Levoglucosan and Other Cellulose Markers in Pyrolysates of Miocene

Mar 12, 2008 - Laboratory of Environmental Sciences “R. Sartori”, CIRSA, University of Bologna, Via S. Alberto 163, 48100 Ravenna, Italy, Faculty ...
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Environ. Sci. Technol. 2008, 42, 2957–2963

Levoglucosan and Other Cellulose Markers in Pyrolysates of Miocene Lignites: Geochemical and Environmental Implications DANIELE FABBRI,† L E S Z E K M A R Y N O W S K I , * ,‡ ´ SKA,‡ MONIKA J. FABIAN ´ ,‡ AND MICHAŁ ZATON BERND R.T. SIMONEIT§ Laboratory of Environmental Sciences “R. Sartori”, CIRSA, University of Bologna, Via S. Alberto 163, 48100 Ravenna, Italy, ´ Faculty of Earth Sciences, University of Silesia, ul. Be˛dzinska 60, 41-200 Sosnowiec, Poland, and Department of Chemistry, Oregon State University, Corvallis, Oregon 97331

Received September 3, 2007. Revised manuscript received December 20, 2007. Accepted January 22, 2008.

Using the pyrolysis-gas chromatography–mass spectrometry and off-line pyrolysis/silylation methods for lignites from three Miocene brown coal basins of Poland resulted in the characterization of many organic compounds, including dominant cellulose degradation products such as levoglucosan, 1,6-anhydro-β-D-glucofuranose, and 1,4:3,6-dianhydroglucopyranose. Levoglucosan is a general source-specific tracer for wood smoke in the atmosphere and recent sediments. The presence of unusually high levels of this compound in brown coal pyrolysates suggests that a portion of this compound concentration in some airsheds may originate from lignite combustion. On the other hand, nonglucose anhydrosaccharides, in particular, mannosan and galactosan, typical of hemicellulose, are not detected in those lignite pyrolysates investigated. This indicates that mannosan and galactosan are better specific tracers for combustion of contemporary biomass in those regions were the utilization of brown coals containing fossilized cellulose is important.

Introduction It is widely known that carbohydrates have a low preservation potential during organic matter (OM) sedimentation and diagenesis (1–3) and, therefore, are rarely detected in ancient sediments. Early diagenetic sulfurization processes are one way for carbohydrates to be preserved in sedimentary environments, where carbohydrates can be incorporated into macromolecular organic matter (OM) through mono- and polysulfidic linkages (4–7). However, sulfurization processes are mainly observed in anoxic depositional environments, such as that of the Jurassic Kimmeridge Clay mudrock succession (4, 8). Some recent reports show that not only sulfurized but normal carbohydrates may also be preserved in ancient materials (9–15). In all those cases it was cellulose present in Miocene and Pliocene lignites, cone scales and seeds from open cast mines, located in the southern part of * Corresponding author e-mail: [email protected]. † Laboratory of Environmental Sciences “R. Sartori”. ‡ University of Silesia. § Oregon State University. 10.1021/es7021472 CCC: $40.75

Published on Web 03/12/2008

 2008 American Chemical Society

the Lower Rhine Embayment, northeast of Aachen, Germany; Zillingdorf, Austria; as well as Oczkowice, Gozdnica, Lubstów, and Ruszow in Poland. The main monosaccharide derivative formed by the thermal breakdown of cellulose is levoglucosan (1,6-anhydroβ-D-glucopyranose 16–19). Because of their ubiquitous occurrence in atmospheric aerosols (17, 20–25), recent soils, and sediment samples (26–28), levoglucosan, coupled with the minor mannosan and galactosan, are utilized as specific indicators for burning of biomass containing cellulose and hemicellulose (17, 25, 29–32). Although levoglucosan is commonly present as a tracer for wood smoke in the atmosphere and in some recent sediments, its detection in pre-Quaternary sedimentary rocks is sporadic, mainly due to the extensive degradation and hydrolysis of cellulose and free levoglucosan over time (26). The mere documentation of levoglucosan using the pyrolysis-gas chromatography– mass spectrometry (Py-GC-MS) method was performed by Stankiewicz et al. (13) and van Bergen and Poole (12) from Miocene to Pliocene fossil cone scales and seeds of Pinus leitzii (Kirchh.) and Sequoia langsdorfii (Brongn.), and wood from Miocene brown coal, respectively. Here we report the occurrence of relatively high concentrations of levoglucosan in pyrolysates of Miocene lignites using Py-GC-MS and off-line pyrolysis/silylation with gas chromatography–mass spectrometry (GC-MS). These results shed light on the geochemical aspects of cellulose preservation in brown coals; thus, caution should be considered when utilizing levoglucosan as a tracer in modeling wood smoke and coal emissions.

Materials and Methods For the geochemical analyses, 125 coals were sampled from four Miocene brown coal basins of Poland. These are the Konin, Bełchatów, Turów, and Western Poland brown coal basins (Table 1 and Supporting Information Figure S1). There, the brown coals are exploited in open cast mines (Kazimierz, Józ´win, Lubstów, Bełchatów, Turów, and Sieniawa) (Table 1). Preliminary investigations of 47 xylites (wood maceral or lithotype) using Py-GC-MS revealed that 15 of them produce levoglucosan. Lignites of any other lithotype beside xylite do not yield levoglucosan. From those lignites that contain levoglucosan in their pyrolysates, we selected six for further investigation (Supporting Information Table S1). They come from the Konin Brown Coal Basin (Józ´win mine, Jsp11; Lubstów mine, Lst6; Kazimierz mine, Ks2), Turoˇw Brown Coal Basin (Turów mine, T3e) and Western Brown Coal Basin (two samples from the Sieniawa mine, S6k and S6s). Levoglucosan was absent in all samples analyzed from the Bełchatów mine and in all xylites from the lower bed of the Turów mine. Extraction and Separation. The general geochemical characteristics of the coals investigated were determined on separated extracts of the samples. Powdered lignites were extracted with dichloromethane (DCM) in an ultrasonic bath until eluates were colorless (4–6 times, each ultrasonication time was 30 min.). Extracts were further separated using preparative prewashed TLC plates coated with silica gel (Merck, 20 × 20 × 0.25 cm and 10 × 20 × 0.25 cm). Prior to separation, the TLC plates were activated at 120 °C for 1 h. The plates were loaded with the n-hexane soluble fraction and developed with n-hexane. Bands comprising aliphatic (Rf ) 0.4–1.0), aromatic (Rf ) 0.05–0.4) and polar (Rf ) 0.0–0.05) fractions were collected. VOL. 42, NO. 8, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. sample

