Environ. Sci. Techno/. 1988, 22, 1191-1196
Identification of Methoxylated Phenols as Candidate Tracers for Atmospheric Wood Smoke Pollution Steven B. Hawthorne,*stDavld J. Miller,t Robert M. Barkley,s and Mark S. Kriegert
Energy and Mineral Research Center, University of North Dakota, Grand Forks, North Dakota 58202,and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309-0449
rn More than 70 organic compounds have been identified in unfractionated methylene chloride extracts of soot from residential wood stoves by a combination of capillary gas chromatography coupled with low-resolution mass spectrometry (GC/MS), GC coupled with high-resolution mass spectrometry, and chemical ionization mass spectrometry with deuteriated methanol as the reagent gas. Thirty of the species are derivatives of guaiacol (2-methoxyphenol) and syringol(2,6-dimethoxyphenol),which result from the pyrolysis of wood lignin. Soots from hardwood and pine show similar proportions of the syringol derivatives, but pine soot has much higher proportions of the guaiacol derivatives. Samples collected onto filters backed up by polyurethane foam (PUF) plugs in the cooled smoke plume showed that some of the methoxylated phenols were primarily in the vapor phase, while the majority were associated with the particulates. These species are expected to be unique to wood smoke in urban atmospheres and are therefore suggested as tracers for atmospheric wood smoke pollution.
Introduction The use of residential wood-burning appliances contributes 30-80% of the winter urban air fine-particulate loading in several communities and has been estimated to account for more emissions of polycyclic organic compounds than any other source (1). Extracts of wood smoke particulates have been reported to have high mutagenic activity (2-5). Studies of the relative impact of wood smoke, vehicle exhaust, and other particulate sources are presently limited by a lack of tracer species unique to wood smoke particulates. Chemical tracers such as methyl chloride and potassium have been applied, but their usefulness has been limited by high and variable background levels (for methyl chloride) and by highly variable concentrations of potassium on wood smoke particulates (6-10). The use of potassium as a tracer is further complicated by its presence in fine particulates from soil. Organic compounds including retene (l-methyl-7-isopropylphenanthrene) and levoglucosan (the anhydride of @-glucose)have also been suggested as tracers for atmospheric pollutants from wood burning, but their use has been limited (11,12). The measurement of 14Ccan be used to distinguish between “new” carbon (from wood burning) and “old” carbon (from fossil fuel combustion), but the analysis takes a relatively long time to perform, requires instrumentation that is not widely available, and yields no additional information about sample constituents (13). Although extensive investigations have been conducted into the identification of organics extracted from wood smoke particulates, these studies have generally subjected extracts to class fractionation prior to analysis and have focused on fractions containing polycyclic aromatic hydrocarbons (PAHs) and oxy-PAHs (4,12,14-17), while University of North Dakota. of Colorado.
t University
0013-936X/88/0922-1191$01.50/0
much less emphasis has been placed on the more polar fractions. This report describes the identification of more than 30 methoxylated phenolic species in unfractionated extracts from wood smoke particulates that may be useful as tracer compounds for determining the contribution of wood smoke to the total atmospheric fine-particulate loading. The species that have been identified have many characteristics of ideal tracer compounds in that they should be unique to wood smoke particulates, they are present in high concentrations, and they can easily be extracted from the particulates and measured by capillary gas chromatography/mass spectrometry (GC/MS) without the need for intermediate class-fractionation steps. The candidate tracer species were identified by using capillary GC/MS with electron impact (EI) ionization and chemical ionization (CI) with deuteriated methanol as the reagent gas. Molecular formulas were confirmed by capillary GC coupled with high-resolution mass spectrometry (GC/ HRMS).
