Transcript Mid-IR Absorption Cross

Mid-IR Absorption
Cross-Sections for
Acetone
PRESENTATION BY: RUQAYYAH F. ASKAR
Outline
Introduction
Experimental Procedure
Results and Conclusion
PNNL IR database
Introduction
Acetone: 𝐶3 𝐻6 𝑂
- Most of acetone released to the environment is of industrial origin.
- Acetone may pose a significant risk of oxygen depletion in aquatic systems
due to microbial consumption.
- Acetone has a short lifetime estimated to be between two and four weeks.
- Acetone budget is poorly constrained.
Experimental Procedure
Spectral region: 830 -1950 𝑐𝑚−1
Spectrometer: High Resolution
FTIR Spectrometer
To improve absorption pathlength: Multi-pass cell with
maximum optical path-length 19.3
m
[1]
Results and Conclusion
Spectra of mixtures of acetone with dry synthetic air were recorded at 0.015 𝑐𝑚−1 .
Spectra recorded at temperatures between 194 – 251 𝑘 𝑜 and atmospheric pressure.
Intensities were calibrated using three acetone spectra ( recorded at 278, 293, and
323 𝑘 𝑜 ) from PNNL infrared database.
New absorption cross-sections are combines with previous high resolution results ->
to create a more complete set appropriate for remote sensing.
These cross-sections will provide an accurate basis for atmospheric retrievals of
acetone in the mid-infrared spectral region.
Due to pressure sensitivity of acetone vapor pressure at low temperatures, the
amount of absorber in the path-length was relatively uncertain. So, the y-axes of
cross sections were calibrated using acetone spectra from the PNNL IR Database.
Results and Conclusion Continues
Spectral absorption cross sections,
with units 𝑐𝑚2 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒 −1 , were
calculated by the equation:
Normalization requirements:
[1]
Results and Conclusion Continues
Acetone
absorption
cross sections
at three
different
pressures to
show the
pressure
dependence of
the sharp
structure:
[1]
Results and Conclusion Continues
Other compounds for which absorption cross-sections were studied
by the same group with similar approach:
Acetonitrile (𝐶𝐻3 𝐶𝑁):
- Majority of emission arise from biomass burning
- High resolution cross-sections determined between 880 – 1700 𝑐𝑚−1
Methanol (𝐶𝐻3 𝑂𝐻):
- Highly toxic to humans, causing blindness and might lead to death.
- High resolution cross-sections determined in the 3.4 and 10 µm regions
[2]
Pacific Northwest National Lab. (PNNL)
Spectral coverage: 600 -6500 𝑐𝑚−1 which corresponds to 16.16 – 1.53 𝜇𝑚.
Composite spectra: based on Beer’s low fit of 5 or more burdens.
Temperature: many spectra apploed at 5, 25, and 50 𝐶 𝑜 .
All spectra include: full documentation and vapor pressure versus
temperature curves.
[2]
Pacific Northwest National Lab. (PNNL) Continues
Growing list: over 400 compounds
planned.
Database emphasis: reactive
compounds, industrial pollutants,
DOE fossil and nuclear fuel
remediation species.
Sources
[1] Jeremy Harrison, Neil Humpage, Nicholas Allen, Alison Waterfall, Peter Bernath, and John
Remedios, Journal of Quantitative Spectroscopy and Radiative Transfer 112 (2011) 457-564.
[2] Northwest Infrared, Vapor Phase infrared Spectral Library, www.pnl.gov, April 30, 2015.
[3]Steven Sharp, T. Johnson, R. Sams, P. Chu, G. Rhoderick, and P. Johnson, “Gas Phase
Databases for Quantitative infrared Spectroscopy”, Society for Applied Spectroscopy, V 58, 12
(2004).
[4]P.O.Wennberg, T. F. Hanisco, L. Jaegle, D. J. Jacob, E. J. Lanzendorf, et al, “Hydrogen radicals,
nitrogen radicals and the production of 𝑂3 in the upper tropodphere”, Science 279, 49 – 53
(1998).