On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols

Radiocarbon (<sup>14</sup>C) measurements of elemental carbon (EC) and organic carbon (OC) separately (as opposed to only total carbon, TC) allow an unambiguous quantification of their non-fossil and fossil sources and represent an improvement in carbonaceous aerosol source apportionment. Isolation of OC and EC for accurate <sup>14</sup>C determination requires complete removal of interfering fractions with maximum recovery. To evaluate the extent of positive and negative artefacts during OC and EC separation, we performed sample preparation with a commercial Thermo-Optical OC/EC Analyser (TOA) by monitoring the optical properties of the sample during the thermal treatments. Extensive attention has been devoted to the set-up of TOA conditions, in particular, heating program and choice of carrier gas. Based on different types of carbonaceous aerosols samples, an optimised TOA protocol (Swiss_4S) with four steps is developed to minimise the charring of OC, the premature combustion of EC and thus artefacts of <sup>14</sup>C-based source apportionment of EC. For the isolation of EC for <sup>14</sup>C analysis, the water-extraction treatment on the filter prior to any thermal treatment is an essential prerequisite for subsequent radiocarbon; otherwise the non-fossil contribution may be overestimated due to the positive bias from charring. The Swiss_4S protocol involves the following consecutive four steps (S1, S2, S3 and S4): (1) S1 in pure oxygen (O<sub>2</sub>) at 375 °C for separation of OC for untreated filters, and water-insoluble organic carbon (WINSOC) for water-extracted filters; (2) S2 in O<sub>2</sub> at 475 °C, followed by (3) S3 in helium (He) at 650 °C, aiming at complete OC removal before EC isolation and leading to better consistency with thermal-optical protocols like EUSAAR_2, compared to pure oxygen methods; and (4) S4 in O<sub>2</sub> at 760 °C for recovery of the remaining EC. <br><br> WINSOC was found to have a significantly higher fossil contribution than the water-soluble OC (WSOC). Moreover, the experimental results demonstrate the lower refractivity of wood-burning EC compared to fossil EC and the difficulty of clearly isolating EC without premature evolution. Hence, simplified techniques of EC isolation for <sup>14</sup>C analysis are prone to a substantial bias and generally tend towards an underestimation of the non-fossil sources. Consequently, the optimal strategy for <sup>14</sup>C-based source apportionment of carbonaceous aerosols should follow an approach to subdivide TC into different carbonaceous aerosol fractions for individual <sup>14</sup>C analyses, as these fractions differ in their origins. To obtain the comprehensive picture of the sources of carbonaceous aerosols, the Swiss_4S protocol is not only implemented to measure OC and EC fractions, but also WINSOC as well as a continuum of refractory OC and non-refractory EC for <sup>14</sup>C source apportionment. In addition, WSOC can be determined by subtraction of the water-soluble fraction of TC from untreated TC. Last, we recommend that <sup>14</sup>C results of EC should in general be reported together with the EC recovery

On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols

Radiocarbon ( 14C) measurements of elemental carbon (EC) and organic carbon (OC) separately (as opposed to only total carbon, TC) allow an unambiguous quantification of their non-fossil and fossil sources and represent an improvement in carbonaceous aerosol source apportionment. Isolation of OC and EC for accurate 14C determination requires complete removal of interfering fractions with maximum recovery. The optimal strategy for 14C-based source apportionment of carbonaceous aerosols should follow an approach to subdivide TC into different carbonaceous aerosol fractions for individual 14C analyses, as these fractions may differ in their origins. To evaluate the extent of positive and negative artefacts during OC and EC separation, we performed sample preparation with a commercial Thermo-Optical OC/EC Analyser (TOA) by monitoring the optical properties of the sample during the thermal treatments. Extensive attention has been devoted to the set-up of TOA conditions, in particular, heating program and choice of carrier gas. Based on different types of carbonaceous aerosols samples, an optimised TOA protocol (Swiss-4S) with four steps is developed to minimise the charring of OC, the premature combustion of EC and thus artefacts of 14C-based source apportionment of EC. For the isolation of EC for 14C analysis, the water-extraction treatment on the filter prior to any thermal treatment is an essential prerequisite for subsequent radiocarbon measurements; otherwise the non-fossil contribution may be overestimated due to the positive bias from charring. The Swiss-4S protocol involves the following consecutive four steps (S1, S2, S3 and S4): (1) S1 in pure oxygen (O2) at 375 °C for separation of OC for untreated filters and water-insoluble organic carbon (WINSOC) for water-extracted filters; (2) S2 in O2 at 475 °C followed by (3) S3 in helium (He) at 650 °C, aiming at complete OC removal before EC isolation and leading to better consistency with thermal-optical protocols like EUSAAR-2, compared to pure oxygen methods; and (4) S4 in O2 at 760 °C for recovery of the remaining EC. WINSOC was found to have a significantly higher fossil contribution than the water-soluble OC (WSOC). Moreover, the experimental results demonstrate the lower refractivity of wood-burning EC compared to fossil EC and the difficulty of clearly isolating EC without premature evolution. Hence, simplified techniques of EC isolation for 14C analysis are prone to a substantial bias and generally tend towards an overestimation of fossil sources. To obtain the comprehensive picture of the sources of carbonaceous aerosols, the Swiss-4S protocol is not only implemented to measure OC and EC fractions, but also WINSOC as well as a continuum of refractory OC and non-refractory EC for 14C source apportionment. In addition, WSOC can be determined by subtraction of the water-soluble fraction of TC from untreated TC. Last, we recommend that 14C results of EC should in general be reported together with the EC recovery. © 2012 Author(s)

