Environ. Sei.
Technol. 1988,22,941-947 Oloffs, P. C.; Albright, L. J.; Szeto, S. Y.; Lau, J. J. Fish. Res. Board Can. 1973,30, 1619-1623. Newland, L. W.; Chesters, G.; Lee, G. F. J.-Water Pollut. Control Fed. 1969,41, R174-Rl88. Benezet, H. L.; Matsumura, F. Nature (London) 1973,243, 480-481. (86) Larsen, B. R.; Lokke, H.; Rasmussen, L. Oikos 1985, 44, 423-429. (87) Mazurek, M.; Simoneit, B. R. T. CRC Crit. Rev. Environ. Control 1986, 16, 1-140. (88) Minnesota Crop and Livestock Reporting Service General Farm Use of Pesticides-1971-1979; Minnesota and U.S. Department of Agriculture: Washington, DC, 1980.
Ulmann, E. Lindane: Monograph of a n Insecticide; Verlag K. Schillinger;Freiberg im Breisgau, 1972. Tanabe, S.; Tatsukawa, R.; Kawano, M.; Hidaka, H. J . Oceanogr. SOC.J p n . 1982, 38, 137-148.
Suryanauya,R. G.; Visweswariah, K.; Galindo, M.; Khan, A.; Majumder, S. K. Pesticides 1982, 16, 3-6. Tanabe, S.; Tatsukawa, R. J. Oceanogr. SOC.J p n . 1980,36, 217-226.
Oehme, M.; Mano, S. Fresenius' Z. Anal. Chem. 1984,319, 141-146.
U.S. International Trade Commission (1945-1982) S y n thetic Organic Chemicals: U.S. Production and Sales; U.S. International Trade Commission: Washington, DC, 1984. Boucher, F. R.; Lee, G. F. Environ. Sci. Technol. 1971,6, 538-543.
Sharom, M. S.; Miles, J. R. W.; Harris, C. R.; McEwen, F. L. Water Res. 1980, 14, 1095-1100. Metcalf, R. L.; Kapoor, I. P.; Lu, Pa-Y.;Schuth, C. K.; Sherman,P. EHP, Environ. Health Perspect 1973,4(June), 35-44.
Received for review M a y I , 1987. Accepted February 5, 1988. This research was supported in part by National Science Foundation Grant DEB 7922142 awarded to E . Gorham, D. Grigal, H . Wright, and S. Eisenreich and a University of Minnesota doctoral dissertation fellowship awarded to R.A.R.
Development and Evaluation of a Novel Gas and Particle Sampler for Semivolatile Chlorinated Organic Compounds in Ambient Air Douglas A. Lane,"9tN. Douglas Johnson,$ Sydney C. Barton,$ Gordon H. S. Thomas,$ and Wllllam H. Schroedert Environment Canada, Atmospheric Environment Service, 4905 Dufferin Street, Downsview, Ontario M3H 5T4, Canada, and Ontario Research Foundation, Sheridan Park Research Community, Mississauga, Ontario L5K 1B3, Canada
A prototype annular diffusion denuder inlet has been adapted to a dichotomous sampler for the collection of organic compounds which occur in both the gas and particulate phase. The inlet selectively removes and efficiently preconcentrates atmospheric vapor-phase components by molecular diffusion prior to the collection of the particulate phase (coarse and fine fractions) by filtration. Backup adsorbent cartridges collect any vapor-phase constituents which might volatilize from the collected particulate matter and submicron particles which might penetrate the filter media. Special techniques were developed for coating the annular denuder with solid adsorbents. Laboratory tests with lindane and hexachlorobenzene have demonstrated better than 98% trapping efficiency over a 24-h sampling period at contaminant concentrations representative of ambient air and under most simulated atmospheric conditions.
