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◦ Compared measurement to Liebe’s unpublished value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