Melissa R. Palmer * and Edward Wahl ASITA Conference * - PowerPoint PPT Presentation

Method to make accurate concentration and isotopic measurements for small gas samples Melissa R. Palmer * and Edward Wahl ASITA Conference * mpalmer@picarro.com June 17 th , 2014

δ 13 C of CO 2 and CH 4 for carbon cycle studies Motivation: Use Picarro CRDS technology to measure concentrations of, and δ 13 C in, CO 2 and CH 4 for continuous monitoring or discrete samples using the same analyzer. With application to: – Atmospheric CO 2 & CH 4 (unlimited sample) – DOC & DIC (acidification to CO 2 ) – Gases evolved from soil respiration – Dissolved gases sampled via headspace equilibration methods – Laboratory-based microbial experiments 1

Measuring discrete samples of CO 2 and CH 4 Challenge: CRDS is easy-to-use, robust and field deployable, but it operates as a continuous flow system: – Ideal for measuring ambient atmospheric conditions – More challenging for small volume samples Objective: Evaluate an improved method using a Small Sample Isotope Module (SSIM) coupled to a continuous-flow Picarro G2201- i .

Instrumentation: G2201- i Molecule Specified Precision @ Ambient : 1- σ of 5 min averages δ 13 C in CO 2 < 0.16 ‰ [ 12 CO 2 ] 200 ppb + 0.05 % of reading δ 13 C in CH 4 < 1.15 ‰ Picarro G2201- i [ 12 CH 4 ] 5 ppb + 0.05 % of reading • Measurement technique: Cavity Ring-Down Spectroscopy • Analyzer data rate: 3-seconds for each species Analyzer flow rate: ~ 25 sccm  ~ 200 mL of gas for a 5-min measurement • • Water concentration is measured and dry mol fraction reported 3

Instrumentation: SSIM2 Molecule Specified Precision with SSIM @ Ambient for 1 replicate: δ 13 C in CO 2 < 1.0 ‰ [ 12 CO 2 ] Results of this study δ 13 C in CH 4 < 1.6 ‰ Picarro SSIM [ 12 CH 4 ] Results of this study • Throughput: 9-12 min per replicate • Recommended sample size: 20 mL (ambient sample) per injection • SSIM aims to: – Take advantage of improved precision with longer averaging time – Optimize sample volume and delivery to prevent dilution – Minimize leaks and dead volumes to prevent dilution and isotopic fractionation 4

SSIM Sample Delivery Sample V 4 Pressure External Valve sensor Vacuum attached V 5 Pump to sample P container V 2 V 1 Zero Air 20mL Cal gas Sample Volume V 3 Sample Out Normally Open Normally Closed Common - Step 1: Pump Down Sample Loop - Step 2: Sample Delivered to Sample Loop - Step 3: Sample Delivered to Analyzer 5

SSIM Sample Delivery Sample V 4 Pressure External Valve sensor Vacuum attached V 5 Pump to sample P container V 2 V 1 Zero Air 20mL Cal gas Sample Volume V 3 Sample Out Normally Open Normally Closed Common - Step 1: Pump Down Sample Loop - Step 2: Sample Delivered to Sample Loop - Step 3: Sample Delivered to Analyzer 6

SSIM Sample Delivery Sample V 4 Pressure External Valve sensor Vacuum attached V 5 Pump to sample P container V 2 V 1 Zero Air 20mL Cal gas Sample Volume V 3 Sample Out Normally Open Normally Closed Common - Step 1: Pump Down Sample Loop - Step 2: Sample Delivered to Sample Loop - Step 3: Sample Delivered to Analyzer 7

Current Methodology: Single injection 12 CO 2 (ppm) Sample injected 10 minutes δ 13 C (‰) ∆ (SSIM-Tank) SSIM Single Direct Tank Injection from Tank Measurement 12 CO 2 (ppm) 366.3 ± 0.15 383.0 ± 0.17 ~ 17 ppm δ 13 CO 2 (‰) -68.55 ± 1.0 -67.33 ± 1.0 ~ 1 ‰ 8