Introduction The potential adverse effects of small amounts of halogenated organic compounds to humans and to the environment continue to be a major concern due to the persistent occurrence and demonstrated toxicity of some species in natural ecosystems. The atmospheric transport and deposition of several classes of chlorinated organic compounds, such as the polychlorobiphenyls (PCBs) and pesticides, is regarded as an important pathway for the input of these contaminants to freshwater bodies such as the Great Lakes ( I , 2 ) , to the oceans (3, 4 ) , and even to the most remote regions of the planet (5-7). Both hexachlorobenzene (HCB) and lindane (y-hexachlorocyclohexane or y-HCH) are regularly detected in water surveillance programs (8)and in rainfall (9, 10). The vapor pressures (derived from solid-phase measurements) of these compounds (1.9E-05Torr at 20 "C for HCB and Environment Canada.
* Ontario Research Foundation. 0013-936X/88/0922-0941$01.50/0
3.263-05 Torr at 20 "C for lindane) suggest that they should exist primarily in the vapor phase under normal ambient atmospheric conditions (11). Although HCB production has declined in recent years, it still occurs as a byproduct or waste material in the production of numerous chemicals (12). Similarly, the production and use of lindane as an insecticide has decreased in North America, but extensive use continues in other countries (13, 14). In addition to direct industrial, commercial, agricultural, and residential emissions, evaporation from contaminated waters, soils, or vegetative surfaces is considered to be an important pathway whereby such compounds may enter the atmosphere (15,16)or reenter the atmosphere, for example, by processes such as volatilization or resuspension. Background concentrations in remote marine atmospheres are reported to be within a range of 0.03-0.23 ng/m3 for HCB (6,17) and 0.01-0.5 ng/m3 for lindane (6, 15,18). In urban and rural locales, HCB concentrations are reported to be within the range of 0.2-0.3 ng/m3 (19) while lindane concentrations are reported to be in the range of 0.02-7 ng/m3 (2, 15, 19,20). Higher concentrations of both compounds (micrograms per cubic meter) have been determined near specific industrial sources (21, 22) and in buildings with known sources (15, 23, 24). Although some data suggest that dry deposition of several trace organic substances is significantly greater than wet deposition (25), the deposition mechanisms for trace chlorinated compounds such as HCB and lindane are not well-known since the atmospheric distribution between the gaseous and particulate phases of these compounds is uncertain. Conventional sampling techniques, which utilize filters and backup adsorbents, may alter the gas/ particle distribution of these compounds during the sampling process since (i) the vapor-phase component may be adsorbed onto the particles collected on the filter or (ii) the components of the particle phase may be volatilized to the gas phase. The deviation of the measured gasphase/particle-phase partitioning of a compound from that
0 1988 American Chemical Society
Environ. Sci. Technol., Vol. 22, No. 8, 1988 941
MULTITUEE EVALUATION
SINGLE TUBE E VA L UAT IO N
MTD
l STD
K
'j A
17.5 Lpm AIR ( Temp. EL RH Controlled
*8 r0'4L -I-
16.7 L p m
nr'
A
U
U
PP S V D SM
= PRESSURE PUMP
SCRUBBERS =VENT =DIFFUSERS = SAMPLING MANIFOLD
T B R H = TEMPERATURE S RELATIVE HUM ID ITY SENSORS
STD = SINGLE TUBE DENUDER MTD i MULTITUEE DENUDER A 2 ADSOREER VP = VACUUM PUMP F = FLOWMETER WM = WATER MANOMETER
I
Flgure 1. Schematic diagram of the diffusion vapor generator and sampling manifold.
