6DWHOOLWH2EVHUYDWLRQVRI$WPRVSKHULF+DORJHQ2[LGHV
'LVVHUWDWLRQ
von
7KRPDV:DJQHU
Heidelberg, Juli 1999
INAUGURAL - DISSERTATION
zur
Erlangung der Doktorwürde
der
der Naturwissenschaftlich - Mathematischen
Gesamtfakultät
der
Ruprecht - Karls - Universität
Heidelberg
vorgelegt von
Dipl.-Phys. Thomas Wagner
aus Mörlenbach
Tag der mündlichen Prüfung: 6. Juli 1999
Satellite Observations of Atmospheric Halogen Oxides
Gutachter: Prof. Dr. Ulrich Platt
Prof. Dr. Konrad Mauersberger
Dissertation
submitted to the
Combined Faculties for the Natural Sciences and for Mathematics
of the Ruperta Calrola University of
Heidelberg, Germany
for the degree of
Doctor of Natural Sciences
6DWHOOLWH2EVHUYDWLRQVRI$WPRVSKHULF+DORJHQ2[LGHV
presented by
Diplom-Physicist: Thomas Wagner
born in: Mörlenbach
Heidelberg, 6. July 1999
Referees: Prof. Dr. Ulrich Platt
Prof. Dr. Konrad Mauersberger
=XVDPPHQIDVVXQJ
Die große Bedeutung von Halogenverbindungen bezüglich der Zerstörung atmosphärischen Ozons
wurde schlagartig offenbar, als Mitte der Achtziger Jahre ein dramatischer Ozonverlust über der
Antarktis beobachtet wurde, seither bekannt als Ozonloch. Während der folgenden Jahre konnten
reaktive Halogenverbindungen auch in der Troposphäre nachgewiesen werden. Seit der
Entdeckung des Ozonlochs erweiterte sich das Wissen der atmosphärischen Halogenchemie
deutlich; hierzu trugen unter anderem auch absorptionsspektroskopische Messungen von BrO und
OClO bei, die beide im ultravioletten Spektralbereich charakteristische Absorptionsstrukturen
aufweisen. Diese Messungen wurden entweder vom Boden, Flugzeug oder Ballon aus
durchgeführt und konnten damit noch kein umfassendes Bild der Atmosphäre erbringen. In dieser
Arbeit wurden Algorithmen für die Auswertung atmosphärischen BrOs und OClOs aus den Daten
des GOME (Global Ozone Monitoring Experiment) Instruments an Bord des europäischen
Forschungssatelliten ERS-2 entwickelt. Dadurch war es möglich, die zeitliche und räumliche
Entwicklung des atmosphärischen BrOs und OClOs global zu bestimmen. Insbesondere gelang es
zum ersten Mal, erhöhte BrO-Konzentrationen in der planetaren Grenzschicht vom Satelliten aus
zu messen. Außerdem konnten starke Indizien für die Existenz von BrO selbst in der freien
Troposphäre gefunden werden. Die OClO-Messungen des GOME Instrumentes erlaubten es, die
Chlor-Aktivierung beider Polargebiete bezüglich der zeitlichen Entwicklung sowie ihrer Stärke zu
untersuchen.
$EVWUDFW
The important role of halogen compounds in atmospheric ozone destruction became obvious after
dramatic ozone loss was observed over Antarctica in the mid 1980s, usually referred to as ‘ozone
hole’. In the following years reactive halogen species were also discovered in the troposphere.
Since the discovery of the ozone hole the understanding of the atmospheric halogen chemistry was
largely extended, in particular by spectroscopic measurements of BrO and OClO which both show
characteristic absorption features in the UV spectral range. These measurements were performed
from ground based and air borne instruments and thus could only provide ‘snapshots’ of the
atmospheric conditions. In this PhD thesis algorithms for the analysis of atmospheric BrO and
OClO from the GOME (Global Ozone Monitoring Experiment) instrument aboard the European
research satellite ERS-2 were developed. It was possible to monitor the spatial and temporal
evolution of atmospheric BrO and OClO on a global scale. In particular, enhanced BrO
concentrations in the boundary layer were first detected from satellite. In addition, strong evidence
for the presence of BrO in the free troposphere was found. From the GOME OClO measurements
it was possible to study stratospheric chlorine activation in both hemispheres with respect to their
temporal evolution and strength.