Sample Description. locality

Ks2

the Konin Brown Coal Basin (Central Lowlands), Kazimierz mine

Jsp11

the Konin Brown Coal Basin, (Central Lowlands), Józ´win mine

Lst6

the Konin Brown Coal Basin, (Central Lowlands), Lubstów mine the Turoszów Brown Coal Basin (the Sudetian Mts), Turów mine

T3e

S6k

S6s

a

the Lubuskie Brown Coal Basin, (Lower Silesia), Sieniawa mine the Lubuskie Brown Coal Basin, (Lower Silesia), Sieniawa mine

lithotype description

Rr [%]a

grey-brown xylitic lignite with well preserved coarse woody texture (sampled in the central part of the seam) brown lignite with well preserved fine woody texture (sampled in the floor of the seam) light brown brittle xylitic lignite (sampled in the upper seam)

0.17

light brown xylitic lignite with low content of clayey material (sampled in the upper part of the seam) detrital light brown lignite with fine xylitic detritus

0.17

red-brown xylitic lignite, brittle

0.16

0.15

0.15

0.23

Rr [%], huminite reflectance.

Gas Chromatography-Mass Spectrometry (GC-MS). The GC-MS analyses of the lignite and pyrolysis extracts described in the section on Py-GC-MS were performed with an Agilent 6890 Series gas chromatograph interfaced to an Agilent 5973 Network mass selective detector and Agilent 7683 Series injector (Agilent Technologies, Palo Alto, California). A 0.5 µl sample was introduced into the cool on-column injector under electronic pressure control. Helium (6.0 grade) was used as the carrier gas at a constant flow rate of 2.6 mL/min. The GC separation was on either of HP-5MS (60 m × 0.32 mm i.d., 0.25 µm film thickness) fused-silica capillary column coated with a chemically bonded phase (95% polydimethylsiloxane, 5% diphenylsiloxane). The GC oven temperature was programmed from 40 °C (isothermal for 1 min) to 120 °C at a rate of 20 °C/min, then to 300 °C at a rate of 3 °C/min. The final temperature was held for 35 min. The GC column outlet was connected directly to the ion source of the mass spectrometer. The GC-MS interface was kept at 280 °C, and the ion source and the quadrupole analyzer were at 230 and 150 °C, respectively. Mass spectra were recorded from m/z 45–550 (0–40 min) and m/z 50–700 (above 40 min). The mass spectrometer was operated in the electron impact mode (ionization energy: 70 eV). All compounds were identified by their mass spectra, comparison of retention times to those of standard compounds and interpretation of MS fragmentation patterns and literature data (34). Py-GC-MS. For preliminary investigations of the lignites we used the flash Py-GC-MS method. The portions of previously extracted lignites were subjected to Py-GC-MS. The analysis was carried out with an Agilent Technology gas chromatograph equipped with a HP-5MS capillary column 2958

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(60m × 0.32 mm, 0.25 µm stationary phase film). The gas chromatograph was coupled to the same mass spectrometer as above operating in the EI mode at 70 eV (full scan from 50 to 650 dalton). Samples were pyrolyzed in a Pye-Unicam Pyrolyser (795050) heating to the Curie point at temperatures to 770 °C. Off-line Pyrolysis/Silylation and GC-MS. The procedure was similar with slight modifications to that already reported for off-line pyrolysis/silylation of polysaccharides (35), humic acids, and coals (36). Briefly, samples (5–10 mg) were pyrolyzed in the presence of excess hexamethyldisilazane (HMDS, 20–40 µl) at 500 °C (set temperature) for 60 s at the maximum heating rate (20 °C ms-1) of a CDS 1000 pyroprobe equipped with a platinum filament. Pyrolyses were performed off-line by means of a glass chamber fluxed with nitrogen at 200 mL min-1, which swept off pyrolysis products into an activated charcoal trap as is used for air monitoring applications (Orbo 32 Supelco). Products adsorbed onto the trap were eluted with 4 mL ethyl acetate and were analyzed directly without preconcentration by GC-MS. Procedural blanks, that is, the overall pyrolysis/trapping/elution procedure without the addition of lignite samples, were run prior to each analysis in order to avoid cross-contamination. GC-MS analyses of derivatized pyrolysates were performed under splitless conditions with a Varian 3400 gas chromatograph connected to a Varian Saturn 2000 ion trap mass spectrometer. Analytes were separated by a MDN-5S (Supelco) fused-silica capillary column (stationary phase poly[5% diphenyl/95% dimethyl]siloxane, 30 m, 0.25 mm I.D., 0.25 µm film thickness) with the following temperature program: from 50 (hold for 2 min) to 310 °C at 10 °C min-1, using helium as carrier gas. GC injector, GC-MS interface, and ion trap were maintained at 260, 280, and 200 °C, respectively. Mass spectra were recorded under electron impact ionization (70 eV) at a frequency of 1 scan s-1 over a range from m/z 45 to 450. The identification of levoglucosan TMS ethers was based on the analysis of the pure compound [silylated with 0.2 mL bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane in 0.5 mL acetonitrile and 0.02 mL pyridine] and on comparison with literature data (37). The relative abundances of 12 silylated pyrolysis products selected as markers of cellulose and lignin were calculated from the peak areas integrated in the total ion current (TIC) traces (base peak as target ion) and expressed as percent peak area.