which occurred in the atmosphere depends upon both the ambient temperature and the vapor pressure of the compound at that temperature. Since computer models, which attempt to track the migration of pollutants through the environment, require a knowledge of the gas-phase/particle-phase partitioning of the contaminant under study, a more reliable sampling approach which will establish the true gas/particle distribution of contaminants in ambient air as well as provide information on this distribution as a function of particle size is required. Diffusion denuders have been used to remove gaseous SOz from air prior to the removal of particulate matter in an effort to reduce the sulfate interference (artifact) caused by the oxidation of SOz on the collected particulate matter (26, 27). In addition, diffusion denuders have been used to remove NH3 (28) and HN03 (29) in order to determine true atmospheric nitrate concentrations. The technique has also been applied to the determination of carbonaceous particulate matter by removing vapors such as those of phenanthrene and octadecane which could be retained on the filter (30). Under conditions of laminar flow in a diffusion denuder tube, the gaseous contaminants migrate to the wall of the tube by molecular diffusion while the particulate matter proceeds unimpeded through the tube to be collected subsequently on some filter medium. Thus, errors associated with the adsorption of gas-phase contaminants onto the trapped particles during sampling are avoided. Possanzini (31) has described an annular denuder which is reported to have a greater trapping efficiency for SO2 than would be predicted by the Gormley-Kennedy equation (32) for a cylindrical tube. The annular denuder configuration should also be more efficient for trapping organic compounds than a single denuder tube. The major objective of this study was to develop a diffusion denuder sampling system so that the vapor/ particle partition coefficients for high molecular weight 942
Environ. Sci. Technol., Vol. 22, No. 8, 1988
organochlorine compounds could be determined in ambient air and to evaluate the sampler performance with HCB and lindane as candidate target compounds.
Experimental Section The development of the diffusion denuder required numerous novel developments, each of which had to be carefully evaluated before the next stage of development could proceed. First, a vapor generator, capable of producing consistent, preset concentrations of both HCB and lindane for long (24-96-h) periods of time under known temperature and relative humidity conditions at a (dichotomous sampler) flow rate of 16.7 L/min, had to be produced and tested. Second, single-tube denuders were produced with a variety of coatings, and each coating was evaluated for its efficiency in removing the target compounds from a flowing gas stream. Once the optimum coating had been determined, a multitube, annular, diffusion denuder was then tested for its contaminant trapping efficiency and for the potential loss of particulate matter to the walls of the denuder. In order for the denuder to be useable in the field, a suitable, rugged prototype sampler was engineered. Vapor Generator. In order to generate the very low concentrations of HCB and/or lindane in air (0-10ng/m3) necessary to test the denuder under realistic conditions, a vapor generator utilizing diffusion tubes (33) was produced. The vapor generator was constructed entirely of solvent-cleaned and silanized glass and Teflon components and is shown schematically in Figure 1. Purified crystals of HCB and lindane were placed in separate vessels containing glass diffusion tubes. The concentration of the individual target compound in the gas flow was controlled by the temperature of the crystals, the length and diameter of the diffusion tube, and the volumetric flow rate of air past the tubes. To minimize condensation effects (of the HCB and lindane in the portion of the diffusion tube which
Train B (Reference I
Train A
Removable COP
.Viton
Clamp
Seal
T I
I
Bevelled Edge? /
Backup Adsortmr
I .Stainless Steel Band Holder \ Pyrex Shell ( 5 . 9 crn 0.D.)
70cm I
Dichotomous Sampler ( V~.tuaI Impactor I
Coated Annulor Pyrex Tubes
\ Flne Particle Filter ( ( 2 . 5 p n )
Coarse Particle
Backup Adsorbers
t
Threaded Connection
4
1.67 15 L / m h
Figure 2. Schematic showing a cross-sectional diagram of the annular diffusion denuder and a diagram of the gas and particle (GAP) sampler showing the denuder (train A) and the conventional sampler (train B).
