Composition and sources of carbonaceous aerosols in Northern Europe during winter

Sources of elemental carbon (EC) and organic carbon (OC) in atmospheric aerosols (carbonaceous aerosols) were investigated by collection of weekly aerosol filter samples at six background sites in Northern Europe (Birkenes, Norway; Vavihill, Sweden; Risoe, Denmark; Cabauw and Rotterdam in The Netherlands; Melpitz, Germany) during winter 2013. Analysis of 14C and a set of molecular tracers were used to constrain the sources of EC and OC. During the four-week campaign, most sites (in particular those in Germany and The Netherlands) were affected by an episode during the first two weeks with high concentrations of aerosol, as continental air masses were transported westward. The analysis results showed a clear, increasing north to south gradient for most molecular tracers. Total carbon (TC = OC + EC) at Birkenes showed an average concentration of 0.5 ± 0.3 μg C m−3, whereas the average concentration at Melpitz was 6.0 ± 4.3 μg C m−3. One weekly mean TC concentration as high as 11 μg C m−3 was observed at Melpitz. Average levoglucosan concentrations varied by an order of magnitude from 25 ± 13 ng m−3 (Birkenes) to 249 ± 13 ng m−3 (Melpitz), while concentrations of tracers of fungal spores (arabitol and mannitol) and vegetative debris (cellulose) were very low, showing a minor influence of primary biological aerosol particles during the North European winter. The fraction of modern carbon generally varied from 0.57 (Melpitz) to 0.91 (Birkenes), showing an opposite trend compared to the molecular tracers and TC. Total concentrations of 10 biogenic and anthropogenic carboxylic acids, mainly of secondary origin, were 4–53 ng m−3, with the lowest concentrations observed at Birkenes and the highest at Melpitz. However, the highest relative concentrations of carboxylic acids (normalized to TC) were observed at the most northern sites. Levels of organosulphates and nitrooxy organosulphates varied more than two orders of magnitude, from 2 to 414 ng m−3, between individual sites and samples. The three sites Melpitz, Rotterdam and Cabauw, located closest to source regions in continental Europe, showed very high levels of organosulphates and nitrooxy organosulphates (up to 414 ng m−3) during the first two weeks of the study, while low levels (40% of TC), while use and combustion of fossil fuels was the second most important source. Furthermore, EC from biomass burning accounted for 7–16% of TC, whereas EC from fossil sources contributed to