Benchmarking source isotopic ratios of levoglucosan to better constrain the contribution of different wood containing fuels to the air pollution

Author: Nana Khundadze
Keywords: Stable isotopes, kinetic isotope effects, levoglucosan, biomass burning, photochemical age, isotopologues, two-dimensional gas chromatography
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Domestic heating as a form of biomass burning is a major source of pollution, comparable with that from traffic. Since it occurs where people live and at times when they are at homes, it has a negative impact on human health. For the necessary mitigation, it is clear that there is a strong interest for detailed description of the sources. Isotopic analyses are an innovative tool for source apportionment. The concept behind is that stable isotopes can give additional information on the source and sinks aerosol, based on two properties of isotopes: fingerprinting of sources and footprinting of the chemical processing. Isotopic ratios of the biomass burning specific tracer levoglucosan are used within complex approaches, combining laboratory kinetic isotope effect (KIE) studies, observed δ^13C at the source and in the field, as well as lagrangian modelling. Recent studies showed that accurate source specific isotope ratios is crucial for a sound interpretation of the field data. This study was designed to improve the knowledge on isotopic signatures of levoglucosan. In this work the stable isotope ratios of levoglucosan in aerosol particles emitted from the combustion of 18 different biomass fuel (Soft and hard woods, corn cobs and coal materials) was studied. Compound specific isotopic measurements were carried out by Thermal Desorption- two-dimensional Gas Chromatographie- Isotope Ratio Mass Spectrometer (TD-2DGC-IRMS). δ^13C values of levoglucosan in C3 plant samples were found in the range from -23.6 to -21.7‰, being a bit higher in case of softwoods. The lignite samples showed higher isotopic composition than soft and hard wood, i.e.-19‰, denoting a heavier plant rest in the coal. Furthermore, the isotopic ratio of levoglucosan from the combustion of corn cob was found to be -12.9‰, as expected for a C4 sample. Isotopic measurements of total carbon in aerosol showed different signatures for the C3 and lignite samples, from -27.2 to -23.7‰, and for the C4 corn cob sample, i.e. -13.8‰, in good agreement with the parent plant material. Additionally, the isotopic composition of hollocelulose, as a parent material, was determined with δ^13C values between - 27.5‰ (for C3 plants) and -10.9‰ (for C4 plants). Moreover, the isotopic fractionation between the cellulose and levoglucosan, showed a mean value of 1.94‰. This work contributes to the database enlargement of source specific isotopic ratios of levoglucosan, which is compulsory to get more insight in the biomass burning aerosol origin.