Experimental Section Samples. Wood smoke particulate samples were collected from four different residential air-tight wood stove installations, two of which were burning a mixture of hardwood species (primarily elm, ash, and oak) and two of which were burning pine. Airborne particulates from hardwood smoke were collected onto 37 mm diameter organic-free glass fiber filters ca. 0.5 m from the chimney outlet. Approximately 2 mg of particulates was collected with a flow rate of 2 L/min for 10 min. A hardwood soot sample and both of the pine soot samples were scraped from the outlet of the chimneys. Each filter sample and approximately 50 mg of the soot scrapings were extracted for 4 h in approximately 20 mL of methylene chloride with the aid of sonication. A l-g sample of the hardwood soot scrapings was extracted in a similar manner in order to yield a more concentrated sample for GC/HRMS analysis. After the extraction, the methylene chloride solutions were evaporated under nitrogen to approximately 1 mL. Samples for estimating the distribution of the candidate tracer species between the particulates and the vapor phase were collected at 4 L/min onto 37 mm glass fiber filters backed up by two 37 mm diameter X 40 mm long polyurethane foam (PUF) sorbent plugs (12,18,19). Prior to sample collection, the PUF plugs were preextracted for 4 h by using several 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 extracted by sonication with 60 mL of acetone for 2 h, followed by evaporation under nitrogen to 1 mL. Gas Chromatography and Mass Spectrometry Analysis. All low-resolution GC/MS (E1and CI) analyses were performed by a Hewlett-Packard Model 5985B GC/MS equipped with a dual EI/CI source. Chromatographic separations were achieved with a 60 m X 0.25 mm i.d. (0.25 pm film thickness) DB-5 capillary gas chromatographic column (J & W Scientific). Both on-column and
0 1988 American Chemical Society
Environ. Sci. Technol., Vol. 22, No. 10, 1988
1191
split injections (split ratio ca. 1:40) were used depending upon the sample concentration. Temperature programming was 80-320 "C at 6 "C/min for split injections. On-column injections were performed at an oven temperature of 40 "C, followed by a temperature ramp of 30 "C/min to 80 "C, and then by a temperature ramp of 6 "C/min to 340 "C. E1 mass spectra were obtained at 70 eV with a typical scan range of 50-350 amu. Gas chromatography with flame ionization detection (GC/FID) was performed under the same chromatographic conditions with a Hewlett-Packard Model 5890 GC. Chemical ionization mass spectrometry was performed with methanol-dl (CH30D) as the reagent gas at a source pressure of 0.2 Torr (20). CI tuning parameters were optimized by maximizing the intensity of the M + 3 ion (m/z 125) of 2,4-dimethylphenol introduced through the direct insertion probe. Because of a prominent background ion at m / z 101 resulting from the reagent ion cluster (CH30D)3D+,the scan range when using CI was 105-350 amu. Capillary gas chromatography/high-resolution mass spectrometry (GC/HRMS) was performed by a VG 7070 EQ-HF equipped with a Hewlett-Packard Model 5890 gas chromatograph with a Hewlett-Packard High Performance 5 % phenylmethyl silicone capillary GC column (25 m X 0.2 mm i.d., 0.33 pm film thickness). Sample injection was at 80 "C followed by a temperature program at 4 "C/min to 320 "C. The mass spectrometer scan range was 50-400 amu at 1.0 s/decade and a resolution of approximately 4000 (10% valley). Results and Discussion Figure 1shows a typical chromatogram obtained from the GC/FID analysis of the unfractionated extract of hardwood smoke particulates. Preliminary GC/MS analyses using E1 ionization showed that all of the hardwood and pine smoke extracts contained a complex mixture of phenols, oxygenated phenols, PAHs, and oxyPAHs. The combined use of GC/MS, GC/MS with CH30D CI, and GC/HRMS allowed the identification of 72 individual species listed in Tables I and 11. Several phenols, PAHs, and oxy-PAHs were identified on the basis of a comparison of their E1 mass spectra with standard spectra and, in several cases, by a comparison of their retention indices with those of known compounds (Table I). Many of these species including the PAHs and oxyPAHs are typical products of combustion processes, while several of the species (i.e., the phenols) would be expected from the pyrolysis of wood lignin. The species listed in Table I1 were more difficult to identify. With the exception of 2-hydroxy-3-methyl-2cyclopenten-1-one (peak number 2), the