Fossil and modern sources of aerosol carbon in the Netherlands – A year-long radiocarbon study

U. Dusek1, M. Monaco1, A. Kappetijn1, T. Röckmann1

S. Szidat2, H. A. J. Meijer3, J. van der Plicht3, 1 Institute for Marine and Atmospheric research Utrecht (IMAU), the Netherlands

2 Center for Isotope Research, Groningen University, the Netherlands3 Laboratory for Radiochemistry and Environmental Chemistry, University of Bern, Switzerland

Radiocarbon

Carbon isotopes:C12 : 98.89 %C13: 1.11 %

C14: 0.0000000001%Half life: 5730 yrs

Produced bycosmic rays

Exchange withBiosphere as 14CO2

Decay whenExchange withBiosphere stops

Unit of measurement:Fraction modern

fm = 14C sample/14C standard

Standard: oxalic acid (typical activity of 1950 biosphere)

fm > 1 possible through bomb tests

Carbonaceous aerosol: 14C for source apportionment

Biomass burning Fossil fuel Biogenic

EC OC

fm = 1.1 - 1.2 fm = 0 fm ~ 1.04

Thermally refractory Volatile - refractory

From aerosol particles to 14C measurement

Sampling: Goal: 50 – 500 ug C

High volume samplers: 500 l/min of air through filter

Convert OC and EC to CO2 Measure 14C content with AMS

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 at450 C

Pump away

Time series

Very dry spring

Very rainy Cold summer

Very dry Fall

Marine

Continental

Mixed

Time series

Marine

Continental

Mixed

Seasonal variation

fm: WSOC > OC > TC > WIOC > ECLeast seasonal variation in WSOC

Most in ECHighest fm in spring

Contribution of biomass burning to EC

Detection level of our method?Why so high in spring?

Possible biological influence?Fires in the spring

Dependence of fm on carbon concentration

Low concentrations of TC: low fmVery high concentrations of TC: low fm

At moderate TC concentrations 1- 5 ug/m3: variations in TC concentration caused by modern source

Pollution events

Correlation of fm WIOC and EC

fm(WIOC), fm(EC) correlatedCommon modern source

Extra biogenic background source for WIOC

Day-night variations

Higher fm during night:Higher traffic emissions during day

Condensation of semi-volatile biogenic organic during night

Conclusions

• Possible components other than EC in refractory material:

Pollen, other biological things?

fM(TC) lowest in summer, highest in spring

• Overall high values of fM(TC) and fM(OC)

• Pollution events with clear low fM signature

• fM(EC) high in continental air masses, except in summer

• Negligible biomass burning contribution in summer

• Distinct day-night variation with lower fM during day

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

Contamination: Analysis of standards with known 14C content

Comparison with typical sample size and handling blank values

Time series

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100Total Carbon

date

fm (%

)