| dc.description.abstract | Recent investigations on aerosol water-soluble organic compounds (WSOCs) formed by burning biomass have become increasingly concerned with the role of these compounds in atmospheric chemistry and their effect on climate, cloud formation and precipitation. Mono- saccharide anhydrides and low-molecular weight dicarboxylic acids are the two most important groups of WSOCs.
The first part of this study is determination the three most commonly monosaccharide anhydrides (levoglucosan, mannosan and galactosan) in atmospheric aerosols using gas chromatography-mass spectrometry (GC-MS). Various silylating agents, mainly trimethylsilylating agents (TMS), were compared, and the effects of various contents of trimethyl- chlorosilane (TMCS, as a stimulator) were evaluated to optimize the conditions for detecting these compounds in aerosol samples. Differe- nces among the abundances of the derivatives were caused by the sterical hindrance of three hydroxyl groups in the structures of monosaccharide anhydrides. The effects of the reaction time and temperature were also examined. The optimal reaction time and temperature were 60 min and 80?C with 1% TMCS. Under these conditions, the percentages of formation of bis-O-TMS derivatives (as by-products) were 23%, 29% and 10% for galactosan, mannosan and levoglucosan, respectively. The concentrations of galactosan, mannosan and levoglucosan in particles of smoke samples ranged from 29 to 88 ng/m3, 23 to 69 ng/m3 and 77 to 380 ng/m3, respectively; and in particles of atmospheric aerosols ranged from 0.06 to 0.75 ng/m3, n.d. to 0.49 ng/m3 and 1.6 to 132 ng/m3, respectively. Levoglucosan was the dominant MAs detected in both type of samples. Less than 10% quantitation difference was obtained when bis-O-TMS derivatives were included in the calculation.
The second part of this study is application of on-line derivatization technique to determine low-molecular weight dicarboxylic acids (from C2 to C10) in atmospheric aerosol samples. The technique involves direct derivatization in the GC injector using a large-volume sample device with tetrabutylammonium hydroxide as the derivatization agent. The butylated dicarboxylic acids were then separated and identified by ion- trap GC-MS with electron impact ionization. Solid-phase extraction method instead of rotary evaporation method was used to concentrate analytes from filter extracts. The recovery from filter extracts ranged from 67 to 86% with RSD less than 13%. The concentrations of dicarboxylated C2, C3, C4, C5 and C6-C10 in atmospheric aerosols ranged from 91-240 ng/m3, 11-56 ng/m3, 12-49 ng/m3, 8-35 ng/m3 and n.d. to 17 ng/m3, respectively. Comparison with off-line butylated method, compatible results were obtained by using on-line derivatization with shorter derivatization time and a small quantity of solvent consumed. | en_US |