Results and Discussion GC-MS and Py-GC-MS Analyses. Several biomarker parameters were applied to assess the thermal maturity of the lignites investigated (Supporting Information Table S2). Their values concur with the measured values of the huminite random reflectance (Rr), indicating low stages of geochemical evolution (Table 1). GC-MS analysis of biomarker distributions and Py-GCMS data of the lignin compositions indicate that all xylites investigated are derived from conifer wood. The xylite pyrolysates are dominated by guaiacol derivatives substituted in the para position such as p-methylguaiacol, p-ethylguaiacol, p-vinylguaiacol, eugenol, isoeugenol, and cerulignol. This feature is characteristic for lignin pyrolysates of conifers (38–42). The characteristic features in biomarker distributions obtained from the GC-MS analysis of extracts indicated that the T3e, Jsp11, S6k, and S6s lignites originated from conifers (33, 43–48). They are characterized by the presence of polar biomolecules such as ferruginol and sugiol, which are characteristic for the Podocarpaceae or Cupressaceae groups (33, 45, 46). On the other hand, the Ks2 and Lst6 samples (both from the Konin Brown Coal Basin) contain abietic acid,

FIGURE 1. Total Ion Chromatograms (TIC) from Py/GC-MS analyses of xylitic lignites showing the presence of levoglucosan (LG). Compound identifications: 1-furan; 2-2pentene; 3-hydroxyacetaldehyde; 4, 2-propanol; 5, 2,3-butanedione; 6, 2-methylfuran; 7, 2-methyl-1,3-pentadiene; 8, benzene; 9 –1-hydroxy-2-propanone; 10, 2,5-dimethylfuran; 11, 2,4pentadienal; 12, toluene; 13, 1-octene; 14, cyclopentanone; 15, ?; 16, 3-furaldehyde; 17, 3-furanmethanol; 18, furfural; 19, 2-cyclopenten-1-one; 20 –2,3-dihydro-2,5-dimethylfuran; 21, 1-(acetyloxy)2-propanone; 22, o-xylene; 23, 2-hydroxy-2-cyclopenten-1-one; 24, p-ethyltoluene; 25, 5-methyfurfural; 26, phenol; 27, 3-methyl-2, 4-imidazolidinedione; 28, 2-hydroxy-3-methyl-2-cyclopenten-1one; 29, o-cresol; 30, p-cresol + m-cresol; 31, (2-methyl-1-propenyl)benzene; 32, guaiacol; 33, 2-furanmethanol; 34, 3,5-xylenol; 35, 2,4xylenol; 36, p-methylguaiacol; 37, 1-undecanol; 38, 1,2benzenediol; 39, p-vinylphenol; 40, 3,4-dimethoxytoluene; 41, 5(hydroxymethyl)-2-furancarboxaldehyde; 42, 3-methyl-1,2-benzenediol; 43, p-ethylguaiacol; 44, 4-methyl-1,2-benzenediol; 45, pvinylguaiacol; 46, ?; 47, eugenol (2-methoxy-4-(2-propenyl)phenol); 48, cerulignol (2-methoxy-4-propylphenol); 49, cisisoeugenol; 50, vanillin; 51, trans-isoeugenol; 52, apocynine (1-(4hydroxy-3-methoxyphenyl)-ethanone); 53, levoglucosan (?); LG, levoglucosan; 54, guaiacylacetone (1-(4-hydroxy-3-methoxyphenyl)-2-propanone); 55, coniferyl alcohol; 56, propiovanillone; 57, levoglucosan (?); 58, ?; 59, 1-(2-ethoxyphenyl)acetone; 60, 1,6anhydro-β-D-glucofuranose; 61, palmitic acid; 62, 4,4′methylenebisphenol. dehydroabietic acid, and their degraded polar products, which suggest that these lignites originated from Pinaceae wood (for examples, see refs 45and 47). Preliminary Py-GC-MS analysis indicated that in 15 of the group of 47 xylites the solvent-insoluble fraction contained levoglucosan in the pyrolysates. This compound was also found in one detroxylitic sample (S6k) from the Sieniawa mine. Apart from that sample, levoglucosan has not been detected in lignites of any other lithotype besides xylite. The relative peak areas of levoglucosan in comparison to other compounds are remarkably high for xylites (Figure 1), indicating well preserved wood cell structures (see Supporting Information Table S1). For more detailed molecular characteristics of the selected lignites, we used the off-line pyrolysis/silylation method and GC-MS, which is recommended for detection of anhydrosugars that evolved from polysaccharides. Off-line Pyrolysis/Silylation GC-MS of Lignites. Pyrolysis combined in situ with a trimethylsilylating reagent, such as HDMS and BSTFA, has been applied to the molecular characterization of natural polymers, including lignin (49),

FIGURE 2. Total ion chromatograms (TIC) of the products evolved from off-line pyrolysis of lignite samples in the presence of HMDS. Peak numbers refer to compounds listed in Table 2. Cellulose derivatives are indicated by the shaded peaks. polysaccharides (19, 35), proteins (50), waxes (51), and resins (52, 53). This technique directly affords the trimethylsilyl (TMS) derivatives of hydroxylated pyrolysis products normally observed in conventional pyrolysis, with the benefit of improved GC-MS behavior. However, under online Py-GC conditions, the derivatization may be incomplete due to the rapid volatilization of the reagent from the hot Py-GC interface, as observed, for example, for phenol derivatives evolved from complex organic materials, such as ancient wood (54), coal, and humic acids (36). The degree of derivatization can be increased with the pyrolyzer in the off-line configuration in order to avoid evaporative loss of the silylating reagent prior to pyrolysis (35, 36). Accordingly, the application of off-line pyrolysis with HMDS for lignite samples resulted in the production of pyrolysates dominated by TMS derivatives of thermal degradation products bearing alcohol, phenol, and carboxyl groups (Figure 2 and Table 2). Structural assignments were performed by comparing the GC-MS characteristics of the evolved compounds with published data related to pyrolysis/silylation products of cellulose (37), lignin (49), and silylated pyrolysate of fossil wood (55). In addition to the well-known pyrolysis products of cellulose (e.g., maltol, 5-hydroxymethyl-2-furaldehyde, 1,4:3,6-dianhydroglucopyranose, levoglucosan, and anhydroglucofuranose), a novel compound, namely 1-hydroxy3,6-dioxabicyclo[3.2.1]octan-2-one as the TMS ether, was included (Table 2). Its mass spectrum was recently reported (56), and that study also presented the mass spectrum of the TMS derivative of 1,4:3,6-dianhydroglucopyranose. Cellulose markers were detected in all Miocene lignite samples analyzed, and with the exception of sample S6k, they are intense peaks in the chromatograms. The highest GC signals were produced by levoglucosan as the 2,4-diVOL. 42, NO. 8, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. Compounds Evolved from Off-line Pyrolysis/Silylation of Lignite Samples No.a