E1 mass spectra indicated that all of the species were oxygenated phenols. GC/HRMS analysis demonstrated that the species in Table I1 contained two or more oxygen atoms. In most cases, however, the HRMS data and the E1 fragmentation patterns were not sufficient to differentiate among the several different structural isomers that were possible for a particular molecular formula. This problem was particularly severe when trying to determine the number of -OH and -OR functionalities present on a particular species (e.g., a dimethoxybenzene versus a methylmethoxyphenol versus a dihydroxydimethylbenzene) since the E1 mass spectra of such isomers are frequently indistinguishable from one another. The identification of these species in the highly complex wood smoke extracts was further complicated by the fact that, even though the separations were performed with high resolution gas chromatography, individual species were not always com1192
Environ. Sci. Technol., Vol. 22, No. 10, 1988
Table I. Identities of Phenols, PAHs, and Oxy-PAHs Shown in Figure 1 peak no." 1 3 4
6 7 8 9 10 15 17 18 37 39 40 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 62 63 64 66 67 69 70 71 72
species phenol 2-methylphenol 3-methylphenol and/or 4-methylphenol C2-phenol C2-phenol C2-phenol C2-phenol C2-phenol 1-indanone methylindanone methylindanone 9-fluorenone phenanthrene anthracene C1-phenanthrene or C1-anthracene isomers C1-phenanthrene or C1-anthracene isomers C1-phenanthrene or C1-anthracene isomers C1-phenanthrene or Cl-anthracene isomers C1-phenanthrene or Cl-anthracene isomers fluoranthene pyrene benzonaphthofuran isomers benzonaphthofuran isomers benzonaphthofuran isomers benzonaphthofuran isomers C1-fluoranthene or C1-pyrene isomers C1-fluoranthene or C1-pyrene isomers C1-fluoranthene or C1-pyrene isomers C1-fluoranthene or Cl-pyrene isomers C1-fluoranthene or C1-pyrene isomers C1-fluoranthene or C1-pyrene isomers C1-fluoranthene or C1-pyrene isomers benzo [ghi]fluoranthene benz[a] anthracene chrysene benzo[ blfluoranthene benzo[k]fluoranthene PAH isomer PAH isomer PAH isomer benzo [alpyrene
ret. confirmed indexb M, by standard' 972.5 94 1049.9 108 1071.3 108 1135.0 1147.0 1166.3 1177.7 1192.8 1291.1 1316.6 1328.5 1765.6 1811.3 1821.3 1927.2
122 122 122 122 122 132 146 146 180 178 178 192
X X X
X X X X
1934.2 192 1943.6 192 1955.0 192 1960.1 192 2103.2 2160.9 2162.7 2180.4 2196.0 2221.7 2227.4
202 202 218 218 218 218 216
X X
2251.4 216 2256.1 216 2273.3 216 2283.4 216 2308.4 216 2315.8 216 2439.2 2493.1 2504.2 2752.5 2757.2 2779.3 2816.2 2825.5 2841.7
226 228 228 252 252 252 252 252 252
X X X X
X
"Peak numbers refer t o the chromatogram in Figure 1. *Retention indices were based on normal alkanes. The standard deviations of three replicate determinations were typically less than 1 unit. 'Identities were confirmed by comparing the retention indices and E1 fragmentation patterns with those of standard compounds. The agreement between retention indices of the standard and samde species was typically within 1 unit.
pletely resolved which resulted in an overlap of their mass spectra. Such overlap made the use of subtle differences in E1 spectra impossible for identifying individual isomers. In order to determine the type of oxygen functionalities present on the oxygenated phenols, chemical ionization GC/MS analysis using CH30D as the reagent gas was used to count the number of -OH groups present on each component (20). As shown by the standard spectra in Figure 2, the number of -OH groups on each species can easily be determined by observing the apparent increase in mass.
I
I
I
Figure 1. GC/FID chromatogram of the unfractionated methylene chloride extract of hardwood soot. Peak numbers refer to species identified in Tables I and 11. 1001
l\l 4 0
OCH, 1 5
6
i I 0
1GO
140
120
M=138
I
180
200
220
120
140
180
180
200
100-
loo]
I
h
.-3 H c O 6 I
C ++
M=154
- ‘ : ), ! , ~
---,-I
0
J 0 . l i l . . 120
140
160
‘1
loo]
180
200
220
120
140
160
180
200
220
144
M=140 0
120
140
0 U 160 180 200 , 220 , , , 140 160 180 200, 220 240> 260 280 300
m/z Flgure 2. Chemical ionization mass spectra of representative standard compounds Using CHaOD as the reagent gas. Compounds with zero, one, and two -OH groups show a base peak (100% relative intensity) 2, M 3, and M 4, respectively. at M
mlz Figure 3. Chemical ionization mass spectra of representative species in the hardwood smoke extract using CH,OD as the reagent gas. The number of -OH groups on each compound was determined as described in the text.
