diurnal cycle of fossil and non-fossil total carbon using 14 c analyses during calnex
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Diurnal cycle of fossil and non-fossil total carbon using 14C analyses during CalNex
P. Zotter1, A.S.H. Prévôt1, Y. Zhang2, S. Szidat2, X. Zhang3, Y.-H. Lin4, P. Hayes5, J. Schnelle-Kreis6, G. Seibert6, R. Zimmermann6, R. Weber3, J. D. Surratt4, J.L. Jimenez5, U. Baltensperger1
CalNex Data Analysis Workshop – 16th to 19th of May
1Paul Scherrer Institute, Laboratory of Atmospheric Chemistry, Villigen, Switzerland2Department of Chemistry and Biochemistry, University of Bern, Switzerland
3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, USA4Department of Environmental Sciences & Engineering, University of North Carolina at Chapel Hill, USA
5Department of Chemistry and CIRES, University of Colorado, Boulder, USA6Institute of Epidemiology, Helmholtz Zentrum München, Neuherberg, Germany
Introduction
• Why is 14C measured for aerosol samples?
• Source apportionment for carbonaceous aerosol by 14C/12C
anthropogenic emissions biogenic emissions
• 14C decayed completely modern 14C/12C ratio
fm…fraction of modern carbon
• fmfossil = 0, fmbiogenic = 1
• After 1950 fm values have to be corrected for the nuclear bomb excess
195012
14
12
14
AD
Sample
CC
CC
fm
14C Measurement of TC and OC
• Sample preparation with THEODORE (see Szidat et al. 2004)
• combustion of a filter punch in pure O2
• TC at 640°C for 12min, OC at 340°C for 10min
• evolving CO2:
• is cryotrapped
• determined manometrically
• sealed in glass ampoules
• 14C measurement with MICIDAS (see Synal et al. 2007)
• Mini Radiocarbon Dating System at the ETH Zürich
• detection limit = 3µg
THEODORE
MICIDAS
Filter Choice
14C Results
TCnon-fossil
OCnon-fossil
04.06 33% - 57%
14.06 34% - 58%
04.06 44% - 80%
14.06 45% - 71%
14C Results
In 1982 (Hildemann et al., 1994)
Hodzic et al. 2010
In 2010
45
55
48
52
04.06 14.06
14C Results
14C Results
14C Results
• Calculation of OCnon-fossil
•Assumption• EC = 100% fossil fmEC = 0
• OCBB = 0
nfnfnf OCECTC
OC
TCfmfm TC
OC
biogenicOCBBOCOC
fossilECBBECEC
OCfmOCfmOCfm
ECfmECfmECfm
biogenicBB
fossilBB
OCfmECfmTCfm OCECTC
EC OC Comparison
• 3 different Sunset Labs ECOC analyzer
• Online Sunset during CalNex-LA– NIOSH protocol
• Bench-top Sunset at University of Bern– EUSAAR_2 protocol (see Cavalli et al. 2010)
• Bench-top Sunset at Georgia Tech– NIOSH protocol
• Differences in EC and OC due to different protocols expected
• TC should agree within 10% - 15%
EC OC Comparison
June 4th
EC 04.06 PM2.5 high resolution sampling
y = 0.9846x
R2 = 0.1573
y = 1.156x
R2 = 0.8562
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 0.2 0.4 0.6 0.8 1.0 1.2
EC [µg/m3] benchtop Sunset BERN
EC
[µ
g/m
3] O
nlin
e S
un
set
/ b
ench
top
Su
nse
t G
eorg
ia T
ech
Online vs BERN
Georgia Tech vs BERN
TC 04.06 PM2.5 high resolution sampling
y = 1.1629x
R2 = 0.8957
y = 0.581x
R2 = 0.8903
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
TC [µg/m3] benchtop Sunset BERN
TC
[µ
g/m
3] O
nlin
e S
un
set
/ b
ench
top
Su
nse
t G
eorg
ia T
ech
Online vs BERN
Georgia Tech vsBERN
EC OC Comparison
24h samples
TC PM2.5 24h samples
y = 0.9532x
R2 = 0.8849
y = 0.6084x
R2 = 0.8661
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
TC [ug/m3] benchtop Sunset BERN
TC
[u
g/m
3] O
nlin
e S
un
set
/ b
ench
top
Su
nse
t G
eorg
ia T
ech
Online vs Sunset BERN
Georgia Tech vs BERN
EC PM2.5 24h samples
y = 0.7157x
R2 = 0.7128
y = 1.0686x
R2 = 0.6022
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
EC benchtop Sunset BERN [ug/m3]
EC
[µ
g/m
3] O
nlin
e S
un
set
/ b
ench
top
Su
nse
t G
eorg
ia T
ech
Online vs BERN
Georgia Tech vs BERN
OC Comparison – AMS vs Sunset
y = 1.2778x
R2 = 0.854
y = 1.8394x
R2 = 0.8954
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7 8 9
OC [µg/m3] Sunset BERN / Online Sunset
OC
[µg
/m3
] A
MS
AMS vs Sunset BERN
AMS vs Online Sunset
Comparison with organic tracers
Measured with a GCMS by the Institute of Epidemiology at the Helmholtz Center Munich
Conclusion• A clear diurnal cycle of fossil and non fossil TC and OC at the Pasadena ground site was found
• Almost no variation of TCnon-fossil and OCnon-fossil values throughout the day
• The enhancement of TC and OC concentrations due to the L.A plume is mainly fossil – this agrees with other findings presented during this meeting
Outlook• Repeat high time resolution filters from May 30th
• Measure a few 24h samples and compare results with EPA 14C measurements
• Measure 14C in EC for a few 24h samples
• We are happy for any suggestions for more (only a few!) interesting periods to analyze
Thank you for your attention!
Thank you for your attention!
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