compound

1 2 3 4 5 6 7 8

phenol, TMS ether levoglucosenone 2-methylphenol, TMS ether 3-methylphenol, TMS ether unknown (compound X1 in ref 37) 4-methylphenol, TMS ether 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one 1-methyl-2-hydroxy-1-cyclopenten-3-one, TMS ether (overlaps with 1-hydroxy-2-TMSoxybenzene) 2-methoxyphenol (guaiacol), TMS ether unknown 2-methyl-3-hydroxy-(4H)-pyran-4-one (maltol), TMS ether 5-hydroxymethyl-2-furaldehyde, TMS ether 4-methylguaiacol, TMS ether 1,2-dihydroxybenzene, diTMS ether (catechol) 1,4:3,6-dianhydro-R-D-glucopyranose, TMS ether 4-ethylguaiacol, TMS ether (overlaps with 3-methylcatechol, diTMS 73, 253, 268) 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one, TMS ether 2-methoxy-4-ethenylphenol (vinylguaiacol), TMS ether 2-methoxy-4-(2-propenyl)phenol (eugenol), TMS ether levoglucosan, 4-TMS ether levoglucosan, 2-TMS ether 2-methoxy-4-(1-Z-propenyl)phenol (Z-isoeugenol), TMS ether 1,2,3-trihydroxybenzene (pyrogallol), triTMS ether 2-methoxy-4-(1-E-propenyl)phenol (E-isoeugenol), TMS ether unknown (anhydroglucose ?) unknown (compound X4 in ref 37) 1,2,4-trihydroxybenzene, triTMS ether levoglucosan, 2,4-diTMS ether 1-(4-hydroxy-3-methoxyphenyl)propan-2-one (guaiacylacetone), TMS ether 2-(4-hydroxy-3-methoxyphenyl)ethanol, diTMS ether levoglucosan, triTMS ether 1,6-anhydro-β-D-glucofuranose, triTMS ether 3-methoxy-4-hydroxybenzoic acid (vanillic acid), TMS ether/ ester 3-guaiacylpropanol (dihydroconiferyl alcohol), diTMS ether

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

b

originc

95, 151, 166 98, (126) 135, 165, 180 165, 180 111, 127, 155 135, 165, 180 69, 116, (144) 97, 169, (184) (151, 166, 182)

L C L L C L C C

m/z 91, 68, 91, 91, 81, 91, 43, 75,

151, 166, 181, 196 43, 75, 143, 185 73, 153, 183, (198) 81, 111, 183, (198) 165, 180, 195, 210 73, 239, 254 73, 129, 170, (216) 179, 194, 209, 224

L C C L C C L

75, 144, 201, (216) 162, 192, 207, 222 205, 206, 221, 236 73, 129, 145, (234) 73, 116, 145, (234) 205, 206, 221, 236 73, 239, 327, 342 205, 206, 221, 236 73, 145, 189, 204 155, 273, 183, 288 73, 239, 327, 342 73, 116, 217 (306) 73, 179, 209, 252

C L L C C L C L C C C C L

73, 209, 297, 312 73, 204, 217, (378) 73, 217, 319, (378) 223, 267, 297, 312

L C C L

206, 236, 311, 326

L

a

Compound numbers refer to peak numbers reported in Figure 2 and in the text. b Mass-to-charge ratio of characteristic ions in the mass spectra (in bold, base peak; in italics, molecular ion; in parenthesis if low abundance). c C, cellulose; L, lignin.

TMSoxy (No. 28, Table 2) and 2,3,4-tri-TMSoxy (No. 31) derivatives. The relatively high abundance of a single disilylated isomer is attributed to the low accessibility of the OH group in position 3 for steric reasons that may preclude its fast derivatization under flash pyrolysis conditions. HMDS/ pyrolysates of lignites also contain two monosilylated levoglucosan derivatives with the TMS-oxy group at position 2 (No. 21) and position 4 (No. 20) (37). These two isomers give rise to rather intense peaks only in the pyrolysate of sample Lst6. This fact suggests that the extent of derivatization may depend on the nature of the sample subjected to pyrolysis, possibly due to differences in the polymerization degree of cellulose and the levels of free over-covalently bound OH groups. In addition to levoglucosan, the following thermal degradation products structurally indicative of cellulose were identified in the HMDS/pyrolysate of lignins: the TMS ethers of 1,6-anhydro-β-D-glucofuranose (No. 32), 1,4:3,6-dianhydroglucopyranose (No. 15), 2-methyl-3-hydroxy-(4H)pyran-4-one (maltol, No. 11), and 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one (No. 17). This latter compound, identified for the first time in the pyrolysates of geopolymers, is an hydroxylactone susceptible to hydrolysis to the corresponding acid; thus, its occurrence in the chromatograms confirms that the cellulose markers are from in situ pyrolysis rather than direct volatilisation of pre-existing compounds. As this lactone contains a sterically hindered tertiary hydroxy group, 2960

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the underivatised form could occasionally be detected in the pyrolysates (No. 7). Several other silylated products were found in the pyrolysates that could also be associated with cellulose (No. 5, 8, 11, 12, 25, and 26), although the molecular structure could not be assigned in a few cases. Such an abundance of cellulose markers is rather unusual for pyrolysates generated from geopolymers of terrestrial origin, which are generally characterized by a preponderance of phenolic compounds. In fact, carbohydrate markers were not detected in pyrolysis/silylation products from ancient wood samples (54) and bituminous coal (36). The HMDS/pyrolysates of the lignites also contained silylated hydroxybenzenes besides anhydrosugars. Phenols and hydroxylated phenols may have multiple sources; but in the case of the lignite samples investigated here, a contribution from carbohydrates is also possible for silylated 1,2-dihydroxybenzene (catechol), 1,2,3-trihydroxybenzene (pyrogallol), and 1,2,4-trihydroxybenzene (hydroxyquinol), which were reported to be pyrolysis/silylation products of cellulose (19) and glucose (57). However, catechol has also been reported in pyrolysates of lignin (for example, see refs 58 and 59). Among the methylphenols (cresols), the 3- and 4-methylphenols could easily be separated by GC as the TMS ethers (No. 4 and 6, respectively), an advantage over conventional and TMAH pyrolysis where the corresponding underivatised and methylated forms coelute on common nonpolar GC

