Environ. Sci. Technol. 1989, 23, 470-475
Keith, L. H., Eds.; Lewis: Chelsea, MI, 1986; pp 79-92. (13) Thompson, H. C., Jr.; Kendall, D. L.; Korfmacher, W. A.; Kominsky, J. R.; Rushing, L. G.; Rowland, K. L. Smith, L. M.; Stalling, D. L. In Chlorinated Dioxins and Dibenzofurans in Perspective; Rappe, C., Choudhary, G., Keith, L. H., Eds.; Lewis: Chelsea, MI, 1986; pp 121-136. (14) Erickson, M. D.; Cole, C. J.; Flora, J. D., Jr.; Gorman, P. G.; Haile, C. L.; Hinshaw, G. D.; Hopkins, F. C.; Swanson, S. E. Thermal Degradation Products from Dielectric Fluids; Environmental Protection Agency Office of Toxic Substances: Washington, DC, 1984; EPA 560/5-84-009. (15) Choudhary, G. G; Hutzinger, 0. Mechanistic Aspects of Thermal Formation of Halogenated Organic Compounds Including Polychlorinated Dibenzo-p-dioxins;University of Amsterdam, Gordon and Breach Science Publishers: New York, 1983. (16) Vuceta, J.; Marsh, J. R.; Kennedy, S.; Hildemann, L.; Wiley, S. State-of-the-ArtReview: PCDDs and PCDFs in Utility PCB Fluid; Electric Power Research Institute: Palo Alto, CA, 1983; CS-3308. (17) U.S. EPA Fed. Regist. 1984, 49 11070-11083. (18) U.S.EPA Fed. Regist. 1985,50, 29170-29201. (19) Erickson, M. D. Analytical Chemistry of PCBs; Butterworth: Boston, MA, 1986. (20) Morita, M.; Nakagawa, J.; Akiyama, N.; Minura, S.; Isono, N. Bull. Environ. Contam. Toxicol. 1977, 18(1), 67-73. (21) Morita, M.; Nakagawa, J.;Rappe, C. Bull. Enuiron. Contam. Toxicol. 1978, 19, 665-670. (22) Buser, H. R.; Bosshardt, H.-P.; Rappe, C. Chemosphere 1978, 7(1), 109-119. (23) Buser, H. R.; Rappe, C. Chemosphere 1979,8(3),157-174. (24) Rappe, C. Environ. Sci. Technol. 1984, 18, 78A. (25) Swanson, J. W.; Tiernan, T. 0. In Workshop Proceedings: PCB By-product Formation; Komai, R. Y., Addis, G., Eds.;
Electric Power Research Institute: Palo Alto, CA, 1984; CS/EL-4104, pp 3-1-3-8. (26) Cooke, M.; De Roos, F. L.; Rising, B.;Martin, W. H.; Rappe, C.; Slayback,J. In Workshop Proceedings: PCB By-Product Formation; Komai, R. Y., Addis, G., Eds.; Electric Power Research Institute: Palo Alto, CA, 1984; CS/EL-4104, pp 3-9-3-12. (27) Rubey, W. A.; Dellinger, B.; Hall, D. L.; Mazer, S. L. Chemosphere 1985, 14, 1483-1494. (28) Swanson, S. E.; Erickson, M.; Moody, L.; Heggem, D. In Chlorinated Dioxins and Dibenzofurans in Perspective; Rappe, C., Choudhary, G., Keith, L. H., Eds.; Lewis: Ann Arbor, MI, 1986; pp 109-119. (29) Swanson, S. E.; Erickson, M. D.; Moody, L. Products of Thermal Degradation of Dielectric Fluids; Environmental Protection Agency, Office of Toxic Substances: Washington, DC, 1985; EPA 560/5-85-022,p 30. (30) Hinshaw, G.; Jungclaus, G. Laboratory-Scale Hazardous Waste Incineration as a Research Tool. National Conference Hazardous Waste and Environmental Engineering; Cincinnati, OH; 1985; pp 14-16. (31) U S . EPA Determination of 2,3,7,8-TCDD in Soil and Sediment. Environmental Protection Agency, Region VI1 Laboratory: Kansas City, KS, 1983. (32) Ballschmiter, K.; Zoller, W.; Buchert, H.; Class, Th. Fresenius 2.Anal. Chem. 1985, 322, 587-594. Received for review April 12,1988. Revised manuscript recieved November 4,1988. Accepted December 19,1988. This research was performed pursuant to Contract No. 68-02-3938 with the U.S. Environmental Protection Agency. Portions of this work were presented at the 189th National Meeting of the American Chemical Society, April 28-May 3, 1985, in Miami, FL.
