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