TABLE 3. Relative Peak Areas (%) of Selected Py/HMDS Products Derived from Cellulose and Lignin (No. as in Table 2) No.

compound

JsP11

S6s

Ks2

T3e

LsT6

S6k

Cellulose Markers 12 15 17 28 31 32

5-hydroxymethyl-2-furaldehyde, TMS ether 1,4:3,6-dianhydro-R-D-glucopyranose, TMS ether 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one, TMS ether levoglucosan, 2,4-diTMS ether levoglucosan, triTMS ether 1,6-anhydro-β-D-glucofuranose, triTMS ether

6.4 8.8 17.8 10.3 35.5 6.6

13.1 8.6 3.7 16.8 28.0 7.5

4.4 1.3 9.7 11.4 35.1 3.3

7.8 2.0 1.1 17.5 24.8 2.3

12.2 3.0 1.3 19.5 8.5 3.6

2.3 1.0 0.1 1.4 3.0 0.6

Lignin Markers 13 16 18 24 29 33

4-methylguaiacol, TMS ether 4-ethylguaiacol, TMS ether vinylguaiacol, TMS ether E-isoeugenol, TMS ether guaiacylacetone, TMS ether vanillic acid, TMS ether/ester

7.9 2.7 1.2 1.0 1.6 0.3

10.5 3.4 2.4 1.2 1.5 3.4

15.3 6.8 5.4 4.2 2.4 0.7

25.8 8.4 4.3 3.6 2.0 0.5

25.9 8.4 7.5 4.6 4.5 1.0

45.6 20.5 10.2 8.8 6.2 0.3

78 22

65 35

55 45

48 52

8 92

Σ cellulose markers Σ lignin markers

stationary phases as the one employed in this study. The distribution of these phenols was dominated by the 4-methyl isomer, with the exception of lignite S6k, which is enriched in 3-methylphenol. Sample S6k was unique in containing a low amount of carbohydrate markers with respect to the other lignites. HMDS/pyrolysates with distributions of silylated cresols dominated by the 4-methyl isomer were observed for humic acids, and those by the 3-methyl isomer in other coals (35). Moreover, several silylated 2-methoxyphenols (guaiacols) indicative of lignin were found in the HMDS/ pyrolysates, whereas silylated derivatives of 2,6-dimethoxyphenols (syringols) were not detected, in agreement with the Py-GC-MS analyses attesting the conifer wood origin. The relative abundances of the principal Py/HMDS markers, representative of cellulose and lignin, evolved from the lignites are reported in Table 3 as relative peak areas. Although the values are affected by significant dispersion [typical rsd is 30% (35, 36)], the data show differences among samples indicating that the relative content of cellulose with respect to lignin is highly variable in the various lignites. Geochemical Implications. Geochemical Implications. Using the Py-GC-MS and off-line pyrolysis/silylation methods for the lignites from three Miocene brown coal basins of Poland resulted in the characterization of many organic compounds, including dominant cellulose degradation products such as levoglucosan, 1,6-anhydro-β-D-glucofuranose, and 1,4:3,6-dianhydroglucopyranose. The presence of cellulose in fossil material, noted earlier by, for example, Schleser et al. (10), Lücke et al. (11), van Bergen and Poole (12), Stankiewicz et al. (13), and Bechtel et al. (14, 15), confirms a greater fossilization potential of cellulose than was considered thus far (see refs 2 and 60) and that it may survive in lignites for millions of years under favorable conditions. The xylite samples with a similar maturity range (Supporting Information Table SI-2) show variably preserved compounds derived from cellulose degradation (Figure 2). The largest relative concentration of cellulose derivatives (especially levoglucosan) was detected in sample Jsp11, and sample S6k produced only a small amount of these compounds (Figure 2). These preliminary results show that the diagenetic alteration and state of preservation of the lignites is not only determined by organic matter maturity, but can also be influenced by other factors such as differences in lithology of the surrounding sediments (see ref 61) and time of diagenetic degradation of the less resistant lignite constituents.

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Currently, there are few data about the preservation potential of hemicellulose in relation to cellulose in fossil wood (62) (also see ref 12), but those reports suggest that cellulose is more resistant to thermal degradation than hemicellulose. The occurrence of levoglucosan and 1,6anhydro-β-D-glucofuranose, anhydrosaccharides derived mainly from cellulose, and the simultaneous lack of mannosan and galactosan from hemicellulose in the xylite pyrolysates confirm those previous conclusions. Environmental Implications. Levoglucosan is a general source-specific tracer for wood smoke in the atmosphere and recent sediments (17, 25, 26, 30) (for review see ref 29). Up to now it was considered an exclusive source indicator present in atmospheric aerosols from any contemporary biomass fuel containing cellulose (17, 20, 22, 27, 30). However, the presence of unusually high levels of levoglucosan in brown coal pyrolysates suggests that a portion of this compound concentration in some airsheds may originate from lignite combustion. For example, brown coal is commonly used in Poland as a fuel in factories (34.2% of the overall electric energy production in Poland is based on brown coal) and domestic fireplaces (63, 64). Other derivatives besides levoglucosan have been detected in the pyrolysates, for example, 1,6-anhydro-β-D-glucofuranose and 1-hydroxy3,6-dioxabicyclo[3.2.1]octan-2-one (Table 2). Some of them (for example, 1,6-anhydro-β-D-glucofuranose) were previously reported in aerosol particulate matter (21, 27, 65). However, the other common anhydromonosaccharides occurring in environmental samples, such as mannosan and galactosan (for examples, see refs 27, 32and 66), have not been detected in these pyrolysates. These nonglucose anhydrosaccharides are typical derivatives from hemicellulose and are not present in cellulose pyrolysates (67). Therefore, mannosan and galactosan may be better tracers for burning of contemporary biomass fuel, whereas levoglucosan present in atmospheric particles may be derived from thermal decomposition of cellulose from both recent wood (contemporary biomass) and some brown coals. In conclusion, unusually high levels of levoglucosan have been detected using Py-GC-MS and off-line pyrolysis/ silylation on lignite samples from different coal mines of three Miocene brown coal basins in Poland. The high levels of levoglucosan indicate that a large amount of cellulose has been preserved in those lignites. The pyrolysates also contained other cellulose degradation products besides levoglucosan, for example, 1,6-anhydro-β-D-glucofuranose, VOL. 42, NO. 8, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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maltol, 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one, as well as lignin degradation products. This study demonstrated that anhydroglucoses derived from cellulose (e.g., levoglucosan, dianhydroglucopyranose, and anhydroglucofuranose) are produced by pyrolysis of some lignites utilized as fuels in Poland. On the other hand, nonglucose anhydrosaccharides, in particular mannosan and galactosan typical of hemicellulose, are not detected in those lignite pyrolysates investigated. This suggests that mannosan and galactosan are supportive specific tracers for combustion of contemporary biomass with levoglucosan in those regions were the utilization of brown coals containing fossilized cellulose is important.

