Environ. Sci. Technol. 1994, 28, 655-661
High-Volume Air Sampler for Particle and Gas Sampling. 2. Use of Backup Filters To Correct for the Adsorption of Gas-Phase Polycyclic Aromatic Hydrocarbons to the Front Filter Kenneth M. Hartt and James F. Pankow’ Department of Environmental Science and Engineering, Oregon Graduate Institute, P.O. Box 9 1000, Poiland, Oregon 97291-1000
Atmospheric polycyclic aromatic hydrocarbon (PAH) levels were measured to determine the degree to which the adsorption of gaseous PAHs to filters can cause artifacts in the differentiation of the gaseous and particulate fractions. Two filterlsorbent samplers were used. In the first sampler, a quartz fiber filter (QFF) and a second backup QFF were used. In the second sampler, a Teflon membrane filter (TMF) and a backup QFF were used. The amounts of material on the backup QFFs in the two samplers provided two estimates of the amounts of gasphase adsorption to the front QFF in the first sampler and allowed corrections for gas adsorption to that QFF. The corrections indicated that gas adsorption to a front QFF in a conventional high-volume sampler would have caused overestimation of the partitioning parameter (Fi TSP)/A by a factor of as much as 1.2-1.6, where F/A is the particle/gas ratio for a given compound and TSP is the total suspended particulate matter concentration (pg/ m3). The sampler with the TMF gave values for (F/TSP)/A that were similar to the corrected QFF values.
(4)and (2) F and A have been measured accurately. In fact, we know that (1)sorption equilibrium is not always present in the atmosphere and (2) during any given sampling event, various artifacts inherent in the sampling methods used can cause measured values of A and F to differ from their actual values in the atmosphere. The manner in which gadparticle equilibrium is attained has been considered by Rounds and Pankow (5) and Rounds et al. (6). This paper will consider how one might correct for one type of sampling artifact encountered when using filter/ adsorbent-type samplers. Specifically, for PAHs, we will examine the overestimation of F values and the underestimation of A values as due to gas sorption to filters. Although gas-denudedfiltedadsorbent samplers attempt to avoid this problem by removing SOCs from the gas phase before the particles reach the filter (e.g., ref 7), denuder-based samplers have their own problems. Indeed, in the denuder section of such a sampler, neither 100% efficient gas collection nor 0 % ’ efficient particle collection can ever be achieved. Effects of Filters o n Measured Values of F and A
Introduction
Present address: 3M Corporate Research Laboratories, 3M Center, 201-15-26, St. Paul, M N 55144.
Volatilization Losses. Loss by uolatilization from a filter was the first artifact mechanism to receive attention by researchers using filter/sorbent samplers. Often referred to as “blow off“, volatilization can be caused by two distinct mechanisms. First, due to the pressure gradient that exists through a filter, particles deep within the filter will be exposed to gas-phase concentrations of the various organic compounds that are lower than at the front of the filter (8). Compounds will therefore tend to be stripped from the filtered particles and then collected on the gassampling sorbent downstream of the filter. This will always cause F values to be underestimated and A values to be overestimated. Secondly, volatilization can occur during a sampling event if contamination levels decrease or if the temperature increases. These changes will cause the partitioning to be shifted in favor of the gas phase, and organic compounds will desorb from the collected particles. The F values (this time as volume averages), will again be underestimated, and the A values (also as volume averages) will be overestimated. (We note that it is also possible that concentration increases and temperature decreases can occur during a sampling event, causing shifts in the partitioning that favor the collected particles; the volume-averaged F values will then be overestimated, and the volume-averageA values will be underestimated.) The simple fact that SOCs on filtered particles are capable of being desorbed to the gas phase when clean air or nitrogen is passed through a loaded glass fiber filter (GFF) is well established (6, 9-18). Several researchers have therefore proposed that the filter should be replaced frequently during a given sampling event (13,15, 16) so
0 1994 American Chemical Society
Environ. Sci. Technol., Vol. 28, No. 4, 1994 655
General. A compound- and temperature-dependent partitioning constant that has been found to be very useful in the study of gas/particle partitioning in the atmosphere is (1-3)
Kp = FITSP A
(1)
