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

 O 2 has a constant mixing ratio – it is used to measure ◦ temperature ◦ pressure ◦ air-mass  O 2 absorption at cm -1 ◦ Known as the ‘A’ band  O 2 absorption at 7900 cm -1 ◦ Known as ‘  ’ band  O 2 absorption at 2 cm -1 (60 GHz) ◦ Known as ‘fine structure’ band

 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 OCO-2 plans to measure CO 2 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

 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 H 2 O 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dependent lineshape of 1 - transition at 118 GHz for several foreign broadeners ◦ Compared measurement to Liebe’s unpublished value

 Two mm-wave studies ◦ Liebe RSI 1977 ◦ Setzer & Pickett 1977  One Raman study ◦ Fanjoux 1996  One NIR (CRDS) study ◦ Vess 2010

 Two mm-wave studies ◦ Liebe RSI 1977 ◦ Setzer & Pickett 1977  One Raman study ◦ Fanjoux 1996  One NIR (CRDS) study ◦ Vess 2010

 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

 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

 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

N = 9, J = 9 ← 10 Water Pressure (Torr) Differential Lineshape (MHz)

Transitions in range 50 – 1850 GHz Absorption strengths from to cm -1 /cm 2 J, N range

 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

Effective parameterization adopted from Long et al. fits experimental data well (black curve)

 O 2 -O 2 inter-band comparison ranges from 0% to 6% back to 1% deviations  O 2 -H 2 O scaling ranges from 24% to 8%

%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

 OCO-2 ABSCO team  Tim Crawford  NASA - ACLAB