S. Szidat

Universität Bern, Berna, Bern, Switzerland

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Publications (102)310.61 Total impact

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    ABSTRACT: Aerosol source apportionment remains a critical challenge for understanding the transport and aging of aerosols, as well as for developing successful air pollution mitigation strategies. The contributions of fossil and non-fossil sources to organic carbon (OC) and elemental carbon (EC) in carbonaceous aerosols can be quantified by measuring the radiocarbon (14C) content of each carbon fraction. However, the use of 14C in studying OC and EC has been limited by technical challenges related to the physical separation of the two fractions and small sample sizes. There is no common procedure for OC/EC 14C analysis, and uncertainty studies have largely focused on the precision of yields. Here, we quantified the uncertainty in 14C measurement of aerosols associated with the isolation and analysis of each carbon fraction with the Swiss_4S thermal-optical analysis (TOA) protocol. We used an OC/EC analyzer (Sunset Laboratory Inc., OR, USA) coupled to vacuum line to separate the two components. Each fraction was thermally desorbed and converted to carbon dioxide (CO2) in pure oxygen (O2). On average 91% of the evolving CO2 was then cryogenically trapped on the vacuum line, reduced to filamentous graphite, and measured for its 14C content via accelerator mass spectrometry (AMS). To test the accuracy of our set-up, we quantified the total amount of extraneous carbon introduced during the TOA sample processing and graphitization as the sum of modern and fossil (14C-depleted) carbon introduced during the analysis of fossil reference materials (adipic acid for OC and coal for EC) and contemporary standards (oxalic acid for OC and rice char for EC) as a function of sample size. We further tested our methodology by analyzing five ambient airborne particulate matter (PM2.5) samples with a range of OC and EC concentrations and 14C contents in an interlaboratory comparison. The total modern and fossil carbon blanks of our set-up were 0.8�0.4 and 0.67�0.34 μgC, respectively, based on multiple measurements of ultra-small samples. The Swiss_4S protocol and the cryo-trapping contributed 0.37�0.18 μg of modern carbon and 0.13�0.07 μg of fossil carbon to the estimated blanks, with consistent estimates obtained for the two laboratories. There was no difference in the background correction between the OC and EC fractions. Our set-up allowed us to e�ciently isolate and trap each carbon fraction with the Swiss_4S protocol and to perform 14C analysis of ultra-small OC and EC samples with high accuracy and low 14C blanks.
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    ABSTRACT: A fast and automatic method for radiocarbon analysis of aerosol samples is presented. This type of analysis requires high number of sample measurements of low carbon masses, but accepts precisions lower than for carbon dating analysis. The method is based on online Trapping CO2 and coupling an elemental analyzer with a MICADAS AMS by means of a gas interface. It gives similar results to a previously validated reference method for the same set of samples. This method is fast and automatic and typically provides uncertainties of 1.5-5% for representative aerosol samples. It proves to be robust and reliable and allows for overnight and unattended measurements. A constant and cross contamination correction is included, which indicates a constant contamination of 1.4 ± 0.2 μg C with 70 ± 7 pMC and a cross contamination of (0.2 ± 0.1)% from the previous sample. A Real-time online coupling version of the method was also investigated. It shows promising results for standard materials with slightly higher uncertainties than the Trapping online approach.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 04/2015; DOI:10.1016/j.nimb.2015.03.051 · 1.19 Impact Factor
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    ABSTRACT: Determining the contribution of wood smoke to air pollution in large cities such as London is becoming increasingly important due to the changing nature of domestic heating in urban areas. During winter, biomass burning emissions have been identified as a major cause of exceedances of European air quality limits. The aim of this work was to quantify the contribution of biomass burning in London to concentrations of PM2:5 and determine whether local emissions or regional contributions were the main source of biomass smoke. To achieve this, a number of biomass burning chemical tracers were analysed at a site within central London and two sites in surrounding rural areas. Concentrations of levoglucosan, elemental carbon (EC), organic carbon (OC) and KC were generally well correlated across the three sites. At all the sites, biomass burning was found to be a source of OC and EC, with the largest contribution of EC from traffic emissions, while for OC the dominant fraction included contributions from secondary organic aerosols, primary biogenic and cooking sources. Source apportionment of the EC and OC was found to give reasonable estimation of the total carbon from non-fossil and fossil fuel sources based upon comparison with estimates derived from 14C analysis. Aethalometer-derived black carbon data were also apportioned into the contributions frombiomass burning and traffic and showed trends similar to those observed for EC. Mean wood smoke mass at the sites was estimated to range from 0.78 to 1.0 μgm􀀀3 during the campaign in January–February 2012. Measurements on a 160m tower in London suggested a similar ratio of brown to black carbon (reflecting wood burning and traffic respectively) in regional and London air.Peaks in the levoglucosan and KC concentrations were observed to coincide with low ambient temperature, consistent with domestic heating as a major contributing local source in London. Overall, the source of biomass smoke in London was concluded to be a background regional source overlaid by contributions from local domestic burning emissions. This could have implications when considering future emission control strategies during winter and may be the focus of future work in order to better determine the contributing local sources.
