Environ. Sci. Technol. 2002, 36, 747-753
Improved Method for Quantifying Levoglucosan and Related Monosaccharide Anhydrides in Atmospheric Aerosols and Application to Samples from Urban and Tropical Locations Z B Y N E K Z D R AÄ H A L , † , ‡ J O S EÄ O L I V E I R A , † REINHILDE VERMEYLEN,† M A G D A C L A E Y S , * ,† A N D WILLY MAENHAUT§ Department of Pharmaceutical Sciences, University of Antwerp (UIA), Universiteitsplein 1, B-2610 Antwerp, Belgium, and Institute for Nuclear Sciences, Ghent University, Proeftuinstraat 86, B-9000 Gent, Belgium
An improved analytical method was developed and validated for the determination of the monosaccharide anhydrides levoglucosan, mannosan, and galactosan in atmospheric aerosol samples. The method uses an external recovery standard, extraction in dichloromethane, trimethylsilylation, addition of an internal standard (1phenyl dodecane), and analysis by gas chromatography with flame ionization detection (GC-FID) and gas chromatography/mass spectrometry (GC/MS). As external recovery standard, we selected 1,2,3-trihydroxyhexane, which has a similar polarity as the monosaccharide anhydrides; furthermore, it was ensured that the trimethylsilylation step leads to complete derivatization into trimethylsilyl ethers. The reproducibility of the combined trimethylsilylation and analysis of levoglucosan was about 2% for standard solutions, whereas the precision of the entire method for the sum of all three monosaccharide anhydrides (MAs) in real aerosol filter samples was about 5%. The method was applied to aerosol samples from urban and tropical locations. The atmospheric concentration of the MAs in fine (0.999). The precision of the whole procedure, including the extraction, was evaluated by analyzing up to four different parts of some aerosol filter samples, and the RSDs for the sum of the three monosaccharide anhydrides were of the order of 5%. 1,2,3-Trihydroxyhexane was found to be a suitable recovery standard because its extraction behavior is similar to that of levoglucosan and because its tritrimethylsilyl ether derivative elutes in an interference-free part of the chromatogram (Figure 2). 1,2,6-Trihydroxyhexane was also evaluated as possible recovery standard, but was found to coelute with other compounds present in the aerosol extracts. The average recoveries of 1,2,3-trihydroxyhexane from aerosol samples for each sampling period (Table 2) were better than 73%. They were higher than those determined from blank filters (65%), which is likely due to carrier effects. The small difference noted between recoveries from Brazilian and Belgian aerosol samples is probably due to the different types of quartz filter used for collection. The longterm reproducibility of the trimethylsilylation reaction was evaluated by repeated derivatizations on a 1,2,3-trihydroxyhexane standard throughout the processing of each sample series (up to 10 days, one derivatization per day) and was better than 2.0%. The derivatized sample kept in the trimethylsilylation mixture was found to be stable for at least 3 weeks at room temperature.
TABLE 3. Atmospheric Concentrations of Monosaccharide Anhydrides MA sum (ng m-3)
levoglucosan (ng m-3)
mannosan (ng m-3)
galactosan (ng m-3)
sample set
Na
mean
(range)
mean
(range)
mean
(range)
mean
(range)
Rondoˆ nia dry Rondoˆ nia wet Gent winter Gent summer
15 6 8 6
2154 5.53 562 24.8
(474-4424) (0.87-15.8) (142-1330) (5.2-43.4)
2006 4.40 477 19.4
(446-4106) (0.40-13.2) (121-1133) (4.1-34.6)
116.1 0.98 65.9 4.69
(21.0-259) (nd-2.05) (17.3-153) (0.70-7.9)
31.2 0.63 19.6 1.03
(7.6-61.5) (nd-1.19) (4.4-44.2) (nd-1.31)
a
N is the number of samples analyzed for monosaccharide anhydrides.