7DEOHRI&RQWHQWV
&KDSWHU,QWURGXFWLRQ...................................................................................................................
&KDSWHU7KHUROHRIKDORJHQVSHFLHVLQDWPRVSKHULFR]RQHFKHPLVWU\....................................
2.1 Atmospheric Ozone................................................................................................................4
2.1.1 Ozone in the stratosphere................................................................................................4
2.1.2 Ozone in the troposphere................................................................................................7
2.2 Sources and sinks of atmospheric halogen species................................................................ 9
2.2.1 Stratospheric halogen compounds, the importance of CFCs and halons......................10
2.2.2 Tropospheric halogen compounds................................................................................ 14
2.2.2.1 Emissions of partly halogenated halocarbons....................................................... 14
2.2.2.2 Release of reactive bromine from sea salt during polar spring.............................15
2.3 Fundamental schemes of atmospheric halogen chemistry....................................................16
2.4 Halogen chemistry of the stratosphere..................................................................................17
2.4.1 Stratospheric halogen chemistry under ‘non-ozone hole’ conditions...........................19
2.4.2 Stratospheric halogen chemistry under ‘ozone hole’ conditions.................................. 21
2.4.3 Open questions of stratospheric halogen chemistry......................................................24
2.4.3.1 Influence of dynamic processes on ozone destruction..........................................25
2.4.3.2 PSC formation.......................................................................................................27
2.4.3.3 Heterogeneous reactions........................................................................................28
2.5 Halogen chemistry of the troposphere..................................................................................28
2.5.1 Open questions of tropospheric halogen chemistry...................................................... 30
&KDSWHU*OREDO2]RQH0RQLWRULQJ([SHULPHQW*20(.....................................................
3.1 The European research satellite ERS-2................................................................................ 32
3.2 The GOME instrument......................................................................................................... 33
3.3 Viewing geometry and coverage of the Earth’s surface.......................................................35
3.4 GOME products and data formats........................................................................................ 36
&KDSWHU$EVRUSWLRQVSHFWURVFRS\RIDWPRVSKHULFWUDFHJDVHV...............................................
4.1 Solar radiation.......................................................................................................................37
4.2 Interaction of radiation and matter in the UV/vis spectral region........................................ 39
4.2.1 The Beer-Lambert Law................................................................................................. 41
4.3 Differential optical absorption spectroscopy (DOAS)..........................................................41
4.3.1 Application of the DOAS method to the measurement of scattered radiation..............43
4.3.2 The spectral fitting process........................................................................................... 44
4.3.3 The influence of the spectral resolution of the instrument............................................46
4.3.4 The Ring effect..............................................................................................................48
4.3.4.1 The Ring spectrum................................................................................................ 49
4.3.4.2 Sensitivity studies for the correction of the Ring effect........................................51
4.3.4.3 An advanced concept for the correction of the Ring effect...................................51
4.3.5 The ‘solar I0-effect’.......................................................................................................53
4.3.6 Instrumental shortcomings and their consideration...................................................... 54
4.3.6.1 Fabry Peron etalon structures................................................................................54
4.3.6.2 Undersampling of GOME spectra.........................................................................54
4.3.6.3 Doppler shift..........................................................................................................55
4.3.7 Development of the BrO analysis for GOME spectra...................................................56
4.3.7.1 Wavelength range and reference spectra...............................................................56
4.3.7.2 Determination of the fitting error for the BrO evaluation.....................................60
4.3.7.2.1 Determination of the statistical error of the fitting process...........................60
4.3.7.2.2 Impact of the undersampling problem of GOME on the BrO analysis.........61
4.3.7.2.3 Errors caused by uncertainties of the wavelength calibration....................... 62
4.3.7.2.4 Total error of the GOME BrO analysis......................................................... 63
4.3.8 Development of the OClO algorithm for GOME spectra ............................................66
4.3.8.1 Wavelength range and reference spectra...............................................................66
4.3.8.2 Determination of the fitting error for the GOME OClO analysis......................... 70
4.3.9 Development of GOME DOAS algorithms O3, NO2, O2 and O4................................. 72
4.3.9.1 O3 analysis.............................................................................................................72
4.3.9.2 NO2 analysis..........................................................................................................74
4.3.9.2 O2 and O4 analysis.................................................................................................76
&KDSWHU0RGHOOLQJRIWKHDWPRVSKHULFUDGLDWLYHWUDQVSRUW...................................................