Collection and Quantitation of Methoxylated Phenol Tracers for Atmospheric Pollution from Residential Wood Stoves Steven B. Hawthorne," Mark S. Krieger, David J. Miller, and Mary B. Mathiason University of North Dakota, Energy and Mineral Research Center, Grand Forks, North Dakota 58202
Samples of particulate- and vapor-phase organics from the smoke plumes of 28 different wood stove and fireplace installations were collected onto quartz fiber filters backed by polyurethane foam (PUF) sorbent plugs. Twenty-seven different organic compounds, primarily syringol (2,6-dimethoxyphenol) and guaiacol (Zmethoxyphenol) derivatives, were quantitated in each sample by GC/MS analysis of the acetone extracts. The concentrations (per weight of particulate carbon) of guaiacol derivatives were consistent whether hardwoods or softwoods were being burned. Total average concentrations of the guaiacol derivatives in hardwood smoke (106 pglmg) and in softwood smoke (111pg/mg) were nearly identical. In contrast, the concentrations of syringol derivatives were consistent in hardwood smoke, but were 2 orders of magnitude lower in softwood smoke. This study demonstrates that guaiacol derivatives should be useful tracers of atmospheric wood smoke pollution regardless of the type of wood burned, while the measurement of syringol derivatives can be used to differentiate the type of wood burned.
Introduction Emissions from residential wood-burning appliances account for as much as 80% of the air fine-particulate loading in several communities and may contribute more mutagenic polycyclic organic compounds to the atmosphere than any other single source (1-5). Wood smoke 470
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particulates are predominantly carbonaceous and are almost entirely in the inhalable size range (3,6-8). Studies of the relative impact of wood smoke, vehicle exhaust, and other sources of atmospheric organic pollutants are presently limited by a lack of tracer species unique to wood smoke particulates. The use of methyl chloride and potassium (and the K/Fe ratio) has been limited by their variable concentrations in smoke, and by high and variable background levels (8-13). Organic compounds including retene (l-methyl-7-isopropylphenanthrene)and levoglucosan (the anhydride of P-glucose) as well as measurements of 14C have also been suggested as tracers for wood smoke pollution, but their use has been limited (14-1 6).
An earlier report has described the identification of approximately 30 guaiacol (2-methoxyphenol)and syringol (2,6-dimethoxyphenol) derivatives in unfractionated extracts from wood smoke particulates (17). As pyrolysis products of wood lignin, these species should be unique to wood smoke in urban atmospheres, and since they are present in high concentrations, their use as tracers for atmospheric wood smoke pollution was suggested (17). The present report describes the development of techniques to collect, extract, and quantitate the particulateand vapor-phase organics from smoke plumes of individual wood-burning appliances. Hardwood and softwood smoke was collected from 28 wood stoves and fireplaces and 27
0013-936X/89/0923-0470$01.50/0
0 1989 American Chemical Society
candidate tracers were quantitated by GC/MS. Experimental Section Sample Collection. Wood smoke samples were collected between December 1987 and February 1988 from 22 different residential wood stoves, 14 of which were burning hardwoods and 8 of which were burning softwoods. Samples from six recreational fireplaces (three burning hardwoods and three burning softwoods) were also collected. Hardwood smoke samples were collected in and near Grand Forks, ND, and softwood samples were collected in and near Salt Lake City, UT, and Boulder, CO. The type of wood burned at each site was determined by asking the owner and/or by a visual inspection of the wood. During sample collection the owners were asked to continue operating their stove or fireplace in a normal manner. Smoke particulates were collected onto 47 mm diameter (37 mm exposed diameter) organic-free quartz fiber filters (Whatman QM-A) which were backed up by two 37 mm diameter x 40 mm long polyurethane foam (PUF) sorbent plugs (Olympic Products, Greensborough, NC, grade no. 