Quantifying black carbon from biomass burning by means of levoglucosan – a one-year time series at the Arctic observatory Zeppelin

摘要

Levoglucosan, a highly specific tracer of particulate matter from biomassburning, has been used to study the influence of residential wood burning,agricultural waste burning and Boreal forest fire emissions on the Arcticatmosphere black carbon (BC) concentration. A one-year time series fromMarch 2008 to March 2009 of levoglucosan has been established at the Zeppelinobservatory in the European Arctic. Elevated concentrations of levoglucosanin winter (mean: 1.02 ng m?3) compared to summer (mean:0.13 ng m?3) were observed, resembling the seasonal variation seen for e.g.sulfate and BC. The mean concentration in the winter period was 2–3orders of magnitude lower than typical values reported for Europeanurban areas in winter, and 1–2 orders of magnitude lower thanEuropean rural background concentrations. Episodes of elevated levoglucosanconcentration lasting from 1 to 6 days were more frequent in winter than insummer and peak values were higher, exceeding 10 ng m?3 at the most.Concentrations of elemental carbon from biomass burning (EC_bb) wereobtained by combining measured concentrations of levoglucosan and emissionratios of levoglucosan and EC for wildfires/agricultural fires and forresidential wood burning. Neglecting chemical degradation by OH providesminimum levoglucosan concentrations, corresponding to a mean EC_bbconcentration of 3.7 ± 1.2 ng m?3 in winter (October–April) and0.8 ± 0.3 ng m?3 in summer (May–September), or8.8 ± 4.5% of the measured equivalent black carbon (EBC) concentration inwinter and 6.1 ± 3.4% in summer. When accounting for chemicaldegradation of levoglucosan by OH, an upper estimate of 31–45% of EBCcould be attributed to EC_bb* (EC_bb adjusted for chemicaldegradation) in winter, whereas no reliable (<100%) upperestimate could be provided for summer for the degradation rates applied.Hence, fossil fuel sources appear to dominate the European Arctic BCconcentrations in winter, whereas the very wide range obtained for summerdoes not allow us to conclude upon this for the warm season.Calculations using the Lagrangian particle dispersion model FLEXPART showthat the seasonal variation of the modeled EC_bb (EC_bb,m)concentration compared relatively well with observationally derivedEC_bb from agricultural fires/wildfires during summer, and residential woodburning in winter. The model overestimates by a factor of 2.2 in winter and4.4 in summer when compared to the observationally derived mean EC_bbconcentration, which provides the minimum estimate, whereas itunderestimates by a factor of 2.3–3.3 in winter and a factor of 4.5 insummer when compared to EC_bb*, which provides the upperestimate. There are indications of too-low emissions of residential woodburning in northern Russia, a region of great importance with respect toobserved concentrations of BC in the European Arctic.