where A is the concentration of the compound of interest in the gas phase (ng/m3),F is its concentration associated with the suspended particles (ng/m3),and TSP is the total suspended particulate matter concentration (pg/m3). Kp gives the ratio of the compound‘s thermodynamic activity in/on the particulate matter (FITSP,ng/pg) to that in the gas phase ( A , ng/m3). Gas/particle partitioning is of greatest interest for compounds with intermediate volatility: such compounds can be present to a significant degree in both phases. These semi-volatile organic compounds (SOCs) have pure compound vapor pressures in the range 10-8-10-2 Torr (10-5.g-100JPa). SOCs of interest include many polycyclic aromatic hydrocarbons (PAHs) as well as numerous organochlorine compounds. SinceKpis a thermodynamic partition coefficient, using the symbol Kp to represent a value of (F/TSP)/A carries with it the assumptions that (1) the atmospheric values of F and A are equilibrium concentrations, with 100% of the value of F available for exchange with the gas phase ~~
~~
* Corresponding author. f
0013-936X/94/0928-0655$04.50/0
that collected particles will only be exposed to the concentration and temperature conditions under which they were initially filtered. When results for PAHs obtained using this approach gave higher F values and lower A values than those found using a single filter over the same 24-h sampling interval, Van Vaeck et al. (13) concluded that volatilization losses were indeed important for SOCs during urban sampling. In a similar manner, Appel et al. (19) measured an average of 21% more filterable total organic carbon (OC)in seven consecutive, 2-h samples than in one corresponding 14-h sample. Degradation reactions involving ozone and other reactive gases in the sample stream can lower the mass amounts of reactive compounds on filters and also on the sorbent beds downstream of the filters (15-18). However, even if degradation reactions on a filter can be ruled out (or corrected for),then the finding of more filterable organics on a series of consecutive filters than on a single filter sample for the same overall sampling period does not necessarily implicate volatilization losses as the cause. Indeed, sorption to the filters from the gas phase may have occurred (20, 21). Sorption of Gas-Phase Compounds. Like the particles making up the TSP in the atmosphere, air filters themselves possess surface area to which gaseous SOCs can adsorb. Sorption of gas-phase compounds to filter surfaces will tend to make the measured values of F artificially high and the measured values of A artificially Iow. This will tend to make the measured values of (F/ TSP)/A artificially high. Moreover, placing a fresh, clean filter surface into an air sample stream at frequent intervals for the purposes of minimizing volatilization losses [as by Van Vaeck et al. (13)] will increase the amounts of individual gaseous SOCs that adsorb directly to the surface area of the filters. This will accentuate the filter sorption artifact. The filter sorption artifact is therefore an explanation for at least a portion of the increases in the filterable amounts that Van Vaeck et al. (13)ascribed to volatilization. In a similar manner, frequent filter changes will cause measured values of total filterable OC to be artificially high; only a relatively small artifact would be needed for each of the seven subsamples taken by Appel et al. (7) in order to account for the overall increase of 21% in filterable OC. Ligocki and Pankow (20) have suggested using a backup filter to provide a measure of the amount of gaseous material that adsorbs to the front filter. During sampling in a suburban area, McDow and Huntzicker (22) found that when two quartz fiber filters (QFFs) were used in series, the total OC concentration on the backup QFF was -1/2 that found on a backup QFF behind a Teflon membrane filter (TMF). Since a TMF has 1/5 the surface area of a QFF of the same area, they concluded that (1)the TMF was causing less depletion of the gas-phase organiccompounds than the QFF; (2) higher gas-phase concentrations of the organic compounds were therefore available for adsorption to the QFF behind the TMF; and (3) so when using a single filter sampler, F values for organic compounds will be more accurately determined using a TMF than using a GFF or a QFF. Avoiding Filter-Related Artifacts. Based on the above discussion, it is clear that when using filtedadsorbent samplers, one needs to consider the following: (1) the possibility of exchanges between the collected particles and the in-coming gas phase (e.g.,volatilization) and (2)
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Environ. Scl. Technol., Vol. 28, No. 4, 1994
flow F1 F2 A1
A2
Sampler 1 QuaWQuattz (QQ) sampler
Flow
J M F4
TMF
backup QR
A3
Potyurethane Foam Sheet
I
to Tenax midges
A4
I
sampler 2 TeflonlQuartr (TQ)sampler Figure 1. Schematic diagrams of quartz/quartz (QQ) sampler and Teflon/quartz (TQ) sampler.
