2012 Canadian Contribution. qos. The poster Was based on the detection of the first ozone hole in the Arctic

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1 2012 Canadian Contribution qos The poster Was based on the detection of the first ozone hole in the Arctic 1

2 Remote Sounding of Atmospheric Composition; Discovery and Depletion of O 3 C.Tom McElroy, York University

3 Topics for Today s Lecture Character of light and its measurement Light absorption and scattering The solar spectrum Ozone measurement Solar occultation measurement the atmosphere from space Further reading July 15-19, 2013 U of T CREATE Summer Program 3

4 Light Property Common Term Units Spectral Intensity Photons/m 2 /s/nm Irradiance Spectral Surface Photons/m 2 /s/sr/nm Radiance Brightness Photon h v m s sr nm Packet of light of energy hv Planck s constant 6.626e-034 J-s Light frequency in Hz Metre Second Steradian (solid angle) Nanometre (10-9 metre) July 15-19, 2013 U of T CREATE Summer Program 4

5 Spectral Irradiance Area = A Photons(λ) / s = Spectral Irradiance(λ) * A Photons / s = Irradiance(λ) * A dλ July 15-19, 2013 U of T CREATE Summer Program 5

6 Spectral Radiance Area = a Area = A Area = A Spectral radiance == S S(λ) - Photons/m 2 /s/sr/nm Photons/s = S(λ) * a * A / r 2 Solid angle subtended by source = A / r 2 And by the detector = a / r 2 r July 15-19, 2013 U of T CREATE Summer Program 6

7 Radiative Transfer in the Atmosphere I(λ,s) Light from all other directions I(λ, s+ds) = - absorption + thermal emission + resonant scattering + Raman scattering + Rayleigh scattering + aerosol scattering I(λ, s+ds) July 15-19, 2013 U of T CREATE Summer Program 7

8 Beer s Law Beer's Law [note the changes from the handout] I (e.g.: Photons / s / m 2 ) I - di di(λ) = I(λ) σ(λ) ρ ds == I(λ) dτ di/i = - dτ Integrated: I = I o e -τ Or log( I ) = log( I o ) - τ Where I o is incident intensity Cross-section [m 2 ] σ cross-section [m 2 ] ρ number density [m -3 ] ds differential length [m] Τ optical depth July 15-19, 2013 U of T CREATE Summer Program 8

9 Other Form The optical depth, τ = σ(λ) ρ s Can also be written as τ = α (λ) X With α (λ) = σ(λ) * L [m -1 ] [m 2 /molec * molec/m 3 ] And X = ρ s / L [m] [molec/m 3 * m / (molec/m 3) ] L = 2.687e+025 molec/m 3 (Loschmidt s number) σ cross-section [m -2 ] α absorption coefficient [m -1 ] ρ s column amount or surface density [molec/m 2 ] X column amount [m] or [DU] Dobson units I(λ) = I o (λ) exp[-τ(λ)] July 15-19, 2013 U of T CREATE Summer Program 9

10 Ozone Absorption Ozone was identified in the atmosphere by Schonbein in 1867 Harley showed that the spectrum of ozone matched the missing light in 1881 Irradiance [W m -2 nm -1 ] Black curve is the solar spectrum 6,000 K 5,500 K Blackbody Radiation Planck's Law The violet curve is the solar spectrum with ozone absorption 5,000 K Sydney Chapman explained the existence of the ozone layer in 1930 Missing UV DU of Ozone 4,000 K Wavelength [nm] July 15-19, 2013 U of T CREATE Summer Program 10

Systematic Total Ozone Measurements Developed the Féry

some basic features of the ozone layer Developed the

11 Systematic Total Ozone Measurements Developed the Féry Spectrometer For a small European network (1926) Deduced some basic features of the ozone layer Developed the Dobson Spectrophotometer (1931) A Canadian Dobson in pieces! There are about 100 around the world still in operation. Gordon M.B. Dobson July 15-19, 2013 U of T CREATE Summer Program 11

