Firewood residential heating - local versus regional influence on the aerosol burden

As a particular form of biomass burning (BB), domesticheating with firewood is a major source of fine dust inthe cold season. Understanding its impact on air qualityrequires reliable aerosol source apportionment andassessment of prevailing loss processes. Further, to establisheffective mitigation policies, it is necessary toaccurately quantify the contribution of local vs. remotesources to the aerosol burden. To this end, source-receptormodelling is employed, such as chemical massbalance or Lagrangian techniques, to calculate concentrationsof the BB specific tracer in aerosol, levoglucosan(Fine et al. 2002, Chunmao et al. 2019). In the lastdecades, it has been shown that combining stable isotoperatios with concentration measurements allows forseparating the impact of chemical degradation fromchanges linked to source strength or atmospherictransport. Based on that, Gensch et al. (2018) developeda numerical approach, comparing stable carbonisotopic ratio and concentration measurements withback trajectory analyses by the Lagrangian particle dispersionmodel FLEXPART (https://www.flexpart.eu/) toinvestigate chemical aging processes in BB aerosol.In the present study, stable carbon isotopes were implementedin the full dispersed output of FLEXPART byexplicitly tracking of the levoglucosan fraction containing13C. Further, sensitivity studies were carried out toexamine the simulation responses to the uncertaintiesof the governing atmospheric processes described inFLEXPART and thus, to determine the model performancefor given conditions. Finally, the set of selectedmodelling routines were applied in a case study with thegoal to assess the contribution of local vs. remotesources of biomass burning emissions from residentialheating to the particulate matter sampled at twomeasurement stations of the North Rhine-WestphaliaEnvironmental Agency, LANUV. Thereby, the measuredlevoglucosan concentration and isotopic composition in50 selected aerosol samples taken at an urbanbackground station in Mülheim-Styrum and at a ruralbackground station in the Eifel, in the cold seasons of2015 - 2017 were compared with the model results.The simulations indicate that the biggest fraction of thesampled aerosol is 1 to 2 days old. Chemical aging, alsolimited by low mean OH concentrations in the cold season,has thus a minor influence on the observedlevoglucosan concentration and δ13C (Fig. 1). Theexperimental data, interpreted as a two end-membermixing series between low-concentration/isotopicallyheavyback-ground and high-concentration/isotopicallylightfresh emissions, support the model outcome,showing similar isotopic ratios for the two constituents.The high variability in the observed δ13C implies that thelocal levoglucosan emissions are characterized by verydifferent isotopic ratios in the range of -25.3 to -21.4 %(Fig. 1 in Pdf). These values are in good agreement withprevious studies on levoglucosan source specificisotopic composition in BB aerosol (Sang et al. 2012).These findings demonstrate that the aerosol burdenfrom residential heating in living areas is of local originand thus, mitigation is possible through reduction oflocal emissions. In this work we show that combiningLagrangian modelling with isotope ratios is valuable toobtain additional insight in source apportionment.There is, though, a need for a better isotopic descriptionof sources. Moreover, studies investigating long rangetransport of BB aerosol from large-scale fires in the dryseason are essential to examine the role of aging amongother loss processes.Fine, P.M., Cass, G.R. and Simoneit, B.R.T. (2002) J. Geophys.Res., [Atmos.], doi 10.1029/2001jd000661Chunmao, Z., Yugo, K., et al. (2019) Environ. Pollut., doi10.1016/j.envpol.2019.01.003Gensch, I., Sang, X.F., et al. (2018) Environ. Sci.&Tech.,doi 10.1021/acs.est.8b03054Sang, X.F., Gensch, I., et al. (2012) Environ. Sci.&Tech.,doi 10.1021/ es204094