resides in the air flow and which is cooled by the flow of air past the diffusion tube), the diffuser was maintained at a temperature approximately 5 OC below ambient temperature. The actual concentrations generated were determined by passing the entire airstream (16.7 L/min) through an adsorbent which was subsequently extracted and analyzed and by subsampling a portion of the airstream at the manifold. Adsorbers. Tenax GC (35/60 mesh) was selected for packed-bed adsorbent cartridges on the basis of its documented success in trapping HCB and lindane (19,34)and its suitability for either solvent extraction or thermal desorption. Two sizes of adsorbent tubes were used. Small tubes, 1.2 cm in diameter and containing 0.6 g of Tenax GC (4 cm long), were used to define the actual concentrations of the test substances delivered by the vapor generator. Large tubes, 4.5 cm in diameter and containing 7.3 g of Tenax GC (3.5 cm long), were used as backup adsorbents for the annular denuder. The Tenax adsorbent was held in the small tubes by glass wool plugs and was retained in the large tube by a coarse fritted glass disc. Glassware, end caps, and glass wool were cleaned by extraction with hexane. Between uses, the packed adsorbers were heat-cleaned for 35 h at 300 "C under a purge of prepurified nitrogen which had been passed through a train of adsorbers containing activated charcoal, Chromosorb, molecular sieves, Carbosieve, and Florisil. The Tenax adsorbent tubes were stored at 4O C for no longer than 1week prior to use and were frequently checked for possible contamination by the target compounds. The tubes were used numerous times but were monitored closely for residual contamination. Any cartridges which could not be cleaned by this method were discarded. Although the Tenax GC was observed to acquire a yellow color, neither the adsorptive properties nor the background
contamination levels were affected. Annular Denuder. An annular denuder was designed and fabricated with six concentric Pyrex glass tubes which were coated (on both sides) to a specific length with a binary, crushed Tepax/silicone gum (SE-54) coating. The theoretical denuder length was derived on the basis of calculations reported by Possanzini et al. (31). The denuder configuration (Figure 2) comprises 60 cm long Pyrex tubes held in place at each end by thin, stainless steel blades so that a gap of approximately 2 mm was maintained between the tube walls. The inlet of each tube was beveled to minimize particle losses, and the entire denuder was enclosed in a Pyrex shell (see Figure 2). At an airflow of 16.7 L/min, the average linear velocity through the denuder was calculated to be 23 cm/s. The residence time for a particle or molecule in a 55 cm coated denuder was 2.4 s. Denuder Coatings. Prior to evaluation of the chemical trapping efficiency of the diffusion denuder, tests were carried out on short (20 cm), single glass tubes to determine the most effective manner in which to coat the surface of the giass tubes with the proposed materials. After techniques were developed to apply the coatings, longer tubes (40 and 60 cm in length) were used to assess the chemical trapping efficiency of a single-tube denuder. Subsequently, a multitube (annular) denuder was fabricated, coated, and tested. Various materials were applied to the inside of 20 cm long, 5 mm i.d. Pyrex glass tubes. Three general types of denuder surface coatings were prepared and evaluated for their adsorption and desorption properties. These included (i) crushed Tenax GC (crushed at liquid nitrogen temperatures and sieved for particles finer than 200 mesh) and Florisil which were deposited onto a thin layer of sodium silicate; (ii) various silicone gums, such as OV-1 Environ. Sci. Technol., Vol. 22, No. 8 , 1988
943
