LAUSR

Abstract. We report the first-time use of the Lagrangian Particle Dispersion Model (LPDM) FLEXPART to simulate isotope ratios of the biomass burning tracer levoglucosan. Here, we combine the model results with observed levoglucosan concentrations and δ13C to assess the contribution 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 days old, and thus originates from local to regional sources. Consequently, photo-chemical aging, also limited by low mean OH concentrations in the cold season, has a minor influence the observed levoglucosan concentration and δ13C. The retro plume ages agree well with those derived from observed δ13C, (the isotopic ages), demonstrating that the limitation of backwards calculations to seven days for this study doesn't introduce any significant bias. A linear regression analysis applied to the experimental levoglucosan δ13C vs. the inverse concentration confirms the young age of aerosol. The high variability in the observed δ13C implies that the local levoglucosan emissions are characterized by very different isotopic ratios in the range of −25.3 to −21.4 ‰. These values are in good agreement with previous studies on levoglucosan source specific isotopic composition in biomass burning aerosol. Comparison between measured and estimated levoglucosan concentrations suggest that emissions are underestimated by a factor of two on average. These findings demonstrate that the aerosol burden from home heating in residential areas is not of remote origin and thus it can be mitigated by reducing local emissions. In this work we show that combining Lagrangian modelling with isotope ratios is valuable to obtain additional insight in source apportionment. Error analysis shows that the largest source of uncertainty is limited information on isotope ratios of levoglucosan emissions. Based on the observed low extent of photochemical processing during cold season, levoglucosan can be used under similar conditions as a conservative tracer without introducing substantial bias.