3014) to collect the vapor-phase organics (15,18-20). All samples were collected ca. l/z m from the chimney outlet for 10 min with a Du Pont Model P4000 personal air sampling pump calibrated with a soap bubble flow meter at ambient temperature to draw 4 L/min. Prior to sample collection, the P U F plugs were preextracted for 4 h with four changes of acetone with sonication, dried under clean air, and stored in brown glass bottles with Teflon-lined caps until used. After the wood smoke samples were collected, each filter and PUF plug was stored in a brown glass bottle a t ca. 4 "C until they were extracted. Storage time was generally less than 3 days. Extraction and Analysis. Total particulate carbon was determined on duplicate one-quarter sections of each particulate filter by a Control Equipment Model 240-XA elemental analyzer with a combustion temperature of 950 "C. Blank values were determined on identical filter sections that had not been used for sample collection. Each PUF plug and the remaining half of each filter were extracted by sonication for 2 h with 60 mL of acetone (Baker Resi-Analyzed) which contained 10 pg each of guaiacol-d, and syringol-d3 as internal standards (both labeled on the aromatic ring; ref 21 and 22). Following extraction, the samples were evaporated to ca. 1mL under a gentle stream of clean nitrogen. GC/MS analyses were performed with a HewlettPackard Model 5985B GC/MS with electron impact (EI) ionization a t 70 eV and a scan range of 60-350 amu. Chromatographic separations were achieved with a 20 m X 0.25 mm i.d. (0.25-pm film thickness) DB-5 capillary gas chromatographic column (J&W Scientific) with split injections (split ratio ca. 1:20). Temperature programming was 80 to 330 "C a t 8 OC/min. Quantitations were based on the integrated area of the molecular ion from GC/MS analysis for each species (divided by the area of the internal standard) and three point standard curves using the standard compounds listed in Table I. In cases where the appropriate standards were not available, the relative response factors were estimated based on the response factors of the most similar standard species. Since the use of either guaiacol-d, or syringol-d, as the internal standard yielded virtually identical results, guaiacol-d, was used for all quantitations in this study. Three experiments were performed to determine extraction and recovery efficiencies. First, filter and P U F plugs that had been used for sample collection were extracted multiple times. Second, a clean filter and P U F plug were spiked with a standard solution containing ap-
Table I. Candidate Tracers for Atmospheric Wood Smoke Pollution peak no.a 1
2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
species phenol o-cresol m- or p-cresol guaiacol catechol 4-methylguaiacol 3-methoxycatechol 4-ethylguaiacol 4-methylcatechol syringol 4-allylguaiacol propylguaiacol C2-catechol 4-formylguaiacol cis-4-propenylguaiacol methylsyringol trans-4-propenylguaiacol 4-acetylguaiacol ethylsyringol acetonylguaiacol 4-allylsyringol propylsyringol cis-propenylsyringol 4-formylsyringol trans-propenylsyringol 4-acetylsyringol acetonylsyringol
retn indexb MW 972.5 1049.9 1071.3 1093.1 1192.2 1196.7 1268.2 1283.8 1293.7 1356.5 1363.5 1373.3 1388.4 1407.4 1414.4 1452.5 1457.7 1496.6 1533.0 1540.6 1608.3 1615.5 1658.5 1670.5 1708.1 1746.1 1781.3
94 108 108 124 110
138 140 152 124 154 164 166 138 152 164 168 164 166 182 180 194 196 194 182 194 196 210
re1 response factorC 3.31 1.68 1.70 1.00 0.47 0.94 0.35 0.68 0.27 0.93 0.70 0.60d 0.30d 0.72 0.92 0.80d 0.92 0.44 0.60d 0.50d 0.43 0.50d 0.80d 0.56 0.80d 0.32 0.50d
"Peak numbers refer to the chromatograms in Figures 1 and 2. *Retention indices were based on normal alkanes. The standard deviations of three replicate determinations were typically less than 1 unit. CResponsefactors relative to guaiacol = 1.00 were based on the integrated areas of the molecular ion of each species. These standard compounds were also used to confirm identifications by comparing the retention index and E1 fragmentation patterns of the standards with those of the sample species (17). No standard was available. The relative response factor was estimated based on that of the most similar standard comDound.
