BRIAN J. DROUIN, VIVIENNE PAYNE, FABIANO OYAFUSO, KEEYOON SUNG, Jet Propulsion Laboratory,...

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◦ Compared measurement to Liebe’s unpublished value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