and SE-54, dissolved in methylene chloride applied in coatings of 2-12 bm by rotating the tubes in a horizontal position while removing the solvent under vacuum (in some cases, di-tert-butyl peroxide was added to produce an even, temperature-stable, chemically bonded stationary phase); and (iii) crushed Tenax GC deposited onto a silicone gum. The trapping efficiency of a coated tube was investigated by drawing air containing known concentrations of the target species through the tube for a known time at a known flow rate. Backup adsorber tubes were used to trap any nonadsorbed organics. Of the three surface coating types assayed, the crushed Tenax on silicone gum proved to be the most effective and was, therefore, the method selected. Silicone gum (Supelco Canada Ltd.) in pesticide-grade methylene chloride (B.D.H.) solution was applied to all denuder tube surfaces by repeatedly filling the (vertically positioned) denuder to the desired height, removing the solution, and evaporating the remaining solvent under vacuum. The top 5 cm of the denuder, where a certain degree of turbulence might be expected, was left uncoated. This procedure was repeated 50 times in order to obtain an estimated 8 pm thick deposit of silicone gum on all surfaces within the denuder shell. To minimize particle loss by impaction, the coating material was removed from the tapered outlet of the denuder by dissolution in toluene. The denuder was then disassembled so that the tubes could be dusted on the inside and outside with powdered Tenax GC (Mandel Scientific Co.). Excess, nonadhering powder was removed under a flow of compressed nitrogen. Vapor removal efficiency tests were conducted for 24-h periods by connecting the denuder and two backup adsorbers to the manifold outlet of the vapor generator (Figure 1)so that the entire airstream passed through the denuder. Inlet vapor concentrations were monitored simultaneously by analysis of adsorbers connected at two manifold ports, and any breakthrough of the denuder was determined by analysis of the backup adsorbers. After use, the denuder was heat cleaned in a tube furnace at 300 "C. Experiments, in which the entire vapor generator and sampling devices were installed in a controlled environmental chamber, were conducted at various temperatures and relative humidities. The denuder was evaluated for potential aerosol loss by passing a known concentration of mixed submicron size sodium fluoride aerosol, from a (SCP Model 7330) fluid atomization aerosol generator equipped with a static charge equilibrator, through an assembled denuder. The flow rate through the denuder was maintained at 16.7 L/min, and the salt particles were trapped on preweighed microquartz filters located behind the denuder. The inlet aerosol concentration was determined by filtration of the stream without the denuder. The loss of aerosol was determined by the gravimetric difference between the two sets of filters and by confirmatory analysis of the fluoride content (by ion chromatography) of the filters and in water extracts of the denuder. After exposure to the target compounds, the denuder was regenerated in a 300 "C tube furnace. A 0.4 L/min flow of precleaned and preheated nitrogen purged the denuder tube of trapped organics in preparation for subsequent use. Analytical Methods. The Tenax GC from a small exposed cartridge was quantitatively transferred to a 10mL vial. A 5-mL aliquot of pesticide-grade hexane was added to the vial which was then sealed with a Teflon-lined silicone septum and an aluminum cap. The Tenax GC from a large cartridge was transferred to a 250-mL stop944
Environ.
Sci. Technol., Vol.
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pered flask and eluted with 60 mL of pesticide-grade hexane. After sonication in an ultrasonic bath for 1 min, the samples were periodically agitated over the next 30 min. A 5-pL aliquot of the extract was analyzed by gas chromatography and electron capture detection with a 63Ni detector. The column was a 2 m by 4 mm glass column packed with 80-100-mesh high-performance Chromosorb W coated with 3% OV-1 and 60% OV-215. An HP-5700A GC was operated isothermally at 190 "C with an injector temperature of 250 "C and a detector temperature of 350 "C. Five percent methane in argon gas flowing at 30 mL/min served as the carrier gas. Because relatively pure target compounds were used in this phase of the development of the sampler, there was less concern in selecting methods to address potential analytical interferences that could be anticipated to occur in real air samples. Nevertheless, refined techniques incorporating extract concentration, sample cleanup, and improved quantitation procedures have been developed for field measurements.