    Atmospheric Chemistry and Physics 03/2015; 15(15):3149-3171. DOI:10.5194/acp-15-3149-2015 · 4.88 Impact Factor
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    Chemical Reviews 02/2015; 115(10). DOI:10.1021/cr5003485 · 45.66 Impact Factor
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    ABSTRACT: During winter 2013, extremely high concentrations (i.e., 4-20 times higher than the World Health Organization guideline) of PM2.5 (particulate matter with an aerodynamic diameter < 2.5 mu m) mass concentrations (24 h samples) were found in four major cities in China including Xi'an, Beijing, Shanghai and Guangzhou. Statistical analysis of a combined data set from elemental carbon (EC), organic carbon (OC), C-14 and biomass-burning marker measurements using Latin hypercube sampling allowed a quantitative source apportionment of carbonaceous aerosols. Based on C-14 measurements of EC fractions (six samples each city), we found that fossil emissions from coal combustion and vehicle exhaust dominated EC with a mean contribution of 75 +/- 8% across all sites. The remaining 25 +/- 8% was exclusively attributed to biomass combustion, consistent with the measurements of biomass-burning markers such as anhydrosugars (levoglucosan and mannosan) and water-soluble potassium (K+). With a combination of the levoglucosan-to-mannosan and levoglucosan-to-K+ ratios, the major source of biomass burning in winter in China is suggested to be combustion of crop residues. The contribution of fossil sources to OC was highest in Beijing (58 +/- 5 %) and decreased from Shanghai (49 +/- 2 %) to Xi'an (38 +/- 3 %) and Guangzhou (35 +/- 7 %). Generally, a larger fraction of fossil OC was from secondary origins than primary sources for all sites. Nonfossil sources accounted on average for 55 +/- 10 and 48 +/- 9% of OC and total carbon (TC), respectively, which suggests that non-fossil emissions were very important contributors of urban carbonaceous aerosols in China. The primary biomassburning emissions accounted for 40 +/- 8, 48 +/- 18, 53 +/- 4 and 65 +/- 26% of non-fossil OC for Xi'an, Beijing, Shanghai and Guangzhou, respectively. Other non-fossil sources excluding primary biomass burning were mainly attributed to formation of secondary organic carbon (SOC) from non-fossil precursors such as biomass-burning emissions. For each site, we also compared samples from moderately to heavily polluted days according to particulate matter mass. Despite a significant increase of the absolute mass concentrations of primary emissions from both fossil and non-fossil sources during the heavily polluted events, their relative contribution to TC was even decreased, whereas the portion of SOC was consistently increased at all sites. This observation indicates that SOC was an important fraction in the increment of carbonaceous aerosols during the haze episode in China.
