Near Infrared CO 2 Spectral Database Charles E. Miller, Linda R. Brown, and Robert A. Toth

1. Near Infrared CO2 Spectral Database Charles E. Miller, Linda R. Brown, and Robert A. Toth Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, California 91109 D. Chris Benner, V. Malathy Devi The College of William and Mary, Box 8795, Williamsburg, Virginia 23187-8795, U.S.A Acknowledgments The research at the Jet Propulsion Laboratory (JPL), California Institute of Technology, was performed under contract with National Aeronautics and Space Administration. We thank NASA’s Upper Atmosphere Research Program for support of the McMath-Pierce laboratory facility. CEM thanks NASA’s Tropospheric Chemistry and Atmospheric Composition programs for support. The material presented in this investigation is based upon work supported by the National Science Foundation under Grant No. ATM-0338475 to the College of William and Mary. The authors express sincere appreciation to M. Dulick of NOAO (National Optical Astronomy Observatory) for the assistance in obtaining the data. We also thank Gregory DiComo for assistance in setting up the multispectrum solution.

2. According to Herzberg… “The spectrum of carbon dioxide has been studied exhaustively by a large number of investigators.” The Spectrum of CO2 Below 1.25 m J. Opt. Soc. Am.43, 1037 (1953)

3. According to Herzberg… “The spectrum of carbon dioxide has been studied exhaustively by a large number of investigators.” The Spectrum of CO2 Below 1.25 m J. Opt. Soc. Am.43, 1037 (1953) Toth et al., JQSRT109, 906 (2008) Toth et al., J. Mol. Spectrosc. 246, 133 (2007) Malathy Devi et al., J. Mol. Spectrosc. 245, 52 (2007) Toth et al., J. Mol. Spectrosc. 243, 43 (2007) Malathy Devi et al., J. Mol. Spectrosc. 242, 90 (2007) Toth et al., J. Mol. Spectrosc. 239, 243 (2006) Toth et al., J. Mol. Spectrosc. 239, 221 (2006) Miller et al., CR Physique 6, 876 (2005) Miller et al., J. Mol. Spectrosc. 228, 329 (2004) Miller et al., J. Mol. Spectrosc. 228, 355 (2004)

4. Return global XCO2 data with 0.3% precision Miller et al., JGR 112, D10314 (2007)

5. Measured Spectra CO2 O2 CO CO O Column Abundance Path Dependent Ratio XCO2 Path Independent Mixing Ratio Remote Sensing of GHGs at the Sub-1% Level Challenges Spectroscopic Databases

6. How well can we retrieve CO2? - Circa 1990 • Wallace and Livingston’s seminal work on CO2 remote sensing [1990] with the Kitt Peak FTS revealed deficiencies in the CO2 spectral database • (HITRAN 1986). • Insufficient NIR Spectroscopic Reference Standard Accuracy • 1. Incomplete knowledge of spectrum • 2. Inadequate position knowledge • 3. Intensities known to 5 – 20% unc. • 4. Unvalidated air-widths • 5. No pressure shifts Wallace & Livingston, J. Geophys. Res. D 95, 9823 (1990)

7. Improved Solar Spectra Retrievals circa 2002 • Kitt Peak solar data reanalyzed • Improved retrieval algorithm • Improved HITRAN 2000 database • (HITRAN 1992 + CO2 DND list) • Results • Systematic residuals in spectra • +5.8% biasbetween observed and in situ column amounts • 0.5%precisionincolumn CO2 • "Remaining errors are dominated by deficiencies in the spectroscopic line lists" Yang et al., Geophys. Res. Lett. 29(10) GL014537 (2002)

8. Ideal 1:1 Line Uncorrected Washenfelder et al. (2006) Park Falls WI The TCCON Prototype • New data acquisition hardware and methodology (based around Bruker 125 HR) • Results • 0.1% XCO2 precision • Systematic residuals persist • +2.12% bias for 30013 • +2.40% bias for 30012 “Systematic differences attributed to known uncertainties in the CO2 line strengths and pressure broadened widths” Washenfelder et al., JGeophys. Res. 111 D22305 (2006)

9. CO2 Nomenclature Vib. Band Notation follows the HITRAN convention ABCDEwhere A = No. v1 quanta B = No. v2 quanta C = v2 vib ang mom D = No. v3 quanta E = 1 : normal E  1: Fermi res. Isotopomer Nomenclature: 16O12C16O  626 16O13C16O  636 16O12C18O  628 16O12C17O  627 16O13C18O  638 16O13C17O  637 18O12C18O  828 18O12C17O  827

