cabinet work and in furniture, and are present In almost every office, home and public building. If large quantities of these products are used In poorly ventilated spaces, high manufacturing quality control is necessary to avoid problems of latent formaldehyde release. Indoor air formaldehyde concentrations depend on the nature of the product, the product surface to air volume (loading) factor, temperature, humidity, age and product emission rates. Standard test methods are now available for measuring product emission rates that make It possible to predict the performance of UF-bonded pressed wood materials If use conditions and environmental parameters are known. Recent modifications In adhesive and board manufacturing parameters have made It possible to reduce formaldehyde emission significantly, and UF-bonded wood products are now capable of meeting indoor air quality standard levels of 0.1 ppm under almost all customary loading conditions.     

The influence of humidity on the emission of di-(2-ethylhexyl) phthalate (DEHP) from vinyl flooring in the emission cell “FLEC”

Asthma in children appears to be associated with both phthalate esters and dampness in buildings. An important question is whether the concentrations of phthalate esters correlate with dampness (expressed as relative humidity—RH) in indoor air. The objective was to study the influence of RH on the specific emission rate (SER) of di-(2-ethylhexyl)phthalate (DEHP) from one type of vinyl flooring in the well characterized Field and Laboratory Emission Cell (FLEC). The vinyl flooring with ca. 17% (w/w) DEHP as plasticizer was tested in 6 FLECs at 22 °C. The RH in the 6 FLECs was 10%, 30%, 50% (in triplicate) and 70%. The RH was changed after 248 d in 2 of the 50%-FLECs to 10% and 70%, and to 50% in the 10%-and 70%-FLECs. The data show that the SER of DEHP from vinyl flooring in FLECs during a 1 yr period is independent of the RH. A new physically based emission model for semivolatile organic compounds was found to be consistent with the experimental data and independent of the RH. The model helps to explain the RH results, because it appears that RH does not significantly influence any of the identified controlling mechanisms.     

The effects of ozone/limonene reactions on indoor secondary organic aerosols

An indoor air quality model was used to predict dynamic particle mass concentrations based on homogeneous chemical mechanisms and partitioning of semi-volatile products to particles. The ozone–limonene reaction mechanism was combined with gas-phase chemistry of common atmospheric organic and inorganic compounds and incorporated into the indoor air quality model. Experiments were conducted in an environmental chamber to investigate secondary particle formation resulting from ozone/limonene reactions. Experimental results indicate that significant fine particle growth occurs due to the interaction of ozone and limonene and subsequent intermediate by-products. Secondary particle mass concentrations were estimated from the measured particle size distribution. Predicted particle mass concentrations were in good agreement with experimental results—generally within ∼25% at steady-state conditions. Both experimental and predicted results suggest that air exchange rate plays a significant role in determining secondary fine particle levels in indoor environments. Secondary particle mass concentrations are predicted to increase substantially with lower air exchange rates, an interesting result given a continuing trend toward more energy efficient buildings. Lower air exchange rates also shifted the particle size distribution toward larger particle diameters. Secondary particle mass concentrations are also predicted to increase with higher outdoor ozone concentrations, higher outdoor particle concentrations, higher indoor limonene emission rates, and lower indoor temperatures.     

A Reexamination of the Ozone Limiting Approach to Estimating Short-Term NO2 Concentrations

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.

Implications: Based on the results of this study, the sink effects of these commonly used materials (conventional and “green” gypsum wallboards, “green” carpet) on indoor formaldehyde concentration could be estimated. The effects of relative humidity on the diffusion and partition coefficients of formaldehyde were found to differ for materials and for different humidity levels, indicating the need for further investigation of the mechanisms through which humidity effects take place.     