gas adsorption to the filter. Volatilization losses can be minimized by keeping sampling times short so as to reduce the fluctuations in temperature and concentration during sampling. However, doing so increases the sorptive importance of the filter relative to the collected TSP. In this work, we seek to determine the effectiveness with which gas adsorption to filters can be (1)minimized by filtering with a TMF and (2) corrected for by using a backup filter to estimate compound-dependent corrections for the values of F measured on a front filter. Experimental Section
Two identical filtedadsorbent air samplers were used. The sampler design is described elsewhere (23,24). Briefly, it is of the high-volume type and can be used with 20 X 25 cm GFFs, QFFs, or TMFs. Two parallel gas sampling channels are downstream of the filter section. One stream at 1.4m3/min uses two 1.27-cm-thick polyurethane foam (PUF) sheets (PUFSs) for the less volatile SOCs, and the other at -600 mL/min uses cartridges of Tenax-TA for the more volatile compounds. The QQ sampler was used with a QFF followed by a backup QFF. As indicated in Figure 1,the front filter in the QQ sampler is abbreviated as F1; the backup filter is abbreviated as F2. In the TQ sampler, the front filter was a TMF (F3) followed by a
-
Table 1. Temperature (K), TSP (pg/ma), log p i (Torr), and Measured Values of log (F/TSP)/A As Calculated by Four Methods, qu, tef, qct, and qo, log (FITSP)IA date
temp (W
TSP (pglm3)
July 20,1988
295
65
July 26,1988
304
58
August 7,1988
292
29
August 19,1988
293
36
August 31,1988
291
55
November 17,1988
281
34
November 23,1988
282
15
November 29,1988
284
81
a
compound phenanthrene fluoranthene PVene fluoranthene PVene chrysene fluoranthene pyrene fluoranthene pwne chrysene fluoranthene PYene benz[a] anthracene phenanthrene fluoranthene PVene benz[alanthracene phenanthrene fluoranthene pyrene phenanthrene anthracene fluoranthene PFene
1% P;. -3.41 -4.33 -4.62 -3.98 -4.17 -5.41 -4.59 -4.78 -4.53 -4.73 -6.05 -4.64 -4.83 -6.14 -4.08 -5.18 -5.39 -6.77 -4.03 -5.13 -5.33 -3.93 -3.96 -5.02 -5.22
w
tef
qct
qcq
-3.45 -2.68 -2.47 -2.89 -2.59 -1.43 -2.15 -2.01 -2.70 -2.57 -1.33 -2.81 -2.75 -1.83 -2.91 -2.56 -2.50 -1.00 -2.98 -2.28 -2.15 -3.33 -3.42 -2.65 -2.50
-3.54 -2.79 -2.59 -3.03 -2.73 -1.71 -2.35 -2.11 -2.67 -2.55 -1.39 -2.81 -2.66 -1.92 -2.82 -2.48 -2.29 -1.23 -3.03 -2.27 -2.22 -3.66 -3.45 -2.79 -2.61
-3.73 -2.96 -2.75 -2.89 -2.59 -1.79 -2.15 -2.01 -2.70 -2.57 -1.33 -2.81 -2.75 -1.83 -2.91 -2.67 -2.58 -1.54 -2.98 -2.47 -2.15 -3.44 -3.42 -2.72 -2.56
-3.73 -2.96 -2.75 -2.89 -2.59 -1.65 -2.15 -2.01 -2.70 -2.57 -1.33 -2.81 -2.75 NAO -2.91 -2.66 -2.50 -1.28 -2.98 -2.34 -2.15 -3.42 -3.42 -2.72 -2.56
NA = not available.