Acknowledgments This research has been financed in part by MNISW grant No. N N307 2379 33 (for L. M). We thank the reviewers for their comments that improved this manuscript.

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Supporting Information Available Background information about petrography analyses of xylites, biomarker maturity parameters for the analyzed samples, and figure showing sampling sites. This information is available free of charge via the Internet at http:// pubs.acs.org.

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Literature Cited (1) Moers, M. E. C.; Baas, M.; Boon, J. J.; de Leeuw, J. W. Molecular characterization of total organic matter and carbohydrates in peat samples from a cypress swamp by pyrolysis-mass spectrometry and wet-chemical methods. Biogeochemistry 1990, 11, 251–277. (2) de Leeuw, J. W.; Largeau, C. A review of macromolecular organic compounds that comprise living organisms and their role in kerogen, coal, and petroleum formation. In Organic Geochemistry, Engel, M. H., Macko, S. A. Eds.; Plenum Press: New York, 1993; pp 23–72.. (3) Arnosti, C.; Repeta, D. J.; Blough, N. V. Rapid bacterial degradation of polysaccharides in anoxic marine systems. Geochim. Cosmochim. Acta 1994, 58, 2639–2652. (4) van Kaam-Peters, H. M. E.; Schouten, S.; Köster, J.; Sinninghe Damsté, J. S. Controls on the molecular and carbon isotopic composition of organic matter deposited in a Kimmeridgian euxinic shelf sea: evidence for preservation of carbohydrates through sulfurisation. Geochim. Cosmochim. Acta 1998, 62, 3259–3283. (5) Sinninghe Damsté, J. S.; Kok, M. D.; Köster, J.; Schouten, S. Sulfurized carbohydrates: an important sedimentary sink for organic carbon. Earth Planet. Sci. Lett. 1998, 164, 7–13. (6) van Dongen, B. E.; Schouten, S.; Sinninghe Damsté, J. S. Sulfurization of carbohydrates results in a sulfur-rich, unresolved complex mixture in kerogen pyrolysates. Energy Fuels 2003, 17, 1109–1118. (7) van Dongen, B. E.; Schouten, S.; Baas, M.; Geenevasen, J. A. J.; Sinninghe Damsté, J. S. An experimental study of the lowtemperature sulfurization of carbohydrates. Org. Geochem. 2003, 34, 1129–1144. (8) van Dongen, B. E.; Schouten, S.; Sinninghe Damsté, J. S. Preservation of carbohydrates through sulfurization: The primary cause of the accumulation of organic matter in a Jurassic euxinic shelf sea. Geol. Ultraiectina 2003, 224, 107–145. (9) Spiker, E. C.; Hatcher, P. G. The effects of early diagenesis on the chemical and stable carbon isotopic composition of wood. Geochim. Cosmochim. Acta 1987, 51, 1385–1391. (10) Schleser, G. H.; Frielingsdorf, J.; Blair, A. Carbon isotope behaviour in wood and cellulose during artificial aging. Chem. Geol. 1999, 158, 121–130. (11) Lücke, A.; Helle, G.; Schleser, G. H.; Figueiral, I.; Mosbrugger, V.; Jones, T. P.; Rowe, N. P. Environmental history of the German Lower Rhine Embayment during the Middle Miocene as reflected by carbon isotopes in brown coal. Palaeogeogr., Palaeoclimatol. Palaeoecol. 1999, 154, 339–352. (12) van Bergen, P. F.; Poole, I. Stable carbon isotopes of wood: a clue to palaeoclimate. Palaeogeogr., Palaeoclimatol. Palaeoecol. 2002, 182, 31–45. (13) Stankiewicz, B. A.; Mastalerz, M.; Kruge, M. A.; van Bergen, P. F.; Sadowska, A. A comparative study of modern and fossil cone 2962

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 8, 2008

(22)

(23)

(24)

(25) (26)

(27)

(28)

(29)

(30)

(31)

(32)

(33) (34)

(35)

