Trends, composition, and sources of carbonaceous aerosol at the Birkenes Observatory, northern Europe, 2001–2018

Yttri, Karl Espen; Canonaco, Francesco; Eckhardt, Sabine; Evangeliou, Nikolaos; Fiebig, Markus; Gundersen, Hans; Hjellbrekke, Anne-Gunn; Lund Myhre, Cathrine; Platt, Stephen Matthew; Prévôt, André S. H.; Simpson, David; Solberg, Sverre; Surratt, Jason; Tørseth, Kjetil; Uggerud, Hilde; Vadset, Marit; Wan, Xin; Aas, Wenche

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 inline-formula M1inlinescrollmathml chem normal OC / normal EC 40pt14ptsvg-formulamathimgcc9f4bcff69d3d15c535bded268fb106 acp-21-7149-2021-ie00001.svg40pt14ptacp-21-7149-2021-ie00001.png (2001–2018) and the levoglucosan (2008–2018) time series are the longest in Europe, with inline-formula M2inlinescrollmathml chem normal OC / normal EC 40pt14ptsvg-formulamathimg8770ee5411af319b1f548cfec09309b4 acp-21-7149-2021-ie00002.svg40pt14ptacp-21-7149-2021-ie00002.png available for the PMinline-formula10, PMinline-formula2.5 (fine), and PMinline-formula10–2.5 (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 (BSOAinline-formulaSRT), primary biological aerosol particles (PBAP), biomass burning aerosol (BB), ammonium-nitrate-dominated aerosol (NHinline-formula4NOinline-formula3), and (one low carbon fraction) sea salt aerosol (SS).

We observed significant (inline-formulap<0.05), large decreases in EC in PMinline-formula10 (inline-formula−3.9 % yrinline-formula−1) and PMinline-formula2.5 (inline-formula−4.2 % yrinline-formula−1) and a smaller decline in levoglucosan (inline-formula−2.8 % yrinline-formula−1), suggesting that inline-formula M18inlinescrollmathml chem normal OC / normal EC 40pt14ptsvg-formulamathimgba1663e62da541dd47acbc62b09db2ca acp-21-7149-2021-ie00003.svg40pt14ptacp-21-7149-2021-ie00003.png from traffic and industry is decreasing, whereas the abatement of inline-formula M19inlinescrollmathml chem normal OC / normal EC 40pt14ptsvg-formulamathimgbf549994892dfb29594c723c96338b37 acp-21-7149-2021-ie00004.svg40pt14ptacp-21-7149-2021-ie00004.png from biomass burning has been slightly less successful. EC abatement with respect to anthropogenic sources is further supported by decreasing EC fractions in PMinline-formula2.5 (inline-formula−3.9 % yrinline-formula−1) and PMinline-formula10 (inline-formula−4.5 % yrinline-formula−1). PMF apportioned 72 % of EC to fossil fuel sources; this was further supported by PMF applied to absorption photometer data, which yielded a two-factor solution with a low aerosol Ångstrøm exponent (AAE inline-formula= 0.93) fraction, assumed to be equivalent black carbon from fossil fuel combustion (eBCinline-formulaFF), contributing 78 % to eBC mass. The higher AAE fraction (AAE inline-formula= 2.04) is likely eBC from BB (eBCinline-formulaBB). Source–receptor model calculations (FLEXPART) showed that continental Europe and western Russia were the main source regions of both elevated eBCinline-formulaBB and eBCinline-formulaFF.

Dominating biogenic sources explain why there was no downward trend for OC. A relative increase in the OC fraction in PMinline-formula2.5 (inline-formula+3.2 % yrinline-formula−1) and PMinline-formula10 (inline-formula+2.4 % yrinline-formula−1) underscores the importance of biogenic sources at Birkenespage7150 (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 PMinline-formula2.5, PMinline-formula10–2.5, and PMinline-formula10 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.

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Yttri, Karl Espen / Canonaco, Francesco / Eckhardt, Sabine / et al: Trends, composition, and sources of carbonaceous aerosol at the Birkenes Observatory, northern Europe, 2001–2018. 2021. Copernicus Publications.

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