Species with no -OH groups (e.g., p-dimethoxybenzene) show a base peak (100% relative intensity) at M + 2 from the addition of D+. In contrast, species with one -OH (e.g., syringol and 4-acetylguaiacol) show a base peak at M + 3 from the addition of D+and the exchange of one -OH for -OD, while species with two -OH groups (e.g., 2hydroxy-3-methoxyphenol) show a base peak at M + 4 from the addition of D+ and the exchange of two -OH hydrogens to form two -OD groups. Each of the hardwood and pine smoke extracts was analyzed by the CH30D CI technique, and the number of -OH groups found for each sample species is reported in Table 11. CH30D CI analysis also confirmed the identification of the phenols listed in Table I. The CH30D CI spectra for several representative sample species (peaks numbered 13, 23, 19, and 61 in Table 11) are shown in Figure 3. Note that even though the sample was very
complex and some interfering ions are present in the spectra, it was simple to determine the number of -OH groups since the ion that was used with the CH30D CI technique to determine the number of -OH groups was the base peak for each sample component. The combined use of GC/MS with CH30D CI, GC/ HRMS, and E1 fragmentation patterns allowed 30 oxygenated phenols to be identified in the wood smoke particulate extracts as listed in Table 11. Nearly all of the compounds are derivatives of either syringol(2,6-dimethoxyphenol) or guaiacol (2-methoxyphenol),and the species that have been identified include several alkyl derivatives as well as the related aldehydes and ketones. Dimer species including 1,2-bis(4-hydroxy-3-methoxyphenyl)ethane, 1-(4-hydroxy-3,&dimethoxypheny1)-2-(4-hydroxy3-methoxyphenyl)ethane, and 1,2-bis(4-hydroxy-3,5-dimethoxypheny1)ethane (designated hereafter as 1,2-di-
+
+
+
Environ. Sci. Technol., Voi. 22, No. 10, 1988
1193
~~
Table 11. Identities of Candidate Tracers for Atmospheric Wood Smoke Pollution
peak nosa 2 5 11 12 13 14 16 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 38 41 42 61 65 68
species
ret. indexb M, 2-hydroxy-3-methyl-2-cyclopenten-l-one 1027.1 112 guaiacol 1093.1 124 catechol 1192.2 110 4-methylguaiacol 1196.7 138 hydroxy guaiacol 1268.2 140 4-ethylguaiacol 152 1283.8 4-methylcatechol 124 1293.7 syringol 1356.5 154 4-allylguaiacol (eugenol) 1363.5 164 propylguaiacol 166 1373.3 C2-catechol 1388.4 138 1407.4 4-formylguaiacol (vanillin) 152 1414.4 cis-4-propenylguaiacol (isoeugenol) 164 1452.5 168 methylsyringol trans-4-propenylguaiacol(isoeugenol) 1457.7 164 4-acetylguaiacol (acetovanillone) 1496.6 166 ethylsyringol 1533.0 182 acetonylguaiacol 1540.6 180 propionylguaiacol 1592.3 180 allylsyringol 1608.3 194 propylsyringol 1615.5 196 4-carboxymethylguaiacol (homovanillic acid) 1659.4 182 4-formylsyringol (syringaldehyde) 182 1670.5 propenylsyringol 1708.1 194 4-acetylsyringol 1746.1 196 acetonylsyringol 1781.3 210 propionylsyringol 1835.6 210 (hydroxypropy1)syringol 1902.9 212 1,2-diguaiacylethane 274 2355.5 1-guaiacyl-2-syringylethane 304 2573.6 1,2-disyringylethane 2772.7 334
fragment ionsC
no. of -OHsd
112, 69, 55 109, 124, 81 110, 64, 63 123, 138, 95 140, 125, 97 137, 152, 122 124, 123, 78 154, 139, 96 164, 149, 77 137, 166, 138 123, 138, 124 151, 152,81 164, 149, 77 168, 153, 125 164, 149, 77 151, 166, 123 167, 182, 168 137, 180, 122 151, 180, 165 194, 91, 119 167, 196, 168 137, 182, 138 182, 181, 167 194, 91, 179 181, 196, 153 167, 210, 168 181, 210, 153 168, 167, 212 137, 274, 138 167, 137, 304 167, 334, 168
1 1
2 1
2 1 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 2 2 2
accuracy of HRMS, mmue -0.1 +0.8 +0.3 +1.8 -10.5 -0.9 -3.3 +0.8 +2.9 -2.1 -3.1 -1.8
-0.3 -2.5 -1.7 -1.9 +2.7 -2.3 -5.1 -2.7 +13.1 -16.4 -5.6 -9.8 -9.5 -4.0 -6.8
confirmed by standardf
X X X X X X X X X X X X
X X X
2
"eak numbers refer to the chromatogram in Figure 1. bRetention indices were based on normal alkanes. The standard deviations of three replicate determinations were typically less than 1 unit. The three most intense fragment ions from each 70 eV electron impact mass spectrum are given in order of decreasing intensity. dThe number of -OH groups was determined by using CH30D chemical ionization GC/MS as described in the text. eDeviations in millimass units (mmu) were calculated from the exact mass for the molecular ion. Species with no listed deviations were not present in sufficient quantity for molecular formulas to be determined using HRMS. /Identities were confirmed by comparing the retention indice and E1 fragmentation patterns with those of standard compounds. Agreement between retention indices of the standard and sample species was typically within 1 unit.
