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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
0
10
20
30
40
50
60
70
80
90
100Total Carbon
date
fm (%
)