TEMPERATURE DEPENDENCES OF
AIR-BROADENING AND SHIFT
PARAMETERS IN THE ν3 BAND OF
OZONE
M. A. H. SMITH
NASA Langley Research Center, Hampton, VA 23681-2199 U.S.A.
V. MALATHY DEVI and D. CHRIS BENNER
The College of William and Mary, Williamsburg, VA 23187-8795 U.S.A.
RF08 – 70th International Symposium on Molecular Spectroscopy, June 22-26, 2015
Why do we need to know the temperature dependences
of spectroscopic line parameters?
Global Average Temperature Profile
Tropopause temperatures vary with latitude
and season, and are typically below
195 K in the tropics.
Change in retrieved atmospheric O3 mixing
ratio as a function of altitude for a 60%
increase in the assumed air-broadened
halfwidth [Smith and Gordley, 1983].
Uncertainties in spectroscopic line
parameters propagate into retrievals
of atmospheric ozone concentrations.
Air-broadened O3 line parameters and their temperature dependences (175–300 K)
in the 9.6 µm region are needed for quantitative analysis of spectroscopic
observations of Earth’s atmosphere, both to retrieve ozone abundances and to
model the O3 absorption overlapping features of other species.
 Previous lab T-dependence studies have involved mostly B-type bands:
Rotational [Larsen et al., 2001], ν1 [Smith et al., 1997] and ν2 [Malathy Devi et al., 1997].
 However, ν3 is A-type!
• One study of N2-broadening for 21 ν3 transitions (180-296K) [Spencer et al., 1992].
• Air-broadened widths and shifts for 9 ν3 R-branch transitions are included in the
[Smith et al., 1997] ν1 results (210-302K).
• [Wagner et al., 2002] reported polynomial representations for ν3 N2- and O2broadened widths and temperature dependences (200-298K), but no shifts.
Present Work: Analyze air-broadened O3
spectra recorded at 160-300K to
determine temperature dependences of
ν3 air-broadening and shift parameters
needed for atmospheric retrievals. ►
used for
calibration
T = 297 K, p = 110 torr, VMR = 0.4%, L = 50 cm
3
Lab Spectra Used for Ozone Fits in the ν3 Band
NO. OF
DATE
SAMPLE
SPECTRA
2
2
4
1
2
3
3
3
5
1
3
1
1
VMR
(%)
10-Nov-94 O3 + Air
10-Nov-94 O3 + Air
7-Feb-96 O3
29-Apr-97 O3
30-Apr-97 O3 + Air
1-May-97 O3 + Air
2-May-97 O3 + Air
4-May-97 O3 + Air
6-May-97 O3 + Air
21-May-98 O3
21-May-98 O3 + Air
22-May-98 O3 + Air
22-May-98 O3 + Air
4.7
3.6
81 - 90
30.3
0.6
0.5
0.4
0.3
0.3
13
1.5
1.9
1.9
TEMPERATURE PRESSURE
(K)
(TORR)
300
300
300
298
297
272
254
233
213
170
186
160
168
101, 204
76, 153
0.3 - 0.5
1.3
110, 201
101 - 220
107 - 216
104 - 220
86 - 201
2.2
94 - 193
203
134
PATH
BAND
RES.
(m)
PASS
(cm-1)
0.0998
0.0998
0.0998
0.500
0.500
0.500
0.500
0.500
0.500
0.095
0.095
0.095
0.095
2
2
2
2
2
1
1
1
1
1
1
2
2
0.0027
0.0027
0.0027
0.0052
0.0052
0.0052
0.0052
0.0052
0.0052
0.005
0.005
0.005
0.005
Band pass 1 = 500-1400 cm-1; Band pass 2 = 800-1400 cm-1
All spectra were recorded using the McMath-Pierce FTS with KCl beam splitter, 8 mm
aperture, and He-cooled As:Si detectors.
February 1996 spectra were used in the previous intensity study [Smith et al., 2001].
May 1998 spectra were recorded using a single detector.
4
Analysis
Nonlinear least squares multispectrum fitting [Benner et al., 1995] is
used to retrieve spectroscopic parameters consistent with the entire set
of laboratory spectra.
 Voigt line shape is assumed; line mixing is allowed for pairs of lines
expected to mix (no mixing observed in intervals fit to date).
 All spectra are calibrated to the same wavenumber scale with
reference to H2O ν2 line positions.
 Room-temperature spectra are fit first; then the lower-temperature
spectra are added sequentially down to 213 K.
 Noisy spectra from 186 to 160 K are added to the fit last with low
weights (poor Signal-to-Noise Ratio due to single detector).
5
Example Fit of Air- and Self-Broadened O3 Spectra
0.04
RESIDUAL
A total of 31 spectra were fit.
(Standard Deviation of this fit = 0.592%)
These 6 spectra were
selected to represent the
range of conditions.
