Measurement of N 2 O and CH 4 Soil Fluxes From Garden and - PowerPoint PPT Presentation

Measurement of N 2 O and CH 4 Soil Fluxes From Garden and Agricultural Soils Using Closed Chamber System Coupled with High-Precision CRDS Analyzer G. Jacobson, N. Saad, Y. He, D. Fleck, C. Alexander, J. Hoffnagle, P. Franz, C. Rella (Picarro Inc.) Bernardo del Campo (Iowa State University) ASA CSSA SSSA 2013 Meeting Nov 6, 2013

Experiment Objectives Motivation: To evaluate the capability of the new Picarro G2508 analyzer coupled with a static chamber to measure soil fluxes of N 2 O, CH 4 , CO 2 . • Objective 1: Characterize the sensitivity of the analyzer to other molecular species which may be present in soil emissions. • Objective 2: Measure agricultural soil samples with a wide range of fluxes in the lab to evaluate the uncertainty of the measurements.

Instrumentation: GHG Analyzer Performance Molecule Specified Precision: 1- σ of 5 min averages N 2 O < 5 ppb CO 2 < 200 ppb CH 4 < 5 ppb NH 3 < 1 ppb + 0.05% of reading H 2 O < 100 ppm • Measurement frequency: 7 seconds for each molecule • Dry mol fraction automatically reported • Ambient-level reference gas measurements made every two days to check for drift • Rough calibration prior to experiment: Estimated 1% error 2

Analyzer Drift Test CO 2 2.5 ppm CH 4 3.5 ppb N 2 O 50 ppb 3

Spectral Interference Testing Most likely interfering molecules are the ones which are measured N 2 O CO 2 CH 4 H 2 O NH 3 4

1-D CO 2 Sensitivity Testing .8ppb per 1000ppm of CO2 -7.1 ppb per 1000ppm of CO2 0.01 0.006 0.00 0.005 -0.01 CH4 (ppm) N2O (ppm) 0.004 -0.02 0.003 -0.03 0.002 -0.04 CH4 0.001 Linear Fit of average_CH4 -0.05 0.000 0 1000 2000 3000 4000 5000 6000 7000 0 1000 2000 3000 4000 5000 6000 7000 CO2 (ppm) CO2 (ppm) 400ppm per 1000ppm of CO2 0.30 0.30 0.25 0.25 NH3 (ppb) 0.20 0.20 H2O (%) 0.15 0.15 0.10 0.10 0.05 0.05 H2O Linear Fit of average_H2O 0.00 0.00 0 1000 2000 3000 4000 5000 6000 7000 0 1000 2000 3000 4000 5000 6000 7000 CO (ppm) CO2 (ppm)

Measured Sensitivities Automatic corrections are made within the instrument for N 2 O , CO 2, CH 4 , NH 3 , H 2 O Hydrocarbon Sensitivities measured but not corrected Test gas N 2 O (ppm) CO 2 (ppm) H 2 O (%) CH 4 (ppm) NH 3 (ppm) C 2 H 2 (ppb) 3 E-4 -1.5 -4 E-4 TBD -1.5 E-3 C 2 H 4 (ppm) -2 E-4 -6.8 E-2 N/A -2.9 E-3 -5.3 E-4 C 2 H 6 (ppm) -2 E-4 4.7 E-3 1.6E-5 TBD -7.1 E-4 Not recommended for use in studies using acetylene

Soil Samples from Iowa Plant Zoo Samples Courtesy of Bernardo del Campo at U of Iowa • Sample History • Sample types: Molisols from Boone Iowa – Samples taken after 15mm rain, capped and shipped to California – Biochar: Plot treated with biochar (equivalent of 25 Ton CO 2 /ha) – First measurements taken 4 days after sampling – No Biochar: Plot without biochar – Samples not re-capped between – Garden: Test garden plot (no measurements biochar treatment) 7

Experimental Set-up Chamber Soil Sample in soil tube 5 cm Perforated tube 8

System Response Time t = 2.5 minutes Add 2.5 minutes to CO 2 recorded start times for all flux calculations System volumes: CH 4 387 – 493 cm 3 N 2 O 9

Flux Measurement & Analysis Methods • Measurement: – Closed path measurements – Minimum 15 min closed chamber – Minimum 10 min chamber flush (open) between measurements • Analysis – Response time of 2.5 min added to recorded chamber close times – Linear fits using different measurement durations tried – Four min of concentration data provided the best uncertainty – Chi-square fitting (linear only) used to model slope & uncertainty • Assume unknown measurement uncertainty • Assume the same standard deviation for all measurements 𝑂 • Variance: 𝜏 2 = [𝑧 𝑗 − 𝑧 𝑦 𝑗 ] 2 /(𝑂 − 𝑁) 𝑗=1 10