FIGURE 3. Temporal variation of the atmospheric concentrations of monosaccharide anhydrides (MA) (sum of levoglucosan, mannosan, and galactosan) and of particulate organic carbon (OC) for Rondoˆ nia, Brazil, dry season (A) and Gent, Belgium, winter (B). The dates for the Brazilian samples are all in 1999; those for the Gent samples are in 1998. Determination of Monosaccharide Anhydrides in Aerosols. Aerosol samples from two different regions of the globe, a Brazilian tropical rainforest and a Belgian urban site, were analyzed. Samples were collected during episodes that were characterized by a different biomass combustion activity (winter vs summer in Belgium, dry vs wet season in Brazil). The difference in the biomass burning activity in Brazil during the dry and wet season is apparent from comparison of the chromatograms of their trimethylsilylated aerosol extracts (Figure 2). While the peak of levoglucosan clearly dominates the chromatogram for dry season aerosol samples, it is very low in the chromatogram for the wet season aerosols, where fatty acids were the prevailing peaks. The concentrations of mannosan and galactosan were substantially lower than those of levoglucosan in all samples as could be expected from the content of their parent monosaccharide residues in wood
TABLE 4. Average Percentage Contribution of Individual Monosaccharide Anhydrides to the Total MA Concentrationa sample set
galactosan
mannosan
levoglucosan
Rondoˆ nia dry Rondoˆ nia wet Gent winter Gent summer
1.5 (35) 5.4 (137) 3.3 (18.6) 3.2 (12.7)
5.4 (17.9) 17.6 (75) 11.8 (16.6) 21.1 (16.9)
93.1 (1.5) 77.0 (26) 84.9 (2.7) 75.8 (4.7)
a
The RSD (in %) is given in parentheses.
(7). The Belgian urban winter and summer aerosol samples showed a comparable pattern for the relative concentrations of the different MAs. The atmospheric MA concentrations derived from the aerosol filter samples are summarized in Table 3. A very high VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
751
FIGURE 4. Correlation between the atmospheric concentrations of the monosaccharide anhydrides (MA) (sum of levoglucosan, mannosan, and galactosan) and elemental carbon (EC) for Brazilian dry season (A) and Gent winter (B) aerosols.
TABLE 5. Concentration Ratios of MA (Sum of Levoglucosan, Mannosan, and Galactosan) and Levoglucosan to EC and Percentage of MA Carbon and Levoglucosan Carbon in OC MA/EC
levoglucosan/EC
% MA carbon in OC
% levoglucosan carbon in OC
sample set
mean
(range)
mean
(range)
mean
(range)
mean
(range)
Rondoˆ nia dry Rondoˆ nia wet Gent winter Gent summer
2.65 0.129 0.125 0.021
(1.39-3.95) (0.013-0.593) (0.073-0.184) (0.005-0.038)
2.47 0.106 0.106 0.017
(1.25-3.67) (0.006-0.493) (0.062-0.155) (0.004-0.031)
5.13 0.41 1.79 0.28
(2.32-7.58) (0.04-1.56) (0.95-2.26) (0.06-0.46)
4.79 0.34 1.52 0.22
(2.10-7.07) (0.02-1.30) (0.80-1.99) (0.05-0.37)
average MA concentration of 2150 ng m-3 with a range of 470-4400 ng‚m-3 was found for the Brazilian dry season, where biomass burning is a dominant source of carbonaceous particulate matter in the atmosphere. The temporal variation of the MA concentration (together with that of OC) during the sampling period is shown in Figure 3. Our MA concentration data and their ratios to OC agree well with those obtained for a different subset of fine aerosol samples from the same site. Graham et al. (24), using a method with a precision of about 20%, found average concentrations of 1180, 49.5, 22.7, and 14 500 ng m-3 for levoglucosan, mannosan, galactosan, and OC, respectively. Thus, their ratios of the mean concentrations of the individual MAs to the mean OC concentration are 0.081, 0.0034, and 0.0016 for levoglucosan, mannosan, and galactosan, respectively. Our corresponding ratios are 0.104, 0.0060, and 0.0016. During the wet season, which is characterized by a low burning activity, the average MA concentration was 5.5 ng m-3 with a range of 0.9-16 ng m-3, which is almost 400 times lower than for the dry season 752
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 4, 2002
