440
(13) (14)
(15) (16) (17) (18) (19)
Anal. Chem. 1984, 56,448-454 rinated Dioxins and Related Compounds"; Tucker, E. J., Young, A. L., Grey. A. P. Eds.: Plenum: New York. 1983. Crummet, W. B. Chemosphere 1983, 72, 429-446. Buser, H. R. Anal. Chem. 1979, 48. 1553-1557. Buser, H. R. Anal. Chem. 1977, 4 9 , 918-922. Buser, H. R.; Rappe, C. Anal. Chem. 1980, 52, 2257-2262. Buser, H. R. J . Chromatog. 1975, 774, 95-108. Kooke, R. M. M.; Lustenhouwer, J. W. A.; Olie, K.; Hutzinger, 0. Anal. Chem. 1981, 53, 481-463. Buser, H. R. Chemosphere 197% 8 , 251-257.
(20) Nestrick, T. J.; Lamparski, L. L.; Stehl, R. H. Anal. Chem. 1979, 57, 2273-2281. (21) Lamparski, L. L.; Nestrick, T. J. Chemosphere 1981, 70,3-18. (22) Schecter, A. Chemosphere 1983, 12, 869-880. (23) Buser, H. R. Chemosphere 1979, 8 , 415-424.
RECEIVED for review April 4, 1983. Resubmitted October 31, 1983. Accepted November 21, 1983.
Formaldehyde Surface Emission Monitor T. G.Matthews,* A. R. Hawthorne, C. R. Daffron, M. D. Corey, T. J. Reed, and J. M. Schrimsher
Instrumentation and Measurements Group, Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
A passlve surface emlsslon monltor has been developed for nondestructive measurement of formaldehyde (CH,O) emisslon rates from CH20 resin-contalnlng malerlals such as urea-formaldehyde foam lnsulatlon (UFFI) and pressed-wood products. EmRted CH,O Is sorbed by a planar dlstrlbutlon of 13X molecular sieve supported inside the monitor and analyzed by uslng a water-rlnse desorptlon, colorlmetrlc analysis procedure. A detectlon llmlt of ~ 0 . 0 2 5mg of CH,0/(m2 h) Is achleved wlth a 20.3 cm dlameter monltor and a 2-h collection period. Measurements of CH20 emlsslon rates from pressed-wood products and UFFI encased In slmulated wall panels show a strong correlation wlth reference chamber technlques. The surface monltor has been used to measure the CH20 emlsslon rate from Interior walls and floors In one UFFI and two non-UFFI homes. By appllcatlon of a simple single compartment model to predlct Indoor CH,O concentratlons from In situ CH20 emlsslon rate and tracer gas Inflltratlon rate measurements, a good correlation between the predlcted and measured CH20 concentratlons was achleved.
Formaldehyde-based resins are incorporated in a wide variety of construction and consumer products (1). Generic product lines include pressed-wood products, urea-formaldehyde foam insulation (UFFI), fiberglass products, and textiles. Exposures to temperature and water vapor concentration levels typical in indoor environments cause degradation of the CHzO resins and release of formaldehyde (CH20) gas. The potential impact of these emissions on indoor air quality is a subject of increased concern, especially with the current emphasis on energy-efficienthomes with reduced air-exchange rates ( 2 ) . Current field monitoring techniques for CHzO focus on the measurement of airborne CH20 concentrations and are generally inappropriate for in situ characterization of individual source emission rates (3-5). Available methods for source identification and measurement are also undesirable because they require the removal of samples for subsequent laboratory analysis (6). The cosmetic problems associated with a destructive sampling procedure can result in inadequate sampling to properly characterize the location and emission rates (ERs) of important CHzO emitters. In addition, unknown changes can occur in the CHzO ERs of specimens upon re0003-2700/84/0356-0448$01.50/0
moval from their original environment. Sample destructive techniques are also currently used for quality control measurements of CHzO emissions from CHzO resin-containing products (7, 8). For example, the 2-h desiccator test of the Hardwood Plywood Manufacturers Association, National Particleboard Association is commonly applied in the U.S. to particleboard and decorative paneling products used in mobile homes (7). Small cut specimens are placed inside a sealed desiccator for 2 h with an open dish of water to collect emitted CH20. Although the procedure is attractively simple to perform, there are several potential disadvantages. First, the destructive sampling protocol discourages the testing of