guaiacylethane, l-guaiacyl-2-syringylethane,and 1,2-disyringylethane, respectively) were also identified (peak numbers 61,65, and 68). The identities of 15 species listed in Table I1 were also confirmed by a comparison of retention indices and E1 fragmentation patterns with those of known standards. Comparisons of retention indices showed that substituent groups on sample species were para to the -OH group. In the cases where standards were not available, the substitution of the substituent group (e.g., methylsyringol) would also be expected to be para to the -OH group on the basis of the reported structure of wood lignin (21). All of the species listed in Table I1 have been identified in each of the four hardwood soot samples and in both of the pine wood soot samples (except for 1,2-disyringylethane, which was not detected in the pine soot extracts). Since all of the species listed in Table I1 are expected to be products resulting from the pyrolysis of wood lignin (22), they should be unique tracers for wood smoke pollution in urban atmospheres. Although several of the species listed in Table I (e.g., the phenols) are also pyrolysis products of lignin (22), they have been reported to be present in the atmosphere from other sources (e.g., vehicle exhaust; ref 23 and 24) and, therefore, have not been included in the list of candidate tracers given in Table 11. The relative concentrations of several of the major species have been estimated by comparing the integrated areas of the molecular ions from GC/MS analysis (E1 1194
Environ. Sci. Technol., Vol. 22, No. 10, 1988
ionization) to that of syringol for each sample (Table 111). All three hardwood particulate samples collected onto filters (A-C in Table 111) and the hardwood scrapings samples (D) had similar distributions of the major guaiacol and syringol derivatives, while the pine soot samples (E and F) showed a much higher proportion of guaiacol derivatives than that found in the hardwood samples. This result might be expected since pine lignin contains a much higher concentration of guaiacol subunits than hardwood lignin (21). Although the results in Table I11 are based only on the relative proportions of the individual species compared to syringol, they indicate that it may be possible to differentiate between smoke from hardwoods and softwoods on the basis of the relative proportions of guaiacol- and syringol-derived species. All of the organic compounds in Tables I and I1 were extracted from wood smoke particulates or chimney scrapings; however, it was apparent that several of the lower molecular weight species could exist in the vapor phase as well as being associated with particulates. In order to investigate the distribution of the candidate tracer species (Table 11) between the vapor and particulate phases, samples of hardwood smoke were collected onto glass fiber filters backed up by two PUF sorbent plugs as described under Experimental Section. The hardwood smoke samples were collected 0.5 m from the chimney outlet for 10 min and 2 m from the chimney outlet for 30 min. During the sample collection the approximate plume
Table 111. Estimated Relative Concentrations of Syringol and Guaiacol Derivatives in Hardwood and Pine Soot
species
19
estimated relative concn: % hardwood sootb pine soot A B C D E F
syringol derivatives syringol 100 100 100 100 100 100 methylsyringol 29 31 59 66 85 44 31 27 27 45 75 30 ethylsyringol 7 6 8 1 0 1 4 8 propylsyringol 17 14 12 2 propenylsyringol 25 22 3 4 1 5 1 4-acetylsyringol 2 1 2 4 6 5 8 1 9 1 0 acetonylsyringol guaiacol derivatives 6 3 3 9 9 9 guaiacol 1 1 3 4 9 4 55 139 4-methylguaiacol 6 7 9 5 3 5 5 3 4-ethylguaiacol 2 1 8 1 2 3 4-propylguaiacol 2 2 7 67 15 cis-4-propenylguaiacol 22 18 10 9 9 9 6 190 198 formylguaiacol 4 4 3 11 78 64 4-acetylguaiacol 16 15 9 9 31 36 acetonylguaiacol a The concentration of each species relative to syringol was estimated by comparing the integrated areas of their molecular ions as described in the text. *Samples of airborne particulates (A-C) were collected 0.5 m from the chimney outlet onto glass fiber filters as previously described. Samples A and B were from two different air-tight wood stove installations that were burning primarily elm and mixed elm and ash, respectively. Sample C was from the same chimney as sample B but was collected while mixed oak and ash were being burned. Sample D was scraped from the outlet of the same chimney and at the same time as sample B. Samples D and E were scraped from chimney outlets of two different airtight wood stoves that burned pine.