10. Kitt Peak FTS used for lab studies

11. Improving Laboratory Accuracies Requires Precise Knowledge/Control of the Experimental State • Pristine new cells – no contamination • Temperature monitoring inside the cell • Isotopic enriched samples • Mass spectrometric standard samples • Stable spectrometer performance Four Temp Probes (PRT) going Inside the Cell Goal for Experimental Uncertainties: Pressure:0.01 Torr (if P > 10 Torr) Temperature: 0.1 K Path: 2 mm (0.1%) Composition: 0.05% SNR: >1000 Resolution: 0.011 cm-1 100% Trans:  0.1% 0% Trans:  0.1% Positions:  0.0001 cm-1 Intensity: 0.1% (Relative)

12. 1. Determining the Complete Spectrum Accurate CO2 remote sensing to 0.3% requires knowledge of all absorption features that contribute to the CO2 absorption spectrum at the level of approximately 0.1% of Imax Examination of the known NIR CO2 features on a LOG scale shows that transitions from many weaker bands contribute detectable absorption to the spectrum Completeness will be a critical requirement for the spectral database Simulations from HITRAN04 Linear Log

13. 1. Determining the Complete Spectrum 30013 16O12C16O = 626 30012 30014 30011 Miller & Brown, J. Mol. Spectrosc. 228, 329 (2004) Path = 97 m Pres = 2.06 Torr Temp= 294 K C2H2 in 2nd cell to calibrate line positions

14. Determining the Complete Spectrum: Characterize Isotopologue Transitions In natural CO2 16O12C18O < 0.4 % 18O12C18O < 0.0004 % Note: 628 has 2 x more lines than symmetric isotopologues (626, 828) due to different spin statistical weights. The 2ν3 band of 628 is allowed, but not for 626, 828. Note: These 828 bands are not in HITRAN 2004 626 2ν3 Toth et al., J. Mol. Spectrosc. 243, 43 (2007) 626: 15% 16O12C16O 628: 48% 16O12C18O 828: 33% 18O12C18O

15. Determining the Complete Spectrum: Characterize Isotopologue Transitions Toth et al., J. Mol. Spectrosc. 243, 43 (2007) 626 828 628 The region below 6920 cm-1 would be transparent in models neglecting 18O species Note: These 828 lines are not in HITRAN 2004 626: 15% 628: 48% 828: 37%

16. 2. Improved Line PositionsAbsolute Uncertainties < 0.0001 cm-1 s = 5x10-5 cm-1 Miller & Brown, J. Mol. Spectrosc. 228, 329 (2004) Line position differences of the experimentally measured line positions of Miller & Brown and Vander Auwera et al.

17. 3. Measured line intensities of 125 Bands Retrievals: Voigt line shape & line-by-line fitting of individual spectra % Differences between HITRAN 2004 and new band strengths Toth et al. J. Mol. Spectrosc. 239, 221 (2006) Reported 58 band strengths of626 Toth et al., J. Mol. Spectrosc. 243, 43 (2007) 21 bands of 628 8 bands of 627 25 bands of 828 626 628

18. Intensities for NIR CO2 bands from multiple laboratories agree at the sub-1% value A more accurate intercomparison requires specific line shape specification Speed dependence Line mixing 3. Measured line intensities of 125 Bands 626 Toth et al. J. Mol. Spectrosc. 239, 221 (2006)

19. 4. & 5. Self-broadened widths and pressure-shifts15 bands of 626 Fermi Triad and ν2+2ν3 4700 – 5400 cm-1 Fermi Tetrad and 3ν3 6000 – 7000 cm-1 (in cm-1/atm) Self- Widths Note vibrational dependence Toth et al., J. Mol. Spectrosc. 239, 243 (2006) Self- Shifts m = J" for P branch, J"+1 for R branch

20. 4. & 5. Air-broadened widths and pressure-shifts626 Fermi Triad and ν2+2ν3 4700 – 5400 cm-1 Fermi Tetrad and 3ν3 6000 – 7000 cm-1 (in cm-1/atm) Air Widths Note vibrational dependence Toth et al., J. Mol. Spectrosc. 246, 133 (2007) Air- Shifts m = J" for P branch, J"+1 for R branch

21. Validate lab results with atmospheric data Observed and calculated balloon-based FTS spectra JPL MkIV (G. Toon) 29 km Tangent Height Top trace: HITRAN 2004 Right trace: Current Best line list