proximately 10 pg each of the standards listed in Table I. The filter was spiked by wetting its surface with the standard solution, and the P U F plug was spiked by injecting the standard solution into the center of the plug. The acetone solvent was evaporated, and the spiked filter and PUF plug were extracted and analyzed in a manner identical with that used for samples. Third, recoveries were determined in a similar manner for guaiacol-d, and syringol-d, that had been spiked onto a filter and into a P U F plug which contained a sample of hardwood smoke (1-chloronaphthalene was used as an internal standard). Results and Discussion Sample Collection. Samples were collected from the smoke plume of stoves and fireplaces that were burning various hardwoods including oak (2 sites), birch (2), elm (l), cottonwood (l), boxelder (l),mixed oak and ash (6), mixed elm and cottonwood (2), mixed oak and elm (l), and mixed oak and boxelder (1). The softwoods being burned were varieties of pine (lodgepole, pinion, and ponderosa), although one site was burning spruce and another was burning fir. Most of the wood stove sites used wood as the main (>75%) heat source, while fireplace use was primarily recreational. The smoke plumes a t the l/z-m collection point were cooled to an average of 12 "C above ambient temperatures (ambient temperatures ranged from -18 to 4 OC). That is, the average temperature of the smoke plume at l/z m was only 15% above ambient based on the difference beEnviron.
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471
tween the ambient temperature and the temperature at the chimney outlet. The temperatures at the chimney outlets ranged from 16 to 160 "C, and the average temperature measured for wood stoves (81 f 42 "C) was lower than that measured for fireplaces (105 f 22 "C). The broad range of temperatures measured a t the outlet of the chimneys and the range of the weight of particulate carbon that was collected (0.2-1.4 mg) reflect the widely varying burning conditions encountered during this study. (Additional details on each sampling site including the type of wood burned, the temperatures, and the weight of particulate carbon are given in Table IA of the supplementary data.) Collection and Extraction Efficiencies. Two PUF sorbent plugs (front and back) were used for each sample collection and analyzed in order to determine the ability of the PUF plugs to quantitatively retain the vapor-phase species under the varying collection conditions. Of all the compounds that were quantitated, only traces of phenol, the cresol isomers, guaiacol, and 4-methylguaiacol were detected in the extracts of the back PUF plug. The retention of even these "worst case" species by the front PUF plug was essentially quantitative, with an average of 97% of the phenol, 98% of the cresol isomers, 98% of the guaiacol, and 99% of the 4-methylguaiacol being found in the front PUF plug. These results demonstrate that P U F is an effective sorbent resin for collecting the vapor-phase organics from wood smoke. The stability of sample species on the filter and PUF plugs after collection was studied by extracting half of a filter and half of a front P U F plug (cut lengthwise) immediately after sample collection and extracting the other half of the filter and PUF plug 5 weeks after sample collection. The extracts of both filter and PUF samples showed no significant changes in the concentrations of each of the candidate tracer species indicating that the sample storage procedure described in the Experimental Section was adequate to prevent degradation and loss of the tracer species. Extraction and recovery efficiencies were determined as described earlier. First, multiple extractions of several of the filter and PUF samples showed no significant species in the second extracts, indicating that the acetone extraction efficiently recovered the collected analytes. Second, recoveries of all of the 18 spiked standard compounds (Table I) were quantitative from the filter (>%YO). Quantitative recovery was also achieved from the PUF plug (>92%) except for