temperature was 95 "C at the chimney outlet, 20 "C at 0.5 m, and 5 "C at 2 m. Ambient temperature was 4 "C. Following sample collection, the samples were extracted as previously described. Extracts of the backup PUF plugs showed no significant species demonstrating that the vapor-phase organics were efficiently collected on the first PUF plug. Extracts of filter and PUF blanks and the second extracts of the sample filter and PUF plugs also showed no significant species, indicating that the acetone extractions were capable of recovering the analyte species without causing sample contamination. GC/MS analyses of the unfractionated extracts from the 0.5-m sample filter and the front PUF plug are shown in Figure 4. Both total ion current chromatogramsare scaled to the same sensitivity. Peak numbers refer to the species listed in Tables I and 11. As shown in Figure 4,the species that elute before syringol (peak number 19) had significant concentrations in the vapor phase, while the majority of species eluting after syringol were primarily collected on the particulate filter. The sample collected at 2 m had a much lower concentration of organics, but the filter and the PUF extracts showed a distribution of the candidate tracers that was similar to that found in the 0.5-m sample. Although the distribution of the tracer organics shown in Figure 4 is not necessarily the exact distribution found in ambient air (e.g., some of the semivolatile organics could be stripped from the particulates during the sample collection, and thus be collected on the PUF plug), this experiment does demonstrate that many of the candidate tracer species listed in Table I1 are primarily associated with the particulates and indicates that lignin pyrolysis products may be useful as tracers for both vapor-phase pollutants and particulates emitted from residential wood burning. The methoxylated phenols identified in Table I1 have several potential advantages as tracers of atmospheric
Retention Time (min) Figure 4. Total Ion current GC/MS chromatograms of hardwood smoke organics collected 0.5 m from the chimney outlet. The chromatograms show the organics extracted from the particulate filter (top chromatogram) and from a PUF sorbent plug (bottom chromatogram) which was downstream of the particulate fllter during sample collection. Peak numbers refer to the species identified in Tables I and 11. Sampling, extraction, and chromatographic conditions are given in the text.
