Instruments and Platforms for Measuring
Atmospheric CO2 Concentration
Britton Stephens
NCAR 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.
What do existing flask measurements tell us?
TransCom1 FF Gradients
Expected from
fossil
fuel emissions
Observations
Dry Mole Fraction of CO2
Brazil
370 molecules of CO2
Boulder
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
• Broadband IR radiation
filtered for 4.26 um
• Cooled emitter and detector
• Pulsed emitter or chopper
wheel
(from www.tsi.com)
• 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
LiCor, Inc. CO2 Analyzer
CMDL Flask Analysis System
Typical LiCor Output Signals
(from www.cmdl.noaa.gov/ccgg)
Intra- and Inter-laboratory agreement
still not better than 0.2 ppm
LiCor Analyzer Specifications
Sensor
Cost
Short-term
Precision
$7-10,000 0.2 ppm in
one second
Zero Drift rate
<1 ppm
per hour
Accuracy
Depends on calibration
scheme
CDAS v 1.0 Implementation
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)
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
(from www.cmdl.noaa.gov/ccgg)
CDAS v 1.0 Implementation
Setup 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
Atmospheric Observing Systems
Boulder, Colorado
• 1 part in 3000 in 1 minute
or less
NOAA SBIR
Robust, Precise, CO2
Analyzer for Unattended
Field Use
Under Development
• 30 cc/min or less gas
usage
• Unattended field
deployment for 6 months
or more
• $5,000 or less when
manufactured in quantity
NOAA/AOS Analyzer Specifications
Sensor
Cost
$5,000
Short-term
Precision
0.1 ppm in
one minute
Zero Drift rate
minimal
Accuracy
Depends on calibration
scheme
CDAS v 1.0 Implementation
Setup Cost
Operational Cost
$500,000 one-time $15,000 per year,
development +
$500 per flight on light
$15,000 ($20,000 aircraft
on light aircraft)
(+$5,000 per level
on tall towers)
Precision
Bias
0.1 ppm
(± 1σ)
0.2 ppm
(± 1σ)
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
RMT, Ltd., Russia
Research items:
Goals:
• Stability of CO2 in
aluminum LPG cylinders
• 1-2 year service schedule
• Correction for zero drift
between calibrations
• Total installation ~ $2000
• 0.5 ppm accuracy
NCAR/RMT Analyzer Specifications
Sensor
Cost
Short-term
Precision
$2,000
0.5 ppm in
one second
Zero Drift rate
< 25 ppm
per hour
Accuracy
Depends on calibration
scheme
CDAS v 1.0 Implementation
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)
Sensors in Development
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
Point Barrow Alaska
CDAS Implementation
v 1.0
Setup Cost
Location
$5000
Off of coast allowed to
simulate clean air
sampling
v 2.0 Scaled based Only allowed on land,
upon location co-located with existing
or
meteorological station
v 3.0
Very Tall Tower
WLEF, Wisconsin, USA
CDAS Implementation
v 1.0
v 2.0
or
v 3.0
Setup Cost
Location
$100 per
meter
Anywhere
Co-located with
existing tower or
budgeted at $1000 per
meter
Towers over 650 feet AGL in U.S. and proximity
Light Aircraft Profile
Carr, Colorado, USA
CDAS Implementation
v 1.0
v 2.0
or
v 3.0
(from www.cmdl.noaa.gov/ccgg)
Setup Cost
Location
$750 per
flight
Anywhere
Only allowed over or
near land, clear air
selection allowed
Volunteer Observing Ship
Blue Star Line
CDAS Implementation
Freighter Travel, Ltd.
v 1.0
v 2.0
or
v 3.0
Setup Cost
Location
$20,000
Great circle route
between any two
points
Only allowed
co-located with existing
shipping lanes
Buoy
ATLAS Buoy, TAO Array
CDAS Implementation
v 1.0
v 2.0
(from NOAA/PMEL)
Setup Cost
Location
$25,000
Anywhere
Co-located with
existing buoy or
budgeted at $100,000
Additional Platforms
(not implemented in CDAS v 1.0)
• Research Aircraft ($1,500-$20,000 per hour)
• Research Ships (~$20,000 per day)
Conclusions
• There are wide ranges of available
instruments and platforms for CO2
concentration measurements
• All have different setup and operation costs,
precisions, and potential biases
• Complexity requires a tool for quantitatively
assessing creatively designed networks