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Short-lived Halocarbon Calibration WorkshopLondon, 2008
Existing Standardization Techniques
• Compressed Gas Standards• Permeation Tubes• Liquid Standards• Reagent Purity
Brad Hall, Lucy Carpenter, Manuela Martino, Ben Miller, Paul Krummel
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Compressed Gas Standards
Basic Idea: Static dilution of a pure compound (or a known mixture) to working concentration levels
Pros: portability, longevity, multiple species, traceableCons: stability, transport issues, multiple steps
NOAA: Gravimetric method, pure starting material(all components added gravimetrically)
SIO: Gravimetric/Bootstrapping, pure starting material
NIES: Gravimetric dilution of commercial mixtures
Short-lived Halocarbon Calibration WorkshopLondon, 2008
NOAA method
Pure gas (g)
Pure liquid (mg)
Ultra-pure air (kg)
Primary standard (level 1)
Ultra-pure air (kg)
Primary standard (level 2)(~ ambient concentrations)
(level 1) aliquot
Short-lived Halocarbon Calibration WorkshopLondon, 2008
SIO method
Pure liquid (mg)
N2O (gravimetric)
“Mixture”
Ultra-pure air
Primary standard(~ ambient concentrations)
GSV
Measure N2O to determine dilution factor.
“Bootstrap to N2O”
N2O bootstrapped to CO2 (Keeling)
“Mixture”
Short-lived Halocarbon Calibration WorkshopLondon, 2008
reagent
ppb ppb ppb
ppt
ppt
ppt
ppt
ppt
ppt
NOAA
Short-lived Halocarbon Calibration WorkshopLondon, 2008
reagent
mixture
ppt
mixture
ppt
mixture
ppt
mixture
ppt
mixture
ppt
mixture
ppt
SIO
Short-lived Halocarbon Calibration WorkshopLondon, 2008
CH3Br: 2008 analysis by ECD
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
5 10 15 20 25
Prepared Value (ppt)
AluminumStainless Steel (Essex)drifting ?Poly. (Stainless Steel (Essex))
Uncertainties (NOAA): ~5% for VSL halocarbons
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Limitations: Stability
0.1
2
3
456
1
CH
3I (p
pt)
1/1/96 1/1/00 1/1/042
3
4
5
6
7
8910
(right axis)
filled circles: stainless steel (Essex Cryogenics) open squares,: other stainless steel open triangles: other stainless steel open circles: Aculife-treated Aluminum
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Permeation Systems
Basic Idea: Dynamic dilution of a pure compound (or a known mixture) to working concentration levels
Pros: multiple species, simple linearity checkCons: ?
Short-lived Halocarbon Calibration WorkshopLondon, 2008
10
100 mL min-1
70oC
40oC
CH3I, C2H5I, CH2ICl, CHCl3, CH2Br2, CHBr2Cl
1-and 2- C3H7I, CH2IBr, CHBr3, CH2I2
Commercial (Ecoscientific) permeation tubes filled in-house
Loop system introduces ppt levelhalocarbons into gas stream
Permeation system used at University of York
See Wevill and Carpenter, 2004
Short-lived Halocarbon Calibration WorkshopLondon, 2008
~ 3%
Inject 0- 3 loops into gas stream, determine moles/PA
Assuming normal dist., standard deviation of the slope, sm:
sm =SSresid/(N-2)
(xi – x)2
CH2I2
y = 1.36E-18xR2 = 9.99E-01
0.0E+00
2.0E-14
4.0E-14
6.0E-14
8.0E-14
1.0E-13
1.2E-13
0 20000 40000 60000 80000 100000
Peak area
No.
mol
es
Calculate no. of moles in 1 loop:
= permeation rate (g/min-1) x loop vol (mL)
RMM (g mol-1) x flow rate (mL/min-1)
10
100 mL min-1
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Uncertainty in permeation weighings
Data points are average of 6 weighings and include error bars
This can be major uncertainty unless several months of weighings are made.
Standard deviation of slope, sm, for 9 month period of weighings ~ + 5 %
y = -0.0003x + 27.788R2 = 0.9948
15.70
15.72
15.74
15.76
15.78
15.80
15.82
09/03/07 28/04/07 17/06/07 06/08/07 25/09/07 14/11/07 03/01/08 22/02/08
Date
Wei
ght/
g
Hotel room
CH2ICl
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Total uncertainty sy/y for y = a x b/c can be estimated as:
sy/y = (sa/a)2 + (sb/b)2 + (sc/c)2Uncertainty associated with gas-phase sampling %RSDa) bias sample line loss 0b) bias sample flow rate 2c) bias atmospheric artefacts 0d) noise reproducibility of repeat air standards (which takes into 4.4
account noise on integration of chromatograms)
Uncertainty associated with water samplinge) bias losses in water sample 0f) bias sample flow rate (manufacturers uncertainty) 2g) noise reproducibility of purge efficiency (which takes into account 10.3
human error on purge volumes + noise on integration of chromatograms)
Uncertainty associated with calibration and detectionh) noise perm tube weighings 5i) bias stated mass balance uncertainty 1j) noise calibration linear regression 3k) bias flow rate through permeation tube + dilution flow 2l) bias loop volume 10
total uncertainty air,% 12.7total uncertainty water,% 15.8
+
+
+
+
+
+
+
+
+
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Comparison with AGAGE CHCl3 measurements at Mace Head:
y = 0.8687xR2 = 0.8547
0
10
20
3040
50
60
70
80
0 10 20 30 40 50 60 70
CHCl3 York (pptv)
CH
Cl 3
AG
AG
E (p
ptv)
2002
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Liquid Standards
Basic Idea: Static dilution of a pure compound in a solvent using volumetric or gravimetric techniques
Pros: simplicity, direct calibration of sea waterCons: ?
Short-lived Halocarbon Calibration WorkshopLondon, 2008
CH3OH
Preparation of liquid halocarbon standards -UEA
1. Preparation of primary standard:• A 50 ml volumetric flask containing methanol near to level is weighed (4 decimals)• The flask is weighed again after addition of 0.5-2 grams of commercial neat halocarbon and then
taken to volume2. Primary standards are shipped into the field on dry ice and are kept in a freezer until use.3. Secondary and tertiary (working) standards are prepared by successive dilution before calibrating.4. For calibrations, variable amounts (µL) of working standard are injected into syringes containing 40 ml of
halocarbon-free seawater. 5. The seawater is injected in the purge vessel and treated in the same manner as the samples.
CH3OH CH3OH
Tertiary (working) standard
By weight
When using class-A glassware and calibrated scales and pipettes, the relative error in the standard concentration is ~ 2%.
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Reagent Purity
CHBr3 (Sigma-Aldrich)98%1% CH2Br21% CHBrCBr2
CHCl3 (Sigma-Aldrich)99+ %
Halon-1211 (Scott Specialty Gases)99%1% CHBrF2
CH3Br (Matheson)99%1% CH3Cl
Short-lived Halocarbon Calibration WorkshopLondon, 2008
Reagent Purity
CHBr3 (Sigma-Aldrich)98%1% CH2Br21% CHBrCBr2
CHCl3 (Sigma-Aldrich)99+ %
Halon-1211 (Scott Specialty Gases)99%1% CHBrF2
CH3Br (Matheson)99%1% CH3Cl
CHBr3 (Spectrum)94%1% CH2Br22% dichloropropanol3% unknown
CH2BrCl (Sigma-Aldrich)96%3% CH2Cl21% CH2Br2
CH2Br2 (Sigma-Aldrich))90%9% CH2BrCl1% CH2Cl2
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