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Temperature dependent O3 absorption cross sections for satellite
spectrometers: new laboratory measurements
Anna Serdyuchenko, Victor Gorshelev, Wissam Chehade, Mark Weber, John P. Burrows
University of Bremen, Institute for Environmental Physics
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Atmospheric species detection:
- Satellite spectrometers- Available databases for the reference data
Challenges of cross-section measurements in laboratory:
- Modern demands on the O3 absorption cross-section quality;
- Experimental equipment;- Absolute calibration.
First results:
- Ozone spectra in UV and IR;- Comparison with existing datasets.
Agenda Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab
3
Long-term atmosphericgases detection
Satellite/airborne/ground spectrometers monitor:
Stratosphere: ozone chemistry, volcanic events, solar proton events
Troposphere: biomass burning, pollution, arctic haze, forest fires, dust storms, industrial plumes
Clouds, aerosols, UV index
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Detected: the solar radiation transmitted, backscattered and reflected from the Earth atmosphere and surface, also direct sun light
Absorption spectra cover: O3 O2 NO2 N2O BrO OClO SO2 H2CO2 CO CO2 CH4 H2O
GOME, GOME2 (Global Ozone Monitoring Experiment): scanning 4 channels grating spectrometer with nadir-view
SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography): scanning 8 channels grating spectrometer with nadir/limb-view
University Bremen, IUP, Molecular Spectroscopy Lab
Long-term time-series of O3 is important for air quality study, Montreal Protocol monitoring of ozone depleting substances, ozone-climate interaction etc
Long-term global data sets covering several decades are only available by combining datasets from multiple sensors (satellite spectrometers and ground based instruments: Brewer, Dobson spectrophotometers ).
At least two decades of observations with global coverage in several days
Spectrometer
Satellite Launch
GOME ERS-2 April 1995
SCIAMACHY ENVISAT March 2002
GOME-2 MetOp -A October 2006
MetOp - B ~ 2012
MetOp - C ~ 2016
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Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab
Long-term atmosphericgases detection
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Prior to launch cross-section measurements Absorption cross-sections can introduce an important error source
For GOME, SCIAMACHY, and GOME2 flight models were used to measure absorption cross-section prior to launch.
Advantage:
exact match of spectral resolution between satellite radiance and cross-sections;
Knowledge for instrumental slit function is not needed
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Spectrometer
Satellite Launch
Pre-launch O3 cross-sections
GOME ERS-2 April 1995 GOME FM (Burrows et al. 1999)
SCIAMACHY ENVISAT March 2002 SCIAMACHY FM (Bogumil et al. 2003)
GOME-2 MetOp -A October 2006 GOME2 FM3 (Gür et al., 2005)
MetOp - B ~ June 2012 GOME2 FM21 (Gür et al., 2005)
MetOp - C ~ 2016 -University Bremen, IUP, Molecular Spectroscopy Lab
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Current O3 datasets in use
Data set Temperatures, K Resolution, nm
Wavelength, nm
GOME FM Burrows et al., 1999
202 221 241 273 293 0.17 @ 330 nm 230 - 800
SCIAMACHY FM Bogumil et al., 2003
203 223 243 273 293 0.20 @ 330 nm 230 - 1070
GOME2 FM Spietz et al., 2005
203 223 243 273 293 0.29 @ 330nm 240 – 790
Paur and Bass, 1985
203 218 228 243 273 298
<0.025 nm(?) 245 - 345
Malicet et al. 1995 Brion et al., 1993Daumont et al., 1992
218 228 243 273 295 0.01-0.02 nm
195-345
UV-FTSVoigt et al., 2001
203 223 246 280 293 0.03 @ 230 nm 230 - 850
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
http:/http://www.iup.uni-bremen.de/gruppen/molspec/databases/index.html
University Bremen, IUP, Molecular Spectroscopy Lab
Inconsistency of satellite instruments cross-section
SCIAMACHY total O3 retrieved (with SCIAMACHY reference
spectra) are 5% higher than GOME (with GOME reference
spectra) in the range 325-335 nm
GOME2 total O3 retrieved (using GOME2 reference spectra) is
9% higher than calculated with resolution adjusted GOME FM
Spurious instrumental trends in multiple instrumenst time
series
Harmonisation of O3 FM cross-sections from GOME and
SCIAMACHY for a consistent retrieval
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Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab
The committee "ACSO" ("Absorption Cross Sections of Ozone") was established in spring 2009 by the World Meteorological Organization (WMO) and the International Association of Meteorology and Atmospheric Sciences (IAMAS) to
Review the presently available ozone absorption cross sections
Determine the impact of changing the reference ozone absorption cross sections for all of the commonly used atmospheric ozone monitoring instruments.
Recommend whether a change needs to be made.
The recommendations are to be discussed with the community of the involved experts. The work will be finished within two years after the first meeting in May 2009.
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Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Inconsistency of satellite instruments cross-section
I. Re-analysis of laboratory data from the measurements campaigns for GOME, GOME2 and SCIAMACHY
II. New laboratory measurements should improve absolute scaling and wavelength scaling.
should have best possible quality to serve as a most reliable reference source:
- wavelength coverage 240–1000 nm;
- vacuum wavelength accuracy better than 0.001 nm;
- spectral resolution of about 0.02 nm;
- absolute intensities accurate to at least 2%;
- more temperatures in range 190K-300K.
sufficient accuracy to detect a 1% pro decade trend!9
New high quality spectra
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab
I / I0 – transmitted intensity with /without
absorber,s – absorption cross sectionOD – optical density, uncertainty depends
on precision of measurementsA – scaling factor, uncertainty depends
on accuracy of the scaling method
N – absorber densityL – absorption path length
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Accuracy and precision
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
LNOD eIeII 00)(
A
OD
High precision Low accuracy
High accuracy Low precision
University Bremen, IUP, Molecular Spectroscopy Lab
Echelle spectrometercoverage
FT spectrometer coverage
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Ozone cross sections at 240- 1000 nm
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Note: s varies over 7 orders of magnitude!
