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.

1. 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 Netherlands
3 Laboratory for Radiochemistry and Environmental Chemistry, University of Bern, Switzerland

2. Radiocarbon
Carbon isotopes:
C12 : 98.89 %
C13: 1.11 %
C14: 0.0000000001%
Half life: 5730 yrs
Produced by
cosmic rays
Exchange with
Biosphere as
14CO2
Decay when
Exchange with
Biosphere 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

3. 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

4. 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

5. Protocol for filter extraction
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. 0
20
40
60
80
100
120
1-Jan-11
1-Feb-111-M
ar-11
1-Apr-111-M
ay-11
1-Jun-11
1-Jul-11
1-Aug-11
1-Sep-11
1-Oct-11
1-Nov-11
1-Dec-11
fm(%)
date
Organic Carbon
Time series
Very dry
spring
Very rainy
Cold summer
Very dry
Fall
Marine
Continental
Mixed
Organic Carbon

7. 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
1-Jan-11
1-Feb-111-M
ar-11
1-Apr-111-M
ay-11
1-Jun-11
1-Jul-111-Aug-11
1-Sep-111-Oct-111-Nov-111-Dec-11
fm(%)
date
Elemental Carbon
Time series
Marine
Continental
Mixed
Elemental Carbon

8. Seasonal variation
fm: WSOC > OC > TC > WIOC > EC
Least seasonal variation in WSOC
Most in EC
Highest fm in spring
0
20
40
60
80
100
120
TC OC WIOC EC WSOC
fm(%)
carbon frac on
Winter
Spring
Summer
Fall
biomass burning
road transport
biogenic

9. Contribution of biomass burning to EC
Detection level of our method?
Why so high in spring?
Possible biological influence?
Fires in the spring
0
2
4
6
8
10
12
14
16
18
winter spring summer fall
%contribuon
Season

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
y = -52x + 88
R² = 0.60976
0.0
20.0
40.0
60.0
80.0
100.0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
fm(%) 1/TC (m3/ug)
20.0
40.0
60.0
80.0
100.0
0.00 5.00 10.00 15.00
fm(%)
Total carbon (ug/m3)
Spring
Summer
Fall
winter
Pollution events
30
40
50
60
70
80
90
100
110
120
0 5 10 15 20 25 30 35 40
fraconmodern(%)
PM10 mass concentra on (mg/m3)
Amsterdam (urban)

11. Correlation of fm WIOC and EC
fm(WIOC), fm(EC) correlated
Common modern source
Extra biogenic background source for WIOC
y = 0.9664x + 34.381
R² = 0.66339
20.0
40.0
60.0
80.0
100.0
0.0 10.0 20.0 30.0 40.0 50.0 60.0
fm(WIOC)
fm (EC)

12. Day-night variations
0
10
20
30
40
50
60
70
80
90
OC EC
fm(%)
mixed day
mixed night
cont. day
cont. night
marine day
marine night
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?
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

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

15. Contamination: Analysis of standards with known 14C content
Comparison with typical sample size and
handling blank values
0.1
1
10
100
TC (3%) OC (2.5%) EC (6%)
carbon[ugcm-2]
typical Sample
handling blank
Modern cont.
Dead cont.

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