    Atmospheric Chemistry and Physics 01/2015; 15(3):1299-1312. DOI:10.5194/acp-15-1299-2015 · 5.51 Impact Factor
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    ABSTRACT: Four different parameterizations for the formation and evolution of secondary organic aerosol (SOA) are evaluated using a 0-D box model representing the Los Angeles Metropolitan Region during the CalNex 2010 field campaign. We constrain the model predictions with measurements from several platforms and compare predictions with particle and gas-phase observations from the CalNex Pasadena ground site. That site provides a unique opportunity to study aerosol formation close to anthropogenic emission sources
    ATMOSPHERIC CHEMISTRY AND PHYSICS 12/2014; 14(23):32325-32391. DOI:10.5194/acpd-14-32325-2014 · 5.30 Impact Factor
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    ABSTRACT: Radiocarbon (14C) measurement of water-soluble organic carbon (WSOC) in ambient aerosols is a quantitative tool for unambiguously distinguishing fossil and non-fossil sources. In this study, a fast and reliable method for measuring 14C in micro-scale (μg) WSOC aerosol samples is successfully developed, which includes three steps: (1) extraction (2) freeze drying, and (3) online 14C analysis of CO2 from WSOC combustion. Procedure blanks are carefully assessed by measuring high-purity water and reference materials. Accurate 14C results could be obtained for WSOC with only 10 μg C, and thus the potential applications are substantially broadened because much less filter material is needed compared to previous reported methods. This method is applied to aerosols samples collected during winter from Switzerland and China. The results demonstrate that non-fossil sources are important if not dominant contributors of WSOC. These non-fossil components are consistently enriched in WSOC compared to bulk OC and water-insoluble OC for all samples, due to high water solubility of primary and secondary biomass burning aerosols. However, the presence of fossil WSOC is still considerable indicating a substantial contribution of secondary OC (SOC) formed from precursors emitted by fossil emissions. Larger fossil contributions to WSOC is found in China than in Switzerland and previously reported values in Europe, USA and South Asia, which may be attributed to higher fossil-derived SOC formation in China.
    Atmospheric Environment 11/2014; 97:1–5. DOI:10.1016/j.atmosenv.2014.07.059 · 3.06 Impact Factor
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    ABSTRACT: We conducted a source apportionment and investigated the atmospheric behavior of carbonaceous aerosols during hazy and normal days using radiocarbon (14C) and biomass burning/secondary organic aerosol (SOA) tracers during winter in Guangzhou, China. Haze episodes were formed either abruptly by local emissions or through the accumulation of particles transported from other areas. The average contributions of fossil carbon to elemental carbon (EC), water-insoluble organic carbon (WIOC), and water-soluble organic carbon (WSOC) were 71±10%, 40±6% and 33±3%, respectively. High contributions of fossil carbon to EC (80-90%) were observed for haze samples that were substantially impacted by local emissions, as were the highest (lowest) ratios for NO3-/SO42- (OC/EC), which indicates that these particles mainly came from local vehicle exhaust. Low contributions of fossil carbon to EC (60-70%) were found for haze particles impacted by regional transport. Secondary organic carbon (SOC) calculated using SOA tracers accounts for only ~20% of the SOC estimated by 14C, which is probably because some important volatile organic carbons are not taken into account in the SOA tracer calculation method and because of the large discrepancy in ambient conditions between the atmosphere and smog chambers. A total of 33±11% of the SOC was of fossil origin, a portion of which could be influenced by humidity.
    Environmental Science and Technology 09/2014; 48(20). DOI:10.1021/es503102w · 5.48 Impact Factor
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    ABSTRACT: Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations. In China, particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health. In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China. Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi'an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China's PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.
    Nature 09/2014; 514(7521). DOI:10.1038/nature13774 · 42.35 Impact Factor
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    ABSTRACT: Radiocarbon (14C) analysis is a unique tool to distinguish fossil/non-fossil sources of carbonaceous aerosols. We present 14C-measurements of organic and total carbon (OC, TC) on highly time resolved filters (3–4 h, typically 12 h or longer have been reported) from 7 days collected during CalNex-2010, in Pasadena. Average non-fossil contributions of 58% ± 15% and 51% ± 15% were found for OC and TC, respectively. Results indicate that non-fossil carbon is a major constituent of the background aerosol, evidenced by its nearly constant concentration (2–3 μgC m−3). Cooking is estimated to contribute at least 25% to non-fossil OC, underlining the importance of urban non-fossil OC sources. In contrast, fossil OC concentrations have prominent and consistent diurnal profiles, with significant afternoon enhancements (~3 μgC m−3), following the arrival of the western Los Angeles (LA) basin plume with the sea breeze. A corresponding increase in semi-volatile oxygenated OC and organic vehicular emissions markers and their photochemical reaction products occurs. This suggests that the increasing OC is mostly from fresh anthropogenic secondary OC (SOC) from mainly fossil precursors formed in the western LA basin plume. We note that in several European cities where the diesel passenger car fraction is higher, SOC is 20% less fossil, despite 2–3 times higher elemental carbon concentrations, suggesting that SOC formation from gasoline emissions most likely dominates over diesel in the LA basin. This would have significant implications for our understanding of the on-road vehicle contribution to ambient aerosols and merits further study.