adequate numbers of boards to properly characterize the distribution of CHzO ERs from each lot of product (9). Second, the small specimens expose an atypically large amount of edge surface area that must often be corrected by sealing the edges with paraffin (9). Third, the low CHzO collection rate of the water sorbent (due to limited exposure in a small dish) and large pressed-wood surface area (i.e., -0.18 m2) allows the buildup of CHzO in the atmosphere inside the desiccator. The elevated CHzO concentrations suppress the CHzO ER of the product in comparison to the CH20 ER that would be observed in typical domestic environments where CH20 concentrations are generally low (e.g., 0.01-0.25 ppm) (10). A passive formaldehyde surface emission monitor (FSEM) has been developed to address a broad need for semiquantitative, nondestructive measurement of CHzO ERs from CHzO resin-containing products. Potential applications include (1)in situ measurements of products incorporated in domestic environments, such as decorative paneling or UFFI that are openly accessible or covered by diffusion barriers and (2) a convenient quality control method for pressed-wood products that is selective to CHzO emission from the face of the product. The FSEM has been designed to closely simulate environmental chamber tests where the CHzO concentration is maintained at levels consistent with those in residential housing. EXPERIMENTAL SECTION Monitor Construction and Use. The FSEM is constructed from a 20 cm brass mechanical sieve (No. 20 mesh) and cover (Figure 1). A circular flange, 3.0 cm wide and 1.9 cm thick, is attached in a concentric manner to the bottom of the mesh container. The flange is fabricated from Plexiglas and 0.3 cm thick neoprene sponge gasket (ASTM D1056). The sorbent-testmedia 0 1984 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 3, MARCH 1984
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separation (distance “a” in Figure 1) is 2.3 cm. The cover is mechanically clamped to the mesh container to form an O-ring seal. The volume of the FSEM is 1.6 L. For horizontal operation of the FSEM, the sorbent, 13X molecular sieve, is sprinkled in a uniform spatial distribution on the screen of the mesh container. For vertical operation, the sorbent is loaded into a parallel array of seven wire mesh trays that is attached directly to the screen of the mesh container. A 10-g sample of molecular sieve is generally used. The cover is then sealed for the duration of a 2 h sampling period. An additional mass of -2 kg is applied against the top of the FSEM to seal the monitor against the test surface. In a vertical orientation this must be accomplished with a mechanical support apparatus such as an “L” bracket that is weighted to the floor and attached to the FSEM with a swivel joint. The analysis of the CHzO exposed sieve is performed by (1)water-rinse desorption of the CH20from the sieve, (2) filtration of the rinse solution, and (3) colorimetric determination of CH20by using the modified pararosaniline (PA) method of Miksch (11). A detailed protocol for the preparation and analysis of the molecular sieve sorbent and its application to the FSEM has been reported (12). Permeation Source. An environmental chamber controlled permeation source was developed to evaluate the dependence of the CHzO sampling rate of the FSEM on sorbent and physical design parameters. Unlike pressed-wood products or UFFI, the CH20ER of the permeation source was insensitive to age, position on the source, or environmental parameters such as temperature and humidity. As a result, a series of FSEM measurements using different sorbent masses or monitor designs could be performed with minimal variation in the CHzO ER of the emission source. The permeation source consisted of a sheet of 0.0025 cm thick semipermeablesilicone membrane (13)glued to a circular Plexiglas disk having 24 holes 1.8 cm in diameter. The holes were evenly spaced within a 0.032 m2 circular area, equal to the opening on the bottom of the FSEM. The permeation source was sealed to a chamber that was connected to a CHzO generation apparatus (3). The CHzOconcentration inside the chamber was monitored with a