the catechol derivatives (catechol, 4methylcatechol, and 3-methoxycatechol) which showed recoveries of 35, 36, and 51 YO, respectively. (The low recoveries of the catechol derivatives from PUF was not expected to be a problem since these highly polar species were expected to be associated with the smoke particulates, as discussed later in the text). Third, the recoveries of the guaiacol-d, and syringol-d3,which were spiked onto a filter and into a PUF plug that had been used to collect a hardwood smoke sample, were also quantitative (>95% 1. The results of these three recovery studies demonstrate that acetone extraction efficiently recovered the candidate tracer species from the filters and PUF plugs (except for the catechol derivatives from the PUF) without causing loss during the sample concentration step. Sample Analysis. Figures 1 and 2 show typical total ion current (TIC) chromatograms along with the reconstructed selected ion chromatograms for the molecular ion of each tracer species obtained from the GC/MS analysis of the unfractionated extracts of hardwood smoke filter and PUF sorbent plug samples. The TIC chromatograms 472
Environ. Sci. Technol., Vol. 23, No. 4, 1989
I
Filter Extract
io1
rank
I
Selected Ions 94
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138
I
182
210
124
194
110
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Retention Time (mid Flgure 1. G U M S analysis of the unfractionated extract of hardwood smoke particulates collected on a glass fiber filter. The masses of the ions plotted in the reconstructed selected ion chromatograms (lower half) are given with the brackets for each retention time window. Peak numbers refer to identifications listed in Table I.
resulting from blank filter and PUF extractions that were performed in the same manner as the sample extracts are also shown at the same sensitivity (based on the peak height of the guaiacol-d4 internal standard) as the sample chromatograms. As shown in Figures 1 and 2, both the filter blanks and the PUF blanks had few significant contaminants, with the major peaks being the added guaiacol-d4 (retention time of 4.6 min) and syringol-d3 (retention time of 9.2 min). The major species found in the filter and PUF samples were guaiacol and syringol derivatives as well as phenol and catechol derivatives that result from the pyrolysis of wood lignin (23). These candidate tracer species, which are indicated with numbers in Figures 1and 2, are identified in Table I along with their retention indices. As would be expected, the more volatile components were collected in the PUF sorbent, while the less volatile species were associated with the particulates. Although the TIC
I
PUF Extract
14
Table 11. Average Concentrations of Guaiacol, Syringol, Phenol, and Catechol Derivatives in Hardwood and Softwood Smoke from 28 Wood Stoves and Fireplaces
tracer species
2
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u
152
108
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c
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3
6
./!
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n
9
Retention Time ( m i d Flgure 2. GUMS analysis of the unfractionated extract of vapor-phase organics from hardwood smoke collected on a PUF sorbent plug placed behind the filter used for the sample in Figure 1. The masses of the ions plotted in the reconstructed selected ion chromatograms (lower half) are given with the brackets for each retention time window. Peak numbers refer to identifications listed in Table I.