wood smoke pollution. Since they are pyrolysis products of wood lignin, they are expected to be unique to wood smoke in urban atmospheres. As shown by the GC/FID chromatogram of the unfractionated extract (Figure l),the candidate tracers are generally the most concentrated organic species present, which should reduce the size of air samples that need to be collected, and also minimize the need for sample concentration and class-fractionation steps. Even if class fractionation is required for extracts from mixed particulate samples, the phenolic -OH present on each of the species listed in Table I1 should make separation of the wood smoke tracer species simple to obtain from the other major organic species present in carbonaceous particulates. The candidate tracers also have E1 fragmentation patterns and intense fragment ions that are highly characteristic of lignin pyrolysis products and are simple to differentiate from the spectra of predominant species (e.g., alkanes, PAHs, oxy-PAHs, and nitro-PAHs) found in particulates from other major sources of carbonaceous particulates such as vehicle exhaust (25-29). The selective detection of such characteristic fragment ions using selected ion monitoring GC/MS analysis should yield good sensitivity and selectivity for the candidate wood smoke tracers when air samples that have been polluted from a variety of sources are analyzed. Since more than 30 candidate tracer species have been identified, their use as tracers should be less susceptible to anomalous behavior than when a single tracer is used for source apportionment studies. Environ. Sci. Technol., Vol. 22, No. 10, 1988
1195
Environ. Sci. Technol. 1988, 22, 1196-1200
Registry No. Phenol, 108-95-2; 2-methylphenol, 95-48-7; 3-methylphenol, 108-39-4;4-methylphenol, 106-44-5; l-indanone, 83-33-0; methylindanone, 87259-53-8; 9-fluorenone, 486-25-9; phenanthrene, 85-01-8; anthracene, 120-12-7;fluoranthene, 20644-0; pyrene, 129-00-0; benzonaphthofuran, 205-39-0; benzo[ghilfluoranthene, 203-12-3;benz[a]anthracene, 56-55-3; chrysene, 218-01-9;benzo[b]fluoranthene, 205-99-2; benzo[k]fluoranthene, 207-08-9; benzo[a]pyrene, 50-32-8; 2-hydroxy-3-methyl-2-cyclopenten-l-one, 80-71-7; guaiacol, 90-05-1; catechol, 120-80-9; 4methylguaiacol, 93-51-6; 4-ethylguaiacol, 2785-89-9; 4-methylcatechol, 452-86-8; syringol, 91-10-1; 4-allylguaiacol, 97-53-0; 4formylguaiacol, 121-33-5; cis-4-propenylguaiaco1, 5912-86-7; trans-4-propenylguaiacol,5932-68-3;4-acetylguaiacol, 498-02-2; 4-acetoxyguaiacol, 57244-88-9; 4-formylsyringol, 134-96-3; 4acetylsyringol, 2478-38-8; 4-propylguaiacol, 2785-87-7. L i t e r a t u r e Cited Peters, J. A. Proc.-Znt. Conf. Resid. Solid Fuels: Environ. Impacts Solutions 1981, 267-284. Kamens, R. M.; Rives, G. D.; Perry, J. M.; Bell, D. A,; Paylor, R. F., Jr.; Goodman, R. G.; Claxton, L. D. Environ. Sci. Technol. 1984, 18, 523-530. Bell, D. A.; Kamens, R. M. Atmos. Enuiron. 1986, 20, 317-321. Kamens, R.; Bell, D.; Dietrich, A.; Perry, J.; Goodman, R.; Claxton, L.; Tejada, S. Environ. Sci. Technol. 1985, 19, 63-69. Kleindienst, T. E.; Shepson, P. B.; Edney, E. 0.;Claxton, L. D.; Cupitt, L. T. Environ. Sci. Technol. 1986,20,493-501. DeCesar, R. T.; Edgerton, S. A.; Khalil, M. A. K.; Rasmussen, R. A. Chemosphere 1985, 14, 1495-1501. Edgerton, S. A,; Khalil, M. A. K.; Rasmussen, R. A. Enuiron. Sci. Technol. 1986, 20, 803-807. Khalil, M. A. K.; Edgerton, S. A.; Rasmussen, R. A. Enuiron. Sci. Technol. 1983, 17, 555-559. Wolff, G. T.; Countess, R. J.; Groblicki, P. G.; Ferman, M. A,; Cadle, S. H.; Muhlbaier, J. L. Atmos. Enuiron. 1981, 15, 2485-2502. Watson, J. G., Ph.D. Thesis, Oregon Graduate Center, Beaverton, OR, 1979. Ramdahl, T. Nature (London) 1983,306, 580-582. Hornig, J. F.; Soderberg, R. H.; Barefoot, A. C.; Galasyn,
(13) (14) (15) (16) (17) (18) (19)
(20) (21)
(22) (23) (24) (25) (26) (27) (28) (29)
