14CO2 measurement in the NOAA/ESRL Global Co-operative Sampling Network: An update on measurement

and data quality

Scott LehmanINSTAAR, University of Colorado at Boulder

Jocelyn Turnbull, Chad Wolak - NOAA & INSTAAR, Boulder

John Miller, Pieter Tans - CIRES & NOAA/ESRL, Boulder

John Southon, UC Irvine, California

outline

• 14C systematics, sensitivity to Fff and Cff• quantification of Cff from 14CO2 and CO2• sampling and measurement protocols• measurement repeatability• measurement programs• representative results

– NWR surface (relatively clean FT as “bg”)– CMA vertical profiles (isolation of Cff and Cbio)

• preliminary results 14CO2 intercomparison (J. Miller)• future effort

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tree ringsVermunt meas.JFJ fit (m_m)NWRfit (ind)

!14C

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year

“Suess effect”

excess 14C

assimilation

secular trends

data: Levin and Kromer

Δ=Δ14C=14 C

C( )sample

14 CC( )

standard

−1[ ] x 1000 ‰

ratio to standard is δ13C corrected for mass dependent fractionationΔ is decay corrected for date of collection

1/λ14C = 8033 yr

fossil fuel CO2 Δ = -1000‰

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NWR fit (ind)JFJ fit (m_m)

!14C

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year

“Suess effect”

excess 14C

assimilation

dΔobs/dt = ~ -5.5 ‰/yrdΔff/dt = ~ -10.5 ‰/yr

dΔoce/dt + dΔbio/dt = ~0 ‰/yr dΔprod+nuc/dt = ~ +5.7 ‰/yr

Fff (“Suess effect”) once again dominating secular trend

secular trends

data: Levin and Kromeranalysis: Naegler et al. 2006; Turnbull et al. in press

Δ=Δ14C=14 C

C( )sample

14 CC( )

standard

−1[ ] x 1000 ‰

sensitivity to Cff

1/λ14C = 8033 yr

fossil fuel CO2 Δ = -1000‰ (i.e. zero 14C content)

ambient atm. (& other CO2 sources) Δ = ~ +55‰

ΔΔ ff-atmCatm

=-1055‰380ppm = ~-2.8 ‰/ppm

- detection of ~1 ppm for recently-added fossil-fuel derivedCO2 (Cff) requires measurement precision of ~2‰

- detection is unbiased if other contributions to tropospheric14C distribution are small

Cff v. 14CO2 in TM5

•Fff is 7 GTC/yr global (1.6 GTC/yr US) distributed according to EDGAR2000, modelrepresents all terms influencing tropospheric 14C budget (except nuclear industry)

•distribution of Cff dominates Δ14CO2 signal over NH land areas (figures scaledaccording to mass balance relation of 2.8‰/ppm)

•ΔΔ14CCBL up to ~10 ‰, implying scientifically meaningful Δ14CO2 precision ~2‰

annual@350 m annual@350 m

• right hand term is correction to Cff of ~0.2 - 0.5 ppm, Cr and Δr can bedetermined independently (i.e. quantifiable)

• Cff detection effectively limited by quadrature sum uncertainty of two 14Cmeasurements (Δobs, Δbg)•psuedo-Lagrangian analysis framework (rel. obs to bg) is itself an “uncertainty”

quantification of Cff

ΔobsCobs= ΔbgCbg+ΔffCff+ΔrCr+ΔpCp

Cobs= Cbg+ Cff+ Cr+ Cp

and setting Δp = Δbg :

Cff =Cobs(Δobs- Δbg)

Δff - Δbg

C r(Δr- Δbg)Δff - Δbg

-

Turnbull et al. 2006

sampling

• ~2-3 L parent air (0.4 - 0.6 mg C)

• to glass (“13C-proven”)– paired NOAA-ESRL network flasks (~2.2L)

• filled in series (several minutes flush/fill time)– NOAA-ESRL PFPʼs (aircraft) (700 cc at 40 psi)

• sequentially-filled pairs (several minutes flush/fill)

experimental

• CO2 extraction via simple cryogenicprocedure (following Zhao et al. 1997)

• graphitization CO2 + 2H2 (Fe) (625° C) C + 2H2O

• hi-count AMS measurement (UC-Irvine)• repeatability evaluated in control tank

– clean dry air from NWR (NWTstd, 2002.9)• process blank evaluated in synthetic air

spiked with dead CO2

measurement• UCI AMS MC-SNICS source 40-position

carousel– 8 primary stds (Ox-I)– 2 secondary stds (Ox-II)– 4 NWTstd control samples (single cylinder)– 1 process blank (14C-free synthetic air)– 25 authentic samples

• 1 wheel/10d at current sampling rates w/innetwork

measurement (future)• UCI AMS MC-SNICS source 40-position

carousel– 8 primary stds (Ox-I)– 0 secondary stds (Ox-II)?– 2 NWTstd control samples– 3 NWT3 control samples (new cylinder)– 3 NWT4 control samples (new cylinder)– 1 process blank (14C-free synthetic air)– 23 authentic samples?

