"Ring 2": High-precision, high-accuracy CO 2 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 ring bound by wild desire I fell in to a ring of fire... I fell in to a burning ring of fire I went down,down,down and the flames went higher. And it burns,burns,burns the ring of fire the ring of fire. CO2 is a burning thing and it makes a warmer ring bound by wild desire I fell in to a ring of CO2... I fell in to a burning ring of CO2 I went down,down,down and the CO2 went higher. And it burns,burns,burns the ring of CO2 the 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 tower with high-quality standard gases. = 447m WLEF tower. LI-820, CMDL in situ and flask measurements.

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, MN 100 ft agl 360 ft agl Kewanee, IL 100 ft agl 460 ft agl Centerville, IA 100 ft agl 360 ft agl Mead, NE 100 ft agl 400 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 (CO 2, 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 –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 AnalyzerSlopeIntercept CADS01Previous Readings CADS03Previous Readings CADS05Previous Readings CADS06Previous Readings

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

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