Results and Discussion Vapor Generator and Collection Methods. In testing the performance of the vapor generation technique, high diffusion rates were established in order to produce concentrations of 35 ng/m3 for HCB and 150 ng/m3 for yHCH. The mean concentrations determined from the tests were similar to those theoretically derived for diffusion systems of that particular flow and diffuser dimensions. To minimize surface losses at these and lower (down to approximately 0.1 ng/m3) concentrations, all glass surfaces were silanized, and Teflon transfer tubes were made as short as possible. Blank Tenax adsorbers that were analyzed to determine the effectiveness of the cleaning procedure showed that there was less than 0.5 ng of either target compound per gram of adsorbent. With very few exceptions, the target compounds were retained on the first of the two Tenax traps placed in series (see Figure 1). Recovery tests, performed after passing low concentrations of the compounds through the adsorption tubes, showed that extraction by hexane would remove 80 f 5% of the HCB and 85 f 5% of the y-HCH. All subsequent tests were normalized accordingly. Analysis of the second adsorbent tube not only provided information on collection efficiency of the packed adsorbent but also provided confirmation that the Tenax adsorbent was adequately cleaned. To approximate more closely the concentrations expected in the ambient air, vapor generation and recovery tests were performed at 2.5 and 0.7 ng/m3 for HCB and 10 and 1.0 ng/m3 for y-HCH. The results are shown in Table I. For each test, the vapor generator was operated for 24 h at a flow rate of 16.7 L/min (the dichotomous sampler flow rate). Series A tests were conducted to establish the performance characteristics of the vapor generator, to assess the reproducibility of tests on a day-to-day basis, and to determine whether or not there were variations from sampling port to sampling port. Series B tests were conducted at concentrations considered to be more representative of ambient concentrations in the general vicinity of a source of the target compounds were generally used in the evaluations of the denuder coating materials. In both series of tests, the mean of the measured values was close to the calculated concentration. The mean experimental value for HCB was almost identical with the calculated value, but the measured values for lindane were, on average, about 25% higher than expected. This discrepancy may be related to the uncertainty in the vapor pressure of lindane which was used in the calculations.
Table I. Vapor Generator Test Results test series
calcd concn, ng/m3 HCB Y-HCH
A B
2.4 0.6
7.5 0.8
HCB
measd concn at manifold ports, ng/m3 Y-HCH 10 (5 ports) [f36% (RSD), n = 341 1.0 (2 ports)b [f55% (RSD), n = 431
2.5 [f59% (RSD), n = 331" 0.7 [f51% (RSD), n = 431
" n is the number of measurements from all ports from 15 tests in series A and 20 tests in series E. bStudent's t test (a = 0.05) shows no significant difference between ports.
Table 11. Single Denuder Tube" Results: 24-h Removal Efficiency Tests
coating type sodium silicate Florisil/sodium silicate Tenax/sodium silicate silicone gum 2 pm thick 4 pm thick 8 pm thick 12 wm thick Tenax/silicone gum
no. of tests 1 2
7 2 1 2
6 2
average removal efficiency, % b HCB yHCH 0 47 100 f 0
9 39 49 72 f 15 100
0
56 98 f 5 26 74 83 94 f 6 100
"Denuder tube lengths of either 40 or 60 cm. bAverage inlet concentrations were 2.5 ng/m3 for HCB and 10 ng/m3 for yHCH.
The vapor pressure for lindane (3.263-05 Torr at 20 "C) reported by Spencer and Cliath (35)was used, but it is approximately 4 times greater than that reported elsewhere (36). Chemical interference in the analytical method was also a possibility but was not considered to be a significant factor. Daily variations of f 6 0 % were considered to be acceptable in view of the subnanogram per cubic meter concentrations being dealt with and since this uncertainty represents an accumulated experimental "error" of vapor generation, collection, extraction, and analysis of the constituents. Although there were minor interport variations in the measured concentrations, a Student's t test (applied to the series B tests) indicated that there were no significant differences between the various ports in the manifold. Concentrations taken at the manifold ports were the same as those obtained when the entire airstream of the generator was sampled. For the denuder performance evaluations, single-tube denuders were placed at the central port, and the average value, determined from measurements at the ports on either side, was used as the inlet concentration for the denuder port. Denuder Coating Evaluation. Various types of coatings on single Pyrex denuder tubes were evaluated for their efficiency in removing HCB and lindane from air drawn through the denuder tube from the manifold of the generator. Tenax cartridges were placed at the exit of the denuders to trap any components which passed through the denuder. Denuder tubes of 40 and 60 cm were prepared and were subjected to concentrations of 2.5 ng/m3 of HCB and 10 ng/m3 of y H C H for 24-h intervals. Table I1 summarizes the experimental results for the various denuder coatings that were evaluated. From the table, it can be seen that neither the sodium silicate nor the Florisil/sodium silicate coatings were effective a t removing the test compounds. On the other hand, almost complete removal occurred for the Tenax/ sodium silicate coated tube. Although this tube was excellent for trapping the compounds (there was no breakthrough from a 40-cm denuder tube even after a continuous 96 h of sampling), all attempts to regenerate the tubes
Table 111. Annular Denuder Results: 24-h Removal Efficiency Tests
denuder coating
denuder length, cm
Tenax/silicone gum silicone gum Tenax/silicone gum
40 55 55b
no, of tests
4 2
7
average removal efficiency, %' HCB yHCH 82 56 99 f 2
69 70 100 f 0
'Average inlet concentrations were 0.6 ng/m3 for HCB and 0.7 ng/m3 for y H C H at a flow rate of 16.7 L/min. bNo breakthrough after 96-h test.
