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Instruments and Platforms for Measuring Atmospheric CO2 Concentration
Britton StephensNCAR Atmospheric Technology Division
Outline• Measurement technologies
• Instruments
• Precision, potential bias, costs, CDAS implementation
• Platforms
• Costs, CDAS implementation
Accuracy, or more formally reproducibility, is determined by calibration procedures
Measurement expenses are largely a function of the cost of the people who carry them out.
Expected from fossil fuel emissions
Observations
TransCom1 FF Gradients
What do existing flask measurements tell us?
Dry Mole Fraction of CO2
Brazil Boulder 370 molecules of CO2 370 molecules of CO2
779630 molecules of N2 779630 molecules of N2
210000 molecules of O2 210000 molecules of O2
10000 molecules of Ar 10000 molecules of Ar
40000 molecules of H2O 5000 molecules of H2O
Mole Fraction = 355.8 ppm Mole Fraction = 368.2 ppm
Dry Mole Fraction = 370.0 ppm Dry Mole Fraction = 370.0 ppm
For ± 0.1 ppm consistency, need to stabilize to ± 300 ppm H2O (or dry to dewpoint of -25 ºC)
Absolute Measurement Techniques: Manometric and Gravimetric
NOAA/CMDL Manometer:
Reproducibility of 0.06 ppm
(C. Zhao et al., 1997)
Relative Measurement Techniques: Non-dispersive Infrared (NDIR) Spectroscopy
(from www.tsi.com)
• Broadband IR radiation filtered for 4.26 um
• Cooled emitter and detector
• Pulsed emitter or chopper wheel
• 1 or 2 detection cells
Advantages: Robust, precise
Disadvantages: Non-linear; sensitivity to pressure, temperature, and optical conditions; pressure broadening; power consumption
NDIR measurements require calibration gases tied to a common scale
NOAA/CMDL scheme for
propagation of WMO CO2 scale:
At least 4 points needed for 0.1 ppm consistency
Recalibration needed ~ every 3 years due to drift
$2000
CDAS v 1.0 Implementation
Sensor Cost
Short-term Precision
Zero Drift
rate
Accuracy
$7-10,000 0.2 ppm in one second
<1 ppm per hour
Depends on calibration scheme
Setup Cost Operational Cost Precision Bias
$50-$150,000 depending on surface platform (+$10,000 per level on tall towers)
$50-100,000 per year depending on surface platform, $1000 per flight on light aircraft
0.05 ppm (± 1σ)
0.2 ppm (± 1σ)
LiCor Analyzer Specifications
Manual Flask Sampling
CDAS v 1.0 Implementation
Setup Cost Operational Cost Precision Bias Sampling
$5000 $200 per flask pair (returned as one sample value) + $20*annual flask total
0.05 ppm (± 1σ)
0.2 ppm (± 1σ)
Weekly interval1
1Selective sampling based on radon in v 2.0
Automated Flask Sampling
CDAS v 1.0 ImplementationSetup Cost Operational Cost Precision Bias Sampling
$50,000 ($75,000 on buoy)
$50 per flask sample ($150 on buoy) + $20*annual flask total
0.1 ppm (± 1σ)
0.2 ppm (± 1σ)
Specified 2-24 day interval1
(from www.cmdl.noaa.gov/ccgg)
Atmospheric Observing Systems
Boulder, Colorado
NOAA SBIR
Robust, Precise, CO2 Analyzer for Unattended
Field Use
Under Development
• 1 part in 3000 in 1 minute or less
• 30 cc/min or less gas usage
• Unattended field deployment for 6 months or more
• $5,000 or less when manufactured in quantity
CDAS v 1.0 Implementation
Sensor Cost
Short-term Precision
Zero Drift
rate
Accuracy
$5,000 0.1 ppm in one minute
minimal Depends on calibration scheme
Setup Cost Operational Cost Precision Bias
$500,000 one-time development + $15,000 ($20,000 on light aircraft) (+$5,000 per level on tall towers)
$15,000 per year, $500 per flight on light aircraft
0.1 ppm (± 1σ)
0.2 ppm (± 1σ)
NOAA/AOS Analyzer Specifications
Niwot Ridge Pilot Study August 2002
Jeilun Sun, Steve Oncley, Alex Guenther, Dave Schimel, Don Lenschow, Britt Stephens, Russ Monson, and others.
Prototype Inexpensive/Autonomous CO2 System
Research items:
• Stability of CO2 in aluminum LPG cylinders
• Correction for zero drift between calibrations
Goals:
• 1-2 year service schedule
• Total installation ~ $2000
• 0.5 ppm accuracy
RMT, Ltd., Russia
CDAS v 1.0 Implementation
Sensor Cost
Short-term Precision
Zero Drift
rate
Accuracy
$2,000 0.5 ppm in one second
< 25 ppm per hour
Depends on calibration scheme
Setup Cost Operational Cost Precision Bias
$200,000 one-time development + $5,000 (+$2,000 per level on tall towers)
$5,000 per year 0.2 ppm (± 1σ)
0.5 ppm (± 1σ)
NCAR/RMT Analyzer Specifications
Remote Sensing Instruments(not implemented in CDAS v 1.0)
• Upward-looking Fourier-transform infrared (FTIR) spectrometers (~$300K+)
• Active and passive satellite CO2 measurements ($200- $300M)
Both ~ 1-3 ppm in column average with potential biases due to land cover type, aerosols, clouds, viewing and sun angle
• Virtual tall towers (~$50K), 0.2-1.0 ppm for weekly-monthly mid-boundary layer values
Ground Station
CDAS ImplementationSetup Cost Location
v 1.0 $5000 Off of coast allowed to simulate clean air sampling
v 2.0
or
v 3.0
Scaled based upon location
Only allowed on land, co-located with existing meteorological station
Point Barrow Alaska
Very Tall Tower
CDAS ImplementationSetup Cost Location
v 1.0 $100 per meter
Anywhere
v 2.0
or
v 3.0
Co-located with existing tower or budgeted at $1000 per meter
WLEF, Wisconsin, USA
Light Aircraft Profile
CDAS ImplementationSetup Cost Location
v 1.0 $750 per flight
Anywhere
v 2.0
or
v 3.0
Only allowed over or near land, clear air selection allowed
Carr, Colorado, USA
(from www.cmdl.noaa.gov/ccgg)
Volunteer Observing Ship
CDAS ImplementationSetup Cost Location
v 1.0 $20,000 Great circle route between any two
points
v 2.0
or
v 3.0
Only allowed co-located with existing shipping lanes
Freighter Travel, Ltd.
Blue Star Line
Buoy
CDAS ImplementationSetup Cost Location
v 1.0 $25,000 Anywhere
v 2.0 Co-located with existing buoy or budgeted at $100,000
ATLAS Buoy, TAO Array
(from NOAA/PMEL)
• Research Aircraft ($1,500-$20,000 per hour)
• Research Ships (~$20,000 per day)
Additional Platforms(not implemented in CDAS v 1.0)