modified CEA instrument (14). A CHzO permeation rate of 0.20 f 0.014 mg of CHzO/(m2h) was achieved over a 0.032 m2 test area per ppm CH20 inside the chamber. A limited CHzO concentration range of 2 to 4 ppm was used. Pressed- Wood Product Measurements. Pressed-wood product samples were obtained both directly from manufacturers and from local commercial sources. The hardboard and plywood samples were constructed with phenol-formaldehyde resins. All other samples incorporated urea-formaldehyde resins. Upon arrival, the 1.2 X 2.4 m sheets were cut into one 0.6 X 1.2 m specimen for FSEM testing and numerous 0.25 X 0.25 m specimens (which were edge coated with paraffin) for environmental chamber testing. All specimens were conditioned at 23 A 2 “C, 50 10% relative humidity (RH), and C0.15 ppm CHzO for at least 2 weeks prior to FSEM or environmental chamber measurements. A lengthy conditioning period was required because the CHzO ER of most of the pressed-wood products was highly variable (i.e., >lo% change/day) for 1to 7 days following cutting and introduction into the conditioning chamber. Most products reached a near-steady-state CH20ER (i.e., 0.99) is observed between results for the two methods for the entire range of CHzO concentrations in the environmental chamber. The consistent increase in the intercept value with increasing CHzO concentration in the chamber is caused by an increasing fraction of the pressed-wood products that have reached a zero ER at the elevated CHzO concentrations. An alternative statistical analysis, which weights data points in an equal manner, is to calculate the average ratio of the CHzO ER determined with the FSEM and environmental chamber tests. Interpolating the chamber CHzO ER data to 0.05,0.1,0.2, and 0.4 ppm, the average ratio of the FSEM/
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chamber results is 0.73 f 0.08, 0.89 f 0.11, 1.15 f 0.24, and 1.35 f 0.38, respectively. (All detection limited data were rejected in these analyses.) The small differences between the average ratios of the FSEM/chamber results and the corresponding slopes (Table I) determined from the regression analyses are caused by the emphasis of the regression analyses on the data near the extremes of the measured CHzO ER range. The average ratios of the FSEM/chamber results indicate that for significant emitters, the FSEM most frequently simulated environmental chamber tests with a 0.1-0.2 ppm CHzO concentration inside the chamber. Direct measurements of the CH20 concentration inside the FSEM were not possible without significant perturbation of the near-static environment inside the monitor. A second comparison of the CHzO ER data determined by using the FSEM and environmental chamber methods for pressed-wood products employs a fixed NIL (m/h) for the chamber test. The N I L values of 0.5-1.5 m/h and 2.0-10 m/h are common for particleboard and decorative paneling products used in mobile homes and residential housing, respectively. The N I L values of 0.5 and 1.2 m/h are commonly used for large scale environmental chamber tests by industry in the U.S. Linear regression analyses for the FSEM ER data and the chamber ER data interpolated to N I L values of 0.5 to 7.5 m/h are given in Table 11. An excellent correlation (i.e., Pearson product moment correlation r > 0.99) is observed between the results of the two methods over the entire range of N I L values. The statistically unweighted averages of the ratios of the CHzO ER data determined with the FSEM and with the environmental chamber interpolated to N I L values of 0.5, 1.2, 2.5, 5.0, and 7.5 (m/h) are 1.74 f 0.67, 1.26 f 0.28, 1.02 f 0.25,0.86 f 0.21, and 0.79 f 0.22. The results of both
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 3, MARCH 1984
Table 111. FSEM Measurements of the CH,O ER from Surfaces with Highest Loading in Three Occupied Homes formaldehyde emission rate, mg/m2 h ) exterior gypsum interior gypsum board dwelling board wall wall and ceiling carpeted floor tiled floor
a