12 Edward Hunter Gowan Married Elsie Park Young, a playwright, in Rhodes Scholar from U.Alberta Exeter College Early Canadian ozone research Suppl. Q. J. Roy. Meteor. Soc., 1936 July 15-19, 2013 U of T CREATE Summer Program 12

13 N c -1 Τ c (λ) = Σα c (λ)x c m C = 0 Optical Depth - Equivalent α c (λ) is the absorption coefficient [m -1 ] for component c at wavelength λ X c column amount of absorber [m] m airmass factor Conventional use has α c == β for attenuation by Rayleigh scattering Sun 1 m Sun Spectrometer July 15-19, 2013 U of T CREATE Summer Program 13

14 θ Slant path at 22 km;, m Μ = sec θ and sec( ) θ h R sin θ sin θ = R R + h With refraction (index of refraction n) N (R+h) sin θ = constant along the ray θ sec θ μ (12.6) m (35) () with refraction Brewer Approximation: airmass = 1/cos[ sin -1 (R/R+h)sin(θ)] July 15-19, 2013 U of T CREATE Summer Program 14

15 Chapman Function Assume a constant mixing ratio in a constant scale height atmosphere: ρ(z) = ρ o exp[-(z-z o )/H] where ρ o H ρ(z) density at height z o scale height (e-folding distance) density at height z Concentration of absorber c with mixing ratio m c will be: ρ c (z) = m c ρ o exp[-(z-z o )/H] (mixing ratio being the ratio of the constituent being considered to the total density of air) July 15-19, 2013 U of T CREATE Summer Program 15

16 Brewer Wavelengths λ[nm] σ[cm -1 ] Order of magnitude change in cross-section in 13.7 nm 306 3x x nm July 15-19, 2013 U of T CREATE Summer Program 16

17 Differential Measurements At Short and Long Wavelengths Sun Sun I(λ s ) = I o (λ s ) exp[-τ(λ s )] 1 m µ Spectrometer (e.g.: Dobson or Brewer) July 15-19, 2013 U of T CREATE Summer Program 17

18 Differential Measurements At Short and Long Wavelengths Sun Sun I(λ s ) = I o (λ s ) exp[-τ(λ s )] I(λ l ) = I o (λ l ) exp[-τ(λ l )] 1 m µ τ = α X µ Θ Spectrometer July 15-19, 2013 (e.g.: Dobson or Brewer) U of T CREATE Summer Program 18

19 Differential Measurements At Short and Long Wavelengths Sun Sun I(λ s ) = I o (λ s ) exp[-τ(λ s )] I(λ l ) = I o (λ l ) exp[-τ(λ l )] τ = α X µ log[i(λ s )/ I(λ l )] = 1 m µ Θ Spectrometer log[i o (λ s ) / I o (λ l )] [α(λ s ) - α(λ l )] X µ July 15-19, 2013 (e.g.: Dobson or Brewer) U of T CREATE Summer Program 19

20 Differential Measurements At Short and Long Wavelengths I(λ s ) = I o (λ s ) exp[-τ(λ s )] I(λ l ) = I o (λ l ) exp[-τ(λ l )] τ = α X µ log[i(λ s )/ I(λ l )] = Sun 1 m µ Θ Spectrometer log[i o (λ s ) / I o (λ l )] [α(λ s ) - α(λ l )] X µ or F = F o ΔαX µ with F == log[i(λ s )/ I(λ l )] Sun July 15-19, 2013 (e.g.: Dobson or Brewer) U of T CREATE Summer Program 20

