ACE Spectroscopy for the Spectroscopy for the Atmospheric Chemistry Atmospheric Chemistry

Experiment (ACE)Experiment (ACE)

Chris Boone, Kaley Walker, and Peter Bernath

HITRAN MeetingJune, 2010

ACE

Atmospheric Chemistry Atmospheric Chemistry ExperimentExperiment

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.

ACE

Line mixing (Voigt)Line mixing (Voigt)

Rosenkranz first order line mixing (Voigt)

gV,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.

zWY1Re12ln

gD

LMV, i

D

L

D

o ln2y,ln2x

yxz

y)L(x,y)K(x,W(z)

i

i

dt

tz

ei t 2

W(z)

ACE

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

ACE

Line mixing (speed-Line mixing (speed-dependent)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

)}ω-ωT,(P, I*] Y-Re{[1γ

1ln2= g oSD

DSDLM, i

ACE

Line mixing plus speed-Line mixing plus speed-dependence (continued)dependence (continued)

)(erfce)(erfce I 2z

1z

SD

22

21 zz

2

2

)sign(2

1

12

222

2221

zz

i

z

22

2

22 2ln4

1and,,

2

3

DoL

m

kTo

oL

2v,

2

3

v

v)v(

2

2

2

ACE

For these lines, speed-dependence appears to be a stronger effect than line mixing. It is the opposite for other CH4 lines in the vicinity.

ACE

With CH4 line mixing and speed-dependent Voigt parameters in place (derived from ACE-FTS spectra), we can now retrieve acetone from the ACE-FTS.

ACE

Line shape benefitsLine 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.

ACE

HH22OO

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.

ACE

ACE

Self-broadened spectra

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Temperature-dependent Pressure-Temperature-dependent Pressure-shiftshift

ACE

Difficult DoubletsDifficult Doublets

Pairs of closely spaced H2O 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.

ACE

HH22O in ACE-FTSO 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 H2O in the troposphere.

Forward model employs a 1-km altitude grid. H2O VMR can double over the span of 1 km in the troposphere.

Changing the forward model.

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Missing HNOMissing HNO33

H15NO3 HNO3 HNO3 HNO3

O2 continuumN2 continuum

Residual spectrafull of missing HNO3.

ACE

CHFCHF33

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.

ACE

ACE

ACE-FTS window for CH3OH retrievals

No CH3OH in this region in HITRAN

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Missing CHMissing CH33ClCl

Red curve = CH3Cl calculated with HITRAN 2008

CH3Cl excluded from calculation

Missing a lot of CH3Cl lines in HITRAN 2008. Looking at the program for this meeting, is this now fixed?

ACE

Wish list: CHWish list: CH33OOHOOH

K.H. Becker et al, “Tunable diode laser measurements of CH3OOH cross-sections near 1320 cm-1”, Geophys Res Lett, 16, 1367-1370 (1989).

ACE

1717OO1212CC1616OO

50556065707580859095

100

0.0E+00 1.0E-04 2.0E-04 3.0E-04 4.0E-04 5.0E-04

Volume mixing ratio (ppv)

Alt

itu

de

(k

m)

CO2 iso 1

CO2 iso 4

50

60

70

80

90

100

0.E+00 1.E-04 2.E-04 3.E-04 4.E-04 5.E-04

Average VMR (ppv)

Alt

itu

de

(k

m)

CO2 iso 1

CO2 iso 4

50

55

60

65

70

75

80

85

90

95

100

0.95 1.00 1.05 1.10 1.15 1.20 1.25

CO2 iso 4 / CO2 iso 1

Alt

itu

de

(km

)Is the isotopic differentiation really this large, or are there problems with the intensities of the isotopologue 4 lines?

ACE

1818OO1313CC1616OO

45

50

55

60

65

70

75

80

0.0E+00 1.0E-04 2.0E-04 3.0E-04 4.0E-04 5.0E-04

Volume mixing ratio (ppv)

Alt

itu

de

(km

)

CO2 iso 1

CO2 iso 5 45

50

55

60

65

70

75

80

0.0E+00 1.0E-04 2.0E-04 3.0E-04 4.0E-04 5.0E-04

Average VMR (ppv)

Alt

itu

de

(km

)

CO2 iso 1

CO2 iso 5

45

55

65

75

0.95 1.00 1.05 1.10 1.15

CO2 iso 5 / CO2 iso 1

Alt

itu

de

(km

)

ACE

ConclusionsConclusions

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 H2O and CH4 from lab spectra.