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Presentation to the Moffett Restoration Advisory Board on November 29, 2012.
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J. Brian Leen
Los Gatos Research67 East Evelyn Avenue, Suite 3
Mountain View, CA 94041
1
About Los Gatos Research
Motivation
Incoherent Cavity Ring-Down Spectroscopy(iCRDS)
Measurement of TCE and PCE
MEW and NAS Moffett Field Superfund Site
Conclusion
Outline
2
About LGR
3
H2O
N2OCO
CO2
NO
NH3O3
VOCs
OCS
CH4HF
HClC2H2
H2O
HONO
C2H4
H2S
NH3
CO2
NO2
Aerosols
• Use optical spectroscopy to make trace gas measurements (ppm, ppb, ppt)
• Operate from the visible to the mid-infrared
• Precise and accurate; also portable, robust and low power
Isotopes
Research Deployments
Deep Sea
UAV
Manned Airborne
Portable Field Station
Why Detect VOCs?
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BacterialDetection/TypingIndustrial Pollution
Benzene Formaldehyde Acetaldehyde SarinTetrachloroethylene
Chemical WeaponsDetection
USEPA Superfund sitesActive (red), Proposed (yellow), Deleted (green)
MIR Spectra: Molecular “Fingerprint”
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C-HO-H
stretch
C=Cstretch
CH2
bend
Single Laser Scanning Range
External Cavity-QCL (EC-QCL):• Broadly tunable (~2.5 µm)• ~1 cm-1 spectral width• Good for large molecules
Out-of-planebending
C-Ostretch
Incoherent Cavity Ring DownSpectroscopy (iCRDS)
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• High reflectivity mirrors → multiple reflections
• Multiple reflections → very long path
• Long path → high sensitivity
• Light ‘leaks’ out of cavity at measurable rate
• Changes in ‘leak’ rate quantify gas absorption
TCE and PCE Absorption Spectra
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• PCE and TCE are measurable at ppb concentrations
• Use linear fit to PNNL Spectroscopic Database
• Amplitude ↔ Concentration
• Spectra add linearly
(a) 97.5 ppb PCE (b) 88.7 ppb TCE
Freon-134a
Measurement Linearity
9
• Measurement is linear (R2 = 0.9971)
• Accurate to a few ppb
(a) PCE (b) TCE
Summary of Performance
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• Field portable
• 50-100’ Teflon sniffing tube
• Robust to H2O, CO2 and other common interferences
• Measurement period: 20 min average
• Precision (1σ):
• PCE – 2.32 ppb (15.9 µg/m3)
• TCE – 1.96 ppb (10.6 µg/m3)
• Limit of Detection:
• PCE < 8 ppb (55 µg/m3)
• TCE < 4 ppb (22 µg/m3)
MEW and Moffett Field
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• Middlefield-Ellis-Whisman(MEW)
• Moffett Field
• Primary contamination:PCE and TCE
o Dry cleaning
o Engine degreasing
o Semiconductormanufacture
Building 10
Previous Measurements
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Sample Location Sample Type
TCE
(µg/m3)
PCE
(µg/m3)
cis-1,2-DCE
(µg/m3)
1,1-DCA
(µg/m3)
1,1-DCE
(µg/m3)
manhole Pathway – Grab 400 300 80J 9 6J
manhole-concrete Pathway – Grab 1,000 900 200 20 10
In B10 near electrical panel Pathway 700 200 100 10 9
In B10 near offices Pathway 1,100 800 200 20 20
In B10 beneath floor Pathway 30 20 6J ND ND
on table in center of B10 Indoor - 24 hr 50 30 8 ND ND
Previous TO-15 measured values (Feb, 2012)
BZ
Mediation Depressurization
Steam TunnelRoute
Steam Gen
Field Setup
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Measurement Protocol:
• Continuous monitoring: Aug. 6-13
• Automatic switching between:
o Tunnel air
o Breathing zone air
o Zero air
o PCE standard
• Remediation fans off Aug 10-13(weekend!)
Building 10 Sample Locations
14
Sample Locations:
• Breathing Zone
• 3 Tunnel Locations:
I: Aug 6 – 8
II: Aug 8 – 10
III: Aug 10 –13
BZ
Mediation Depressurization
Steam TunnelRoute
Steam Gen
PCE Standard Repeatability
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• Calculated from first principles
→ No calibration!
• Measured value closely matchesactual value (97.5 ppb)
• Dropouts from liquid nitrogenrefilling
• 1σ precision = 2.9 ppb (19.81 µg/m3)
Breathing Zone:Measured Spectra
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• Recorded sample spectrum every 20 min avg. (each line is a measurement)
• Narrow vertical lines are H2O
• iCRDS accommodates unexpected species
• E.g., characteristic absorption from Freon-152a
Steam Tunnel:Measured Spectra
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• PCE, TCE and cis-1,2-DCE increase visibly when remediation is turned off (8/10)
• TCE & PCE decrease when remediation turned on
• Buildup time constant is about 14 hrs
• Can immediately evaluate remediation efficacy!