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Table IV. Comparison of Measured CH,O Concentrations in Three Homes with Levels Predicted from FSEM and Air Infiltration Rate Measurements estimated contribution to [CH,O], ppm air infiltration interior wall, carpeted tiled measd dwelling rate, k 1 exterior wall ceiling floor floor total tCH*Ol,PPm 1. non-UFFI' 0.33 i 0.08 0 0.04 i 0.02 0.04 f 0.01 0.01 t 0.01 0.02 i 0.02 0.01 i 0.01 0.15 + 0.05 2. UFFI 0.82 i 0.25 0.02 ?r 0.01 0 0.18 i 0.05 0.08 i 0.03 0.08 i 0.03 0.18 i 0.02 3. non-UFFI 1.1 i 0.07 0.06 i 0.04 0 0.24 i 0.10 0.06 t 0.04 0.12 i 0.08 a Urea-formaldehyde foam insulation. the linear regression and statistically unweighted ratio analyses indicate a near one-to-one correlation between the FSEM and the environmental chamber tests having high NIL values (e.g., 22.5 m/h). Measurements of UFFI Panels. The results of the intermethod comparison between the FSEM and airflow monitoring techniques for measurements of CH20ERs from five UFFI panels are presented in Figure 5. In contrast to the treatment of the pressed-wood product chamber data, no interpolation of the airflow monitoring data to fixed CH20 concentrations was required. Previous studies indicate that the CH20 E% from UFFI panels tend to maximize at sub 0.2 ppm concentrations (which were maintained during the current work) and become insensitive to variation in CH20 concentration (15). A significant variation in the CH20ERs of the UFFI panels was detected with both the FSEM and airflow monitoring methods between measurement periods. This is probably caused by changes in environmental conditions. The ranking of the 12/81,09/82 (set B), and 09/82 (set A) data sets in order of increasing CH20 ERs directly correlates with increasing laboratory temperatures from approximately 17 to 22 to 24 "C, respectively. An excellent (approximately one-to-one) correlation is observed between the results of the FSEM and airflow monitoring methods for all of the data taken during the three different measurement periods with different environmental conditions. The average ratio of the FSEM/airflow monitoring results is 1.1f 0.2. The ratio and the slope of 1.25 f 0.06 from the regression analysis (Figure 5) may be biased slightly higher than unity due to the presence of the flange on the monitor; both results are within one standard deviation of the ratio (i.e., 1.14 f 0.06) of the flanged/flangeless FSEM measurements of the UFFI panels. Field Measurements. An important goal of the preliminary field study was to test the utility of the FSEM for locating and ranking the important CHzO emission sources in homes. The results for one UFFI and two non-UFFI homes are presented in Table 111. In dwelling 1,no significant CH2O emission sources (i.e., >0.02 mg of CH20/(m2h)) were found. In dwelling 2, the strongest emitter was UFFI in the exterior walls. The strongest emitter in dwelling 3 was a combination of the underlayment and carpeting (these components could not be measured separately). In all three dwellings, floor tile was an effective diffusion barrier for CHzO emission from the underlayment. In dwellings 2 and 3, significant CH2O emissions were also measured from interior-partition gypsum board walls with empty wall cavities. This indicates the strong
sorptive and desorptive potential of construction materials having significant water content. Such products may behave as CHzO sinks at high CHzO gas concentrations and indirect CHzO sources a t low CH20 vapor concentrations. A second objective was a comparison of the measured CHzO concentrations with concentrations estimated from FSEM and air infiltration rate (AIF) measurements. Each dwelling was mathematically treated as a single compartment equal in volume to an average room in the home. The areas of the principal emitting surfaces, including the interior walls and ceiling, external walls, and carpeted and tiled floors, were estimated based upon their respective amounts in the main level of the home. The CH20 ER for the estimated UFFI component in dwelling 2 was reduced by 25% in accordance with the results of the regression analyses for all of the data from the UFFI panel study (Figure 5 ) . No additional correction factors were applied to the results of FSEM measurements taken on other emitting surfaces because the CHzO concentrations in the homes were all