0.02
0.00
-0.02
-0.04
1021.5
T
(Kelvin)
P
(torr)
L
(cm)
O3 VMR
(%)
702
300
0.475
9.98
85.5
613
300
75.5
9.98
3.3
794
233
220
50.0
0.3
815
213
165
50.0
0.3
857
160
202
9.50
1.6
858
170
134
9.50
1.6
Noisy spectra (e.g., 857 and 858)
were given lower weights in the fits.
1022.5
1.0
0.8
SIGNAL
Run
1022.0
0.6
0.4
Run 702
Run 613
Run 794
Run 815
Run 857
Run 858
0.2
0.0
1021.5
1022.0
WAVENUMBER (cm-1)
1022.5
6
Measured Line Widths and Shifts and Their Temperature
Dependences in A-type O3 bands
P-branch lines, J˝ = 15 – 26, Ka˝ = 0 – 11 (● ν3 [Present Work]; ■ ν3 N2-broadening [Spencer et al.,
1992]; □ 3ν3 air-broadening [Smith et al., 1994]).
R-branch lines, J˝ = 23 – 36, Ka˝ = 2 – 3, ∆Ka = 2 (○ ν3 air-broadening [Smith et al., 1997]).
7
Two ν3 transitions with three independent measurements
T range
Broadener (K)
HITRAN08/12
air
Spencer et al. (1992)
N2
Wagner et al. (2002)
air (N2, O2) 200 - 296
0.0758
0.721
Present Work
1021.8008 cm−1
(18,7,12 – 19,7,13)
air
0.0759(2)
0.660(10) −0.0017(1)
HITRAN08/12
air
0.0768
0.72
Spencer et al. (1992)
N2
Wagner et al. (2002)
air (N2, O2) 200 - 296
0.0768
0.716
Present Work
air
0.0778(2)
0.647(16) −0.0018(2)
Source
1021.6451 cm−1
(20,3,18 – 21,3,19)
180 - 296
160 - 300
180 - 296
160 - 300
Width
Width
Tdep
Shift
0.0758
0.72
−0.0007
Shift Tdep
0.0751(12) 0.68(6)
1.8(3)E-05
−0.0007
0.0755(14) 0.71(7)
1.8(5)E-05
Note: Units of Width and Shift are cm-1 atm-1 at 296K, units of Shift Tdep are cm-1 atm-1 K-1, and Width Tdep is unitless.
Values in parentheses are 1σ statistical errors in units of the last digit quoted.
8
Comparison with Other Fundamentals and Rotational Band
Measured values: ν3 from Present Work, ν2 from [Malathy Devi et al., 1997], ν1 from [Smith et
al., 1997] and Rotational from [Larsen et al., 2001].
Calculated values are from empirical formulas given by [Wagner et al., 2002] based on their N2and O2-broadening measurements at 200 – 298 K.
Remember that Rotational, ν1 and ν2 are B-type bands, while ν3 is A-type. Only the lower-state
rotational quantum numbers are the same for the transitions compared.
9
Measured ν3 air-broadening parameters vs. HITRAN
HITRAN O3 air-broadening and shift
parameters are the same in the last three
editions [Rothman et al., 2005, 2009, 2013].
◄ (Upper Left) Half widths.
◄ (Lower Left) Temperature dependence
exponents of the half widths.
▼ (Below) Pressure-induced line shifts.
10
Summary
Present ν3 results vs. HITRAN
•
•
•
•
Measured half widths are 3-5% larger than HITRAN values, especially for
transitions with Jʺ < 18.
Measured n values are up to 15-20% smaller than HITRAN values and have a
wider range.
Measured shift coefficients are mostly larger in magnitude than the constant
−0.0007 cm-1 atm-1 HITRAN default value for ν3.
Shift coefficients with the value 0.0000 are not acceptable (unless measured)!
Future Work
 Complete the analyses of the laboratory spectra in the entire ν3 band.
 Provide preliminary results for use in atmospheric retrievals and/or
comparison to calculated widths and shifts.
 Final results will be included in future spectroscopic database updates (e.g.,
HITRAN).
11
Acknowledgements
The research at NASA Langley Research Center, and the College of William
and Mary is supported by the Atmospheric Composition Laboratory Research
program of the National Aeronautics and Space Administration.
We thank Mike Dulick, Detrick Branston, Claude Plymate and the late Jeremy
Wagner of the National Solar Observatory for their assistance in recording the
spectra at Kitt Peak over many years. NSO is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA), under contract with the
National Science Foundation.
We especially thank Charles Solomon and Harry Walthall, now retired from the
NASA Langley glass shop, for their assistance in the design, construction and
testing of the 50 cm coolable cell and the 9.98 cm cell. We are grateful to the
late Dr. Charles Chackerian of NASA Ames Research Center for the loan of the
9.5 cm coolable cell.
12
References
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