Improved methodology: Double injection Approach: Reduce systematic dilution effect by injecting each sample twice. Analyze the second injection and improve precision of concentration measurement. Experimental design: 1. Directly measure three tanks of variable concentration and isotopic composition on the G2201- i ( reference ) 2. Analyze the tanks using the Single Inject (SI) method and determine accuracy over 25 injections. 3. Analyze the tanks using the new Double Inject (DI) method and determine accuracy over 25 injections. 9

Visible Improvement: Double Injection Second injection 12 CO 2 (ppm) First injection δ 13 C (‰) 25 minutes ∆ (SSIM 2 nd SSIM First SSIM Second Direct Tank Injection Injection Measurement Inject-Tank) 12 CO 2 (ppm) 366.4 ± 0.15 383.2 ± 0.15 383.0 ± 0.17 ~ 0.2 ppm δ 13 CO 2 (‰) -68.54 ± 1.0 -67.3 ± 1.0 -67.3 ± 1.0 ~ 0.1 ‰ 10

Single Injection vs. Double Injection: Concentration of 12 CO 2 and 12 CH 4 - = Double Inject (DI) - = Single Inject (SI) - = Tank High Range 12 CH 4 12 CO 2 92.9% 93.5% Tank 1 99.7% 99.8% 100% 100% 1.5 1.6 1.7 1.8 350 360 370 380 390 94. 8% Tank 2 94.2% 99.8% 99.8% 100% 100% 920 940 960 980 1000 1020 9 9.2 9.4 9.6 9.8 10 Tank 3 92.6% 91.8% 99.8% 99.8% 100% 100% 330 340 350 360 370 380 390 17 17.5 18 18.5 19 19.5 20 n = 25 injections for DI and SI on each tank % = average SSIM measurement / tank measurement (%) 11

Single Injection vs. Double Injection: Concentration of δ 13 CO2 and δ 13 CH4 - = Double Inject (DI) - = Single Inject (SI) - = Tank High Range δ 13 CH 4 δ 13 CO 2 1 σ ~ 0.8 ‰ Tank 1 1 σ ~ 6 ‰ -45 -40 -35 -30 -25 -20 -38 -37 -36 -35 -34 Tank 2 1 σ ~ 0.4 ‰ 1 σ ~ 1 ‰ -42 -41 -40 -39 -38 -37 -36 -41.4 -41.2 -41 -40.8 -40.6 -40.4 -40.2 -40 -39.8 Tank 3 1 σ ~ 0.5 ‰ 1 σ ~ 0.8 ‰ -41.5 -41 -40.5 -40 -39.5 -39 -38.5 -38 -36.5 -36 -35.5 -35 -34.5 -34 -33.5 -33 n = 25 injections for DI and SI on each tank 12

Conclusions and Recommendations – Double injection conclusions: • Improves relative error of concentration measurements from 5% to < 0.5% error • Has no effect on the relative error of the isotopic measurements, and performance remains high – Recommended sample criteria: • Sample size ≥ 40 mL • Sample concentration of CO 2 between ambient and 2,000 ppm • Sample concentration of CH 4 between ambient and 500 ppm • Sample container: tedlar bag, ss or glass flasks Note: this presentation reflects development work at Picarro, and does not represent a standard configuration of the SSIM2. This information should not be relied upon in making a purchasing decision. Please contact Picarro if you have additional questions. 13

Thank you! Visit us at the Picarro booth or email me at mpalmer@picarro.com

SSIM Cleaning – Reducing Memory Sample V 4 Pressure External Valve sensor Vacuum attached V 5 Pump to sample P container V 2 V 1 Zero Air 20mL Cal gas Sample Volume V 3 Sample Out Normally Open Normally Closed Common - Step 1: Pump Down Sample Loop - Step 2: Flush SSIM with ZA to the Analyzer 15

SSIM Cleaning – Reducing Memory Sample V 4 Pressure External Valve sensor Vacuum attached V 5 Pump to sample P container V 2 V 1 Zero Air 20mL Cal gas Sample Volume V 3 Sample Out Normally Open Normally Closed Common - Step 1: Pump Down Sample Loop - Step 2: Flush SSIM with ZA to the Analyzer 16

Double Injection: SSIM Pressure 17