backup QFF (F4). The PUFSs in the QQ sampler are abbreviated as A1 and A2, and those in the TQ sampler are abbreviated as A3 and A4. The QFFs were of type QAOT-UP (Pallflex Corp., Putnam, CT). The Teflonbacked Zefluor TMFs (Gelman, Ann Arbor, MI) used had a pore size of 2 pm. There were no significant differences between the PAH data obtained from the PUFSs and the Tenax cartridges. Therefore, only the PUFS data will be discussed here. PAHs were determined for a total of eight events sampled a t the Oregon Department of Environmental Quality (ODEQ) air monitoring station at 5824 SE Lafayette St. in Portland, OR. The station is in an urban/ residential area. The samplers were located on top of the 10-mhigh roof of the station and were on opposite corners of an 8 X 8 m platform. The sampling days coincided with ODEQs measurement days for TSP. For each event, sampling began at 0600 and ended at 1200. After sampling, each filter head was wrapped in mufflefurnace-baked aluminum foil and returned to the laboratory. A 47-mm diameter punch was taken from each of the front and backup QFFs, placed in an aluminum-foillined petri dish, and stored at 0 "C. The punches were analyzed by Sunset Laboratories (Forest Grove, OR) for elemental carbon (EC) and OC using a thermo-optical method (25,26). Each remaining filter portion and each PUFS was Soxhlet extracted within 1 h of the end of sampling. The sealed Tenax-TA cartridges were stored at 5 "C and then analyzed by thermal desorption using the procedures described elsewhere(27). All analyses were complete within 60 days of sampling. The target PAHs included acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[alanthracene, chrysene, benzo[blfluoranthene, benzo[alpyrene, and benzo[elpyrene. Detectable levels of the last three compounds
were usually not found in the gas phase. All of the filter and PUFS extracts were analyzed in duplicate by GUMS. The precision of the sample volume and GC/MS measurements was &lo%. Thus, by propagation of error, the coefficient of variation (CV)associated with each air concentration was f14%. All quantitative comparisons discussed in this paper are statistically significant at the 95% confidence level or higher. Results and Discussion
Sorption of PAHs to Backup Filters. For each sampler, event, and PAH, each total concentration (ng/ m3) was computed as the sum of the concentrations determined on the filters plus the concentrations found on the sorbents. In general, the total concentrations of the PAHs obtained using the two samplers agreed very well; the event-averaged, between-sampler coefficient of variation (CV) values ranged from 8 to 3575,depending on the compound. The TSP and mean temperature values during sampling are given in Table 1. Since the method used to measure EC detects only particulate carbon, and since no detectable EC was found on the backup filters, we assume that essentially 100% of any organic compound found on a backup filter was due to adsorption from the gas phase. Thus, the F2 and F4 values provide different estimates of the compounddependent extent of the adsorption to a front QFF. Since QFFs will be used more commonly than TMFs, one question which this study sought to answer was whether F2 or F4 values provide better estimates of sorption to a front QFF. Based on the work of Turpin (281, it is known that the QFFs used here have a higher surface area/m2of area (- 130 m2/m2)than do the TMFs used (-26 m2/m2). Therefore, one might expect QFFs to Envlron. Scl. Technol., Vol. 28. No. 4, 1994 657
Table 2. Methods Used to Calculate Measured Values of log (F/TSP)/A method quartz uncorrected (qu) F = F1 A = F2 + A1 A2
approach makes no correction for sorption to the front QFF; is analogous to conventional high-volume sampling with a single QFF; assumes that F2 should be assigned to the gas phase; values of qu will always be greater than or equal to both qQ and qc,
Teflon (ten
makes no correction for sorption to the front TMF filter; but tries to minimize such sorption through use of a TMF, which has a relatively low surface area; assumes that F4 should be assigned to the gas phase
+
F=F3 A = F4
+ A3 + A4
quartz correctedbflon(qct)
F=Fl-F4 A = F4 + F2+ AI
+ A2
quartz correctedqUhz(qcq)
F = Fl -F2 A = 2 X F2+ A1 + A2
makes correction for sorption to the front QFF by subtracting F4 from F1; subscript in qct indicates that the value subtracted from F1 was obtained from the TQ sampler; adds F4 back to the gas-phase concentration, as with F2; assumes that a front TMF will not deplete the gas-phase concentration, but that a front QFF will deplete that concentration, the depletion equaling F4 makes correction for sorption to the front QFF by subtracting F2 from F1; subscript in qc, indicates that the value subtracted from Fl waa obtained from the QQ sampler; adds 2 X F2 to gasphase concentration; this correction needs only one sampler and so is easier to carry out than is the qct correction; however, if a QFF depletes the gas-phase concentration more than does a TMF, this correction may be incomplete relative to qct values.
