Abstract
Biomass burning activities constitute a major source of both gaseous and particulate pollutants on global scale. Aerosol particles released from biomass burning processes typically have sizes of less than 2.5 μm aerodynamic diameter (PM2.5), and they constitute a particularly large source of organic particles on global scale. Those particles can be transported over long distances and impact the air quality even in remote areas. Especially the Western and Northwestern US experience numerous and large-scale wildfires in each year. In this study, samples were collected from 2001 to 2004, totally 3 and half years in Fort Collins, Colorado, US. Water-soluble organic carbon (WSOC), organic carbons (OC), elemental carbons (EC), inorganic ions, anhydrosugars were analyzed in this study. Biomass burning tracers (levoglucosan, mannosan and galactosan) and secondary organic aerosol tracers (methylerythritol and methylthreitol) clearly showed seasonal pattern. The biomass burning tracer ratio (LG/MN) can be a fingerprint for the burning sources. The result showed the burning sources in winter were softwood. Levoglucosan to organic carbon ratios (LG-C/OC) were used to quantitatively estimate the contributions from biomass burning to ambient PM. 15.3% of the OC came from biomass burning in winter average. WSOC has been found to have two main sources: SOA formation and biomass burning emissions (both primary and secondary). The concentration in summer is 10 times higher than winter, which was discussed in the study. OC and EC aerosol components typically account for a significant proportion of fine particulate matter (PM2.5) in the atmosphere. Biomass burning can generate large amounts of OC and EC, and OC/EC can also provide fingerprints for the type of emission source. For example, biomass burning is usually higher than those from fossil fuel combustion source. One part of the samples were analyzed by the novel TD-2D-GC-IRMS/MSD as well, in order to obtain compound-specific carbon isotope composition. δ13C values can be a fingerprint for the burning sources, which showed good agreement between the biomass burning tracer ratios. Serious matrixs effect make it harder to do quantitative analysis, which not only influences the retention time but also makes the tracers not easy to be identified. In order to lower the matrixs effect, water was used as solvent for extraction, followed by freeze drying to dehydrate the samples. No isotopic fractionation occurred with this new method, and the resolution was significnatly impoved.