| 1. |
- Gilardoni, S., et al.
(author)
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Better constraints on sources of carbonaceous aerosols using a combined C-14 - macro tracer analysis in a European rural background site
- 2011
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 11:12, s. 5685-5700
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Journal article (peer-reviewed)abstract
- The source contributions to carbonaceous PM2.5 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 C-14 measurements. This was the first time that C-14 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 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 back-trajectory analysis applying the Potential Source Contribution Function method to identify potential source regions.
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| 2. |
- Paglione, M., et al.
(author)
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Primary and secondary biomass burning aerosols determined by proton nuclear magnetic resonance (H-1-NMR) spectroscopy during the 2008 EUCAARI campaign in the Po Valley (Italy)
- 2014
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 14:10, s. 5089-5110
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Journal article (peer-reviewed)abstract
- Atmospheric organic aerosols are generally classified as primary and secondary (POA and SOA) according to their formation processes. An actual separation, however, is challenging when the timescales of emission and gas-to-particle formation overlap. The presence of SOA formation in biomass burning plumes leads to scientific questions about whether the oxidized fraction of biomass burning aerosol is rather of secondary or primary origin, as some studies would suggest, and about the chemical compositions of oxidized biomass burning POA and SOA. In this study, we apply nuclear magnetic resonance (NMR) spectroscopy to investigate the functional group composition of fresh and aged biomass burning aerosols during an intensive field campaign in the Po Valley, Italy. The campaign was part of the EUCAARI project and was held at the rural station of San Pietro Capofiume in spring 2008. Factor analysis applied to the set of NMR spectra was used to apportion the wood burning contribution and other organic carbon (OC) source contributions, including aliphatic amines. Our NMR results, referred to the polar, water-soluble fraction of OC, show that fresh wood burning particles are composed of polyols and aromatic compounds, with a sharp resemblance to wood burning POA produced in wood stoves, while aged samples are clearly depleted of alcohols and are enriched in aliphatic acids with a smaller contribution of aromatic compounds. The comparison with biomass burning organic aerosols (BBOA) determined by high-resolution aerosol mass spectrometry (HR-TOF-AMS) at the site shows only a partial overlap between NMR BB-POA and AMS BBOA, which can be explained by either the inability of BBOA to capture all BB-POA composition, especially the alcohol fraction, or the fact that BBOA account for insoluble organic compounds unmeasured by the NMR. Therefore, an unambiguous composition for biomass burning POA could not be derived from this study, with NMR analysis indicating a higher O / C ratio compared to that measured for AMS BBOA. The comparison between the two techniques substantially improves when adding factors tracing possible contributions from biomass burning SOA, showing that the operational definitions of biomass burning organic aerosols are more consistent between techniques when including more factors tracing chemical classes over a range of oxidation levels. Overall, the non-fossil total carbon fraction was 50-57%, depending on the assumptions about the C-14 content of non-fossil carbon, and the fraction of organic carbon estimated to be oxidized organic aerosol (OOA) from HR-TOF-AMS measurements was 73-100% modern.
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| 3. |
- Szidat, S., et al.
(author)
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Intercomparison of 14C Analysis of Carbonaceous Aerosols : Exercise 2009
- 2013
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In: Radiocarbon. - : Cambridge University Press (CUP). - 0033-8222 .- 1945-5755. ; 55:2-3, s. 1496-1509
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Journal article (peer-reviewed)abstract
- Radiocarbon analysis of the carbonaceous aerosol allows an apportionment of fossil and non-fossil sources of airborne particulate matter (PM). A chemical separation of total carbon (TC) into its subfractions organic carbon (OC) and elemental carbon (EC) refines this powerful technique, as OC and EC originate from different sources and undergo different processes in the atmosphere. Although C-14 analysis of TC, EC, and OC has recently gained increasing attention, interlaboratory quality assurance measures have largely been missing, especially for the isolation of EC and OC. In this work, we present results from an intercomparison of 9 laboratories for C-14 analysis of carbonaceous aerosol samples on quartz fiber filters. Two ambient PM samples and 1 reference material (RM 8785) were provided with representative filter blanks. All laboratories performed C-14 determinations of TC and a subset of isolated EC and OC for isotopic measurement. In general, C-14 measurements of TC and OC agreed acceptably well between the laboratories, i.e. for TC within 0.015-0.025 (FC)-C-14 for the ambient filters and within 0.041 (FC)-C-14 for RM 8785. Due to inhomogeneous filter loading, RM 8785 demonstrated only limited applicability as a reference material for C-14 analysis of carbonaceous aerosols. C-14 analysis of EC revealed a large deviation between the laboratories of 28-79% as a consequence of different separation techniques. This result indicates a need for further discussion on optimal methods of EC isolation for C-14 analysis and a second stage of this intercomparison.
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