"Ring 2":  High-precision, high-accuracy CO2 mixing ratio measurements in support of the NACP Mid Continent Intensive

ring2.psu.edu

Scott Richardson, Natasha Miles, Kenneth Davis (PSU), Eric Crosson (Picarro, Inc.), Scott Denning, Marek Uliasz, Dusanke Zupanski (CSU)

The Ring of Fire• Love is a burning thing

and it makes a firery ringbound by wild desireI fell in to a ring of fire...

I fell in to a burning ring of fireI went down,down,downand the flames went higher.And it burns,burns,burnsthe ring of firethe ring of fire.

• CO2 is a burning thingand it makes a warmer ringbound by wild desireI fell in to a ring of CO2...

I fell in to a burning ring of CO2I went down,down,downand the CO2 went higher.And it burns,burns,burnsthe ring of CO2the ring of CO2.

The Ring of Towers

ChEAS Regional Flux Experiment Domain

= LI-820 sampling from 75m above ground on a communications tower.

= 40m Sylvania flux towerwith high-quality standardgases.

= 447m WLEF tower. LI-820, CMDLin situ and flaskmeasurements.

Mid-Continent Intensive

• Overall goal: Seek convergence between top-down and bottom-up ecological estimates of the regional flux

• Focus on upper Midwest of the U.S.

• Add regional network of 5 communications-tower based atmospheric CO2 obs in the midcontinent intensive region– April 2007 through October 2008– In addition to the planned long-term atmospheric CO2 observing network

• Tall towers• Aircraft profiles• Well-calibrated CO2 measurements on AmeriFlux towers

• The communications towers will “oversample” the atmosphere in the study region for more than a full year

• A coupled atmosphere/terrestrial carbon model and a Lagrangian particle dispersion model will be used to conduct an atmospheric inversion and convert these mixing ratio measurements into highly data-constrained regional carbon balance estimates.

• This work builds upon the Ring of Towers which deployed similar methodology in a forested region of northern Wisconsin

The role of Ring 2 in the Mid-Continent Intensive

   • Kewanee, IL• Centerville, IA• Mead, NE• Round Lake, MN• Highland, WI

Ring 2 sites

Round Lake, MN100 ft agl360 ft agl

Kewanee, IL100 ft agl460 ft agl

Centerville, IA100 ft agl360 ft agl

Mead, NE100 ft agl400 ft agl

Cavity Ring-Down Spectroscopy

=> A laser-based optical technique=> Sensitivity Extremely long effective path length Insensitive to optical power fluctuations=> Chemical Specificity Able to distinguish individual absorption features=> Linearity Beer-Lambert Law

• Picarro, Inc. has developed an ultra-sensitive trace gas (CO2, methane, CO) monitoring system. Advantages include:

Cavity Ring-Down Spectroscopy

– High precision and accuracy long-term stability: days to weeks

1.5-sec sample precision and accuracy of ≤ 0.2 ppm and in tests

– Measurement rate in seconds rather than minutes

– No drying is required; water vapor is measured and correction to CO2 is applied

– Stable and robust long-term measurement

• Prior to deployment, the five cavity ring-down systems were tested together with two PSU Ameriflux systems. – For details on the low-cost systems, see www.amerifluxco2.psu.edu. – Overall agreement ~0.2 ppm

Predeployment tests

• Long-term stability is unknown

• Lab tests indicate calibration changed by 0.1–0.2 over 6 weeks between calibrations

Cavity Ring-Down Spectroscopy

Standards 338.81 369.39 401.68 431.78

Analyzer Slope Intercept

CADS01 Previous Readings 339.030 369.633 401.940 431.890

1.000972 -0.582508 338.772 369.413 401.747 431.727

CADS03 Previous Readings 338.834 369.441 401.743 431.667

1.001269 -0.495369 338.768 369.414 401.758 431.719

CADS05 Previous Readings 338.931 369.554 401.882 431.823

1.000640 -0.379726 338.771 369.410 401.759 431.719

CADS06 Previous Readings 338.885 369.499 401.809 431.741

1.001027 -0.464082 338.769 369.414 401.757 431.720

• Two levels sampled at each tower

– 100 ft AGL (15 min every hour)

– 360–460 ft AGL (45 min every hour)

• Two reference gases

– sampled for 15 min each day(time of day changes)

– Used to post-process calibrated data (if necessary)

Sampling Strategy

Sunset Sunrise

Nighttime 100 ft. level

• In-field agreement between sensors first two weeks following deployment

ring2.psu.edu

ring2.psu.edu

Site specific information

• Latitude• Longitude• Installation date• Sampling heights• Reference tank

information• Calibration date

ring2.psu.edu

• Four of five Ring 2 sites installed– Fifth sites to be installed soon

• Data available near real-time• Necessary calibration frequency to be determined

– Expected to be ~monthly

• Network designed to oversample the region• Will be used to calculate the regional flux for

comparison with bottom-up methods

Summary