J. F. In Polynuclear Aromatic Hydrocarbons: Mechanisms, Methods, and Metabolism; Cooke, M., Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1985; pp 561-568. Cooper, J. A.; Currie, L. A.; Klouda, G. A. Enuiron. Sci. Technol. 1981,15, 1045-1050. Ramdahl, T.; Becher, G. Anal. Chim. Acta 1982,144,83-91. Zeedijk, I. H. J. Aerosol Sci. 1986, 17, 635-638. Sexton, K.; Liu, K. S.; Hayward, S. B.; Spengler, J. D. Atmos. Enuiron. 1985, 19, 1225-1236. Cretney, J. R.; Lee, H. K.; Wright, G. J.; Swallow, W. H.; Taylor, M. C. Enuiron. Sci. Technol. 1985, 19, 397-404. Lewis, R. G.; Jackson, M. D. Anal. Chem. 1982,54,592-594. Ligocki, M. P.; Pankow, J. F. Anal. Chem. 1985, 57, 1138-1144. Buchanan, M. V. Anal. Chem. 1984,56, 546-549. Sarkanen, K. V.; Hergert, H. L. In Lignins: Occurrence, Formation, Structure, and Reactions; Sarkanen, K. V., Ludwig, C. H., Eds.; Wiley-Interscience: New York, 1971; pp 43-94. Boon, J. J.; Pouwels, A. D.; Eijkel, G. B. Biochem. SOC. Trans. 1987, 15, 170-174. Hampton, C. V.; Pierson, W. R.; Harvey, T. M.; Updegrove, W. S.; Marano, R. S. Enuiron. Sci. Technol. 1982, 16, 287-298. Hampton, C. V.; Pierson, W. R.; Schuetzle, D.; Harvey, T. M. Environ. Sci. Technol. 1983, 17, 699-708. Simoneit, B. R. T. Znt. J.Enuiron. Anal. Chem. 1985,22, 203-233. Schuetzle, D.; Riley, T. L.; Prater, T. J.; Harvey, T. M.; Hunt, D. F. Anal. Chem. 1982,54, 265-271. Ramdahl, T. Environ. Sci. Technol. 1983, 17, 666-670. Konig, J.; Balfanz, E.; Funcke, W.; Romanowski, T. Anal. Chem. 1983,55, 599-603. Behymer, T. D.; Hites, R. A. Enuiron. Sci. Technol. 1984, 18, 203-206.
Received for review December 11,1987. Accepted March 23,1988. The financial support of the U.S. Environmental Protection Agency, Office of Exploratory Research (Grant R-813257-01-O), is gratefully acknowledged. R.M.B. also acknowledges the support of the National Science Foundation (NSF ATM8618793).
Removal of Nitric Oxide from Flue Gas Using Water-Soluble Iron(I1) Dithiocarbamates David K. Liu and Shih-Ger Chang" Applied Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
The reactions of glycine and iminodiacetic acid with carbon disulfide in strongly alkaline solution yield N(carboxymethy1)dithiocarbamate (1)and N,N-bidcarboxymethy1)dithiocarbamate (2), respectively. These dithiocarbamates have been characterized by UV-visible and laser Raman spectroscopies and have been isolated as S-benzylthiuronate derivatives. Aqueous solutions containing iron(I1) chelates of 1 and 2 have been shown to be effective in removing NO from a simulated flue gas mixture over the pH range of 3-10. Most of the absorbed NO was reduced to Nz, and oxidative coupling of the dithiocarbamates occurred to form the corresponding dithiuram disulfides. Evidence is also presented for the absorption of NO by iron(I1) chelates of dithiocarbamates derived from diethanolamine and urea. Introduction
The simultaneous removal of NO, and SOz from flue gas using scrubbing liquors containing various iron(I1) chelates 1196
Environ. Sci. Technol., Vol. 22, No. 10, 1988
has been the subject of extensive research efforts over the last 15 years. The iron(I1) chelates serve to enhance the solubility of NO via the formation of iron nitrosyl complexes. This activated NO can then react with dissolved SOz and O2to produce Nz, NzO, dithionate, sulfate, and various nitrogen-sulfur compounds. Examples of these iron(I1) chelates include those of aminocarboxylates such as ethylenediaminetetraacetate (EDTA) and iminodi, acetate (IDA) (1-3), acetylacetonate (Z), citrate ( 2 , 4 ) and aminopolyphosphonates (5). More recently, we reported (6-8) that iron(I1) chelates of SH-containing amino acids and peptides are capable of removing NO from flue gas and that these systems might be more cost-effective compared to the Fe2+(EDTA)-typeadditives. In this paper, we describe the use of a new type of iron chelate, iron(I1) dithiocarbamates, for the removal of NO in wet flue gas scrubbing systems. The reaction of metal dithiocarbamates with NO was first reported over 50 years ago by Cambi (9). However, the metal dithiocarbamates and their nitrosyl complexes
0013-936X/88/0922-1196$01.50/0
0 1988 American Chemical Society