be more inherently sorptive than TMFs. It seems possible then that a front TMF will deplete the gaseous concentrations of the target analytes less than will a front QFF, making the F4 values better than F2 values as estimates of what sorbs to a front QQF. In addition, we note that there can be sorption not only of the target analytes but also of any gaseous compound. Such general adsorption might affect the sorption properties of a filter surface (20), possibly making the F4 filter more similar than the F2 filter to the F1 filter. Table 2 summarizes four different methods that were used to calculate measured values of log (F/TSP)/A. The qct and qc, methods are backup filter subtraction methods, which attempt to explicitly correct for gas adsorption to a front filter. The tef method represents an attempt to minimize such adsorption by using a front TMF rather than a front QFF. (Note that, in a general sampling effort using a front TMF, there would be no need for the backup QFF, Le., F4, depicted in Figure 1.) The qu method provides no correction for sorption to a front QFF. Table 1 contains the values of log (F/TSP)/A for selected PAHs calculated using the four methods in Table 2. Figure 2 is a plot of the log (F/TSP)/A vs log pi regression equations obtained for the November 29,1988, sample by the four methods. As is required by the formulas in Table 2, both the qct and qc, regression lines lie below the qu regression line: both correction methods subtract something from FI and add something to (AI + A2). If a TMF is indeed less sorptive than a QFF (and if there are no analytical biases associated with TMFs), then one would also expect to find the tef line below the qu line. However, this latter result is not required by the formulas in Table 1: the tef values of log (F/TSP)/A are derived from independent measurements, and so analytical variability can make them greater than qu values (see Table 1 for individual examples). Therefore, rather than preparing a plot like Figure 2 for each of the events and trying to 858
Environ. Sci. Technol., Vol. 28, No. 4, 1994
-0.726
-6.494
0.98
\tef
extract quantitative conclusions from the numerous similar plots, a more concise way to represent the data is to plot the differences between various combinations of measured values of log (F/TSP)/A vs log p i . Figures 3-6represent four difference plots of this type. For Figures 3 and 4, in a manner that is analogous to the relative locations of the lines in Figure 2, we see from Table 1that in every case, (qu - qct) 2 0 and (qu - qc,) I0. Since there is no trend in the difference values with log p i in either figure, the mean values of the differences provide rough estimates of the filter sorption artifact on log (F/TSP)/A. The overall means are very similar, 0.094 and 0.072, respectively. Thus, for PAHs sampled using high-volumes and QFFs under the specific conditions encountered in this study, these means indicate a factor 1.2 error in measured (F/TSP)/A values. of only N
,
0.8
I
0.6 0.4 a,
0.2
E
0.0
u
b
-0.4 -0.6- q u a r t z uncor. m e a n = 0.094
- quartz con./tef
-0.6
m e a n ezcluding zeros = 0.215
-0.8
I
I
-0.8
I
4
1
quartz c o n . / q u a r t z - teflon m e a n = 0.002 95% conf. int. = -0.054 t o 0.050
1
-7
I
I
I
-6
-5
-4
Log Figure 6. Values of (qc,
q u - qcq
0.6 -
0.4
u
4
1
0.2
;
1
-0.4
i
-0.6 -0.8
I
-7
0
q u a r t z uncor. - quartz corr./quartz m e a n = 0.072 m e a n excluding zeros = 0 . f 7 2 I
I
I
-6
-5
-4
log
&. 1
I
qu
-
I
tef
0.6 0.4
-0.4
-I
I I
0
0
1
-0.6 -0.8
i I
I
-3
POL
Flgure 4. Values of (qu - qc,) vs log 0.8
1
quartz uncor. - teflon m e a n = 0.070 95% conf. i n t . = 0.021 to 0.120 I
I
I
i 1
-3
P"L
- tef) vs log &.