Effectiveness of photocatalytic filter for removing volatile organic compounds in the heating, ventilation, and air conditioning system

Nowadays, the heating, ventilation, and air conditioning (HVAC) system has been an important facility for maintaining indoor air quality. However, the primary function of typical HVAC systems is to control the temperature and humidity of the supply air. Most indoor air pollutants, such as volatile organic compounds (VOCs), cannot be removed by typical HVAC systems. Thus, some air handling units for removing VOCs should be added in typical HVAC systems. Among all of the air cleaning techniques used to remove indoor VOCs, photocatalytic oxidation is an attractive alternative technique for indoor air purification and deodorization. The objective of this research is to investigate the VOC removal efficiency of the photocatalytic filter in a HVAC system. Toluene and formaldehyde were chosen as the target pollutants. The experiments were conducted in a stainless steel chamber equipped with a simplified HVAC system. A mechanical filter coated with Degussa P25 titania photocatalyst and two commercial photocatalytic filters were used as the photocatalytic filters in this simplified HVAC system. The total air change rates were controlled at 0.5, 0.75, 1, 1.25, and 1.5 hr(-1), and the relative humidity (RH) was controlled at 30%, 50%, and 70%. The ultraviolet lamp used was a 4-W, ultraviolet-C (central wavelength at 254 nm) strip light bulb. The first-order decay constant of toluene and formaldehyde found in this study ranged from 0.381 to 1.01 hr(-1) under different total air change rates, from 0.34 to 0.433 hr(-1) under different RH, and from 0.381 to 0.433 hr(-1) for different photocatalytic filters.     

Effect of temperature and humidity on formaldehyde emissions in temporary housing units

The effect of temperature and humidity on formaldehyde emissions from samples collected from temporary housing units (THUs) was studied. The THUs were supplied by the U.S. Federal Emergency Management Administration (FEMA) to families that lost their homes in Louisiana and Mississippi during the Hurricane Katrina and Rita disasters. On the basis of a previous study, four of the composite wood surface materials that dominated contributions to indoor formaldehyde were selected to analyze the effects of temperature and humidity on the emission factors. Humidity equilibration experiments were carried out on two of the samples to determine how long the samples take to equilibrate with the surrounding environmental conditions. Small chamber experiments were then conducted to measure emission factors for the four surface materials at various temperature and humidity conditions. The samples were analyzed for formaldehyde via high-performance liquid chromatography. The experiments showed that increases in temperature or humidity contributed to an increase in emission factors. A linear regression model was built using the natural log of the percent relative humidity (RH) and inverse of temperature (in K) as independent variables and the natural log of emission factors as the dependent variable. The coefficients for the inverse of temperature and log RH with log emission factor were found to be statistically significant for all of the samples at the 95% confidence level. This study should assist in retrospectively estimating indoor formaldehyde exposure of occupants of THUs.     

Formaldehyde and carbon dioxide air concentrations and their relationship with indoor environmental factors in daycare centers

The aim of this study was to measure the air concentrations of carbon dioxide (CO₂) and formaldehyde (HCHO) in daycare centers to determine relevant influencing factors, including temperature, relative humidity (RH), type of facility, number of children, type of ventilation system, ventilation time, and air cleaning system. The authors measured HCHO, CO₂, temperature, and RH in the center of classrooms in 289 daycare centers. Spearman’s correlation and Mann–Whitney analyses were used to examine the relationships and differences in HCHO and CO₂ for varying temperatures, RH values, and categorical indoor environmental factors. There were no significant differences in the HCHO and CO₂ air concentrations with varying numbers of children, ventilation times, or ventilation and air cleaning system types. However, both the HCHO and CO₂ air concentrations were significantly different for varying RH values, which were divided into five categories (p < 0.001). Only the HCHO air concentrations were significantly different for varying temperatures, which were divided into five categories (p < 0.001). Significant correlations were found between HCHO air concentrations and the temperature (r = 0.35, p < 0.0001), RH (r = 0.51, p < 0.0001), and CO₂ (r = 0.36, p < 0.0001). The study results support maintaining an appropriate temperature and RH range for reducing airborne HCHO in daycare centers. Further research is needed to elucidate the precise mechanisms responsible for the relationships observed in this study.

Implications: Data from 289 daycare centers in Seoul, South Korea, indicate that HCHO concentrations show a positive correlation with indoor temperature and relative humidity. This indicates that keeping temperatures low will help keep HCHO concentrations low, by both a direct and an indirect effect, since low temperatures also cause low relative humidity.     