Flux trends over time 11

Flux trends over time 12

Flux trends over time 13

Flux Comparison Range of Fluxes Repeatability Uncertainty of Fluxes Uncertainty of (kg/ha/year) 1-sigma Flux (model) (kg/ha/year) Fluxes (SE) (kg/ha/year) (kg/ha/year) (kg/ha/year) N 2 O -3.9 - 40 0.34 – 1.9 0.1 – 1.9 6-120 1 2.4 - 24 1 2,800 – 74,600 0 - 96 1 4.8 - 12 1 CO 2 7,900 - 205,400 320 – 1,700 CH 4 -2.7 - 1.6 0.013 – 0.34 0.3 – 1.7 n/a n/a 1 Ventera et al 2010 SSSA (Minnesota Corn field using GC) 14

Conclusions & Next Steps • Conclusions – Uncertainty and repeatability of the flux measurements were encouraging compared to GC measurements – We have only scratched the surface.. • Next investigations: – Effect of changing oxygen concentration – Compare measurements with GC, PAC, IRGA in Iowa – Other potential interfering species (small molecules which absorb in MIR) 15

Thank You.

Additional Material

1-D CH 4 Sensitivity Results The sensitivity of CH 4 , N 2 O and NH 3 0.0 .07ppm per ppm of CH4 was less than the specified -0.5 measurement precision over 100 CO2 (ppm) ppm CH 4 , see NH 3 graph (below, -1.0 green) for example. -1.5 -2.0 CO2 Linear Fit of Combine_CO2 -2.5 0 5 10 15 20 25 30 35 CH4 (ppm) NH3 0.45 0.001ppb per ppm CH4 0.40 NH3 (ppm) 0.35 0.30 0.25 0.20 0 5 10 15 20 25 30 35 CH4 (ppm)

1-D N 2 O Sensitivity Results • N 2 O has essentially has zero cross talk to other molecules because it is so week in NIR, except NH 3 CO2 0.9 11ppb per 100ppm of N2O 0.50 0.8 0.45 0.7 0.6 CO2 (ppm) NH3 (ppb) 0.40 0.5 0.35 0.4 0.30 0.3 NH3 0.25 0.2 Linear Fit of average_NH3 0.1 0.20 0 10 20 30 40 50 60 0 10 20 30 40 50 60 N2O (ppm) N2O (ppm)

1-D NH 3 Sensitivity Results 0.000 -0.1ppm per ppm of NH3 1 -.1ppb per ppm of NH3 -0.001 0 CO2 (ppm) -1 CH4 (ppm) -0.002 -2 -0.003 -3 -0.004 -4 CO2 CH4 Linear Fit of Combined2_CO2 -0.005 Linear Fit of Combined2_CH4 -5 0 5000 10000 15000 20000 25000 30000 0 5000 10000 15000 20000 25000 30000 NH3 (ppb) NH3 (ppb) 0.5 0.30 10ppm per ppm of NH3 10 ppb per ppm of NH3 0.25 0.4 0.20 H2O (%) N2O (ppm) 0.3 0.15 0.2 0.10 0.1 0.05 H2O N2O Linear Fit of Combined2_H2O Linear Fit of Combined2_N2O 0.00 0.0 0 5000 10000 15000 20000 25000 30000 0 5000 10000 15000 20000 25000 30000 NH3 (ppb) NH3 (ppb)

N 2 O Allan Standard Deviation Instrument performance results from the analyzer used in this experiment 10 1 ppb 0.1 0.01 10,000 1 1,000 10 100 seconds 21

CO 2 Allan Standard Deviation Instrument performance results from the analyzer used in this experiment 1 0.1 σ ( τ ) ppm 0.01 0.001 10,000 100,000 1 1,000 10 100 seconds 22

CH 4 Allan Standard Deviation Instrument performance results from the analyzer used in this experiment σ ( τ ) 1 ppb 0.1 0.1 0.01 0.001 0.0001 10,000 1 1,000 10 100 seconds 23

NH 3 Allan Standard Deviation Instrument performance results from the analyzer used in this experiment 1 σ ( τ ) 0.1 ppb 0.01 1 10 10,000 100,000 100 1,000 seconds

Ambient N 2 O Thermal Sensitivity Test Instrument performance results from the analyzer used in this experiment • Sensitivity is < 0.02 ppb per ̊C • Effect over 30 ̊ C change in ambient temperature is < 0.6 ppb 25

Ambient CH 4 Thermal Sensitivity Test Instrument performance results from the analyzer used in this experiment • Sensitivity is < 0.007 ppb per ̊C • Effect over 30 ̊ C change in ambient temperature is < 0.2 ppb 26

Ambient CO 2 Thermal Sensitivity Test Instrument performance results from the analyzer used in this experiment • Sensitivity is < 0.5 ppb per ̊C • Effect over 30 ̊ C change in ambient temperature is < 15 ppb 27

Zoom in on time response CO 2 CH 4 N 2 O 28