zeros underestimates the true value of (qu - qct) or (qu qc,). Thus, the overall means given in the figures must be underestimates of the true means of the difference values. If we excludethe zeros when calculating the means, we obtain 0.215 and 0.172, respectively, for an error factor of about = 1.6. Based on these results, we conclude that for the sampling conditions of this study, the error factor was as large as 1.2-1.6. The mean values of (qct qc,) are not statistically different from zero. As has been done in prior studies (21, 22, 28), it is instructive to.,compare the amounts of surface area on a filter that are due to the collected particles and to the filter itself. In this work, a typical TSP level was 50 bg/m3 and a typical sample volume was 500 m3. These values give a particle mass of 25 mg. For a specific surface area of -3 m2/g ( Z ) , we obtain a particle surface area of about 0.075 m2. The QFFs used here have been estimated to have a surface area of -126 m2/m2of filter. For a 20 X 25 cm high-volume filter, we then have -6 m2 of surface area. In this work then, the filter/particle surface area ratio was -80. If the uncorrected FIA artifact factor is no larger than 1.6 (see above), then the results suggest that a QFF filter is considerably less sorptive per unit area than the particles collected in this study. The similarity in the mean values of (qu - qct) and (qu - qc,) discussed above suggests that in this study at least, the qc, method is as effective as the qct method in correcting for gas adsorption to a front QFF. This is an advantage since the qc, method requires just one sampler with conventional QFFs; only a backup filter needs to be added. While the qc, and qct methods attempt to correct for adsorption to a front filter, the tef method seeks to minimize it by using a filter with a relatively low surface area. In Figure 5, we plot the values of (qu - tef). As in Figures 3 and 4, there is no trend in the values with log p i . While the data points are distributed both above and below zero, the mean is greater than zero at the 95% confidence level. Thus, as expected during the planning of this work, less adsorption occurs to a front TMF than to a front QFF. The fact that the mean value of (qu - tef) is similar to the means (including zeros) for (qu - qc,) and (qu - qct) indicates that using a TMF as a front filter (no backup filter would then be needed) is as effective as the qc, and qct approaches are in correcting for filter adsorption. We also note that using a TMF without a backup
-
Envlron. Sci. Technol., Voi. 28, No. 4. 1994 659
filter removes the need for one of the filter analyses that is required with the qc, method. However, if QFFs are to be used because of the ability to heat them at high temperatures to reduce blank levels, then the qc, method will be preferred over the qct method because the qc, method requires only one sampler. Elemental Carbon (EC)and Organic Carbon ( O C ) Concentrations. The OC concentrations measured on the F l filters averaged 10.5 pg C/m3for the 12 events and were always larger than the corresponding EC concentrations, which averaged 2.2 pg/m3. The highest EC and OC concentrations were measured in the winter. The average concentrations are consistent with values reported by Shah et al. (29) for samples taken at 46 urban sites around the United States. Significant OC concentrations were found on the F2 filters for all 12 events, averaging 1.6 pg C/m3. As mentioned above, since no EC could be detected on any of the F2 filters, we assume that the front filters were essentially 100% efficient in filtering particulate carbon. Therefore, the F2 concentrations of OC are presumed to be due to the adsorption of gaseous OC. The OC values found on the F2 filters averaged 14 f 4% of that found on the Fl filters. The OC values found on the F4 filters averaged about 3 pg C/m3. For each event, the value of this concentration was significantly higher than that measured on the F2 filters. The OC values found on the F4 filters averaged 31% of that found on the F1 filters, about twice that on the F2 filters. In addition to the PAHs discussed here, a parallel project in our laboratory examined the concentrations of a