    06/2014; 119(11). DOI:10.1002/2013JD021114
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    ABSTRACT: DAURE (Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the Western Mediterranean) was a multidisciplinary international field campaign aimed at investigating the sources and meteorological controls of particulate matter in the Western Mediterranean Basin (WMB). Measurements were simultaneously performed at an urban-coastal (Barcelona; BCN) and a rural-elevated (Montseny; MSY) site pair in NE-Spain during winter and summer. State-of-the-art methods such as 14C analysis, Proton-Transfer Reaction Mass Spectrometry and High-Resolution Aerosol Mass Spectrometry were applied for the first time in the WMB as part of DAURE. WMB regional pollution episodes were associated with high concentrations of inorganic and organic species formed during the transport to inland areas and built up at regional scales. Winter pollutants accumulation depended on the degree of regional stagnation of an air mass under anticyclonic conditions and the planetary boundary layer height. In summer, regional recirculation and biogenic secondary organic aerosols (SOA) formation mainly determined the regional pollutant concentrations. The contribution from fossil sources to organic carbon (OC) and elemental carbon (EC) and hydrocarbon-like organic aerosol (HOA) concentrations were higher at BCN compared with MSY due to traffic emissions. The relative contribution of non-fossil OC was higher at MSY especially in summer due to biogenic emissions. The fossil OC/EC ratio at MSY was twice the corresponding ratio at BCN indicating that a substantial fraction of fossil OC was due to fossil SOA. In winter, BCN cooking emissions were identified as important source of modern carbon in primary OA.
    04/2014; 119(8). DOI:10.1002/2013JD021079
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    ABSTRACT: To assign fossil and non-fossil contributions to carbonaceous particles, radiocarbon (14C) measurements were performed on organic carbon (OC), elemental carbon (EC) and water-insoluble OC (WINSOC) of aerosol samples from a regional background site in South China under different seasonal conditions. The average contributions of fossil sources to EC, OC and WINSOC were 38±11%, 19±10% and 17±10%, respectively, indicating generally a dominance of non-fossil emissions. A higher contribution from fossil sources to EC (~51%) and OC (~30%) was observed with air-mass pathway from Southeast China during low fire periods, associated to large fossil-fuel combustion and vehicle emissions in highly urbanized regions of China. In contrast, an increase of the non-fossil contribution by 5-10% was observed during the periods with enhanced open biomass-burning activities in Southeast Asia or Southeast China. A modified EC tracer method was used to estimate the fossil-derived SOC by determining 14C-derived fossil WINSOC and fossil EC. This approach indicates a dominating secondary component (70±7%) of fossil OC. Furthermore, contributions of biogenic and biomass-burning emissions to contemporary OC were estimated to be 56±16% and 44±14%, respectively.
    Environmental Science & Technology 02/2014; 48(5). DOI:10.1021/es4050852 · 5.48 Impact Factor
  • Atmospheric Chemistry and Physics 01/2014; 14(10):15591-15643. DOI:10.5194/acpd-14-15591-2014 · 4.88 Impact Factor
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    ABSTRACT: In 2005, two ice cores with lengths of 58.7 and 57.6 m respectively to bedrock were recovered from the Miaoergou flat-topped glacier (43°03′19′′ N, 94°19′21′′ E; 4512 m a.s.l.), eastern Tien Shan. 210Pb dating of one of the ice cores (57.6 m) was performed, and an age of AD 1851±6 at a depth of 35.2 m w.e. was determined. For the periodAD 1851–2005, a mean annual net accumulation of 229±7 mm w.e.a–1 was calculated. At the nearby oasis city of Hami (∼80 km from the Miaoergou flat-topped glacier) the annual precipitation rate is 38 mm w.e.a–1, hence glacial meltwater is a major water supply for local residents. The surface activity concentration of 210Pbex was found to be ∼400 mBq kg–1, which is higher than observed at other continental sites such as Belukha, Russia, and Tsambagarav, Mongolia, which have surface activity concentrations of 280 mBq kg–1. The 210Pb dating agrees well with the chronological sequence deduced from the annual-layer counting resulting from the seasonalities of δ18O and trace metals for the period AD 1953–2005, and β-activity horizons resulting from atmospheric nuclear testing during the period AD 1962–63. We conclude that 210Pb analysis is a suitable method for obtaining a continuous dating of the Miaoergou ice core for ∼160 years, which can also be applied to other ice cores recovered from the mountains of western China.