ON
OFF
Quantitative PCE and TCE
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• Levels are low with remediation on
• Tunnel air shows consistently higher concentrations
• Huge increase in tunnel concentration with remediation off
• Results match TO-15 measured values (esp. for TCE)
(b) TCE(a) PCE
Practical Implications
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• High resolution site mapping
• Data immediately available
• On site decision making – rapid in, rapid out
• Mobile monitoring
• Minimizes sample handling artifacts
• Potential for measuring reactive species(e.g., acrolein)
• Reduced cost of sampling
Next Steps
20
Improved sensitivity
• Optical configuration
• Data processing
• Thermal stability
• Preconcentration
Non-cryogenic detector
• Stirling cooled
• Thermo-electrically cooled
Reduced instrument size
• Improved cavity mirrors
ே
ୀଵ
Spectral acquisition
• Rapid laser scanning
• Improved laser stability
Conclusions
21
MIR spectra uniquely identify pollutants inambient air
iCRDS provides sensitivity at the low ppb level
Successfully measured TCE & PCE at MoffettField
Continuous and autonomous for 1 week
iCRDS results agree with TO-15
Observed site remediation dynamics
Doug BaerManish GuptaRobert ProvencalFeng DongElena BermanTom OwanoJim Liem
Acknowledgments
Funding Agencies: DOE, DOD, EPA, NASA, CARB, NIH
Joe HsuCristina Vasquez-Guillamet
Russell DickersonJeffrey W. StehrPatricia CastellanosWinston T. Luke PaulKelleySheryl H. EhrmanLacey Brent
22
Marc FisherKen Reichl
Xiao-Ying YuCeline KluzekJohn Hubbe
Alana LeeJoe LukasDaniel MendollaGreg Nagle
Heather Henry
Supplemental Material
23
CompoundLOD (3s)
[ppb]Measured Office Levels†
[ppb]
Acetone 0.60 21.8
Benzene 3 0.3 – 18.9
Formaldehyde 4 25.8 – 52.5
Methanol 0.3 ND
Toluene 7 2.6 – 76.9
Acrolein 0.5 ND
Styrene 0.75 0.4 – 18.4
Trimethyl Benzene 5 0.4 – 8.51
m-Xylene 3 3.2 – 75
o-Xylene 3.6 0.7 – 15.5
Trichloroethylene 0.14 0.02 – 23.7
Tetrachloroethylene 0.11 0.1 – 67.8
Simulated Sensitivity Analysis:VOCs in Office Air
†L. C. Holcomb, et al., "Review : Indoor Concentrations of Volatile Organic Compounds: Implications for Comfort, Health andRegulation," Indoor and Built Environment 4, 7-26 (1995). 24
Lab Precision
25
TCE Repeated MeasurementsPCE Repeated Measurements
Minimum DetectableConcentration
26
PCE MDC TCE MDC
Previous Measurements (ppb)
27
Sample Location Sample Type
TCE
(ppb)
PCE
(ppb)
cis-1,2-DCE
(ppb) 1,1-DCA (ppb) 1,1-DCE (ppb)
manhole Pathway - Grab 74 44 20 2.2 1.5
manhole-concrete Pathway - Grab 185 132 50 5 2.5
In B10 near electrical panel Pathway 129 29 25 2.5 2.2
In B10 near offices Pathway 203 117 50 5 5
In B10 beneath floor Pathway 6 3 1.5 ND ND
on table in center of B10 Indoor - 24 hr 9 4 2 ND ND
Previous TO-15 measured values (Feb, 2012)
BZ
Remediation suction
Steam TunnelRoute
Steam Gen
Cost Estimates
28
Cost Category Portable GC/MS iCRDSPurchase $75,000 – 175,3751, 2 $45,000 – 110,000Daily Operation $200 – 2502,3 $4 – 10*Personnel (per day) $380 – 540† $0‡ – 230Per Sample Cost - -Total 1st Year $214,200 – 364,975 $45,960 – 165,210
* Includes pump rebuild, electricity, periodic calibration gas, and drying agents ($1-2k/year)† Loaded labor for skilled technician (e.g., BS in Chemistry)‡ Assumes a one in 10 day visitation for data transfer. This may be performed remotely by researches.
(1) C. M. Harris, "Product Review: GC To Go," Analytical Chemistry 74, 585 A-589 A (2002).(2) USEPA, “ENVIRONMENTAL TECHNOLOGY VERIFICATION PROGRAM: FIELD-PORTABLE GC/MS” (Washington, D.C., 1998).(3) USEPA, “Innovations in Site Characterization: Technology Evaluation: Real-Time VOC Analysis Using a Field Portable GC/MS”, Aug 2001.