Abstract
Abstract. In the present study, natural and anthropogenic sources of particulate organic carbon (OCp) and elemental carbon (EC) have been quantified based on weekly filter samples of PM10 (particles with aerodynamic diameter <10 μm) collected at four Nordic rural background sites [Birkenes (Norway), Hyytiälä (Finland), Vavihill (Sweden), Lille Valby, (Denmark)] during late summer (5 August–2 September 2009). Levels of source specific tracers, i.e. cellulose, levoglucosan, mannitol and the 14C/12C ratio of total carbon (TC), have been used as input for source apportionment of the carbonaceous aerosol, whereas Latin Hypercube Sampling (LHS) was used to statistically treat the multitude of possible combinations resulting from this approach. The carbonaceous aerosol (here: TCp; i.e. particulate TC) was totally dominated by natural sources (69–86%), with biogenic secondary organic aerosol (BSOA) being the single most important source (48–57%). Interestingly, primary biological aerosol particles (PBAP) were the second most important source (20–32%). The anthropogenic contribution was mainly attributed to fossil fuel sources (OCff and ECff) (10–24%), whereas no more than 3–7% was explained by combustion of biomass (OCbb and ECbb) in this late summer campaign i.e. emissions from residential wood burning and/or wild/agricultural fires. Fossil fuel sources totally dominated the ambient EC loading, which accounted for 4–12% of TCp, whereas <1.5% of EC was attributed to combustion of biomass. The carbonaceous aerosol source apportionment showed only minor variation between the four selected sites. However, Hyytiälä and Birkenes showed greater resemblance to each other, as did Lille Valby and Vavihill, the two latter being somewhat more influenced by anthropogenic sources. Ambient levels of organosulphates and nitrooxy-organosulphates in the Nordic rural background environment are reported for the first time in the present study. The most abundant organosulphate compounds were an organosulphate of isoprene and nitrooxy-organosulphates of α- and β-pinene and limonene.
Highlights
The ambient air carbonaceous aerosol (here: particulate carbonaceous matter (PCM) = organic matter (OM) + elemental carbon (EC)) is found to be abundant in the European rural background environment, accounting for 10–40 % of PM10 (Yttri et al, 2007a; Putaud et al, 2004)
Both anthropogenic and biogenic sources contribute to the carbonaceous aerosol loading, and its complexity in terms of composition, formation mechanisms and sources has been the topic of a number of recent studies (e.g. Donahue et al, 2005, 2009; Kanakidou et al, 2005; Hallquist et al, 2009)
The levels appear to be in the lower range of that previously reported for the Nordic rural background environment during summer (Yttri et al, 2007a), different sampling-times and techniques are likely to contribute at least partly to the observed differences
Summary
During the last few years a number of studies have become available which point towards natural sources as important contributors to the carbonaceous aerosol loading in Europe, during summertime, including both the rural and the urban environment (e.g. Gelenscer et al, 2007; Szidat et al, 2006, 2009; Yttri et al, 2011). In contrast to continental European rural background sites, the Nordic ones experienced 30 % higher levels of organic carbon (OC) in summer compared to winter (Yttri et al, 2007a) This distinct pattern likely reflects a seasonal increase in (B)SOA and PBAP, as well as low influence of anthropogenic sources. In the current paper we present the main findings from the SONORA study
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