    Annals of Glaciology 01/2014; 55(66). DOI:10.3189/2014AoG66A151 · 2.52 Impact Factor
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    ABSTRACT: Measurement of the radioactive carbon isotope 14C in aerosols can provide a direct estimate of the contribution of fossil fuel sources to aerosol carbon. In aerosol science, measurements of 14C/12C ratios are usually reported as fraction modern (fm). The radiocarbon signature gives a clear distinction between 'modern' carbon sources (fm around 1.1-1.2 for biomass burning and around 1.05 for biogenic secondary organic aerosol) and 'fossil' carbon sources (fm =0 for primary and secondary formation from fossil fuel combustion). Due to the high cost of 14C analyses very few long-term studies have been conducted to date. The data that will be presented offer a unique insight into the seasonal variation of source contributions to the carbonaceous aerosol in a highly industrialized region. High volume filter samples have been collected roughly twice per month from February 2011 - July 2012 at Cabauw, a rural location in the Netherlands surrounded by major urban centers and highways. This site provides a regional background aerosol contamination in the Netherlands. We report measurements of fm for total carbon (TC), organic carbon (OC), water insoluble OC (WIOC) and thermally refractory carbon (RC) as a proxy for elemental carbon. The fraction modern of OC lies between 0.65 - 1 and shows only a moderate seasonal variation with highest values in the spring and lowest values in the summer. Elemental carbon is generally dominated by fossil fuel emissions, but shows a distinct seasonal variation with higher contribution of modern sources from November - Mai. This contribution is attributed to wood combustion. It is low when air masses arrive from the ocean and high for air masses with European continental origin, pointing to a main source outside the Netherlands. Water soluble organic carbon is dominated by modern sources throughout the year. For TC concentrations between 1.2 and 8 μg/m3, fm(TC) increases with TC concentration. A Keeling plot implies that synoptic scale variation in fm(TC) are mainly due to a modern source, imposed on a regional background with a relatively high contribution from fossil sources. TC concentrations > 8 μg/m3 are associated with pollution events transported from Germany/Eastern Europe and can have much high fossil contributions. However, fm in all carbon fractions is usually reduced in day time compared to night time, most likely due to traffic variations, which modify the carbonaceous aerosol on shorter time scales. Using a simple model the contributions of fossil emissions, biomass burning, and biogenic emissions will be estimated for all carbon fractions. The seasonal variation in the source contributions will be presented and discussed.
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    ABSTRACT: Carbonaceous particles (total carbon, TC) are a major fraction of the fine aerosol and affect climate and human health. TC is classified into the sub-fractions elemental carbon (EC) and organic carbon (OC). EC originates only from fossil fuel combustion and biomass burning. OC can be emitted directly as primary organic aerosol from biogenic emissions, wood burning and fossil fuel combustion or can be formed in-situ in the atmosphere (secondary organic aerosol) (Szidat et al. 2006). Radiocarbon (14C) analysis is a direct and quantitative tool for distinguishing fossil and non-fossil sources, since 14C in fossil fuels is completely depleted whereas other sources have a contemporary 14C level. This study presents source apportionment results from the winter season over a time period of 5 years (2007/2008-2011/2012) using 14C measurements on aerosol filters collected simultaneously at 16 air quality monitoring stations across Switzerland. For every year 5 winter smog episode days were selected from which filters from all stations were analyzed. To resolve a good spatial variability 11 stations north and 5 stations south of the Alps were selected. This 14C data set is unique around the world concerning the number of analyzed filters and the duration. The filter sampling was conducted using high volume samplers with PM10 inlets and a time resolution of 24h. Separation of OC and EC was carried out using the THEODORE system (Szidat et al. 2004) and a Sunset EC/OC analyzer (Zhang et al. 2012), respectively. The resulting CO2 was cryo-trapped and sealed in glass ampoules for 14C measurements, performed with the Mini Carbon Dating System MICADAS (Ruff et al. 2007) at the Swiss Federal Institute of Technology (ETH) Zürich. The results for non-fossil (NF) OC (5 year average) are 81% ± 10% for north and 85% ± 8% for south of the