chromatograms are fairly complex, the selected ion chromatograms for the molecular ions of the tracer species are quite simple. This makes the quantitation of each individual tracer species relatively easy to perform using GC/MS without requiring any class fractionation of the acetone extracts. Several other species were also tentatively identified in the wood smoke samples. The filter samples contained polycyclic aromatic hydrocarbons (PAHs) ranging from phenanthrene (M = 178) to benzo[a]pyrene and isomers (M = 252) along with their alkyl derivatives. Several oxy-PAHs including indanone and methylindanone isomers, 9-fluorenone, dibenzofuran, and benzonaphthofuran isomers were also detected in most of the filter samples (I 7). P U F samples contained significant concentrations of several alkylbenzene isomers, indane, indene, naphthalene, biphenyl, acenaphthylene, acenaphthene, and fluorene as well as alkyl derivatives of indane, indene, and naphthalene. Oxygen-containing species (other than the candidate tracer species listed in Table I) including methylcyclopentenone, benzofuran, (hydroxymethy1)cyclopentenone, methylbenzofuran isomers, and naphthol were also identified in the PUF extracts. The PUF samples collected from pine burning also contained high concentrations of terpenes. Although all of the PAHs and oxyPAHs identified in the filter and PUF samples are products of wood combustion, they were not included in the list of candidate tracers (Table I) since they have been reported to be emitted in high concentrations from other combustion sources (24-30). Quantitations of the individual species were based on three point standard curves (r2typically >0.999) generated
guaiacol deriv guaiacol 4-methylguaiacol 4-ethylguaiacol 4-allylguaiacol propylguaiacol 4-formylguaiacol cis-4-propenylguaiacol trans-4-propenylguaiacol 4-acetylguaiacol acetonylguaiacol total guaiacol deriv syringol deriv syringol methylsyringol ethylsyringol 4-allylsyringol propylsyringol cis-propenylsyringol 4-formylsyringol trans-propenylsyringol 4-acetylsyringol acetonylsyringol total syringol deriv phenol deriv phenol o-cresol m- or p-cresol total phenol deriv catechol deriv catechol 4-methylcatechol C2-catechol 3-methoxycatechol total catechol deriv
particulate carbon; pg/mg hardwood softwood f (%RSD) .f ( % RSD) 45.7 (45) 18.7 (48) 10.7 (45) 1.8 (54) 1.8 (50) 6.0 (53) 1.5 (35) 10.3 (49) 3.9 (56) 5.5 (55) 105.9 (39) 50.9 (34) 40.1 (42) 28.9 (32) 8.5 (48) 8.6 (36) 3.1 (62) 11.3 (57) 15.5 (65) 7.4 (68) 7.1 (51) 181.4 (36)
34.9 (25) 36.6 (22) 13.8 (28) 2.3 (79) 2.4 (63) 4.3 (90) 1.0 (81) 7.6 (65) 3.4 (64) 4.8 (44) 111.1(27) 2.5 (202) 2.8 (219) 1.5 (229) 0.3 (287) 0.5 (289) 0.1 (289) 0.4 (317) 0.4 (332) 0.2 (332) 0.3 (321) 9.0 (203)
42.6 (74) 12.3 (39) 19.7 (44) 74.6 (52)
20.0 (55) 8.7 (32) 15.8 (39) 44.5 (44)
35.8 (93) 16.9 (78) 5.3 (91) 15.2 (77) 73.2 (82)
12.0 (166) 13.1 (126) 7.5 (88) 2.6 (111) 35.2 (121)
Concentrations are reported based on the total weight of carbon collected on the filter for each sample. Relative standard deviations (in percent) are given in parentheses after each concentration.
by use of the compounds listed in Table I and the guaiacol-d, internal standard. Replicate sample analyses of both filter and PUF extracts showed good reproducibility with relative standard deviations for individual compounds typically ranging from 2 to 8%, except for the catechol derivatives which had typical relative standard deviations of 20%. (Total concentrations and the distribution between the filter and P U F plug for each species in each sample are given in Tables IIA and IIIA in the supplementary data.) The total concentrations (filter plus PUF) of the candidate tracers are given in Table 11. Several important results are contained in this data set. First, even though the samples were collected from 22 different wood stoves and six different fireplaces that were burning a variety of hardwoods and softwoods, and even though these woodburning appliances were operated under widely varying conditions, the concentrations of the guaiacol derivatives are surprisingly consistent. Relative standard deviations (RSDs) for the concentrations of the three major individual guaiacol derivatives in hardwood smoke were 45-48%, while the RSDs of the three major guaiacol species in the softwood smoke were only 22-28%. The average concentrations of each guaiacol derivative in hardwood and softwood smoke were also quite similar, and a relatively low value for one species appears to be compensated for Environ. Sci. Technol., Vol. 23, No. 4, 1989
473