scales and seeds of conifers: A geochemical approach. New Phytol. 1997, 135, 375–393. Bechtel, A.; Reischenbacher, D.; Sachsenhofer, R. F.; Gratzer, R.; Lücke, A. Paleogeography and paleoecology of the upper Miocene Zillingdorf lignite deposit (Austria). Int. J. Coal Geol. 2007, 69, 119–143. Bechtel, A.; Widera, M.; Sachsenhofer, R. F.; Gratzer, R.; Lücke, A.; Woszczyk, M. Biomarker and stable carbon isotope systematics of fossil wood from the 2nd Lusatian lignite seam of the Lubstów deposit (Poland). Org. Geochem. 2007, 38, 1850– 1864. Shafizadeh, F.; Fu, Y. L. Pyrolysis of cellulose. Carbohydr. Res. 1973, 29, 113–122. Simoneit, B. R. T.; Schauer, J. J.; Nolte, C. G.; Oros, D. R.; Elias, V. O.; Fraser, M. P.; Rogge, W. F.; Cass, G. R. Levoglucosan, a tracer for cellulose in biomass burning and atmospheric particles. Atmos. Environ. 1999, 33, 173–182. Schwarzinger, C.; Tanczos, I.; Schmidt, H. Levoglucosan, cellobiose and their acetates as model compounds for the thermally assisted hydrolysis and methylation of cellulose and cellulose acetate. J. Anal. Appl. Pyrolysis 2002, 62, 179–196. Fabbri, D.; Chiavari, G. Analytical pyrolysis of carbohydrates in the presence of hexamethyldisilazane. Anal. Chim. Acta 2001, 449, 271–280. Simoneit, B. R. T.; Kobayashi, M.; Mochida, M.; Kawamura, K.; Huebert, B. Aerosol particles collected on aircraft flights over the northwestern Pacific region during the ACE-Asia campaign: Composition and major sources of the organic compounds. J. Geophys. Res. 2004, 109, D19S10, doi:10.1029/2004JD004565. Simoneit, B. R. T.; Kobayashi, M.; Mochida, M.; Kawamura, K.; Lee, M.; Lim, H. J.; Turpin, B. J.; Komazaki, Y. Composition and major sources of organic compounds of aerosol particulate matter sampled during the ACE-Asia campaign. J. Geophys. Res. 2004, 109, D19S10, doi:10.1029/2004JD004598. Simoneit, B. R. T.; Elias, V. O. Organic tracers from biomass burning in atmospheric particulate matter over the ocean. Mar. Chem. 2000, 69, 301–312. Simoneit, B. R. T.; Elias, V. O. Detecting organic tracers from biomass burning in the atmosphere. Mar. Pollut. Bull. 2001, 42, 805–810. Simpson, C. D.; Katz, B. S.; Paulsen, M.; Dills, R. L.; Kalman, D. A. Determination of levoglucosan in atmospheric fine particulate matter. J. Air Waste Manage. Assoc. 2004, 54, 689– 694. Jordan, T.; Seen, A.; Jacobsen, G. Levoglucosan as an atmospheric tracer for woodsmoke. Atmos. Environ. 2006, 40, 5316–5321. Elias, V. O.; Simoneit, B. R. T.; Cordeiro, R. C.; Turcq, B. Evaluating levoglucosan as an indicator of biomass burning in Carajas, Amazonia: A comparison to the charcoal record. Geochim. Cosmochim. Acta 2001, 65, 267–272. Simoneit, B. R. T.; Elias, V. O.; Kobayashi, M.; Kawamura, K.; Rushdi, A. I.; Medeiros, P. M.; Rogge, W. F.; Didyk, B. M. Sugars— Dominant water-soluble organic compounds in soils and characterization as tracers in atmospheric particulate matter. Environ. Sci. Technol. 2004, 38, 5939–5949. Medeiros, P. M.; Simoneit, B. R. T. Analysis of sugars in environmental samples by gas chromatography-mass spectrometry. J. Chromatogr. A 2007, 1141, 271–278. Simoneit, B. R. T. Biomass burning — a review of organic tracers for smoke from incomplete combustion. Appl. Geochem. 2002, 17, 129–162. Schkolnik, G.; Rudich, Y. Detection and quantification of levoglucosan in atmospheric aerosols — A review. Anal. Bioanal. Chem. 2006, 385, 26–33. Leithead, A.; Li, S. M.; Hoff, R.; Cheng, Y.; Brook, J. Levoglucosan and dehydroabietic acid: Evidence of biomass burning impact on aerosols in the Lower Fraser Valley. Atmos. Environ. 2006, 40, 2721–2734. Medeiros, P. M.; Conte, M. H.; Weber, J. C.; Simoneit, B. R. T. Sugars as source indicators of biogenic organic carbon in aerosols collected above the Howland Experimental Forest, Maine. Atmos. Environ. 2006, 40, 1694–1705. Marynowski, L.; Otto, A.; Zaton ´ , M.; Philippe, M.; Simoneit, B. R. T. Biomolecules preserved in ca.168 million year old fossil conifer wood. Naturwissenschaften 2007, 94, 228–236. Philp, R. P. Fossil Fuel Biomarkers. Applications and Spectra; Methods in Geochemistry and Geophysics; Elsevier, Amsterdam, 1985; Vol. 23, p 294. Fabbri, D.; Prati, S.; Vassura, I.; Chiavari, G. Off-line pyrolysis/ silylation of cellulose and chitin. J. Anal. Appl. Pyrolysis 2003, 68/69, 163–171.

(36) Fabbri, D.; Vassura, I.; Snape, C. E. Simple off-line flash pyrolysis procedure with in situ silylation for the analysis of hydroxybenzenes in humic acids and coals. J. Chromatogr. A 2002, 967, 235–242. (37) Fabbri, D.; Chiavari, G.; Prati, S.; Vassura, I.; Vangelista, M. Gas chromatography/mass spectrometric characterisation of pyrolysis/silylation products of glucose and cellulose. Rapid Commun. Mass Spectrom. 2002, 16, 2349–2355. (38) Ohta, K.; Venkatesan, M. I. Pyrolysis of wood specimens with and without minerals: Implications for lignin diagenesis. Energy Fuels 1992, 6, 271–277. (39) Hatcher, P. G.; Faulon, J-L.; Wenzel, K. A.; Cody, G. D. A structural model for lignin-derived vitrinite from high-volatile bituminous coal (coalified wood). Energy Fuels 1992, 6, 813–820. (40) Hatcher, P. G.; Minard, R. D. Comparison of dehydrogenase polymer (DHP) lignin with native lignin from gymnosperm wood by thermochemolysis by tetramethylammonium hydroxide (TMAH). Org. Geochem. 1996, 24, 593–600. (41) Hatcher, P. G.; Clifford, D. J. The organic geochemistry of coal: From plant materials to coal. Org. Geochem. 1997, 27, 251–274. (42) Cotrim da Cunha, L.; Serve, L.; Gadel, F.; Blazi, J.-L. Ligninderived phenolic compounds in the particulate organic matter of a French Mediterranean river: Seasonal and spatial variations. Org. Geochem. 2001, 32, 305–320. (43) Otto, A.; Simoneit, B. R. T. Chemosystematics and diagenesis of terpenoids in fossil conifer species and sediment from the Eocene Zeitz formation, Saxony, Germany. Geochim. Cosmochim. Acta 2001, 65, 3505–3527. (44) Otto, A.; Simoneit, B. R. T. Biomarkers of Holocene buried conifer logs from Bella Coola and north Vancouver, British Columbia, Canada. Org. Geochem. 2002, 33, 1241–1251. (45) Otto, A.; Wilde, V. Sesqui-, di- and triterpenoids as chemosystematic markers in conifers. — A review. Bot. Rev. 2001, 67, 141–238. (46) Otto, A.; Simoneit, B. R. T.; Wilde, V.; Kunzmann, L.; Püttmann, W. Terpenoid composition of three fossil resins from Cretaceous and Tertiary conifers. Rev. Paleobot. Palynol. 2002, 120, 203– 215. (47) Otto, A.; Simoneit, B. R. T.; Wilde, V. Terpenoids as chemosystematic markers in selected fossil and extant species of pine (Pinus, Pinaceae). Bot. J. Linnean Soc. 2007, 154, 129–140. (48) Fabian ´ ska, M. GC-MS and Py/GC-MS in investigation of biological origin of brown coal organic matter. In Chromatographic Methods of Organic Compounds Investigations, Szczyrk, Poland Vol. 06 2003. Abstract in conference materials. (49) Kuroda, K.-I. Pyrolysis-trimethylsilylation analysis of lignin: preferential formation of cinnamyl alcohol derivatives. J. Anal. Appl. Pyrolysis 2000, 56, 79–87. (50) Chiavari, G.; Fabbri, D.; Prati, S. Gas-chromatographic-mass spectrometric analysis of products arising from pyrolysis of amino acids in the presence of hexamethyldisilazane. J. Chromatogr. A 2001, 922, 235–241. (51) Bonaduce, I.; Colombini, M. P. Characterisation of beeswax in works of art by gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry procedures. J. Chromatogr. A 2004, 1028, 297–306. (52) Osete-Cortina, L.; Doménech-Carbó, M.-T. Characterization of acrylic resins used for restoration of artworks by pyrolysissilylation-gas chromatography/mass spectrometry with hexamethyldisilazane. J. Chromatogr. A 2006, 1127, 228–236.

