The fraction of soluble potassium not related to sea-salt and soil particles (hereafter, denoted nss-ndust-K) was formerly used widely as tracer element for the qualitative identification of biomass combustion [Cachier et al., 1991]. However, the emission of this tracer element is highly variable for different combustion conditions and, accordingly to Sheffield et al. , may be determined empirically for each situation. Muller-Hagedorn et al.  showed that inorganic salts have strong influence on pyrolysis and as well on product distribution, e.g., the yield of levoglucosan. From this follows, that potassium from wood smoke is not necessarily correlated with levoglucosan.
 We note from Table 2 that the nss-ndust-K/levoglucosan ratio is quite variable between season and sites. In summer (JJA), the ratio is on average 5.7 for all sites with a range of 3.3–9, while in winter (DJF), the average ratio is 0.9 with a range of 0.2–2.1 (Table 2).
 The different behavior of nss-ndust-K and levoglucosan between the sites and seasons might originate from (1) different emission fluxes for different biomass combustion types (fuel types, oven types, agricultural fires, forest fires) or (2) additional nss-ndust-K inputs from other sources, e.g., coal burning or bioparticles.
 We have derived potassium/levoglucosan ratios from data from different studies of biomass combustion (Table 3). It appears, that potassium/levoglucosan ratios are rather below 0.2 for wood combustion in fire places and ovens, while the ratio approaches 0.5 for open fires (Table 3). Thus a K/levoglucosan ratio <0.2 may indicate the prevalence of domestic heating with wood, while a K/levoglucosan ratio around 0.5 may indicate open fires or combustion of fuels such as slash, or straw. The winter values of the K/levoglucosan ratio of 0.2–2.1 at CARBOSOL sites are somewhat higher than those expected for wood stove and fire place emissions, except for Aveiro, where the K/levoglucosan ratio of 0.2 is relatively close to that expected for fire places and stoves. At KPZ, the K/levoglucosan ratio of 0.5 might be indicative for a notable contribution to the fine K from biomass fuels. For summer periods, the K/levoglucosan ratios of 3.3–9 at CARBOSOL sites are around a factor of 10–20 higher than those expected for wild fires. In this case, other potassium sources possibly prevail in the atmosphere.
 Table 3 contains levoglucosan emission data from various studies (levoglucosan compound expressed in mg/g OC). The reciprocal factor (OC/levoglucosan) is used for deriving the amount of OC from wood or biomass combustion in ambient aerosol. The OC/levoglucosan relationship is quite variable for different burning conditions and wood types. For U.S. stoves and fire places, a factor of 7.35 [Fine et al., 2002] is used. In Austria, test burns of wood common for alpine environments have been performed [Schmidl, 2005]. A mass-weighted average for beech and spruce yielded an OC/levoglucosan relationship of 7.1 which is quite close to the U.S. value. We think, that the value of 7.35 holds for conditions typical for the alpine region where generally a mixture of hard and softwood fuel is used for domestic heating. European Alpine conditions are considered for the sites in France (PDD), Germany (SIL) and Austria (SBO). In the work by Gelencsér et al. , a factor of 7.35 is used with a range of 6.0–12.5. The lower factor is more typical for softwood fires in stoves and fire places, while the higher factor is typical for certain hardwood types (e.g., beech). The higher ratio was also observed for wild fires in Amazonia. It has to be proven yet, whether this holds also for wild fires in Europe. In Hungary, main tree species in forests are oaks (Quercus petraea, Qu. peduncularis and Qu. cerris, 30%), black locust (Robinia pseudoacacia, 19%), different species of poplar (Populus, 10%), and Scots Pine (Pinus sylvestris, 9%). Although except for some oak species no emission data are available for those wood types, we assume that the 7.35 ratio can be applied since the trees belong mainly to hardwood species, where generally ratios around 7 and up to 13 were reported (Table 3). In Portugal, main tree species are Mediterranean Pine (Pinus pinaster, 30%), Eucalyptus (mainly Eucalyptus globulus, 20%), and oaks (Quercus robur and Quercus faginea). While Eucalyptus is not well suited for firing stoves, it can be assumed that most fuel wood in small combustion units is pine, oak and other local species. For pine and oak OC/levoglucosan ratios from U.S. studies were on the lower end of the range indicated above. Thus, for the Portuguese site a factor on the low end is applied (6.0). There is some uncertainty as levoglucosan emission data for western European tree species are currently only available for a few species indigenous in the eastern Alpine region [Schmidl, 2005]. The uncertainty of the OC/levoglucosan ratio for Austrian biomass combustion emissions stems from the unknown ratio of softwood and hardwood use in Austrian stoves and fire places. From the test burns of indigenous wood for Austria and information about use of wood types in Austria we derived an uncertainty of the OC/levoglucosan ratio of 15%, based on an assumed range of the softwood fraction in the combustion from 50 to 80%. As the other CARBOSOL countries outside the Alpine area, Hungary and Portugal, have distinctly other tree species in their woods, the uncertainty is assumed to be up to 30%, e.g., up to 30% lower in Portugal because of wood species emitting on the lower end of the range, and up to 30% higher in Hungary because of hardwood species emitting on the higher end of the 7.3 ± 30% range.