Improved method for quantifying levoglucosan and related monosaccharide anhydrides in atmospheric aerosols and application to samples from urban and tropical locations

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 (1-phenyl 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 (<2.5 mum) aerosols at a primary forest site in Rondonia, Brazil, was on average 2.15 m(-3) during the dry season when intensive biomass burning occurs, which was almost 400 times higher than during the wet (nonburning) season. Urban total aerosols collected in Gent, Belgium, showed an average atmospheric concentration of MAs of 0.56 mug m(-3) for the winter season, which was a factor of 20 higher than for the summer season. The carbon in the MAs accounted on average for about 5.1% and 1.8% of the organic carbon in the Brazilian dry season and Gent winter aerosols, respectively. Levoglucosan was the major MA, with a relative abundance in the range of 76-93%.