1. APPLICATIONS OF HIGH RESOLUTION MID-INFRARED SPECTROSCOPY FOR ATMOSPHERIC AND ENVIRONMENTAL MEASUREMENTS
Rob Roscioli, Barry McManus, David Nelson, Mark Zahniser, Scott Herndon, Joanne Shorter, Tara Yacovitch, Dylan Jervis, Christoph Dyroff, Charles Kolb
Aerodyne Research, Inc.
Billerica, MA

2. Overview Gas detection using direct absorption spectroscopy
3 principal technologies
Light Source
Path Length
Detection
Implementation into portable spectrometer
Field applications
HNO3 measurements at BAO Tower
Quantification of Aliso Canyon methane leak using tracer ratio
O2 measurements at Cupp & Cupp Greenhouse

3. Measurement Approach 𝐼 𝜈 = 𝐼 0 𝑒 −𝑛𝑆𝐿Φ(𝜈− 𝜈 0 )
𝒏: density of molecules
𝑺: line-strength (intrinsic property of molecule)
𝑳: optical path length
𝚽 𝝂− 𝝂 𝟎 : absorption line-shape
𝝂 𝟎 : molecular transition frequency
Light (I)
Frequency (n)
We measure the absorption area: 𝐴𝑟𝑒𝑎=𝑛𝑆𝐿→ 𝑛=𝐴𝑟𝑒𝑎/𝑆𝐿
𝐼 𝜈 = 𝐼 0 𝑒 −𝑛𝑆𝐿Φ(𝜈− 𝜈 0 )
3 Principal Technologies: DETECTION PATH LENGTH LIGHT SOURCE

4. 3 principal technologies – Light Source
Pb-salt diodes
Tunable diodes
Quantum Cascade
Interband Cascade
Laser Components
Norcada
Alpes
nanoplus
Wavelength 3-20 mm – 6 mm mm mm
Power mW mW mW mW
Current mA mA mA mA
Temperature < 100 K – 30 °C – 0 °C 0 – 30 °C
Cooling Liquid N2 TE TE TE
Resolution <30 MHz <30 MHz <30 MHz <30 MHz

5. 3 principal technologies – Path Length
200 m
simulated
observed
m path length
Astigmatic Herriot cell
Mirror reflectivity 99.2% % ( % throughput)
Need particulate protection
McManus et al, Appl. Optics, 50, A74

6. 3 principal technologies – Detection
More light from QCLs, TDLs and ICLs → less need for high sensitivity detectors
Teledyne Judson Technologies
InAs (3-6 mm) (TE4)
HgCdTe (3-12 mm) (TE4)
InSb (3-6 mm) (LN2)
HgCdTe (3-12 mm) (LN2)
Infrared Associates

7. Implementation 1 ppt = 3.2 x 104 molecules/cm3/Torr Trace gas
Wavenumber
Precision
LOD
[cm-1]
(1 s) [ppt]
(100 s) [ppt]
CH4
1271
200 -- CO
2190 20 10
N2O 60
2250 30
NH3
967
NO2
1600 5
HONO
1279
150 80
HCHO
1765 50
HCOOH
1766 40 NO
1900
C2H6
2990
C2H2
1350
100
C2H4
970
OCS
2056 2 1
HNO3
1722 8
SO2
1 ppt = 3.2 x 104 molecules/cm3/Torr

8. HNO3 Fluxes at BAO tower - Sensitivity
BAO tower Erie, CO
HNO3 O3
VOCs (HC-GC)
NO, NO2, NOy
PAN (GC-ECD)
CO, CO2, CH4
H2O
SO2
MOPS
Eddy covariance method:
Fast, precise mixing ratios
Fast wind measurement
Correlate vertical wind fluctuations with rapid [HNO3] fluctuations
10 Hz wind
8 m inlet

9. HNO3 Fluxes at BAO tower - Sensitivity
High Sensitivity
Fast Time Response
t75 = 0.55 s
t90 = 0.96 s
HNO3 (ppb)
Time
1s: 35 ppt 100s: 8 ppt

10. HNO3 Fluxes at BAO tower - Sensitivity
Fluxes over the course of a day
Sun comes up
H2O Flux
Water evaporates from ground
Heat Flux
Ground warms up
HNO3 deposits onto ground
HNO3 flux

11. Mobile Sampling – Tracer Release
C2H2
CH4
N2O CO
CO2
𝒍𝒆𝒂𝒌 𝒓𝒂𝒕𝒆 𝑪𝑯 𝟒 = [𝐶𝐻 4 ] [𝑡𝑟𝑎𝑐𝑒𝑟] × 𝑓𝑙𝑜𝑤 𝑡𝑟𝑎𝑐𝑒𝑟
Tracer N2O
Tracer C2H2
CH4
Tracer release: model-less means by which to quantify unknown emission rates
Use sensitive trace gas detection to measure < 10 SLPM leak rates >1 km from leak source

12. Mobile Sampling – Aliso Canyon CH4 Leak
103 kg/hr
CH4
N2O
kg/hr
- CH4 emission rates of ~20 tons/hr
- Well kill → dramatic drop in leak rate

13. Conclusions Acknowledgements
Technological advances in high-resolution mid-IR spectroscopy
- Light sources: Thermoelectrically-cooled TDL’s, QCL’s, ICL’s
- Absorption cells: up to 400 m path lengths in 50 cm package
- Detectors: Thermoelectrically-cooled InAs, HgCdTe detection
Field applications
- HNO3 flux measurement in CO
- CH4 emission rate measurement at Aliso Canyon leak
Acknowledgements
Scott Herndon Emily Fischer
Mark Zahniser Ilana Pollack
David Nelson Jake Zaragoza
Tara Yacovitch
Cody Floerchinger
Conner Daube

15. O2 measurement - Precision
O2 transition at 760 nm
O2 precision of 3.3 per meg at 15 min

16. O2 measurement - Precision
respiration
photosynthesis

17. Implementation Mirror to aim at cell hole Mirror to aim at detector
IR Detector
Red Trace
Laser
76 m Multi-pass Cell
15X
QC Laser
Housing
Flip-in
Ref. Cell
Flip-in
Etalon
15X, X-Y-Z
Adjust
Pressure
Sensor
Mirror to aim
cell pattern size
Pinhole