1. Fossil and modern sources of aerosol carbon in the Netherlands – A year-long radiocarbon study Fossil and modern sources of aerosol carbon in the Netherlands – A year-long radiocarbon study U. Dusek 1, M. Monaco 1, A. Kappetijn 1, T. Röckmann 1 S. Szidat 2, H. A. J. Meijer 3, J. van der Plicht 3, 1 Institute for Marine and Atmospheric research Utrecht (IMAU), the Netherlands 2 Center for Isotope Research, Groningen University, the Netherlands 3 Laboratory for Radiochemistry and Environmental Chemistry, University of Bern, Switzerland U. Dusek 1, M. Monaco 1, A. Kappetijn 1, T. Röckmann 1 S. Szidat 2, H. A. J. Meijer 3, J. van der Plicht 3, 1 Institute for Marine and Atmospheric research Utrecht (IMAU), the Netherlands 2 Center for Isotope Research, Groningen University, the Netherlands 3 Laboratory for Radiochemistry and Environmental Chemistry, University of Bern, Switzerland

2. Radiocarbon Carbon isotopes: C 12 : 98.89 % C 13 : 1.11 % C 14 : 0.0000000001% Half life: 5730 yrs Carbon isotopes: C 12 : 98.89 % C 13 : 1.11 % C 14 : 0.0000000001% Half life: 5730 yrs Produced by cosmic rays Exchange with Biosphere as 14 CO 2 Decay when Exchange with Biosphere stops Unit of measurement: Fraction modern f m = 14 C sample / 14 C standard Standard: oxalic acid ( typical activity of 1950 biosphere ) f m > 1 possible through bomb tests Unit of measurement: Fraction modern f m = 14 C sample / 14 C standard Standard: oxalic acid ( typical activity of 1950 biosphere ) f m > 1 possible through bomb tests

3. Carbonaceous aerosol: 14 C for source apportionment Biomass burning Fossil fuel Biogenic ECOC f m = 1.1 - 1.2f m = 0f m ~ 1.04 Thermally refractoryVolatile - refractory

4. From aerosol particles to 14 C measurement Sampling: Goal: 50 – 500 ug C High volume samplers: 500 l/min of air through filter Sampling: Goal: 50 – 500 ug C High volume samplers: 500 l/min of air through filter Convert OC and EC to CO 2 Measure 14 C content with AMS

5. Combustion in pure oxygen Carbonaceous aerosol 15 min at 650 C TC 15 min at 360 C OC Water extraction 15 min at 360 C WIOC 15 min at 650 C RC 2 min at 450 C Pump away

6. Time series Very dry spring Very rainy Cold summer Very dry Fall Marine Continental Mixed

7. Time series Marine Continental Mixed

8. Seasonal variation fm: WSOC > OC > TC > WIOC > EC Least seasonal variation in WSOC Most in EC Highest fm in spring

9. Contribution of biomass burning to EC Detection level of our method? Why so high in spring? Possible biological influence? Fires in the spring

10. Dependence of fm on carbon concentration Low concentrations of TC: low fm Very high concentrations of TC: low fm At moderate TC concentrations 1- 5 ug/m3: variations in TC concentration caused by modern source Pollution events

11. Correlation of f m WIOC and EC f m (WIOC), f m (EC) correlated Common modern source Extra biogenic background source for WIOC

12. Day-night variations Higher fm during night: Higher traffic emissions during day Condensation of semi-volatile biogenic organic during night

13. Conclusions Possible components other than EC in refractory material: Pollen, other biological things? f M (TC) lowest in summer, highest in spring Overall high values of f M (TC) and f M (OC) Pollution events with clear low f M signature f M (EC) high in continental air masses, except in summer Negligible biomass burning contribution in summer Distinct day-night variation with lower f M during day

14. Acknowledgements Thanks to B. Oyama for assistance with sampling and filter preparation This study was funded by the Dutch NWO grant number 820.01.001

15. Contamination: Analysis of standards with known 14 C content Comparison with typical sample size and handling blank values

16. Time series