Effectiveness of Photocatalytic Filter for Removing Volatile Organic Compounds in the Heating,Ventilation, and Air Conditioning System

Abstract

Nowadays, the heating, ventilation, and air conditioning (HVAC) system has been an important facility for maintaining indoor air quality. However, the primary function of typical HVAC systems is to control the temperature and humidity of the supply air. Most indoor air pollutants, such as volatile organic compounds (VOCs), cannot be removed by typical HVAC systems. Thus, some air handling units for removing VOCs should be added in typical HVAC systems. Among all of the air cleaning techniques used to remove indoor VOCs, photocatalytic oxidation is an attractive alternative technique for indoor air purification and deodorization. The objective of this research is to investigate the VOC removal efficiency of the photocatalytic filter in a HVAC system. Toluene and formaldehyde were chosen as the target pollutants. The experiments were conducted in a stainless steel chamber equipped with a simplified HVAC system. A mechanical filter coated with Degussa P25 titania photocatalyst and two commercial photocatalytic filters were used as the photo-catalytic filters in this simplified HVAC system. The total air change rates were controlled at 0.5, 0.75, 1, 1.25, and 1.5 hr^?1, and the relative humidity (RH) was controlled at 30%, 50%, and 70%. The ultraviolet lamp used was a 4-W, ultraviolet-C (central wavelength at 254 nm) strip light bulb. The first-order decay constant of toluene and form-aldehyde found in this study ranged from 0.381 to 1.01 hr^?1 under different total air change rates, from 0.34 to 0.433 hr^?1 under different RH, and from 0.381 to 0.433 hr^?1 for different photocatalytic filters.     

Emission rates of chlorinated volatile organics from new and used consumer products found during vapor intrusion investigations: Impact on indoor air concentrations

Consumer products can emit chlorinated volatile organic compounds (CVOCs) that complicate vapor intrusion (VI) assessments. Assessment protocols acknowledge the need to remove these products during VI investigations, but they can be problematic to identify and locate. Predicting if the products cause detectable air concentrations is also difficult since emission rate information is limited and can vary with product use and age. In this study, the emission rates of 1,2-dichloroethane, trichloroethene, tetrachloroethene, and carbon tetrachloride from four consumer products identified as indoor sources during VI field investigations were measured under laboratory conditions using a flow through system. Emissions of PCE from an adhesive container tube ranged from 1.33 ± 1.13 μg/min (unopened) to 23.9 ± 2.93 μg/min (previously opened). The laboratory-measured emission rates were used to estimate indoor air concentrations, which were then compared to concentrations measured after the products placed were into an actual residence. The estimated and measured indoor air concentrations were generally comparable, showing that emission rate information can be used to determine the relative impact of internal CVOC sources.     

Volatile organic compound concentrations, emission rates, and source apportionment in newly-built apartments at pre-occupancy stage

The present study investigated the indoor concentrations of selected volatile organic compounds (VOCs) and formaldehyde and their indoor emission characteristics in newly-built apartments at the pre-occupancy stage. In total, 107 apartments were surveyed for indoor and outdoor VOC concentrations in two metropolitan cities and one rural area in Korea. A mass balanced model was used to estimate surface area-specific emission rates of individual VOCs and formaldehyde. Seven (benzene, ethyl benzene, toluene, m,p-xylene, o-xylene, n-hexane, and n-heptane) of 40 target compounds were detectable in all indoor air samples, whereas the first five were detected in all outdoor air samples. Formaldehyde was also predominant in the indoor air samples, with a high detection frequency of 96%. The indoor concentrations were significantly higher than the outdoor concentrations for aromatics, alcohols, terpenes, and ketones. However, six halogenated VOCs exhibited similar concentrations for indoor and outdoor air samples, suggesting that they are not major components emitted from building materials. It was also suggested that a certain portion of the apartments surveyed were constructed by not following the Korean Ministry of Environment guidelines for formaldehyde emissions. Toluene exhibited the highest emission rate with a median value of 138 μg m⁻² h⁻¹. The target compounds with median emission rates greater than 20 μg m⁻² h⁻¹ were toluene, 1-propanol, formaldehyde, and 2-butanone. The wood panels/vinyl floor coverings were the largest indoor pollutant source, followed by floorings, wall coverings, adhesives, and paints. The wood panels/vinyl floor coverings contributed nearly three times more to indoor VOC concentrations than paints.     