21 Differential Measurements At Short and Long Wavelengths Sun Sun I(λ s ) = I o (λ s ) exp[-τ(λ s )] I(λ l ) = I o (λ l ) exp[-τ(λ l )] τ = α X µ log[i(λ s )/ I(λ l )] = 1 m µ Spectrometer (e.g.: Dobson or Brewer) July 15-19, 2013 U of T CREATE Summer Program 21 Θ log[i o (λ s ) / I o (λ l )] [α(λ s ) - α(λ l )] X µ or F = F o ΔαX µ with F == log[i(λ s )/ I(λ l )] µ == 1.0 / cos(θ) (or a more accurate value) Δα = α(λ s ) - α(λ l )

22 log I 0 Langley plot Short and Long Long Method Previous slide: F = F o ΔαX µ log I 0 (given) Methods Short Method Log I µ { } µ Intercept = F o = log[ I os / I ol ] Slope = Δα µ X = Ozone = Slope / Δα Ozone = (F F o ) / ΔαX µ In practice, both methods applied to single-wavelength measurements give large uncertainties due to sources of attenuation other than air and ozone. The uncertainties can be greatly reduced by using ratios of measurements at two or more wavelengths instead measurements at any single wavelength. July 15-19, 2013 U of T CREATE Summer Program 22

23 Dobson Spectrophotometer #77 July 15-19, 2013 U of T CREATE Summer Program 23

24 Dobson Optics July 15-19, 2013 U of T CREATE Summer Program 24

25 Brewer Optics Micrometer ~ 15 cm Chopper motor Grating angle adjusting lever arm To Photomultiplier Housing Five fixed exit slits Crossed spring rotation bearing Entrance Slit Stepper motor July 15-19, 2013 U of T CREATE Summer Program 25

26 Brewer Ozone Spectrophotometer A Triad of Instruments on the roof in Downsview are the world network reference July 15-19, 2013 U of T CREATE Summer Program 26

27 The Double Brewer Designed in 1992 July 15-19, 2013 U of T CREATE Summer Program 27

28 Solar Occultation Geometry ACE Solar Spectra Vertical Profiles Atmosphere X Tangent Point Sun Earth July 15-19, 2013 U of T CREATE Summer Program 28

29 Occultation Geometry Re Earth Radius For a 1 km thick layer at height h: Tangent ray = sqrt[ (R e +h+1.0) 2 (R e +h) 2 ] For h = 22 this is 113 km for half the tangent and 226 for the full tangent ray. The layer above has only a 47 km path. July 15-19, 2013 U of T CREATE Summer Program 29

30 Assembly at the ACE Payload at David Florida Laboratories in Ottawa Instruments: ACE-FTS MAESTRO ACE [Atmospheric Chemistry Experiment] PI: Peter Bernath University of Waterloo Funded by the Canadian Space Agency ACE Satellite Launched August 2003 Still working July 15-19, 2013 U of T CREATE Summer Program 30

31 Where do we go from here? UV Vis spectroscopy Spectral fitting Differential spectroscopy (Tomorrow) July 15-19, 2013 U of T CREATE Summer Program 31

32 UVS Target Species O 3 NO 2 BrO OClO O 4 H 2 O HCHO CHOCHO Aerosol optical depth Cross-sections [cm 2 ] 1.0E E E E E E E E E E-25 OClO SO 2 BrO CHOCHO O 3 HCHO O 4 NO 2 H 2 O nm Wavelength [280 to 650 nm] 650 nm July 15-19, 2013 U of T CREATE Summer Program 32