samples. The average atmospheric MA concentration in Gent during winter was 560 ng m-3, with a range of 140-1300 ng m-3, which was 23 times higher than for the summer samples. A decrease of the MA concentration at the end of the winter season is apparent from Figure 3. The average MA concentration at Gent during summer was 25 ng m-3, with a range of 5-43 ng m-3. The levoglucosan data for Gent during winter may be compared with those for fine aerosols in the San Joaquin Valley, CA, where residential wood burning is significant during winter (6). The average atmospheric concentration of levoglucosan at Gent during winter was 0.48 µg m-3, whereas levels of 2.4 and 3.0 µg m-3 were found at Bakersfield and Fresno, respectively, during a 1995-1996 winter episode. The contribution of levoglucosan to the total MA concentration was higher for the Brazilian dry season samples than in the Gent winter aerosol (93% vs 85%; Table 4), and this contribution was quite constant at each of the sites. The difference is due to the different composition of the combusted wood, because combustion of different tree
species is known to yield variable relative amounts of levoglucosan, mannosan, and galactosan (6). Also differences in combustion processes are likely to play a role. The impact of biomass burning during the dry season in Rondoˆnia, Brazil, is clearly evident from the ratio of MA to EC. While the average MA/EC ratio for the Brazilian dry season aerosols was 2.65, the ratio for the Gent winter aerosols was only 0.13 (Table 5). This low MA/EC ratio indicates that biomass burning is only a minor source of EC, a general marker of combustion processes, at Gent during winter, and that other combustion sources, such as automotive emissions and oil and coal combustion, contribute to a large extent to the EC at Gent. The mean levoglucosan/EC ratios in our four sample sets (Table 5) vary from 0.017 to 2.5 and may be compared with levoglucosan/EC ratios obtained for PM10 aerosols that were collected in Texas during a haze episode (14). The levoglucosan/EC ratios reported in the latter study were in the range of 0.3-6.0, with the highest ratios found for the coastal locations that were more affected by longrange transport of smoke aerosols from southern Mexico and Central America. Good correlations between MA and EC concentrations were obtained for both the Brazilian dry season samples (R2 ) 0.60) and for the Gent winter samples (R2 ) 0.80) (Figure 4). Similar R2 values were also obtained for the correlations between the individual MAs and EC. The correlations between MA and OC were also good, with R2 values of 0.67 and 0.90 for the Brazilian dry season and Gent winter samples, respectively. Substantial differences between the Brazilian dry season and Belgian urban winter aerosols were found with respect to the concentration ratio of MA carbon to OC (Table 5). The carbon in the MAs accounts on average for 5.1% of the OC in Brazilian dry season samples (with a range of 2.3-7.6%) whereas for the Belgian urban winter samples they account for much less, namely, 1.8% with a range of 1.0-2.3%. The average contributions of levoglucosan carbon to the OC concentrations are 4.8 and 1.52% for the Brazilian dry season and Gent winter aerosols, respectively. Recently, Fine et al. (16) reported concentrations of levoglucocan in fine particle (PM2.5) emissions from fireplace combustion of woods in the northeastern United States. They found an average concentration of 100 ( 40 mg of levoglucosan/g of OC in the emitted particles, which corresponds to 44 ( 18 mg of levoglucosan carbon/g of OC. If we assume that the composition of the emission of wood burning emissions in Gent is roughly similar to that from the fireplaces in the northeastern United States, we can derive a first, rough estimate for the contribution of wood combustion to the OC in Gent during winter and arrive at an average percentage contribution of 35%. Clearly, this contribution should be verified by further work. In their source apportionment study for the fine OC of the year 1982 in the Los Angeles area, Schauer et al. (25) attributed 19% and 22% of the OC to wood smoke for the Pasadena and West Los Angeles sites, respectively.
Acknowledgments The authors are indebted to the Belgian Federal Office of Scientific, Technical and Cultural Affairs (OSTC), and to the “Fonds voor Wetenschappelijk Onderzoek-Vlaanderen” (FWO) for research support. This work was also partially supported by the Regional Government of Flanders through a bilateral scientific and technological cooperation project
with South Africa. Z.Z. acknowledges the OSTC and the FWO for postdoctoral fellowships. The authors thank Pascal Guyon from the Max Planck Institute for Chemistry (Mainz) for providing the tropical rainforest aerosol samples.