Adsorption and desorption of selected VOCs in dust collected on air filters

Adsorption and desorption properties of the dust accumulated on air filters were examined by using a small-scale test apparatus with model compounds. The dust samples were loaded with the model compounds either by adsorption from a constant concentration in air flow or by direct injection into the dust. Desorption was measured at three different relative humidities of air (4–5%, 40–50%, 70–80%). Results indicated that constant relative humidity (RH) of air did not affect the rate of desorption in the test conditions. However, an increase in humidity substantially increased desorption of the model compounds. Similar results were obtained when experiments were conducted using dirty filters without added model compounds. In addition, emission products from clean and dusty filter materials were analyzed at two temperatures (50°C and 100°C) by using an automatic thermodesorption device. The main compounds released were carboxylic acids, aldehydes and terpenes. The emission profiles were similar for the pre-filters and main filters, but the emissions were higher from pre-filters than from the main filters. This result is consistent with the earlier findings of higher odor emissions from pre-filters.     

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

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.     

Impact of Indoor Environmental Parameters on Formaldehyde Concentrations in Unoccupied Research Houses

An environmental parameters study has examined the impact of indoor temperature (T) and relative humidity (RH) levels on formaldehyde (CH₂O) concentrations inside two unoccupied research houses where the primary CH₂O emitter is particleboard underlayment. The data were fit to a simple three-term, steady state model describing the T and RH dependence of CH₂O concentration in a single compartment with a single CH₂O emitter. The model incorporates an Arrhenius T dependence and a nonlinear RH dependence of the CH₂O vapor concentration within the solid CH₂O emitter. The RH dependence is based on Freundlich's theory of the adsorption of water vapor on solid surfaces. The model is used to estimate potential seasonal variation in CH₂O concentrations under specified experimental conditions inside the research houses. The modeled results indicate six- to ninefold variation between 18°C, 20% RH and 32°C, 80% RH, simulating potential winter/summer conditions with minimal indoor climate control. In comparison, Indoor conditions ranging from 20°C, 30% RH to 26°C, 60% RH yielded approximate two- to fourfold fluctuations in CH₂O concentration.

The research house data were also used to evaluate the limitations and applicability of more complex five-term models developed from small-scale chamber studies of the environmental dependence of CH₂O emissions from particleboard underlayment. These models also incorporate a linear T and RH dependence of the CH₂O transport rate through the CH₂O emitter in addition to the T and RH dependence of the CH₂O concentration within the emitter. Good correlation is observed between the results of the research house studies and 1) a selected (i.e., single) underlayment model over a broad range of environmental conditions and 2) a combined underlayment model over a restricted range of environmental conditions.     

环境测试舱自吸附甲醛重释放规律与影响因素研究

广泛用于板材污染物释放量测试、空气净化产品净化效果测试等实验中的环境测试舱,往往由于其内壁黏附性杂质而对目标测试物产生不可忽视的自吸附作用,自吸附污染物将作为二次释放源出现重释放,研究目标测试物的自吸附消耗量及重释放规律,探索有效控制措施,有利于对环境测试舱实验应用及室内污染控制提出指导性实际意义。分别选取0.2%甲醛溶液、大芯板作为同一自制玻璃环境测试舱2期实验(I期、Ⅱ期)的不同甲醛释放源,通过近90 d追踪测试,经不同释放源、不同控制条件下舱内壁自吸附甲醛的多次重释放实验,结合非线性拟合分析方法,总结出舱内壁自吸附甲醛重释放甲醛浓度变化符合一阶递增指数函数:y=A1×exp(-x/t1)+y0,(A1<0、t1>0)。曲线参数y0值可用于评价实验条件下测试舱内自吸附甲醛残余量;y0值与环境舱舱体材质、环境温湿度、舱外甲醛浓度及空气交换手段有关,而与释放源及其释放平衡浓度高低无明显关系。大开舱门短时间抽气式空气交换对舱内自吸附甲醛残余有适度清除效果,使y0值降低,同时有利于再次平衡状态的快速建立;而长时间的无动力空气交换,或者自来水洗及去离子水洗等处理手段对舱内壁自吸附甲醛残余无明显清除作用。     