33 Some References DeLuisi, J.J., D.U. Longenecker, C.L. Mateer, and D.J. Wuebbles, An analysis of northern middle-latitude Umkehr measurements corrected for stratospheric aerosols for , J. Geophys. Res., 94, , Kerr, J.B., C.T. McElroy, D.I. Wardle, R.A. Olafson, and W.F.J. Evans, The automated Brewer spectrophotometer, Proc. Quad. Int'l Ozone Symp., Halkidiki, Greece, Reidel, , Kerr, J.B., and C.T. McElroy, Total ozone measurements made with the Brewer Ozone Spectrophotometer during STOIC 1989, J. Geophys. Res., 100, , Margitan, J.J., RA. Barnes, G.B. Brothers, J. Butler, J. Burris, B.J. Connor, R.A. Ferrare, J.B. Kerr, W.D. Komyhr, M.P. McCormick, I.S. McDermid, C.T. McElroy, T.J. McGee, A.J. Miller, M. Owens, A.D. Parrish, C.L. Parsons, A.L. Torres, J.J. Tsou, T.D. Walsh, and D. Whiteman, Stratospheric ozone intercomparison campaign (STOIC) 1989: Overview, J. Geophys. Res., 100, , Mateer, C.L., J.J. Deluisi, and C.C. Porco, The short Umkehr method, part I: Standard ozone profiles for use in the estimation of ozone profiles by the inversion of short Umkehr observations, NOAA Tech. Memo. ERL ARL-86, 20 pp., NOAA Air Resources Laboratories, Silver Springs, MD, Mateer, C.L., and H.U. Dutsch, Uniform evaluation of Umkehr observations from the World Ozone Network. Part 1, NCAR, Boulder Colorado, 105 pp., Mateer, C.L., and J.J. Deluisi, The estimation of the vertical distribution of ozone by the short Umkehr method, Proc. Quad. Ozone Symp., 1, Boulder, Colorado, 64-73, Mateer, C.L., and J.J. Deluisi, A new Umkehr inversion algorithm, J. Atmos. and terr. Phys., 54, , McElroy C.T., E.W. Hare, and J.B. Kerr, Ozone trends estimated from Umkehr measurements made at Edmonton Alberta, Canada, in Ozone in the Troposphere and Stratosphere, Proc. Quad. Ozone Symp., Charlottesville VA, June, 1992, NASA Conf. Publ. 3266, , McElroy, C.T. and J.B. Kerr, Table Mountain Ozone Intercomparison: Brewer Spectrophotometer Umkehr Observations, J. Geophys. Res., 100, , McElroy, C.T., C.L. Mateer, J.B. Kerr, and D.I. Wardle, Umkehr observations made with the Brewer Ozone Spectrophotometer, in Proc. Quad. Ozone Symp., Gottingen, Federal Republic of Germany, Ed. R.D. Bojkov and P. Fabian, Deepak Publishing, , Rodgers, C.D., Retrieval of atmospheric temperature and composition from remote sounding measurements of thermal radiation, Rev. Geophys. and Space Phys., 95, , Rodgers, C.D., Characterization and error analysis of profiles retrieved from remote sounding measurements, J. Geophys. Res., 95, , July 15-19, 2013 U of T CREATE Summer Program 33

Funding for this work is provided by: The CSA/ABB/NSERC Industrial Research Chair in Atmospheric Remote sounding at York University CSA The Canadian Space Agency ABB Incorporated, Quebec City, Canada

34 Funding for this work is provided by: The CSA/ABB/NSERC Industrial Research Chair in Atmospheric Remote sounding at York University CSA The Canadian Space Agency ABB Incorporated, Quebec City, Canada ASC Agence spatiale canadienne Natural Sciences and Engineering Conseil de recherches en sciences Research Council of Canada naturelles et en génie du Canada Acknowledgement: David Barton, York University July 15-19, 2013 U of T CREATE Summer Program -34-

35 Thank you for your attention! McElroy with inukshuk At Eureka, Nunavut 80N Photo: P.F. Fogal, UofT My work is supported by the Canadian Space Agency, July 15-19, 2013 U of T CREATE Summer Program ABB, NSERC and York 35 Universit

A Calibration Procedure Which Accounts for Non-linearity in Singlemonochromator Brewer Ozone Spectrophotometer Measurements

Atmos. Meas. Tech. Discuss., https://doi.org/.194/amt-18-17 A Calibration Procedure Which Accounts for Non-linearity in Singlemonochromator Brewer Ozone Spectrophotometer Measurements Zahra Vaziri Zanjani