Alps. ECNF values range from 31% to 53% north and from 36% to 66% south of the Alps. Both, the OCNF and ECNF show higher values south of the Alps. The highest values were found in alpine valleys with OCNF of max. 100% and ECNF of max. 87%. The station-to-station variation north of the Alps is low, whereas in the south a spatial trend was found with an increase of the non-fossil values towards the north showing the influence of more fossil air masses advected from the Po-valley. No real time trend over the 5 winters was found. The high ECNF and OCNF values together with a good correlation with levoglucosan show that wood burning is the major source of TC in Switzerland during winter smog episodes. This work was funded by the Swiss Federal Office for the Environment, inNet Monitoring AG, Liechtenstein and the Swiss cantons Basel-Stadt, Basel-Landschaft, Graubünden, Solothurn, Valais and Ticino. Ruff, M. et al (2007) Radiocarbon 49(2), 307-314 Szidat, S. et al. (2004) Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 223-224: 829-836 Szidat, S. et al. (2006) J. Geophys. Res. 111, D07206 Zhang, Y.L. et al. (2012), Atmos. Chem. Phys. 12(22): 10841-10856
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    ABSTRACT: In 2010 more than 600 radiocarbon samples were measured with the gas ion source at the MIni CArbon DAting System (MICADAS) at ETH Zurich and the number of measurements is rising quickly. While most samples contain less than 50 μg C at present, the gas ion source is attractive as well for larger samples because the time-consuming graphitization is omitted. Additionally, modern samples are now measured down to 5 per-mill counting statistics in less than 30 min with the recently improved gas ion source.In the versatile gas handling system, a stepping-motor-driven syringe presses a mixture of helium and sample CO2 into the gas ion source, allowing continuous and stable measurements of different kinds of samples. CO2 can be provided in four different ways to the versatile gas interface. As a primary method, CO2 is delivered in glass or quartz ampoules. In this case, the CO2 is released in an automated ampoule cracker with 8 positions for individual samples. Secondly, OX-1 and blank gas in helium can be provided to the syringe by directly connecting gas bottles to the gas interface at the stage of the cracker. Thirdly, solid samples can be combusted in an elemental analyzer or in a thermo-optical OC/EC aerosol analyzer where the produced CO2 is transferred to the syringe via a zeolite trap for gas concentration. As a fourth method, CO2 is released from carbonates with phosphoric acid in septum-sealed vials and loaded onto the same trap used for the elemental analyzer. All four methods allow complete automation of the measurement, even though minor user input is presently still required. Details on the setup, versatility and applications of the gas handling system are given.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2013; 294:315–319. DOI:10.1016/j.nimb.2012.02.009 · 1.19 Impact Factor
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    ABSTRACT: Carbonaceous particles that comprise organic carbon (OC) and elemental carbon (EC) are of increasing interest in climate research because of their influence on the radiation balance of the Earth. The radiocarbon determination of particulate OC and EC extracted from ice cores provides a powerful tool to reconstruct the long-term natural and anthropogenic emissions of carbonaceous particles. However, this C-14-based source apportionment method has not been applied for the firn section, which is the uppermost part of Alpine glaciers with a typical thickness of up to 50 m. In contrast to glacier ice, firn samples are more easily contaminated through drilling and handling operations. In this study, an alternative decontamination method for firn samples consisting of chiselling off the outer parts instead of rinsing them was developed and verified. The obtained procedural blank of 2.8 +/- 0.8 mu g C for OC is a factor of 2 higher compared to the rinsing method used for ice, but still relatively low compared to the typical OC concentration in firn samples from Alpine glaciers. The EC blank of 0.3 +/- 0.1 mu g C is similar for both methods. For separation of OC and EC for subsequent C-14 analysis, a thermal-optical method instead of the purely thermal method was applied for the first time to firn and ice samples, resulting in a reduced uncertainty of both the mass and C-14 determination. OC and EC concentrations as well as their corresponding fraction of modern for firn and ice samples from Fiescherhorn and Jungfraujoch agree well with published results, validating the new method.
    Radiocarbon 01/2013; 55(2-3):383-390. · 1.04 Impact Factor