Photoacoustic Spectroscopy of the Oxygen A-band PAS Signal (mV/W) Wavenumber (cm-1) Elizabeth M. Lunny1, Thinh Q. Bui1, Caitlin K. Bray2, Priyanka Milinda Rupasinghe1, Brian J. Drouin3, Mitchio Okumura1 1 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 2 Department of Chemistry, Wesleyan University, Middletown, CT 3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

OCO-2 GOAL: to understand the nature, geographic distribution and temporal variability of CO2 sources and sinks through space-based remote sensing of atmospheric CO2 Equipped with 3 spectrometers to simultaneously measure reflected sunlight at: 0.76 μm-O2 A-band 1.61 μm-CO2 weak band 2.06 μm-CO2 strong band Measures CO2/O2 ratio to retrieve column integrated CO2 dry air mole fraction, χCO2 GOAL: 0.25% (1 ppm) precision in χCO2 ----- Meeting Notes (6/4/15 10:23) ----- line mixing, real oco spectrum, www.jpl.nasa.gov

Oxygen A-band Advantages Uniform, well-known mixing ratio Spectral isolation Triply forbidden by electric dipole selection rules Magnetic Dipole Allowed ΔJ=0,±1 b1Σg+ X3Σg- PAS Signal (mV/W) Wavenumber (cm-1)

OCO-2 Spectra O2 A-band (0.76 μm) CO2 weak band (1.61 μm) CO2 strong band (2.06 μm) Crisp, OCO-2’s first light spectra (2014)

A-band Residuals ABSCO telecon Sept 22, 2014 slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence ABSCO telecon Sept 22, 2014

A-band Residuals slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence Similarities in OCO-2 and GOSAT residuals suggest unsatisfactory spectroscopic model rather than instrumental errors ABSCO telecon Sept 22, 2014

Line Mixing and Collision Induced Absorption ----- Meeting Notes (6/4/15 10:23) ----- slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence Hartman, Boulet, Robert Collisional effects on molecular spectra (2008)

Line Mixing and Collision Induced Absorption Results from a transient dipole induced during collisions at sufficiently high gas densities broad weak absorption underlying the entire band ----- Meeting Notes (6/4/15 10:23) ----- slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence Hartman, Boulet, Robert Collisional effects on molecular spectra (2008) Long and Hodges, J. Geophys. Res., 111, D12309 (2012)

Multispectrum Fitting Approach Advantages Disadvantages FTS Capable of high pressures Relatively fast acquisition time Instrumental background PAS Large dynamic range Zero-background Difficulty in quantifying intensity axis Long acquisition times FS-CRDS Long optical pathlength Precise frequency axis Absolute intensities Limited dynamic range Increasing S/N ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges

Multispectrum Fitting Approach Advantages Disadvantages FTS Capable of high pressures Relatively fast acquisition time Instrumental background PAS Large dynamic range Zero-background Difficulty in quantifying intensity axis Long acquisition times FS-CRDS Long optical pathlength Precise frequency axis Absolute intensities Limited dynamic range Increasing S/N ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges Brian Drouin RF02

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges 1% to wavemeter, 99% to tapered amplifier Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges AOM for intensity modulation at acoustic frequency of the resonator Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges AOM for intensity modulation at acoustic frequency of the resonator Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges Non-radiative de-excitation Energy is released in translational modes Heat dissipation creates pressure wave Optical Excitation Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges Non-radiative de-excitation Energy is released in translational modes Heat dissipation creates pressure wave Optical Excitation Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

Photoacoustic Spectrometer ----- Meeting Notes (6/4/15 10:23) ----- add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges Microphone signal is detected by lock-in and normalized to transmitted power measurement Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, 064902 (2010)

PAS A-band spectra

PAS A-band spectra

PAS A-band spectra

PAS A-band spectra mention dicke narrowing ect. elaborate more on basics

Multispectrum Fits

Multispectrum Fits

Multispectrum Fits

Multispectrum Fits Line mixing

Multispectrum Fits

Multispectrum Fits Line mixing

Multispectrum Fits

Multispectrum Fits First order, nearest neighbor line mixing is not sufficient

Acknowledgements