Evaluation of δ¹³C in Carbonaceous Aerosol Source Apportionment at a Rural Measurement Site

The stable isotope of carbon, ¹³C, has been used in several studies for source characterization of carbonaceous aerosol since there are specific signatures for different sources. In rural areas, the influence of different sources is complex and the application of δ¹³C for source characterization of the total carbonaceous aerosol (TC) can therefore be difficult, especially the separation between biomass burning and biogenic sources. We measured δ¹³C from 25 filter samples collected during one year at a rural background site in southern Sweden. Throughout the year, the measured δ¹³C showed low variability (–26.73 to –25.64‰). We found that the measured δ¹³C did not correlate with other commonly used source apportionment tracers (¹⁴C, levoglucosan). δ¹³C values showed lower variability during the cold months compared to the summer, and this narrowing of the δ¹³C values together with elevated levoglucosan concentrations may indicate contribution from sources with lower δ¹³C variation, such as biomass or fossil fuel combustion. Comparison of two Monte Carlo based source apportionment models showed no significant difference in results when δ¹³C was incorporated in the model. The insignificant change of redistributed fraction of carbon between the sources was mainly a consequence of relatively narrow range of δ¹³C values and was complicated by an unaccounted kinetic isotopic effect and overlapping δ¹³C end-member values for biomass burning and biogenic sources.