Articles | Volume 17, issue 6
Atmos. Chem. Phys., 17, 4265–4281, 2017
Atmos. Chem. Phys., 17, 4265–4281, 2017

Research article 29 Mar 2017

Research article | 29 Mar 2017

Carbonaceous aerosol source apportionment using the Aethalometer model – evaluation by radiocarbon and levoglucosan analysis at a rural background site in southern Sweden

Johan Martinsson1,2, Hafiz Abdul Azeem3, Moa K. Sporre4, Robert Bergström5,6, Erik Ahlberg1,2, Emilie Öström1,2, Adam Kristensson1, Erik Swietlicki1, and Kristina Eriksson Stenström1 Johan Martinsson et al.
  • 1Division of Nuclear Physics, Lund University, Box 118, 22100, Lund, Sweden
  • 2Centre for Environmental and Climate Research, Lund University, Ecology Building, 22362, Lund, Sweden
  • 3Centre for Analysis and Synthesis, Department of Chemistry, Lund University, Lund, Box 118, 22100, Lund, Sweden
  • 4Department of Geosciences, University of Oslo, Postboks 1022, Blindern, 0315, Oslo, Norway
  • 5Swedish Meteorological and Hydrological Institute, 60176, Norrköping, Sweden
  • 6Department of Chemistry, University of Gothenburg, 41296, Gothenburg, Sweden

Abstract. With the present demand on fast and inexpensive aerosol source apportionment methods, the Aethalometer model was evaluated for a full seasonal cycle (June 2014–June 2015) at a rural atmospheric measurement station in southern Sweden by using radiocarbon and levoglucosan measurements. By utilizing differences in absorption of UV and IR, the Aethalometer model apportions carbon mass into wood burning (WB) and fossil fuel combustion (FF) aerosol. In this study, a small modification in the model in conjunction with carbon measurements from thermal–optical analysis allowed apportioned non-light-absorbing biogenic aerosol to vary in time. The absorption differences between WB and FF can be quantified by the absorption Ångström exponent (AAE). In this study AAEWB was set to 1.81 and AAEFF to 1.0. Our observations show that the AAE was elevated during winter (1.36 ± 0.07) compared to summer (1.12 ± 0.07). Quantified WB aerosol showed good agreement with levoglucosan concentrations, both in terms of correlation (R2 = 0.70) and in comparison to reference emission inventories. WB aerosol showed strong seasonal variation with high concentrations during winter (0.65 µg m−3, 56 % of total carbon) and low concentrations during summer (0.07 µg m−3, 6 % of total carbon). FF aerosol showed less seasonal dependence; however, black carbon (BC) FF showed clear diurnal patterns corresponding to traffic rush hour peaks. The presumed non-light-absorbing biogenic carbonaceous aerosol concentration was high during summer (1.04 µg m−3, 72 % of total carbon) and low during winter (0.13 µg m−3, 8 % of total carbon). Aethalometer model results were further compared to radiocarbon and levoglucosan source apportionment results. The comparison showed good agreement for apportioned mass of WB and biogenic carbonaceous aerosol, but discrepancies were found for FF aerosol mass. The Aethalometer model overestimated FF aerosol mass by a factor of 1.3 compared to radiocarbon and levoglucosan source apportionment. A performed sensitivity analysis suggests that this discrepancy can be explained by interference of non-light-absorbing biogenic carbon during winter. In summary, the Aethalometer model offers a cost-effective yet robust high-time-resolution source apportionment at rural background stations compared to a radiocarbon and levoglucosan alternative.

Short summary
In this study we have focused our attention on the sources atmospheric carbon particles. More specifically, we evaluate a fast and inexpensive method which determines the source of these particles by utilizing light absorption by the particles. We found that this method is suitable for source estimation by comparing it to another method based on carbon isotopes and chemical tracer molecules. Cheap and fast methods based on light absorption can be utilized widely to deduce particle sources.
Final-revised paper