Indoor and outdoor air quality investigation at schools in Hong Kong

Five classrooms in Hong Kong (HK), air-conditioned or ceiling fans ventilated, were chosen for investigation of indoor and outdoor air quality. Parameters such as temperature, relative humidity (RH), carbon dioxide (CO2), sulphur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), respirable particulate matter (PM10), formaldehyde (HCHO), and total bacteria counts were monitored indoors and outdoors simultaneously. The average respirable particulate matter concentrations were higher than the HK Objective, and the maximum indoor PM10 level exceeded 1000 microg/m3. Indoor CO2 concentrations often exceeded 1000 microl/l in air-conditioning and ceiling fan classrooms, indicating inadequate ventilation. Maximum indoor CO2 level reached 5900 microl/l during class at the classroom with cooling tower ventilation. Increasing the rate of ventilation or implementation of breaks between classes is recommended to alleviate the high CO2 level. Other pollution parameters measured in this study complied with the standards. The two most important classroom air quality problems in Hong Kong were PM10 and CO2 levels.     

Heterogeneous photocatalysis of aromatic and chlorinated volatile organic compounds (VOCs) for non-occupational indoor air application

The current study evaluated the technical feasibility of applying TiO2 photocatalysis to the removal of low-ppb concentrations of volatile organic compounds (VOCs) commonly associated with non-occupational indoor air quality issues. A series of experiments was conducted to evaluate five parameters (relative humidity (RH), hydraulic diameter (HD), feeding type (FT) for VOCs, photocatalytic oxidation (PCO) reactor material (RM), and inlet port size (IPS) of PCO reactor) in relation to the PCO destruction efficiencies of the selected target VOCs. None of the target VOCs exhibited any significant dependence on the RH, which is inconsistent with a previous study where, under conditions of low humidity and a ppm toluene inlet level, a drop in the PCO efficiency was reported with a decreasing humidity. However, the other four parameters (HD, RM, FT, and IPS) were found to be important for better VOC removal efficiencies as regards the application of TiO2 photocatalytic technology for cleansing non-occupational indoor air. The PCO destruction of VOCs at concentrations associated with non-occupational indoor air quality issues was up to nearly 100%, and the CO generated during PCO was a negligible addition to indoor CO levels. Accordingly, a PCO reactor would appear to be an important tool in the effort to improve non-occupational indoor air quality.     

Evaluation of a Test Method for Measuring Indoor Air Emissions from Dry-Process Photocopiers

ABSTRACT

A large chamber test method for measuring indoor air emissions from office equipment was developed, evaluated, and revised based on the initial testing of four dry-process photocopiers. Because all chambers may not necessarily produce similar results (e.g., due to differences in sink effects, temperature and humidity control, air exchange, pollutant monitoring, and measurement biases), a preliminary four-laboratory evaluation of the revised test method was conducted. To minimize variability, the evaluation used a single dry-process photocopier that was shipped to each of the four laboratories along with supplies (i.e., toner and paper).

The results of this preliminary four-laboratory evaluation demonstrate that the test method was used successfully in the different chambers to measure emissions from dry-process photocopiers. Differences in chamber design and construction appeared to have had minimal effect on the results for the volatile organic compounds (VOCs). Perhaps more important than the chamber itself is the sample analysis as identified by duplicate samples that were analyzed by a different laboratory. Percent relative standard deviation (%RSD) was used to provide a simplistic view of interlaboratory precision for this evaluation. Excluding problems with suspected analytical bias observed from one of the laboratories, the precision was excellent for the VOCs with RSDs of less than 10% in most cases. Less precision was observed among the laboratories for aldehydes/ketones (RSD of 23.2% for formaldehyde). The precision for ozone emission rates among three of the laboratories was excellent (RSD of 7.9%), but emission rates measured at the fourth laboratory were much higher.     