• relatively short life time of control tanks (6 yrs on NWTstd)

• multiple, staggered tanks required for long term surveillance

atom counting• typically, 15 acquisition cycles at 50k 14C

events each (n = 750,000 cts.)

• statistical limit on precision ~1.2‰

• typical single-sample precision afterstandardization ~1.7‰

• ( i.e. “AMS system error” of ~1.2‰)

• repeatability ………..

1-σ repeatability

• assign uncertainty as the greater of the 1-σ NWTstd repeatability or the1-σ single sample analytical precision

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!1

4C

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wheel no.

Ox1 >.4mgC

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!1

4C

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wheel

NWTstd 1" stdevOxI 1" stdev

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!1

4C

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NWTstd>.4mgC

NBS OxI:since 241: 1.99 ‰since 289: 1.75 ‰

(wheel means normalized)

NWTstd:since 241: 2.03 ‰since 289: 1.95 ‰

whe

el s

tdev

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John Southon, UCI

4/04 3/06 11/08date pres.

(in)stability

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NWTstd, wheel mean & stdev.y = 73.357 + 0.018013x R= 0.24317

!1

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O2 ‰

wheel order

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CU/NOAA 14CO2 measurement sites

• NWR ( 3523 masl, rel. clean cont. FT)• NA aircraft sampling sites ( )

– CMA, NHA, BNE, LEF• NA tower sites ( )

– WKT, LEF, SCT, WGC• Asia

– WLG, UUM, TAP– (Lin’An, Shangdianzi)

North America

Asia

WGC

SCT

BNENWR

see Turnbull ICDC poster forrecent results

NWR (3523 masl, 40.5° N, 105.6° E)

•local pollution flagged based on CO (COa >15 ppb)

•scrubbed record can be used to provide representative “bg” meas. in psuedo-Lagrangian analysis framework (as m_m or harmonic fit) [i.e. Turnbull et al. JGR 2007]

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NWR rawclean NWRfit (clean)

!14C

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date

3-ht sampling CMA

• Δ14CO2 difference signal is large w.r.t. measurement precision• data also resolves limitations of analysis framework - for example,enhanced N -> S transport of 14C-rich air in late summer

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CMA NWRfit3962m2134m305m

!14CO2 ‰

date

late summer

isolation of Cff and Cbio, CMA

Cobs= Cbg+ Cff+ Cbio

(ΔC)obs= (ΔC)bg+ (ΔC)ff

- NWRfit

above (below) 2400m

isolation of Cff and Cbio, CMA

• includes correction for ΔCr

• Cbio large even in winter• Cff detectable year round, evenabove CBL• Cff & Cbio from same sample butindependently useful:

- constrain Fff, Fbio

- evaluate other Cff tracers

Cobs= Cbg+ Cff+ Cbio

(ΔC)obs= (ΔC)bg+ (ΔC)ff

above (below) 2400m

International Atmospheric 14CO2 Inter-comparisonto evaluate measurement precision, repeatability, and

laboratory inter-comparability to aid integration ofregional and global observations of 14CO2

EXTRACTION MEASUREMENT

UC-Irvine (US) UC-Irvine Keck AMS

Scripps (US) LLNL-CAMS

CU-INSTAAR (US) UC-Irvine Keck AMS

CIO - Groningen

(Netherlands)

Groningen-AMS

CAOS-Tohuku (Japan) Nagoya-AMS

ANSTO (Australia) ANSTO

•initial participants:

•progress•round two of flask inter-comparison complete

•interested parties may contact•John Miller (NOAA)

preliminary 14CO2 intercomparison results

• 2005 Experts’ Recommendation forlab intercomparability was 1 per mil.

• Labs 3,4,6 within 2 per mil range forA and B.

• Blue= Round1; Red= Round2, witherror bars indicating reported errorbars of measurements

• Black = unweighted means of bothrounds with error bars indicatingstd. dev. of values.

• Grey lines = weighted meansacross all labs.

• No outliers excluded.

from John Miller CIRES/NOAA

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B

future• estimates of regional US emissions ratios for

various long-lived anthropogenic trace gases(R’ = T/Cff)

• introduction of additional surveillance tanks• renewed effort to reduce sources of variance

– automation of CO2 extraction (C-Rex)– improved handling of primary standard

• expansion of graphitization capability• additional measurement partners

• continue 14C ICP, w/ greater frequencyTHANK YOU