Literature Cited (1) Rogge, W. F.; Mazurek, M. A.; Hildemann, L. M.; Cass, G. R.; Simoneit, B. R. T. Atmos. Environ. Part A 1993, 27, 1309-1330. (2) Saxena, P.; Hildemann, L. M. J. Atmos. Chem. 1996, 24, 57-109. (3) Kuba´tova´, A.; Vermeylen, R.; Claeys, M.; Cafmeyer, J.; Maenhaut, W.; Roberts, G.; Artaxo, P. Atmos. Environ. 2000, 34, 50375051. (4) Wauters, E.; Vangaever, F.; Sandra, P.; Verzele, M. J. Chromatogr. 1979, 170, 133-138. (5) Simoneit, B. R. T.; Schauer, J. J.; Nolte, C. G.; Oros, D. R.; Elias, V. O.; Frazer, M. P.; Rogge, W. F.; Cass, G. R. Atmos. Environ. 1999, 33, 173-182. (6) Nolte, C. G.; Schauer, J. J.; Cass, G. R.; Simoneit, B. R. T. Environ. Sci. Technol. 2001, 35, 1912-1919. (7) Shafizadek, F. In The Chemistry of Pyrolysis and Combustion; Rowell, R., Ed.; Advances in Chemistry Series 207; American Chemical Society: Washington, DC, 1984; pp 489-529. (8) Ramdahl, T. Nature 1983, 306, 580-582. (9) Standley, L. J.; Simoneit, B. R. T. J. Atmos. Chem. 1994, 18, 1-15. (10) Simoneit, B. R. T.; Abas, M. R.; Cass, G. R.; Rogge, W. F.; Mazurek, M. A.; Standley, L. J.; Hildemann, L. M. Natural Organic Compounds as Tracers for Biomass Combustion in Aerosols. In Biomass Burning and Global Change; Levine. J. S., Ed.; MIT Press: Cambridge, MA, 1996; pp 509-518. (11) Hawthorne, S. B.; Miller, D. J.; Barkley, R. M.; Krieger, M. S. Environ. Sci. Technol. 1988, 22, 1191-1196. (12) Hawthorne, S. B.; Krieger, M. S.; Miller, D. J.; Mathiason, M. B. Environ. Sci. Technol. 1989, 23, 470-475. (13) Simoneit, B. R. T.; Elias, V. O. Mar. Chem. 2000, 69, 301-312. (14) Frazer, M. P.; Lakshmanan, K. Environ. Sci. Technol. 2000, 34, 4560-4564. (15) Elias, V. O.; Simoneit, B. R. T.; Cordeiro, R. C.; Turcq, B. Geochim. Cosmochim. Acta 2001, 65, 267-272. (16) Fine, P. M.; Cass, G. R.; Simoneit, B. R. T. Environ. Sci. Technol. 2001, 35, 2665-2675. (17) Andreae, M. O. Science 1983, 220, 1148-1151. (18) Claeys, M.; Vermeylen, R.; Kuba´tova´, A.; Cafmeyer, J.; Maenhaut, W. Characterisation of Organic Compounds in Atmospheric Aerosols. In Proceedings of EUROTRAC Symposium ‘98, Transport and Chemical Transformation in the Troposphere; Borrell, P. M., Borrell, P., Eds.; WIT Press: Southampton, UK, 1999; Vol. 1, pp 501-505. (19) Kuba´tova´, A.; Vermeylen, R.; Claeys, M.; Cafmeyer, J.; Maenhaut, W. J. Aerosol Sci. 1999, 30 (Suppl. 1), S905-S906. (20) Solomon, P. A.; Moyers, J. L.; Fletcher, R. A. Aerosol Sci. Technol. 1983, 2, 455-464. (21) Birch, M. E.; Cary, R. A. Aerosol Sci. Technol. 1996, 25, 221-241. (22) Schmid, H.; Laskus, L.; Abraham, H. J.; Baltensperger, U.; Lavanchy, V.; Bizjak, M.; Burba, P.; Cachier, H.; Crow, D.; Chow, J.; Gnauk, T.; Even, A.; ten Brink, H. M.; Giesen, K.-P.; Hitzenberger, R.; Hueglin, C.; Maenhaut, W.; Pio, C.; Carvalho, A.; Putaud, J.-P.; Toom-Sauntry, D.; Puxbaum, H. Atmos. Environ. 2001, 35, 2111-2121. (23) Decesari, S.; Facchini, M. C.; Fuzzi, S.; Tagliavini, E. J. Geophys. Res. 2000, 105, 1481-1489. (24) Graham, B.; Mayol-Bracero, O. L.; Guyon, P.; Roberts, G. C.; Decesari, S.; Facchini, M. C.; Artaxo, P.; Maenhaut, W.; Ko¨ll, P.; Andreae, M. O. J. Geophys. Res., in press. (25) Schauer, J. J.; Rogge, W. F.; Hildemann, L. M.; Mazurek, M. A.; Cass, G. R.; Simoneit, B. R. T. Atmos. Environ. 1996, 30, 38373855.
Received for review July 22, 2001. Revised manuscript received November 1, 2001. Accepted November 6, 2001. ES015619V
VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
753