22. Small Changes in Widths Affect Retrievals at High Airmass Test Line List B Test Line List A

23. Accuracy of ± 0.3% using new Voigt line list Precision ~0.1% [Washenfelder et al. 2006]

24. Active Remote Sensing of CO2 Requires Even Greater Line Shape Accuracy ASCENDS ASCOPE GOSAT-II P = 269.03 Torr L = 0.347 m T = 297.04K. Candidate transition: R(30) of 20013  00001 @ 2050.967 nm (4875.748 cm-1)

25. Fit all lines and spectra simultaneously Use quantum mechanical constraints for positions and intensities Increases sensitivity to subtle effects in line shapes Updated capabilities include non-Voigt line shapes, line mixing, speed dependence (Benner et al., in preparation) Improved Multispectrum Fitting[Benner et al., JQSRT 53, 705 (1995)] Line Positions: ni = n0 + B(J(J+1)) + D(J(J+1))2 + H(J(J+1))3 + … ni resonant frequency n0 band origin B, D, H rotational constants J rotational quantum number Line Shape Parameters: i = a1 + a2m + a3m2 +a4m3 + ….. Measured half-width at half-max at each line position Line Intensities: Si = (ni/n0)(Sv/Li) exp(-hcEi″/kT)[1-exp(hcvi/kT)].F Si, observed individual line intensity Sv vibrational band intensity, Li Hönl-London factor, where li= (m2-l″2)/|m| for CO2 m = J″+1 for the R branch, m = -J″ for the P branch J″ lower-state rotational quantum number. l angular momentum quantum number. Qr lower state rotational partition function at T0=296 K Ei″ lower state rotational energy F Herman-Wallis factor = [1+A1m+A2m2+A3m3]

26. Line Shape Problems!Line Mixing Occurs in CO2 P and R Branches Miller et al. Comptes Rendus Physique 6 (2005) 876-887.

27. Multispectral Fitting of the30012 Spectrum Malathy Devi et al. J. Mol. Spectrosc. 242, 90 (2007).

28. Line mixing observed at 6220 cm-1 even though this band has no Q-branch, no perturbations and adjacent lines are spaced by ~ 1 cm-1 CO2 Line Mixing Coefficients Off diagonal relaxation matrix Rosenkranz

29. Line Mixing & Speed Dependence Observed for Self- and Air-broadened Spectra

30. Accurate remote sensing of CO2 is critical for climate change science CO2 remote sensing poses a significant spectroscopic and algorithm challenge This is NOT YET a solved problem Consideration of strong 16O12C16O (626) transitions alone is insufficient Must include hot bands Must include 16O13C16O (636), 16O12C18O (628), etc Line shape choice is crucial to simulate high quality spectra within their experimental uncertainty Non-Voigt line shapes improve fits 30% - 50% vs Voigt fits Line Mixing is needed to remove systematic residuals Conclusions

31. Kitt Peak Co-Conspirators Chris Benner (W&M) Malathy Devi (LaRC) Not shown Linda Brown Bob Toth (JPL) Mike Dulick (KPNO) $$$ NASA, NSF

32. Backup

33. Grassi et al., Planet. Space Sci. 53, 1017 (2005) Measured & modeled PFS/Mars spectra PFS/Mars Express (2004) Isotopic Fractionation in Martian CO20.2% precision desired * * * *

34. 638 Unanticipated Behavior for High-J Transitions High-J transitions may show large (>10-4 cm-1), unexpected deviations from their predicted positions due to • Poor spectroscopic parameter extrapolations • Perturbations not observed at low-J Rare isotopologues and hot bands are especially susceptible to these problems since they are much more difficult to characterize accurately 636 This work – R92 Miller & Brown, J. Mol. Spectrosc. 228, 329 (2004) Miller et al., J. Mol. Spectrosc. 228, 355 (2004) 626

35. Uncharacterized High-J Perturbations May Lead to Gross Retrieval Errors Short scans of CO2 covering the perturbed R74, R76, R78 and R80 lines in the 20012-00001 band of 626. The calculated positions refer to unperturbed locations calculated from parameters derived from lower J transitions. Toth et al., J. Mol. Spectrosc. 239, 221 (2006)

36. Filling the 2 um Atmospheric Window (1/2) 13CO2 constitutes only ~1% of the natural CO2 Isotopic substitution shifts the band centers in the Fermi triad region such that the 13CO2 bands effectively fill the 2 um (5000 cm-1) atmospheric windows • Significant radiative impact under saturated absorption conditions The allowed 2v3 band of 638 (NEW) is seen in the 4300 – 4700 cm-1 window 626 CO C2H2 636 NEW CO C2H2