Seasonal Variations of Biomass Burning Tracers in Alaskan Aerosols

Abstract:

Biomass burning (BB) is a large source of atmospheric trace gases and aerosols. During the burning, several organic and inorganic gases and particles are emitted into the atmosphere. Here, we present seasonal variations of specific BB tracers such as levoglucosan, mannosan and galactosan, which are produced by pyrolysis of cellulose and hemicelluloses. We collected TSP aerosol samples (n= 32) from Fairbanks, Alaska in June 2008 to June 2009. Levoglucosan was detected as the dominant anhydrosugar followed by its isomers, mannosan and galactosan. The result of levoglucosan showed clear seasonal trends with winter maximum (ave.145 ng m^-3) and spring minimum (12.3 ng m^-3). The analyses of air mass back trajectories and fire spots demonstrated that anhydrosugars may be associated from residential heating and cooking in local region and Siberia in winter time. Levoglucosan showed significant positive correlation with EC (r= 0.67, p= 0.001) and OC (r= 0.51, p= 0.002) but there was no correlation with nss-K⁺ (r= -0.16, p= 0.37). The emission of K⁺ from biomass burning depends on burning condition and types of material burned. There are two possible reasons, which can be explained for the lack of correlation between levoglucosan and K⁺. First, specific burning materials may be used for residential heating, which can’t produce K⁺. Secondly, K⁺ could be deposit on the surface of chimney breast and it can’t emit into the atmosphere. Anhydrosugars contributed 4.4% to water-soluble organic carbon (WSOC) and 2.4% to organic carbon (OC). Their highest values of WSOC (8.1%) and OC (4.9%) in wintertime indicate that contribution of BB to Alaskan aerosols is important in winter period. The current study presents for the first time one-year observation on BB tracers in the subarctic region, which provide useful information to better understand the effect of biomass burning on subarctic atmosphere. It will also be helpful for further long-term climate studies in this region.