We present 18 years (2001-2018) of aerosol measurements, including organic and elemental carbon (OC and EC), organic tracers (levoglucosan, arabitol, mannitol, trehalose, glucose, and 2-methyltetrols), trace elements, and ions, at the Birkenes Observatory (southern Norway) - a site representative of the northern European region. The OC/EC (2001-2018) and the levoglucosan (2008-2018) time series are the longest in Europe, with OC/EC available for the PM.sub.10, PM.sub.2.5 (fine), and PM.sub.10-2.5 (coarse) size fractions, providing the opportunity for a nearly 2-decade-long assessment. Using positive matrix factorization (PMF), we identify seven carbonaceous aerosol sources at Birkenes: mineral-dust-dominated aerosol (MIN), traffic/industry-like aerosol (TRA/IND), short-range-transported biogenic secondary organic aerosol (BSOA.sub.SRT ), primary biological aerosol particles (PBAP), biomass burning aerosol (BB), ammonium-nitrate-dominated aerosol (NH.sub.4 NO.sub.3 ), and (one low carbon fraction) sea salt aerosol (SS). We observed significant (p Dominating biogenic sources explain why there was no downward trend for OC. A relative increase in the OC fraction in PM.sub.2.5 (+3.2 % yr.sup.-1) and PM.sub.10 (+2.4 % yr.sup.-1) underscores the importance of biogenic sources at Birkenes (BSOA and PBAP), which were higher in the vegetative season and dominated both fine (53 %) and coarse (78 %) OC. Furthermore, 77 %-91 % of OC in PM.sub.2.5, PM.sub.10-2.5, and PM.sub.10 was attributed to biogenic sources in summer vs. 22 %-37 % in winter. The coarse fraction had the highest share of biogenic sources regardless of season and was dominated by PBAP, except in winter. Our results show a shift in the aerosol composition at Birkenes and, thus, also in the relative source contributions. The need for diverse offline and online carbonaceous aerosol speciation to understand carbonaceous aerosol sources, including their seasonal, annual, and long-term variability, has been demonstrated.