Better constraints on sources of carbonaceous aerosols using a combined <sup>14</sup>C – macro tracer analysis in a European rural background site

Abstract

Abstract. The source contributions to carbonaceous PM 2.5 aerosol were investigated at a European background site at the edge of the Po Valley, in Northern Italy, during the period January-December 2007. Carbonaceous aerosol was described as the sum of 8 source components: primary (1) and secondary (2) biomass burning organic carbon, biomass burning elemental carbon (3), primary (4) and secondary (5) fossil organic carbon, fossil fuel burning elemental carbon (6), primary (7) and secondary (8) biogenic organic carbon. The mass concentration of each component was quantified using a set of macro tracers (organic carbon OC, elemental carbon EC, and levoglucosan), micro tracers (arabitol and mannitol), and 14 C measurements. This was the first time that 14 C measurements covered a full annual cycle with daily resolution. This set of 6 tracers, together with assumed uncertainty ranges of the ratios of OC-to-EC, and the reference fraction of modern carbon in the 8 source categories, provides strong constraints to the source contributions to carbonaceous aerosol. The uncertainty of contributions was assessed with a Quasi-Monte Carlo (QMC) method accounting for the variability of OC and EC emission factors, the uncertainty of reference fractions of modern carbon, and the measurement uncertainty.During winter, biomass burning composed 64 % (±15 %) of the total carbon (TC) concentration, while in summer secondary biogenic OC accounted for 50 % (±16 %) of TC. The contribution of primary biogenic aerosol particles was Correspondence to: E. Vignati (elisabetta.vignati@jrc.ec.europa.eu) negligible during the entire year. Moreover, aerosol associated with fossil sources represented 27 % (±16 %) and 41 % (±26 %) of TC in winter and summer, respectively. The contribution of secondary organic aerosol (SOA) to the organic mass (OM) was significant during the entire year. SOA accounted for 30 % (±16 %) and 85 % (±12 %) of OM during winter and summer, respectively. While the summer SOA was dominated by biogenic sources, winter SOA was mainly due to biomass burning and fossil sources. This indicates that the oxidation of semi-volatile and intermediate volatility organic compounds co-emitted with primary organics is a significant source of SOA, as suggested by recent model results and Aerosol Mass Spectrometer measurements. Comparison with previous global model simulations, indicates a strong underestimate of wintertime primary aerosol emissions in this region. The comparison of source apportionment results in different urban and rural areas showed that the sampling site was mainly affected by local aerosol sources during winter and regional air masses from the nearby Po Valley in summer. This observation was further confirmed by backtrajectory analysis applying the Potential Source Contribution Function method to identify potential source regions.

Direct observation of aqueous secondary organic aerosol from biomass-burning emissions

“…In Europe, combustion of biomass for residential heating has increased in recent years. One study at a rural site in northern Italy showed that SOA from biomass burning in winter accounts for 10% of organic carbon and 7% of fine particle mass (43); in the urban area of Paris, processing of biomassburning emissions accounted for up to 40% of the OA during another field study (44); similarly, in rural areas nearby London, aged biomass-burning emissions are a likely important contribution to the overall OA (45). This study highlights the relevance of aqueousphase chemistry for processing of wood-burning emissions.…”

Functionalization and fragmentation during ambient organic aerosol aging: application of the 2-D volatility basis set to field studies

“…These source-resolved results can be compared to existing literature reporting observations at sites in Europe (Szidat et al, 2006;Gelencser et al, 2007;Gilardoni et al, 2011;Yttri et al, 2011). These studies focus on distinguishing fossil from non-fossil carbon measured at field sites using radiocarbon analysis and then using levoglucosan/OC and fossil EC/OC ratios to calculate the contributions of biomass burning and fossil fuel POA, respectively, to the total carbon.…”

“…When bSOA was ignored and aSOA was allowed to age the model performed the best for both urban and rural, forested sites. Due to new evidence from chamber studies that biogenic SOA compounds do age (Ng et al, 2006;Tritscher et al, 2011), as well as field observations from radiocarbon analyses that find high contributions from modern (biogenic) carbon to the total OA mass (Szidat et al, 2006;Gilardoni et al, 2011;Yttri et al, 2011), we relax here our assumption and explore a scenario where biogenic SOA compounds age similarly to anthropogenic SOA compounds.…”

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

“…A clear annual variability in the carbon f M (TC) was observed at the Ispra site in northern Italy, with f M = 90 % in winter and f M = 50 % in summer. Residential wood combustion for heating purposes clearly has a major impact on the organic wintertime aerosol at Ispra (Gilardoni et al, 2011). At Montseny (ES) and Vavihill in Southern Sweden , f M was more constant over the year.…”

“…Residential wood combustion was shown to be a major source of wintertime OA at Ispra in northern Italy (Gilardoni et al, 2011) in Oslo and a nearby background site in southern Norway (Yttri et al, 2011a, b), as well as at Vavihill in southern Sweden . Despite these congruent observations, it is not possible to say at this stage if such contributions are a local problem or reflect more widespread problems with the wood-burning inventories.…”