Technical Aspects of Automated Greenhouse Gas Monitoring Kevin Kahmark, Neville Millar, Sven Bohm, Iurii Shcherbak, and G. Philip Robertson

Michigan State University-Kellogg Biological Station, Hickory Corners, Michigan

System Control Center

Mobile Automated Greenhouse Gas Sampling and Monitoring System

Automated System Imagery and Schematic Website: http://lter.kbs.msu.edu/datasets/64

Gas Sampling Data Output and Organization

04/6 04/13 04/20 04/27 05/4 05/11

-40

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Continuous CornC-S-CaS-Ca-CCa-C-S

Flu

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g N

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m-2 h

-1)

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04/6 04/13 04/20 04/27 05/4 05/11

Grass mixOld fieldNative prairieSwitch grass

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MiscanthusPoplar

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Agroecosystem

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Agroecosystem

N2O

flux

(g N

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Static chamber – average daily N2O fluxes

Automated chamber – average hourly N2O fluxes

Fig. 5 The gas standards are run at the beginning and end of each chamber closure period. Two chambers are closed and analyzed during each period. The chamber sample is carried by nitrogen to the gas chromatograph. Air and hydrogen serve as the flame gases for CH4 analysis. An air compressor supplies pressure for the chamber pneumatics and injection ports.

Fig. 4 Ruby automation code sends digital commands to the data modules which act as electronic switches for the pneumatic system. The chromatographic software runs in a virtual machine that allows the user to check the system remotely.

Fig. 6 Data control modules send electronic (on/off) signals to the pneumatic control solenoids.

Fig. 8 An SRI Gas Chromatograph analyzes the collected gas sample using an electron capture detector (ECD) for N2O and a flame ionization detector (FID) for CH4.

Fig. 7 The pneumatic and injection control center regulates the delivery of samples to the gas chromatograph and the infrared gas analyzer (IRGA).

Fig. 9 The Licor-840 IRGA analyzes CO2 and water vapor prior to each sample injection.

Fig. 12 Comparison of static and automated chamber measurements. Results from the automated near-continuous system resolves sub-daily fluxes.

CH4

N2O

Fig. 10 Tracing of CH4 and N2O during a chamber run. Fig. 1 Automated chambers deployed in continuous corn treatment. Chambers are removed only during necessary farm operations.

Fig. 2 Comparison of the automated system (dark boxes) and static chambers (white cylinders). The automated system control is in the trailer.

Fig. 3 Closing of chambers. At set intervals, a pneumatic signal closes (yellow and blue tubes) the butterfly lids, creating a gastight headspace until the lids are signaled to open 40 minutes later. Clamps assure a complete airtight seal. At ten minute intervals, while closed, headspace gas is pumped to the gas analyzers (white tubing) in the system control center where it is analyzed for N2O, CO2, and CH4 concentrations. Note the static chamber in the background.

SYSTEM ADVANTAGES

Ready capture of intense episodic N2O emissions following meteorological and agronomic events, e.g. heavy rainfall, fertilization.

Flexible closure time, sampling duration, and experimental design.

Minimal site disturbance.

Conforms to recommended GHG chamber design.

High chromatographic resolution and sensitivity.

JUSTIFICATION

Automation provides accurate estimates of the Global Warming Potential (GWP) of bioenergy production systems and is advantageous in constructing energy balances.

High temporal resolution is needed for accurate determination of source or sink strength of the three major agricultural greenhouse gases (N2O, CO2, CH4) in potential bioenergy crops.

Long-term, near-continuous automated gas flux measurements provide needed temporal resolution for testing and validation of agroecological models.

N2O

CH4

CO2

Fig. 11 Data flux analyzer allows each chamber event to be viewed and analyzed separately. Placing a cursor over a chamber event (left graph) displays the flux and chromatographic trace for that event. Questionable fluxes can be identified and rejected.

Chamber event(four conc.)

Single fluxevent Single Peak

Integration