(53) De la Cruz-Cañizares, J.; Doménech-Carbó, M.-T.; GimenoAdelantado, J.-V.; Mateo-Castro, R.; Bosch-Reig, F. Study of Burseraceae resins used in binding media and varnishes from artworks by gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry. J. Chromatogr. A 2005, 1093, 177–194. (54) Colombini, M. P.; Orlandi, M.; Modugno, F.; Tolppa, E.-L.; Sardelli, M.; Zoia, L.; Crestini, C. Archaeological wood characterisation by PY/GC/MS, GC/MS, NMR and GCP techniques. Microchem. J. 2007, 85, 164–173. (55) Poole, I.; van Bergen, P. F. Carbon isotope ratio analysis of organic moieties from fossil mummified wood: Establishing optimum conditions for off-line pyrolysis extraction using gas chromatography/mass spectrometry. Rapid Commun. Mass Spectrom. 2002, 16, 1976–1981. (56) Fabbri, D.; Torri, C.; Baravelli, V. Effect of zeolites and nanopowder metal oxides on the distribution of chiral anhydrosugars evolved from pyrolysis of cellulose. An analytical study. J. Anal. Appl. Pyrolysis 2007, 80, 24–29. (57) Haffenden, L. J. W.; Yaylayan, V. A. Mechanism of formation of redox-active hydroxylated benzenes and pyrazione in 13Clabeled glycine/D-glucose model systems. J. Agric. Food Chem. 2005, 53, 9742–9746. (58) Vane, C. H. The molecular composition of lignin in spruce decayed by white-rot fungi (Phanerochaete chrysosporium and Trametes versicolor) using pyrolysis-GC-MS and thermochemolysis with tetramethylammonium hydroxide. Int. Biodeterior. Biodegrad. 2003, 51, 67–75. (59) del Río, J. C.; Gutiérrez, A.; Rodríguez, I. M.; Ibarra, D.; Martínez, Á. T. Composition of non-woody plant lignins and cinnamic acids by Py-GC/MS, Py/TMAH and FT-IR. J. Anal. Appl. Pyrolysis 2007, 79, 39–46. (60) Tissot, B. P.; Welte, D. H. Petroleum Formation and Occurrence. 2nd ed.; Springer Verlag: Berlin, 1984; p 669. (61) van Bergen, P. F.; Collinson, M. E.; Hatcher, P. G.; de Leeuw, J. W. Lithological control on the state of preservation of fossil seed coats of water plants In Advances in Organic Geochemistry 1993 Telnæs, N., van Graas, G., Øygard, K. Eds.; Org. Geochem. 1994; Vol. 22, pp 683-702. (62) Hedges, J. I.; Cowie, G. L.; Ertel, J. R.; Barbour, R. J.; Hatcher, P. G. Degradation of carbohydrates and lignins in buried woods. Geochim. Cosmochim. Acta 1985, 49, 701–711. (63) Czapla, Z. Today and tomorrow of the brown coal (in Polish). Karbo-Energochem.-Ekol. 1997, 42, 279–283. (64) Dylag, J. Brown coals (In Polish). In Bilans Zasobów Kopalin i Wód Podziemnych w Polsce; Warszawa: Vol 31, 2004; XII PIG. (65) Graham, B.; Mayol-Bracero, O.; Guyon, P.; Roberts, G. C.; Decesari, S.; Facchini, M. C.; Artaxo, P.; Maenhaut, W.; Köll, P.; Andreae, M. O. Water-soluble organic compounds in biomass burning aerosols over Amazonia: 1. Characterization by NMR and GC-MS. J. Geophys. Res. 2002, 107 (D20), 8047, doi:10.1029/ 2001JD000336. (66) Abas, M. R. B.; Rahman, N. A.; Omar, N. Y. M. J.; Jamil Maah, M.; Abu Samah, A.; Oros, D. R.; Otto, A.; Simoneit, B. R. T. Organic composition of aerosol particulate matter during a haze episode in Kuala Lumpur, Malaysia. Atmos. Environ. 2004, 38, 4223– 4241. (67) Nolte, C. G.; Schauer, J. J.; Cass, G. R.; Simoneit, B. R. T. Highly polar organic compounds present in wood smoke and in the ambient atmosphere. Environ. Sci. Technol. 2001, 35, 1912–1919.

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