by a relatively high value for a different species. This is demonstrated by the fact that the total average concentration of the guaiacol derivatives for hardwood smoke was 106 pg/mg, which is in excellent agreement with the total average concentration for softwoods of 111pg/mg. The variation in the total concentrations of guaiacol derivatives in the hardwood and softwood smoke was also surprisingly small with RSDs of only 39% and 27%, respectively. In contrast to the similarity in the concentrations of the guaiacol derivatives, the concentrations of the syringol derivatives were 20 times higher in the hardwood smoke than in the softwood smoke, as might be expected considering the higher proportion of syringol derivatives in hardwood lignin (31). Even though the concentrations reported in Table I1 for the syringol derivatives in softwood smoke are much lower than those in hardwood smoke, they may actually be artificially high since some of the owners that were burning softwood during sample collection reported that they burned hardwood on an occasional basis. Chimney scrapings from both hardwood and softwood burning have been previously reported to contain syringol derivatives (17),and even though only softwoods were burned during sample collection, earlier burning of hardwood may have contributed to the concentrations of syringol derivatives found in some softwood smoke samples. The larger relative standard deviations (202-332 % ) found for the syringol derivatives in the softwood smoke reflects the fact that two of the samples had significantly higher concentrations of the syringol derivatives than the smoke from the other softwood sites. Indeed, the owners of these two softwood sites both reported burning some hardwood within 2 days before sampling was performed. On the basis of the concentrations reported in Table 11, either syringol or guaiacol derivatives should be useful tracers of atmospheric wood smoke pollution in geographic areas where hardwoods are burned, while guaiacol derivatives should be useful tracers for smoke from softwoods. The results in Table I1 also indicate that the relative contributions of hardwood and softwood smoke could be estimated by determining the relative concentrations of the syringol and guaiacol derivatives. Table I1 also shows the concentrations of the other major pyrolysis products of wood lignin, the phenol and catechol derivatives. The phenol derivatives were present in fairly high concentrations ih all of the samples, and the concentrations of the cresol isomers in the hardwood and softwood smoke were consistent (relative standard deviations ranged from 32 to 44%). The concentrations of the cresol isomers also showed relatively good agreement between the hardwood and softwood smoke indicating that, like the guaiacol derivatives, cresols may be useful tracers for both hardwood and softwood smoke. The use of cresols as tracers for wood smoke pollution may be somewhat limited, however, by the fact that trace amounts of phenols and cresols have been reported in vehicle exhaust (29,30). Catechol and its derivatives were also present in relatively high concentrations in both the hardwood and softwood smoke (Table 11), but the concentrations found in individual samples were quite variable. The values reported for the catechol derivatives are for the filter extracts only, because the recoveries of the catechol standards from P U F were not quantitative, Le., recoveries ranged from 35 to 51%. However, the values reported in Table I1 should represent the total concentrations since catechol derivatives were found only in the filter extracts from all of the samples except for the three hardwood fireplace samples. Since each of the hardwood fireplace samples had significant concentrations of catechol derivatives in the 474
Environ. Sci. Technol., Vol. 23, No. 4, 1989
%
In Filter Extract
guaiacol 4-methyiguaiacol 4-ethylguaiacol
propylguaiacol
cis-4-propenylguaiacol trans-4-propenylguaiacol 4-acetylguaiacol
1 I
acetonylguaiacoi
I
Figure 3. Average distribution of the guaiacol derivatives in smoke from residential wood stoves between the filter and the PUF extracts.