Models for estimating organic emissions from building materials: Formaldehyde example

One important source of chronic exposure to low levels of organic compounds in the indoor environment is emissions from building materials. Because removal of offending products may be costly or otherwise impractical, it is important that the emissions of organic pollutants be understood prior to incorporation of these materials into buildings. Once the organic pollutants of concern are identified, based on potential health effects and emission potential from the building material, it is necessary that an emission model be developed to predict the behavior of emission rates under various indoor conditions. Examples of the type of requirements that must be addressed in developing models for estimating organic emissions from building materials into the indoor environment are presented. Important factors include the products' characteristic source strengths at standard test conditions, impact of variations in environmental conditions (such as temperature and humidity), concentrations of the modeled organic pollutants in indoor environments and product ages. Ideally, emission models should have physical/chemical bases so that the important physical factors can be identified and their relative importance quantified. Although a universal model describing organic emissions from all building materials may not be feasible due to the tremendous variety of organic products and building materials in use, the most studied of the volatile organic compounds from building materials, formaldehyde, is used to illustrate an approach to the development of a specific model for organic emissions.     

Influence of air flow rate on emission of DEHP from vinyl flooring in the emission cell FLEC: Measurements and CFD simulation

The emission of di-(2-ethylhexyl)phthalate (DEHP) from one type of vinyl flooring with ～15% (w/w) DEHP as plasticizer was measured at 22 °C in five FLECs + one blank FLEC (Field and Laboratory Emission Cell). Initially, the flow through all FLECs was 450 ml min^?1. After 689 days the flows were changed to 1000 ml min^?1, 1600 ml min^?1, 2300 ml min^?1, and 3000 ml min^?1, respectively, in four FLECs, and kept at 450 ml min^?1 in one FLEC. Air samples were collected from the effluent air at regular intervals. After 1190 days the experiments were terminated and the interior surfaces of all six FLECs were rinsed with methanol to estimate the internal surface concentrations of DEHP. The DEHP air concentration and specific emission rate (SER) at steady state was estimated for the five different flow rates. The steady-state concentrations decreased slightly with increasing air flow with only the two highest flow rates resulting in significantly lower concentrations. In contrast, the SERs increased significantly. Despite large variation, the internal surface concentrations appeared to decrease slightly with increasing FLEC flow. Computational fluid dynamic (CFD) simulations suggest that the interior gas and surface concentrations were roughly uniform for the low flow case (450 ml min^?1), under which, the partitioning between the FLEC internal surface and chamber air was examined. Although paired t-tests showed no difference between CFD and experimental results for DEHP air concentrations and SERs at steady-state conditions, CFD indicated that the experimental DEHP surface concentrations in the FLECs were underestimated. In conclusion, the experiments showed that the emission of DEHP from vinyl flooring is subject to “external” control and that the SER is strongly and positively dependent on the air exchange rate. However, the increased SER almost compensates for the decrease in gas-phase concentration caused by the increased air exchange.     

Changes in indoor pollutants since the 1950s

Over the past half-century there have been major changes in building materials and consumer products used indoors. Composite-wood, synthetic carpets, polymeric flooring, foam cushioning, plastic items and scented cleaning agents have become ubiquitous. The same is true for mechanical and electrical appliances such as washer/dryers, TVs and computers. These materials and products emit an array of chemicals including solvents, unreacted monomers, and additives. The consequent changes in emission profiles for indoor pollutants have been accompanied by modifications in building operations. Residences and non-residences are less ventilated than they were decades ago. Air-conditioned buildings are more numerous, especially in certain parts of the world. Most of these recirculate a high fraction of their air. The personal habits of building occupants, including the fraction who smoke indoors, have also changed. Taken together, these changes have altered the kind and concentrations of chemicals that occupants are exposed to in their homes, workplaces and schools. Since the 1950s, levels of certain indoor pollutants (e.g., formaldehyde, aromatic and chlorinated solvents, chlorinated pesticides, PCBs) have increased and then decreased. Levels of other indoor pollutants have increased and remain high (e.g., phthalate esters, brominated flame-retardants, nonionic surfactants and their degradation products). Many of the chemicals presently found in indoor environments, as well as in the blood and urine of occupants, were not present 50 years ago. Given the public's exposure to such species, there would be exceptional value in monitoring networks that provided cross-sectional and longitudinal information regarding pollutants found in representative buildings.