5.1 Air mass factors for ground based and satellite observations...............................................77
5.2 Calculation of air mass factors for GOME...........................................................................79
5.2.1 Air mass factors for stratospheric BrO..........................................................................80
5.2.1.1 Influence of the ground albedo..............................................................................83
5.2.1.2 Influence of the atmospheric aerosol profile.........................................................85
5.2.1.3 Influence of the atmospheric temperature and pressure profile............................ 88
5.2.1.4 Influence of the atmospheric ozone profile...........................................................89
5.2.1.5 The uncertainty of the air mass factor...................................................................90
5.2.2 Air mass factors for tropospheric BrO..........................................................................90
5.2.3 Air mass factors for stratospheric OClO.......................................................................92
5.3 Influence of clouds on the air mass factor for ground based and satellite measurements....93
5.3.1 Influence on satellite air mass factors for stratospheric species................................... 93
5.3.2 Influence on satellite air mass factors for tropospheric species....................................94
5.3.3 Broken cloudiness across one ground pixel, sensitivity of GOME measurements for
tropospheric species..................................................................................................... 96
5.3.4 Conclusions ..................................................................................................................98
&KDSWHU5HVXOWVRIWKH%U2PHDVXUHPHQWV..............................................................................
6.1 Latitudinal and seasonal variability of the BrO VCD measured by GOME.........................99
6.2. Stratospheric BrO...............................................................................................................101
6.2.1 Summary of the GOME observations of stratospheric BrO........................................106
6.3. BrO in the boundary layer..................................................................................................106
6.3.1 Discovery.....................................................................................................................106
6.3.2 Quantitative determination of the BrO concentration in the boundary layer...............109
6.3.3 Comparison to ground based observations of O3 and BrO..........................................110
6.3.3.2 Comparison of GOME BrO to in-situ BrO observations at Spitsbergen.............110
6.3.3.2 Comparison of GOME BrO to in-situ O3 observations at Spitsbergen............... 111
6.3.4 Examples of polar boundary layer BrO events observed in 1997...............................113
6.3.5 Time series for both hemispheres................................................................................118
6.3.5.1 Total area............................................................................................................. 118
6.3.5.2 Dependence on the latitude..................................................................................119
6.3.5.3 Longitudinal distribution..................................................................................... 122
6.3.5.4 Summary of the GOME observations of BrO in the boundary layer...................123
6.4. BrO in the free troposphere................................................................................................125
6.4.1 Comparison with balloon borne measurements.......................................................... 125
6.4.2 Comparison of the GOME BrO SCDs with GOME O4 measurements...................... 129
6.4.3 Comparison with ground based BrO measurements................................................... 132
6.4.4 Summary of the GOME observations of BrO in the free troposphere........................136
&KDSWHU5HVXOWVRIWKH2&O2PHDVXUHPHQWV.........................................................................
7.1 OClO in the Stratosphere.................................................................................................... 138
7.1.1 General features, SZA dependence............................................................................. 138
7.1.2 Comparison with ground based instruments............................................................... 140
7.1.3 Time series of GOME OClO observations in the northern hemisphere......................144
7.1.4 Temperature dependence of chlorine activation in the Arctic.................................... 147
7.1.5 Comparison between both hemispheres......................................................................149
7.1.6 OClO outside the polar vortices?................................................................................ 150
7.1.7 Time constant of chlorine activation, mixing inside the vortex..................................151
7.2 OClO maps for THESEO....................................................................................................154
7.3 OClO in the troposphere?................................................................................................... 154
7.4 Summary of the GOME OClO measurements....................................................................155
6XPPDU\DQGRXWORRN.................................................................................................................
5HIHUHQFHV.....................................................................................................................................
$SSHQGL[$...................................................................................................................................
$SSHQGL[%...................................................................................................................................
