Development of a Near-IR Cavity Enhanced Absorption Spectrometer for the detection of atmospheric...
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Development of a Near-IR Cavity Enhanced Absorption Spectrometer for the detection of atmospheric oxidation
products and amines
Nathan C. Eddingsaas
Breanna Jewell and Emily Thurnherr
Rochester Institute of Technology
69th International Symposium on Molecular SpectroscopyJune 17, 2014
Atmospheric oxidation
R'R
O O
O
R'R
O O
O
O
O O
R R'
ketonesAldehydesCarboxylic acidsR'
O
HO
O3
R
R' OH
R
R'
OHO2
R
R'
OH
OO
NO
NO2 h
O + O2 O3
R
R'
OH
O
HO2
Oxygenated species
HydroperoxidesAlcoholsCarbonylsCarboxylic acids
Depositionor CO/CO2
Aerosols
Atmospheric oxidation is complex leadingto many different products.
Important to isolate a single reactionpathway to understand the chemistry.
To date there are many unknowns aboutgas phase oxidation and particle formationand composition.
Studying atmospheric oxidation in the lab
Want to promote relevant reactions and minimize competing reactionEx. RO2 + HO2 not RO2 + RO2
Need to take kinetics and thermodynamics into accountR-OO bond has been shown to be labile.Peroxy radicals have lifetimes of up to 10s of seconds in the atmosphere.
Want to be able to detect a wide range of oxidation productsMany methods to detect alcohols, carbonyls, and carboxylic acidsMore difficult to detect hydroperoxides and amines.
Want a system with high sensitivity that can detect many oxidation productscontinuously and in real time.
Our plan is to use IR absorption spectroscopy.
Vibrational spectra of hydroxyethyl hydroperoxide
OO-HO-H
OO-H O-H
Fry, J. L.; et al. JPC A, 2006.
HOOOH
Fundamental bands First overtones
O-H stretch mid- vs near-IR
0.E+00
1.E-05
2.E-05
3.E-05
1375 1395 1415 1435
Abso
rban
ceWavelength (nm)
0.E+00
1.E-04
2.E-04
3.E-04
4.E-04
2650 2700 2750 2800 2850
Abso
rban
ce
Wavelength (nm)
Fundamental bands First overtones
ButanolButyric acidHydrogen peroxide
PNNL IR database
Better spectral separation of functional groups in the near-IR.Clean window for amines: 1510-1550 nm, terminal epoxides: ~1600 nm.Loss an order of magnitude of sensitivity using the first overtone (σ: 10-19 – 10-21 cm2 molecules-1). Need a highly-sensitive technique
IBBCEASIncoherent Broadband Cavity Enhanced Absorption Spectroscopy
Direct absorption technique.
Highly reflective mirrors: 99.9 – 99.998 % reflective giving path length in the 10s of km.
Has been implemented in the visible region with sensitivity of sub ppt.
IBBCEAS only recently been implemented in the near-IR, only with FT detection.
Simple to operate, robust, sensitive and selective.
CEAS setup
CEAS setup
Xe arc lamp
Optical cell
HeNe laser
To spec. via fiber optic
Atmosphericchamber
Pt catalyst
Air or N2
Purgegas
PurgegasTo
pump
Mirror Valve
Lens
¼” tubing
Light path
Gas pathFilter
Broadband dielectric mirrors
1350 1400 1450 1500 15500.999
0.9991
0.9992
0.9993
0.9994
0.9995
0.9996
0.9997
0.9998
0.9999
Wavelength (nm)
Refle
ctivi
tyExperimentally determined reflectivityPolynomial fit
Raw CEAS data
0.0E+00
1.5E+04
3.0E+04
4.5E+04
6.0E+04
1470 1500 1530 1560 1590
Inte
nsity
(au)
Wavelength (nm)
Reference
SignalDry airDiethylamine
CEAS detection of diethylamine
0.0E+00
3.0E-08
6.0E-08
9.0E-08
1490 1510 1530 1550 1570
Abso
rban
ce (c
m-1
)
Wavelength (nm)
PNNL (3.2 ppm)
IBBCEAS
Testing the sensitivity and detection limit
0.0E+00
3.0E-08
6.0E-08
9.0E-08
1500 1520 1540 1560
Abso
rban
ce (c
m-1
)
Wavelength (nm)
1.9 ppm
1.3 ppm
0.9 ppm
0.53 ppm
0.76 ppm
0.37 ppm
0.17 ppm
0.0E+00
1.0E-06
2.0E-06
3.0E-06
0 0.5 1 1.5 2
Inte
grat
ed a
bsor
banc
e
Concentration (ppm)
Have detected diisopropyl amine down to 50 ppb.Still working on improving the limits of detection of CEAS instrument.
Inference from water vaporCEAS spectrum of 2% Relative Humidity (~525 ppm water vapor)
0.0E+00
2.0E-06
4.0E-06
6.0E-06
8.0E-06
1350 1370 1390 1410 1430 1450
Abso
rban
ce (c
m-1
)
Wavelength (nm)
Linear response tested up to 30 % RH
Accounting for water vapor
Spectrum of 8 ppm ethanol and 8 ppm acetic acid from 500 L teflon bag.
Same sample passed through anPt catalyst at 350° C.
0.0E+00
1.0E-06
2.0E-06
3.0E-06
4.0E-06
1370 1400 1430 1460
Abso
rban
ce (c
m-1
)
Wavelength (nm)
0.0E+00
1.0E-06
2.0E-06
3.0E-06
4.0E-06
1370 1400 1430 1460Ab
sorb
ance
(cm
-1)
Wavelength (nm)
CEAS using Pt catalyst as reference
0.0E+00
3.0E-07
6.0E-07
9.0E-07
1.2E-06
1370 1400 1430 1460
Abso
rban
ce (c
m-1
)
Wavelength (nm)
CEAS using C-trap reference
Pt catalyst converts organic compounds into water vapor and carbon dioxide.As long as the water vapor does not result in nonlinear absorption, the absorption from water can be accounted for.
0.0E+00
3.0E-07
6.0E-07
9.0E-07
1.2E-06
1370 1400 1430 1460
Abso
rban
ce (c
m-1
)
Wavelength (nm)
8 ppm ethanol, 7 ppm acetic acid
Summary
Near-IR CEAS can be used to qualitatively and quantitatively detect the oxidized species of atmospheric oxidation.
Water vapor can be accounted for using a carbon trap.
Amines can be monitored in real time using near-IR CEAS.
Working on improving limits of detection.
At this time we are studying the overtone spectra of hydroperoxides.
Next will look at compounds with multiple functional groups.
Future plans include studying gas phase oxidation and determining the composition of semi-volatile fraction of aerosols using thermal desorption.
Acknowledgments
Undergraduates at RITBreanna JewellEmily Thurnherr
Funding:RIT School of Chemistry and Material ScienceRIT College of ScienceRIT Grant writers bootcamp