series of n-alkanes from C I to ~ (231. It was found that the sum of all PAHs plus all of these n-alkanes on the backup filters (F2 and 3’4) made up less that about 1 % of the total OC found on those filters. Compositionof the OC on the Backup Filters. Some effort was made to identify some of the important, nontarget compounds on the F2 filters. The mass spectral data for the chromatogramsof the extracts were examined in search of ion fragments that are characteristic of classes of compounds that might be present at high concentrations in the urban atmosphere. For example, ion chromatograms for m/z = 73 amu were plotted since [CH&H2COOHI+ is a characteristic ion fragment of fatty acids. Unfortunately, this search yielded little useful information. The chromatograms were very complex, and all QFF extracts exhibited the type of unresolved hump that is commonly observed for air samples. No homologous series for classes of compounds could be distinguished from the relatively high baseline levels of all ions in the mass spectra. In the case of the fatty acids, it is possible that these polar compounds were largely removed during the silica gel cleanup step that was part of the analysis procedure. Conclusions Since no elemental carbon (EC) was detected on any of the backup filters, it was assumed that essentially 100% of any SOC found on a backup filter was due to adsorption from the gas phase. Although the data indicated that a front TMF depletes the gas phase less than does a front QFF, similar amounts of individual SOCs were found adsorbed on backup QFFs behind front filters of these two types. Thus, for the conditions encountered in this study, the two correction methods qct and qc, provided 660
Envlron. Scl. Technol., Vol. 28, No. 4, 1994
values of log (F/TSP)/A that were, on average, indistinguishable from one another. They were also indistinguishable from those obtained by the tef method. This suggests that, for this study, using a single TMF with no backup filter would have been as effective in avoiding filter sorption effects as the qct and qc, methods were in correcting for them. There was no apparent trend in the magnitude of the correction with increasing log p i . Without the correction for adsorption, the values of (F/TSP)/A were found to be too large by a factor as large as 1.2-1.6. Of the three methods found here to be of equivalent utility in removing or avoiding filter sorption effects on log (F/TSP)/A (i.e., qct, qcq, and tef), the qc, and tef methods are the most likely candidates for routine sampling; the qct method would require using two samplers for every event and that will not be attractive. Acknowledgments This work was supported in part by the U.S. Environmental Protection Agency, Officeof Exploratory Research (USEPA/OER) under Grant R-8163543-01-0. Glossary A A1 A2 A3 A4 EC F F1 F2 F3 F4
GFF KP
oc
Pi
PAH PUF PUFS qc, Wt qu QFF
QQ
gas-phase concentration (ng/m3) front PUFS value for QQ sampler (ng/m3) backup PUFS value for QQ sampler (ng/m3) front PUFS value for TQ sampler (ng/m3) backup PUFS value for TQ sampler (ng/m3) elemental carbon particle-associated concentration (ng/m3) front QQF value for QQ sampler (ng/m3) backup QQF value for QQ sampler (ng/m3) front TMF value for TQ sampler (ng/m3) backup QQF value for TQ sampler (ng/m3) glass fiber filter equilibrium partition coefficient (m3/~g) organic carbon subcooled liquid vapor pressure (Torr) polycyclic aromatic hydrocarbon polyurethane foam polyurethane foam sheet “quartz corrected using F2”method to calculate (F/TSP)/A (see Table 2) “quartz corrected using F4”method to calculate (F/TSP)/A (see Table 2) “quartz-uncorrected“ method to calculate (Fl TSP)/A (see Table 2) quartz fiber filter QQF/QQF sampler
samp1er
SOC
tef
semi-volatileorganic compound Teflon filter method to calculate(F/TSP)/A (see Table 2) Teflon membrane filter TMF/QQF sampler
TMF TQ sampler concentration of total suspended particulate TSP matter (pg/m3) Literature Cited (1) Yamasaki, H.; Kuwata, K.; Miyamoto, H. Enuiron. Sci. Technol. 1982,16, 189-194.
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e Abstract published in Advance ACSAbstracts, February 1,1994.
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