brian j. drouin, vivienne payne, fabiano oyafuso, keeyoon sung, jet propulsion laboratory,...
TRANSCRIPT
Water Broadening of Oxygen
BRIAN J. DROUIN, VIVIENNE PAYNE, FABIANO OYAFUSO, KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,
Pasadena, CA 91109; ELI MLAWER, Atmospheric and Environmental Research, 131 Hartwell Avenue,
Lexington, MA 02421.
O2 has a constant mixing ratio – it is used to measure◦ temperature ◦ pressure◦ air-mass
O2 absorption at 13100 cm-1
◦ Known as the ‘A’ band O2 absorption at 7900 cm-1
◦ Known as ‘d’ band O2 absorption at 2 cm-1 (60 GHz)
◦ Known as ‘fine structure’ band
Measuring the Atmosphere
Oxygen absorption cross-section Temperature dependent air-broadening
coefficients Instrument function (ratio this away) Air index of refraction Water content Continuum absorption Temperature dependent air-pressure shift
coefficients Temperature dependent water-pressure
broadening
What do we need to accuratelymeasure air mass?
OCO-2 plans to measure CO2 concentration to 1 ppm, for a 350 ppm signal, that requires airmass to be known to better than 0.3%.
Two mm-wave studies◦ Liebe RSI 1977◦ Setzer & Pickett 1977
One Raman study◦ Fanjoux 1996
One NIR (CRDS) study◦ Vess 2010
What is known about O2-H2O broadening?
Liebe 1977◦ Measurements of pressure dependence of
dispersion in the vicinity of 9+ transition at 65 GHz for several foreign broadeners
◦ Decided not to publish H2O broadening value Pickett 1977
◦ Measurements of pressure dependent lineshape of 1- transition at 118 GHz for several foreign broadeners
◦ Compared measurement to Liebe’s unpublished value
Early millimeter Work
Two mm-wave studies◦ Liebe RSI 1977◦ Setzer & Pickett 1977
One Raman study◦ Fanjoux 1996
One NIR (CRDS) study◦ Vess 2010
What is known about O2-H2O broadening?
Two mm-wave studies◦ Liebe RSI 1977◦ Setzer & Pickett 1977
One Raman study◦ Fanjoux 1996
One NIR (CRDS) study◦ Vess 2010
What is known about O2-H2O broadening?
Vess et al. measured water broadening directly for a few transitions A-band
Due to its small effect at room temperature and ambient water vapor pressures the measurements are noisy
Values are large compared with Fanjoux
A-band data
0 5 10 15 20 25 30 35 40
0.02
0.04
0.06
0.08
0.10
0.12
296 K (extropolated) 446 K (Fanjoux) 650 K (Fanjoux) 990 K (Fanjoux) 296 K (Vess) 296 K (Pickett)
H2O
- O
2 B
road
enin
g
Coe
ffici
ent (
cm-1/a
tm)
J '
In A-band◦ Repeat Vess’s work ◦ Perform FTS study
In Fine-structure band◦ Improve on Pickett and Liebe’s work
In rotational band◦ Test band variability
Choices for new measurement
Experimental Design
Spectrometer – Modulated microwave synthesizer, multiplier, detector and lock-in-amplifier
Gas Cell – metal-quartz conflat seals, z-cut quartz windows, Capacitance manometer, TE-cooled cold finger
Oxygen Broadening by Water
P
1 5 .0 0 0 0 0 0 0 0 1 G H zF M 1 6 .6 6 6 6 kH z
x4
X 0 .2 0 0 1 Y 0 .0 0 0 1S Y N C 1 6 .6 6 6 6 kH z
T
O 2 , H 2 O
Spectra Example
N = 9, J = 9 ← 10
0 0.5 1 1.5 2 2.5
-1
0
1
2
3
4
5
f(x) = − 0.0402634278375593 xR² = 0.96290578728481
f(x) = 2.08988809831739 xR² = 0.999897691978484
Water Pressure (Torr)D
iffere
nti
al Li
nesh
ap
e (
MH
z)
Results
Transitions in range50 – 1850 GHzAbsorption strengths from 10-26 to 10-27.5 cm-1/cm2
J, N range 1 - 25
The new data for the fine structure band extends over a broader range of J
The error bars are a few percent
It agrees best with Fanjoux
Compare with other datasets
0 5 10 15 20 25 30 35 40
0.02
0.04
0.06
0.08
0.10
0.12
296 K (extropolated) 446 K (Fanjoux) 650 K (Fanjoux) 990 K (Fanjoux) 296 K (Vess) 296 K (Pickett) 296 K (Drouin 2013)
H2O
- O
2 B
road
enin
g
Coe
ffici
ent (
cm-1/a
tm)
J '
Effective parameterization adopted from Long et al. fits experimental data well (black curve)
Numerical Comparisons I
O2-O2 inter-band comparison ranges from 0% to 6% back to 1% deviations
O2-H2O scaling ranges from 24% to 8%
Numerical Comparisons II
0 5 10 15 20 25 30 351.3
1.8
2.3
2.8O2-O2 Tretyakov
O2-O2 Long
O2-H2O this work
Long x 1.08
Tretyakov x 1.08
J'
Pre
ssure
Bro
adenin
g (
MH
z/T
orr
)
Effects on atmospheric data
%T
Water Broadening of oxygen is (just barely) relevant to the accurate retrieval of air-mass and volume mixing ratios
Values assumed for microwave radiometry were very close to new measurements
Values used for A-band retrievals should be very similar to microwave values, using the same values will be a reasonable assumption
Conclusions
OCO-2 ABSCO team Tim Crawford NASA - ACLAB
Acknowledgements