by thermal desorption failed because the coating deteriorated completely at temperatures above 200 "C despite extended curing periods below this temperature. Evolution of water from the sodium silicate was thought to be the cause. In addition, the coating was easily washed away with water. This would mean that any tubes using this coating would have to be recoated after every use. To satisfy the requirement that the tubes be reuseable, other coatings were investigated. Various silicone gums (OV-1, and SE-54) and gum thicknesses (2-12 pm) were evaluated. As was expected, the trapping efficiency increased with gum thickness. An attempt to add a cross-linking agent (di-tert-butylperoxide) to the SE-54 failed to yield a more efficient coating. Substantial breakthrough occurred for the gum-coated denuder tubes during 48-h tests. A significant improvement was realized with the addition of crushed Tenax to the SE-54 coated tubes, and adherence of the Tenax to the SE-54was improved without the use of the cross-linking agent. The denuder could be rinsed with water without deteriorating the coating and with minimal loss of the Tenax. Annular Denuder Evaluation. Prototype annular denuders were prepared and coated with SE-54: one to 40 cm,iil length and mother to 55 cm in length. The Pyrex shell of the longer denuder was also coated with the SE-54; the shell of the shorter was not. As a final check of the necessity of adding the crushed Tenax, the denuders were tested for their trapping efficiency with and without the Tenax. The removal efficiency test results are shown in Table I11 for compound concentrations of 0.6 ng/m3. Significant breakthrough occurred for the annular denuder coated only with SE-54. Even when the Tenax was added, there was breakthrough for the 40-cm denuder. However, when the Tenax was added to the 55-cm denuder, there was no breakthrough even when the denuder was used for a continuous 96 h at a temperature of 25 OC and 35% relative humidity. As a further demonstration of the effectiveness of the coating, clean air was passed through the denuder for 24 h after the 96-h test. Neither of the test compounds was detected, indicating that the vapor-phase components could be retained effectively by the denuder surface. The performance of this denuder was evaluated over a range of temperature and humidity conditions. The results are reproduced in Table IV. Although practically comEnviron. Sci. Technol., Vol. 22, No. 8, 1988
945
Table IV. Annular Denuder Results at Various Temperatures and Relative Humidities: 24-h Removal Efficiency Tests" test conditions temp, OC RH, % 24-25 3 26 26 41 41 41
25-35* 11 82 82 26 82 82
inlet concn, ng/m3 HCB y H C H 0.6 0.4 0.6 0.4 0.6 1.9 0.6
0.6 1.1 0.7 0.6 1.0 2.0 1.3
removal efficiency, % HCB yHCH 99 f 2 100 98 100 60 83 89
100 f 0 100 100 100 18 9
trace
" Using the 55-cm Tenax/silicone gum coated denuder. bResults of seven tests shown in Table 111. Table V. Aerosol Penetration through the Denuder" average aerosol mass generated
average aerosol mass penetrating denuder
% loss in denuder
mean = 21.1 mg RSD = 7.2% no. of samples = 5
20.5 mg RSD = 4.4%
3
5
"Approximate aerosol size distribution: 70% 2.2 pm.
< 0.5 pm; 90%
