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Nolwenn PERRON Göteborg, 25.06. 2008 1 OC and EC separation for 14 C analyses N. Perron 1, L. Besnier 1, S. Szidat 2, A. S. H. Prévôt.

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Presentation on theme: "Nolwenn PERRON Göteborg, 25.06. 2008 1 OC and EC separation for 14 C analyses N. Perron 1, L. Besnier 1, S. Szidat 2, A. S. H. Prévôt."— Presentation transcript:

1 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 1 OC and EC separation for 14 C analyses N. Perron 1, L. Besnier 1, S. Szidat 2, A. S. H. Prévôt 1, U. Baltensperger 1 1 Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland, 2 Dept. of Chemistry and Biochemistry, University of Bern, Bern, Switzerland

2 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 2 Carbonaceous aerosols: OC and EC Increasing: thermal and chemical refractiveness degree of polymerisation aromaticity carbon content density optical absorption Low molecular-mass hydrocarbons Polycyclic aromatics Humic-like substances Biopolymers Graphene layers Volatile Colourless Less volatile Coloured Refractory Black Method- dependent OCEC

3 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 3 OC and EC quantification : the Sunset EC/OC analyser MnO 2 oxidiser CO 2 detector (NDIR) Carrier gas (He or He/O 2 ) 2cm 2 -filter punch Front oven Back oven Photodetector Laser Thermo-optical method

4 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 4 OC charring: optical correction

5 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 5 14 C in carbonaceous aerosols Biogenic production 14 C-depletedContemporary 14 C/ 12 C ratios 14 7 N 7 14 6 C 8 proton 14 CO 2 Oxidation 14 12 14 12 14 12 neutrons Absorption Decomposition Biomass burning Fossil emissions OC EC Primary and secondary production Absorption Primary production (Primary and) secondary production Primary and secondary production

6 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 6 Combustion at 650°C under pure O 2 Muffle furnace for 4h at 390°C 1) 20mL HCl 0.5M 2) 50mL water Combustion at 340°C under pure O 2 Sampling and analyses: current procedure Bern University: 14 C sample preparation PSI : TC, EC and OC determination Termo-optical ECOC analyser Residual OC evaporation OC: CO 2 sample Water treatment EC: CO 2 sample

7 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 7 fm=fm= [ 14 C/ 12 C] sampl e [ 14 C/ 12 C] before 1950 Acceleration Mass Spectrometer M. Ruff, PSI/UniBern Synal 2007 14 C analysis using acceleration mass spectrometry Feeding system CO 2 sample

8 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 8 Source apportionment at two alpine valley sites Moleno Feb 2005 Roveredo Jan 2005 EC fossil EC biomass burning OC fossil OC non fossil Moleno Jun 2005

9 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 9 Can we do better? The current combustion system used for 14 C samples preparation is „blind“ to charring and to early EC removal. 2cm 2 -filter punch Front oven Back oven Photodetector Exhaust CO 2 recovered for 14 C analysis O2O2 Contamination of EC by OC: strong f m bias Loss of the „lighter“ EC: underestimation of wood burning contribution Idea:

10 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 10 Temperature (voltage ) OC charring under pure oxygen Original filter Moleno, winter: biomass-burning influenced site 600°C 550°C 500°C 475°C 450°C 425°C 400°C 375°C 350°C 325°C 300°C 180°C 90°C Charring starts around 200°C

11 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 11 Temperature (voltage ) OC charring under pure oxygen Original Water-treated Moleno, winter: biomass-burning influenced site 600°C 550°C 500°C 475°C 450°C 425°C 400°C 375°C 350°C 325°C 300°C 180°C 90°C Keeping the water-extraction step is wishable. Charring starts around 200°C Bleaching at higher temperatures No charring

12 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 12 TransmittanceAbsorbance Temperature CO 2 400°C 700°C 550°C EC removal under pure oxygen Water-extracted filter Light EC removal above 400°C Simultaneous EC and OC removal Mainly EC removal

13 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 13 Conclusions for a further method -OC charring: avoiding it even under pure O 2 is not realistic on original material, but it is on water-treated samples OC: analyses on water-treated filters instead of original filters would avoid loosing the charring fraction. The water-soluble part could be analysed either from the eluate, or by TC analysis and subtraction. EC: work on water-extracted-filters prevents from contamination due to OC pyrolysis. -Simultaneous EC an OC removal: Starts above 400°C Probably reduced when water treatment is performed, since filter bleaching starts and finishes at higher temperatures. Still to be worked on.

14 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 14 Overall conclusions -Sources of OC are dominated by non-fossil emissions, sources of EC by fossil emissions. Hence, a relevant 14 C-based source apportionment requires to analyse those fractions separately. -Separating OC and EC with a maximal recovery is challenging, because of OC pyrolysis and simultaneous EC and OC removal. Working under oxygen with water-treated samples suppresses the first issue almost totally, and possibly limits the second one. -As a conservative tracer, radiocarbon enables to discriminate between fossil and non-fossil sources of carbonaceous aerosols.

15 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 15

16 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 16

17 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 17 Elemental carbon (EC) EC/TC = 0.2 f M (EC) = 0.1 When 4% of the original OC cannot be removed from the EC, f M (EC) = 0.2 100% error! Organic carbon (OC) OC/TC = 0.8 f M (OC) = 0.8 Necessity to separate OC and EC for radiocarbon analysis

18 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 18 Higher oven T: lower recovery Tests for f m (EC) at different OC removal temperatures EC: temperature removal and fossility Lower recoveries: lower f m s: „Fossility“ increases with thermal refractiveness: EC does not behave homogeneously. fmfm

19 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 19 Can the f m of the recovered part always be applied to the whole fraction ? Recovered: f m (OC) Whole OC Recovered: f m (EC) Whole EC pure quartz filterfilter with binder OC lost OC fossil OC non fossil Example for an industrial- influenced site, winter campaign

20 Nolwenn PERRON nolwenn.perron@psi.ch Göteborg, 25.06. 2008 20 Can we do better? The current combustion system used for 14 C samples preparation is „blind“ to charring and to early EC removal. 2cm 2 -filter punch Front oven Back oven Photodetector Exhaust CO 2 recovered for 14 C analysis O2O2 Adapting the present thermal method to a thermo-optical device would help understand better those phenomena and possibly reduce them.

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