PUF extracts, the catechol derivative concentrations for these three samples were not included in Table 11. The wide range in volatility of the species listed in Table I1 and the concentrations of the individual species in the PUF versus filter extracts indicates that some of the candidate tracers will exist primarily in the vapor phase while others will be primarily associated with particulates in ambient air. (The distribution of the individual compounds between the filter and PUF plugs in each smoke sample is given in Table IIIA in the supplementary data.) Average distributions of the individual species in the smoke from all of the wood stove sites shows, as expected, that the more volatile species including phenol, the cresol isomers, and guaiacol were found primarily (>96%) in the PUF extracts. Less volatile and more polar species including all of the catechol derivatives were found (>99%) in the filter extracts. Syringol and methylsyringol averaged 93% and 96%, respectively, in the filter extracts and the remaining syringol derivatives were almost exclusively (>99%) found in the filter extracts. The average distribution of individual guaiacol derivatives shifted from the vapor phase to the particulates as the molecular weight and polarity increased. As shown in Figure 3, guaiacol and its methyl and ethyl derivatives were present mostly in the PUF extracts, while the more polar and higher molecular weight guaiacol derivatives (e.g., the formyl, cis and trans propenyl, acetyl, and acetonyl derivatives of guaiacol), were found predominately in the filter extracts. The filter versus PUF distributions can only be used as an indication of the actual particulate- versus vapor-phase distribution that exists in the urban atmosphere since, at the 1/2-m sampling point the smoke was slightly above ambient temperature, the distribution between the particulate and vapor phases may not have been at equilibrium, and the sampling itself may have stripped some of the particulate-associated organics so that they were collected on the PUF plug. Dilution of the smoke plume would also be expected to increase the partitioning of the semivolatile compounds into the vapor phase. However, the distributions just discussed do demonstrate that guaiacol derivatives should be useful tracers for both particulate- and vapor-phase wood smoke pollution, while
syringol derivatives are expected to be associated primarily with atmospheric particulates. These estimates are also supported by preliminary high-volume air samples (68 m3/h for 12 h) that have been collected onto filters backed up by PUF in a neighborhood with several wood stoves and fireplaces burning hardwood. These high-volume air samples have shown distributions of the guaiacol, syringol, phenol, and catechol derivatives between the filter and PUF that are very similar to those found in the individual chimney samples. For example, the phenols and guaiacol were found only in the PUF extracts, while acetonylguaiacol, methylsyringol, and catechol were found only in the filter extracts. Conclusions
The use of quartz fiber filters backed up with PUF plugs followed by acetone extraction yields quantitative collection and recovery of both particulate- and vapor-phase organics emitted from residential wood stoves and fireplaces. Since the concentrations of guaiacol derivatives emitted from 28 different wood stoves and fireplaces were consistent regardless of the type of wood burned, guaiacol and its derivatives should be useful tracers for atmospheric wood smoke pollution. Syringol derivatives should also be useful tracers for hardwood burning and could be used to determine the relative contribution of hardwood and softwood burning to a polluted air mass. The use of the methoxylated phenols as tracers has several potential advantages since, as pyrolysis products of lignin, they are unique to wood smoke in urban atmospheres, they are present in high concentrations and can be measured by conventional GC/MS techniques, and since more than 25 candidate tracer species have been identified, their use should be less susceptible to anomalous behavior than when a single tracer is used for source apportionment studies. Future work will compare the methoxylated phenols described in this work to 14C as tracers of atmospheric wood smoke pollution in high-volume air samples of urban air. Supplementary Material Available Tables of additional details on each sampling site including type of wood burned, temperatures, and particulate carbon weight (Table IA), and total concentrations and filter/PUF plug distributions for each species analyzed in each sample (Tables IIA and IIIA) (9 pages) will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper or microfiche (105 X 148 mm, 24X reduction, negatives) may be obtained from Microforms Office, American Chemical Society, 1155 16th St., N.W., Washington, DC 20036. Full bibliographic citation (journal, title of article, authors’ names, inclusive pagination, volume number, and issue number) and prepayment, check or money order for $19.00 for photocopy ($21.00 foreign) or $10.00 for microfiche ($11.00 foreign), are required. Registry No. Phenol, 108-95-2; o-cresol, 95-48-7; m-cresol, 108-39-4;p-cresol, 106-44-5;guaiacol, 90-05-1; catechol, 120-80-9; 4-methylguaiacol, 93-51-6; 3-methoxycatechol, 934-00-9; 4ethylguaiacol, 2785-89-9; 4-methylcatechol, 452-86-8; syringol, 91-10-1; 4-allylguaiacol, 97-53-0; 4-formylguaiacol, 121-33-5;cis4-propenylguaiacol,5912-86-7; trans-4-propenylguaiacol,5932-68-3; 4-acetylguaiacol, 498-02-2; 4-allylsyringol, 6627-88-9; 4-formylsyringol, 134-96-3; 4-acetylsyringol, 2478-38-8.
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Received for review April 28,1988. Revised manuscript received November 18,1988. Accepted December 19,1988. The financial support of the US.Environmental Protection Agency, Office of Exploratory Research (Grant R-813257-01-0) is gratefully acknowledged.
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