Description:
Abstract. We report the first-time use of the Lagrangian particledispersion model (LPDM) FLEXPART to simulate isotope ratios of the biomassburning tracer levoglucosan. Here, we combine the model results withobserved levoglucosan concentrations and δ13C to assess thecontribution of local vs. remote emissions from firewood domestic heating to the particulate matter sampled during the cold season at two measurements stations of the Environmental Agency of North Rhine-Westphalia, Germany. For the investigated samples, the simulations indicate that the largest part of the sampled aerosol is 1 to 2 d old and thus originates from local to regional sources. Consequently, ageing, also limited by the reducedphotochemical activity in the dark cold season, has a minor influence onthe observed levoglucosan concentration and δ13C. The retroplume ages agree well with those derived from observed δ13C(the “isotopic” ages), demonstrating that the limitation of backwardscalculations to 7 d for this study does not introduce any significantbias. A linear regression analysis applied to the experimental levoglucosanδ13C vs. the inverse concentration confirms the young age ofaerosol. The high variability in the observed δ13C implies thatthe local levoglucosan emissions are characterized by different isotopicratios in the range of −26.3 ‰ to −21.3 ‰. These valuesare in good agreement with previous studies on levoglucosan source-specificisotopic composition in biomass burning aerosol. Comparison between measuredand estimated levoglucosan concentrations suggests that emissions areunderestimated by a factor of 2 on average. These findings demonstratethat the aerosol burden from home heating in residential areas is not ofremote origin. In this work we show that combining Lagrangian modelling withisotope ratios is valuable to obtain additional insight into sourceapportionment. Error analysis shows that the largest source of uncertaintyis limited information on isotope ratios of levoglucosan emissions. Based onthe observed low extent of photochemical processing during the cold season,levoglucosan can be used under similar conditions as a conservative tracerwithout introducing substantial bias.