1. ACE Spectroscopy for the Atmospheric Chemistry Experiment (ACE) Chris Boone, Kaley Walker, and Peter Bernath HITRAN Meeting June, 2010

2. ACE Atmospheric Chemistry Experiment  Satellite mission for remote sensing of the Earth’s atmosphere, with a primary focus on Arctic ozone  Developed by the Canadian Space Agency  Launched August 2003, science operations began February 2004  Operating well, no major problems yet.  Primary instrument ACE-FTS: 0.02 cm -1 resolution, 750-4400 cm -1, ~300:1 SNR.

3. ACE Line mixing (Voigt)  Rosenkranz first order line mixing (Voigt)  g V,LM is the Voigt function with line mixing, W(z) is the complex probability function, and Y is the line mixing parameter. In the absence of line mixing (Y = 0), only the K(x,y) term contributes to the line shape.

4. ACE Analytical expressions derived for L(x,y) using the Humlicek algorithm. A paper describing these expressions is about to be submitted to JQSRT.

5. ACE Line mixing (speed-dependent)  Some methane lines feature both line mixing and speed dependence.  Simple empirical extension of the first order Rosenkranz approximation for line mixing  Assume coupling coefficient Y has no speed dependence

6. ACE Line mixing plus speed- dependence (continued)

7. ACE For these lines, speed- dependence appears to be a stronger effect than line mixing. It is the opposite for other CH 4 lines in the vicinity.

8. ACE With CH 4 line mixing and speed-dependent Voigt parameters in place (derived from ACE-FTS spectra), we can now retrieve acetone from the ACE-FTS.

9. ACE Line shape benefits  Analytical, simple, and efficient. The most complicated is line mixing + SDV: requires real parts + imaginary parts of 2 Voigt-type functions.  Well-suited to line-by-line calculations. One extra parameter per line for speed-dependence (  2 ) and one extra parameter per line for line mixing (Y). Extra parameters for temperature dependences?  Not aiming for the truest physical model or the most accurate calculation approach. Aiming for “accurate enough:” a significant improvement over the Voigt function, improved fitting residuals, improved VMRs  Geared toward atmospheric VMR retrievals.

10. ACE H2OH2OH2OH2O  Obtained a set of 27 lab spectra from Manfred Birk at DLR (23 air-broadening), covering the range 1250-1750 cm -1.  Currently exclude 4 with poorer SNR but will include them in final analysis.  Awaiting a few higher-P measurements.  Analyzing spectra with a speed-dependent Voigt line shape, generating spectroscopic parameters.

11. ACE

12. Self-broadened spectra

13. ACE Temperature-dependent Pressure-shift

14. ACE Difficult Doublets  Pairs of closely spaced H 2 O lines (same isotopologue, nearly the same E’’, etc.) can often be difficult to fit  Something else going on. Including line mixing improves results, but far from perfect.

15. ACE H 2 O in ACE-FTS  Speed-dependent Voigt parameters derived from gas cell measurements improve fitting residuals in ACE-FTS, but problems remain.  Deficiencies in the forward model for H 2 O in the troposphere.  Forward model employs a 1-km altitude grid. H 2 O VMR can double over the span of 1 km in the troposphere.  Changing the forward model.

16. ACE Missing HNO 3 H 15 NO 3 HNO 3 O 2 continuum N 2 continuum Residual spectra full of missing HNO 3.

17. ACE CHF 3  Fluorine budget in the stratosphere is an important measure of anthropogenic activity (unlike Chlorine, few natural sources).  No spectroscopic data available for the molecule. Found a set of lab measurements with various problems.  Used low-resolution measurements from PNNL for absolute calibration, and then Geoff Toon generated a set of pseudo-lines for the molecule.

18. ACE

19. ACE-FTS window for CH 3 OH retrievals No CH 3 OH in this region in HITRAN

20. ACE Missing CH 3 Cl Red curve = CH 3 Cl calculated with HITRAN 2008 CH 3 Cl excluded from calculation Missing a lot of CH 3 Cl lines in HITRAN 2008. Looking at the program for this meeting, is this now fixed?

21. ACE Wish list: CH 3 OOH K.H. Becker et al, “Tunable diode laser measurements of CH 3 OOH cross-sections near 1320 cm-1”, Geophys Res Lett, 16, 1367-1370 (1989).

22. ACE 17 O 12 C 16 O Is the isotopic differentiation really this large, or are there problems with the intensities of the isotopologue 4 lines?

23. ACE 18 O 13 C 16 O

24. ACE Conclusions  Refining ACE-FTS line shape calculations to improve residuals (and thereby retrievals).  Continuing to search for weak absorbers.  Would especially like spectroscopy for the 3-micron region.  Generating spectroscopic parameters for H 2 O and CH 4 from lab spectra.