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Main parts of experimental set-ups
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Setup VIS/IR
Setup UV/VIS
Spectrometer Fourier Transform Echelle (‘cross dispersion’)
Source Xe and Tungsten lamps Xe and D2 lamp
Detector Si/GaP photodiode ICCD
Resolution 0.02 nm @ 300 nm 0.02 nm @ 300 nm
Wavelength region 300 – 1000 nm 210 nm – 600 nm
Acquisition time
Slow (tens of minutes) Fast (minutes)
Wavelength calibration Excellent
Excellent (agrees with NIST Hg line at 253 nm better than 0.001 nm )
Optical path 135 and 270 cm 5 cm, 140 cm – 30 m
Cooling Double jacket quartz cell, pre-cooler, cryogenic cooling (193 K)
University Bremen, IUP, Molecular Spectroscopy Lab
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Absorption cell Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
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Instrument: Echelle
Averaged: over 250
scans Time: ~ 5
minutes
Source: xenon lamp
Single spectrum quality (OD)
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab
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Instrument: Echelle, FTS
Averaged: over 2000 (100)
scans
Time: ~ 30 minutes
Source: Xe and deuterium
lamps
Concatenated spectrum quality (OD)
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
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Methods for absolute calibration
I. Reference points, averaged from several datasets
II. Least squares fit to the selected dataset
III. Absolute measurements of the ozone density:
Pressure (ozone is not stable!);
Absorption path length;
Temperature.
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
s – absorption cross section
OD – optical densityA = N L – scaling factorN – absorber
densityL – absorption path
length
A
OD
University Bremen, IUP, Molecular Spectroscopy Lab
University Bremen, IUP, Molecular Spectroscopy Lab 17
Dataset Resolution, nm (FWHM)
Wavelength region, nm
Current work
FTS 0.02 – 0.20 450 – 1000
Echellet 0.02 211 – 830
SCIAMACHY 0.32 – 1.45 230 – 1070
GOME, GOME-2 0.2 – 0.4 231 – 794
High Resolution Brion et al. 0.02 195 – 830
External datasets: GOME, GOME2, SCIAMACHY, Brion et al (high resolution)
First approximation: no resolution matching
Absolute calibration: fit to external datasets
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab 18
Absolute calibration: fit to reference datasets in VIS/IR
Least squares fit for 293K to SCIAMACHY
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
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Absolute calibration: fit to reference datasets in VIS/IR
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Least squares fit for 293K to Brion
University Bremen, IUP, Molecular Spectroscopy Lab 20
Absolute calibration: fit to reference datasets in VIS/IR
Least squares fit for 293K to SCIAMACHY and Brion
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab 21
Second attempt for absolute calibration: by pressure measurements (Echelle) Independent measurements in UV at 4 temperatures with Echelle
spectrometer Each spectrum is absolutely calibrated from temperature and pressure
measurements
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
High resolution data by Brion et al Current work
Serial measurements of ozone absorption cross-sections:
for temperatures 196 K, 203 K, 223K, 243K, 273K and 293K;.
uncertainty of about 1-2%;
resolution 0.02 nm in the region 240 - 600 nm.
Absolute calibration and validation are in progress
Database release expected by the end of 2010
Other atmospheric species: under consideration22
We just started !
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab
23
Thank you for attention !
University Bremen, IUP, Molecular Spectroscopy Lab 25
Least squares fit to Brion et al (293K):
Absolute calibration: fit to reference datasets in VIS/IR
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University of Bremen, IUP, Molecular Spectroscopy Lab 26
High resolution O3 cross-sections before 1995
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
Cooling system: priorities/challenges
University of Bremen, IUP 27
Upgraded cooling systemMax possible cooling: down to 193 K
Temperature stabilization at intermediate points with step of 10 K Reliable temperature determination (better than 5% accuracy) : Pt
sensors, spectroscopic method
Upgraded gas pre-cooler features 10 meter Cu pipe bound to fit cryostat bathguaranteed cooling down to cryostat vessel temperature;ozone-friendly internal coatingminimal heat gain between precooler ant test cell
Sensors: Precooler: Goals and strategy Re-analysis
Experimental set-up
Serial measurements and
preliminary results
FTS measurements 293K :comparison with GOME
University of Bremen, IUP 28
Goals and strategy
Re-analysis
Experimental set-up
Serial measurements and preliminary results
University of Bremen, IUP, Molecular Spectroscopy Lab 29
Ozone cross-sections: temperature dependence
larger deviations for GOME2below 325 nm „noise“ in Bass Paur
above 335 nm
University of Bremen, IUP, Molecular Spectroscopy Lab 30
Consistency of cross-sections: temperature dependence
• Spietz et al. (GOME2 FM3)– At some temperatures deviation of 2% (223 K,
243K)
h
University Bremen, IUP, Molecular Spectroscopy Lab 31
Echelle wavelength calibration
Relative to NIST database
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook
University Bremen, IUP, Molecular Spectroscopy Lab 32
Temperature control
Cooling: double jacket (vacuum/ethanol) cell, cryostat with pre-cooling: 10 m Cu tube coil with inert coating
Control: O2-A band at 760 nm, experimental spectrum: from FTS at 0.5 cm, model spectrum: using HITRAN line parametersaccuracy: 5 K or better
Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook