University of Illinois Urbana-Champaign

High precision measurements of line mixing and collisional induced absorption in the O2 A-band

Adkins, Erin M.

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2369.pdf
869423.pptx

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https://hdl.handle.net/2142/97198

Description

Title
High precision measurements of line mixing and collisional induced absorption in the O2 A-band
Author(s)
Adkins, Erin M.
Contributor(s)
  • Hodges, Joseph T.
  • Long, David A.
  • Ghysels, Mélanie
Issue Date
2017-06-21
Keyword(s)
  • Lineshapes
  • Collisional effects
Date of Ingest
  • 2017-07-27T20:15:59Z
  • 2018-01-29T23:02:56Z
Abstract
Molecular oxygen (O$_{2}$) has a well-known and uniform molar fraction within the Earth’s atmosphere. Consequently, the O$_{2}$ A-band is commonly used in satellite and remote sensing measurements (GOSAT, OCO-2, TCCON) to determine the surface pressure-pathlength product for transmittance measurements that involve light propagation through the atmospheric column. For these missions, physics-based spectroscopic models and experimentally determined line-by-line parameters are used to predict the temperature- and pressure-dependence of the absorption cross-section as a function of wave number, pressure, temperature and water vapor concentration. At present, there remain airmass-dependent biases in retrievals of CO$_{2}$ which are linked to limitations in existing models of line mixing (LM) and collisional induced absorption (CIA) footnote{Long D.A and J.T. Hodges, textit{J. Geophys. Res.} 2012, 117: p. D12309.}. In order to better quantify these effects, we measured O$_{2}$ A-band spectra with a frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) system. Because of the high molar fraction of O$_{2}$ in air samples, line cores and near wings of the dominant absorption transitions are heavily saturated, which makes it impossible to obtain continuous FS-CRDS spectra over the entire range of optical depth. Here, we focused on LM and CIA effects which dominate the valleys between strongly absorbing transitions. To this end, the FS-CRDS system employs a thresholding mechanism that avoids the optically thick regions and scans over the entire O$_{2}$ A-band and beyond the band head region. This approach provides high signal-to-noise ratio spectra that can be fit to yield LM and CIA parameters. These results are intended to provide strong constraints on multispectrum fits of continuous and broadband Fourier-transform-spectroscopy based O$_{2}$ A-band spectra._x000d_
Publisher
International Symposium on Molecular Spectroscopy
Type of Resource
text
Genre of Resource
Conference Paper / Presentation
Language
eng
Permalink
http://hdl.handle.net/2142/97198
DOI
https://doi.org/10.15278/isms.2017.WJ10
Copyright and License Information
Copyright 2017 Erin M. Adkins

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Abstracts & Presentations - 2017 International Symposium on Molecular Spectroscopy PRIMARY