Assessing the wintertime contribution of biomass smoke to organic aerosol at 15 sites in Switzerland by analysing filter samples using aerosol mass spectrometry

Burning biomass and other human activities lead to the emission of particle matter (PM) consisting of ions, elemental (EC) and organic carbon (OA). In winter, high proportions of OA are related to biomass burning in the alpine region as well as in urban regions as Grenoble and Zurich (Lanz et al. 2010; Richard et al. 2011). Besides traffic and cooking, biomass burning contributes even in the megacity Paris considerable amounts of OA (Crippa et al. 2013). Due to the carcinogenic potential of biogenic smoke, it is crucial to examine its contribution in different regions in order to allow an effective mitigation process. The Aerosol mass spectrometer (AMS, Aerodyne) provides measurements of OA for which positive matrix factorization (PMF) is able to separate the proportion of biomass burning (BBOA) from other primary sources such as traffic (hydrocarbon-like OA, HOA) , or from secondary oxygenated OA (OOA), formed in-situ in the atmosphere via the oxidation of volatile organic compound precursors (e.g. Lanz et al. 2010). While the information accessible through analysis of AMS mass spectra is highly useful, widespread or long-term AMS data collection is greatly restricted by the high instrument cost and complex maintenance. On the other hand, the Aerosol Chemical Speciation Monitor (ACSM) is designed for low costs and maintenance, but it also operates only at unit mass resolution, preventing the assessment of oxidation state. In order to overcome these limitations and to assess the contribution of BBOA compared to other sources, we explored the application of laboratory AMS measurements on aerosol filter samples. Such samples are relatively easy and inexpensive to collect and store, and are already routinely collected at many air quality stations over the world. The approach consists of water extraction of the particulate material from quartz filters and subsequent atomization of the resulting solutions into the AMS. The extraction efficiency is estimated as ~80% and the mass spectra obtained by this methodology are very similar to the corresponding on-line measurements and that for different settings (e.g. different sites and different seasons). We present here the first application of this technique to filter samples collected during 2 consecutive winters (2008 and 2009) at 15 stations in Switzerland with different exposure characteristics (including a complete yearly cycle for one of the stations). Data are analysed by PMF and combined with other measurements, including organic and elemental carbon (OC/EC), ions, levoglucosan (marker for biomass burning), and radiocarbon content (14C), to provide an improved estimation of the biomass smoke contribution to OA (Figure 1). BBOA contribution and emission profiles at different stations will be discussed and related to the prevailing topographical, meteorological and combustion conditions. This work was supported by the Swiss Federal office for the Environment and the Swiss National Science Foundation. Lanz, V. et al. (2010) Atmos. Chem. Phys., 10, 10453-10471. Richard, A. et al. (2011) Atmos. Chem. Phys., 11, 8945-8963. Crippa, M. et al. (2013) Atmos. Chem. Phys., 13, 961 981

ALICE: Physics performance report, volume I

ALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC. It currently includes more than 900 physicists and senior engineers, from both nuclear and high-energy physics, from about 80 institutions in 28 countries. The experimentwas approved in February 1997. The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2001 and construction has started for most detectors. Since the last comprehensive information on detector and physics performance was published in the ALICE Technical Proposal in 1996, the detector as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) will give an updated and comprehensive summary of the current status and performance of the various ALICE subsystems, including updates to the Technical Design Reports, where appropriate, as well as a description of systems which have not been published in a Technical Design Report. The PPR will be published in two volumes. The currentVolume I contains: 1. a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, 2. relevant experimental conditions at the LHC, 3. a short summary and update of the subsystem designs, and 4. a description of the offline framework and Monte Carlo generators. Volume II, which will be published separately, will contain detailed simulations of combined detector performance, event reconstruction, and analysis of a representative sample of relevant physics observables from global event characteristics to hard processes. © 2004 IOP Publishing Ltd

ALICE Technical Design Report on Forward Detectors : FMD, T0 and V0

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ALICE Technical Design Report of the Computing

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