Anna Serdyuchenko, Victor Gorshelev, Wissam Chehade, Mark Weber, John P. Burrows University of Bremen, Institute for Environmental Physics.

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

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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

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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

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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

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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

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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

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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

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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

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Thank you for attention !

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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

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High resolution O3 cross-sections before 1995

Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook

Cooling system: priorities/challenges

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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

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Goals and strategy

Re-analysis

Experimental set-up

Serial measurements and preliminary results

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Ozone cross-sections: temperature dependence

larger deviations for GOME2below 325 nm „noise“ in Bass Paur

above 335 nm

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Consistency of cross-sections: temperature dependence

• Spietz et al. (GOME2 FM3)– At some temperatures deviation of 2% (223 K,

243K)

h

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Echelle wavelength calibration

Relative to NIST database

Introduction and motivationExperimental set-up Analysis of sources of uncertainty Results and Outlook

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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