Zusammenfassung
Anorganische Bromverbindungen spielen eine bedeutende Rolle in katalytischen Ozonabbauzyklen der Stratosphäre. Im Rahmen dieser Doktorarbeit wurden ballongetragene DOAS (Differentielle Optische Absorptions Spektroskopie) BrO Vertikalprolmessungen mittels direkten Sonnenlichts mit bisher nicht erreichter Genauigkeit (+-12%) durchgeführt. Die spektroskopischen Messungen fanden während acht erfolgreicher Flüge mit der gemeinsamen deutsch-französischen Nutzlast LPMA/DOAS unter sehr verschiedenen geophysikalischen Bedingungen in den Jahren 1996-2000 statt. Dabei ergaben
sich völlig neue Einblicke in die Chemie und das Budget des stratosphärischen Broms. Die neuartigen Erkenntnisse
umfassen (1) eine genaue und vollständige Erfassung des stratosphärischen Bromgehaltes der letzten vier Jahre, (2) ein
verbessertes Verständnis der Chemie des stratosphärischen anorganischen Broms, und (3) den erstmaligen Nachweis und
die Messung von Höhenprolen der BrO Konzentration in der freien Troposphäre. Mit Hilfe der BrO Messungen konnte
der stratosphärische Gehalt an anorganischem Brom zu Brin
y =(21.5+-3) ppt in 5.6 Jahre alter Luft für 1999 bestimmt
werden. Hingegen zeigt die erstmalige gleichzeitige Bestimmung des stratosphärischen Bromgehaltes aus Messungen organischer Bromverbindungen nur Brorg y =(18.4+-1.8) ppt. Die Übereinstimmung des Gesamtbrommischungsverhältnisses ist befriedigend, jedoch deutet das konsistent gröÿere Brin y darauf hin, daÿ vermutlich anorganisches Brom (3.1+-3.5 ppt) aus der Troposphäre in die Stratosphäre eingetragen wird. Diese Vermutung wird durch den Befund (3) und den kürzlich erfolgten Nachweis von im Aerosol der oberen Troposphäre gebundenem, anorganischem Brom von etwa 1 ppt
qualitativ gestützt.
Als weiterer Teil der Arbeit wurde ein Algorithmus zur Auswertung der vom Ballon aus gemessenen Sonnenspektren für den Nachweis von Chlordioxid (OClO) neu entwickelt. OClO konnte in allen arktischen Winterügen auch bei geringer Chloraktivierung detektiert werden. Überraschenderweise wurde OClO auch während eines Ballonuges über Spanien im Herbst 1996 nachgewiesen (5-10 ppt in 20-30 km Höhe bei einem Sonnenzenitwinkel von 88-93o). Zur Interpretation der
erhöhten OClO Werte wurden Ergebnisse des 3-D CTM Modells SLIMCAT und des dafür eigens entwickelten Lagrange Boxmodells LABMOS mit den Messungen verglichen.
[...]
Table of Contents
1 Introduction
2 Halogen species and their importance in atmospheric chemistry
2.1 Stratospheric Ozone
2.2 Tropospheric Ozone
2.3 Stratospheric gas phase chemistry related to ozone
2.3.1 Chapman Chemistry
2.3.2 Catalytic Cycles
2.3.3 Nitrogen chemistry in the stratosphere
2.3.4 Halogen chemistry in the stratosphere
2.4 Heterogeneous chemistry on PSCs leading to the Ozone Hole
2.4.1 Heterogeneous chemistry on sulphate aerosols
2.5 Fundamental Stratospheric Dynamics
2.6 The atmospheric halogen budget
3 Measurement Technique : Direct Sunlight Balloon Borne DOAS (Differential Optical Absorption Spectroscopy)
3.1 Solar Radiation and the Solar Spectrum
3.1.1 Interaction of light with matter
3.1.2 Lambert-Beer's Law - Optical Absorption Spectroscopy
3.2 Differential Optical Absorption Spectroscopy (DOAS)
3.3 The DOAS double spectrograph for balloon-borne measurements
3.3.1 Noise sources of the measurements
3.4 The LPMA/DOAS balloon payload
3.4.1 The behaviour of the DOAS spectrograph during the balloon flights and its impact on the BrO evaluation
3.4.2 The BrO DOAS evaluation
3.4.3 The OClO DOAS evaluation
3.5 Determination of the SCD offset in the Fraunhofer reference - Langley Plot
3.6 Summary of the error sources of the bromine oxide SCD measurements
3.7 Profile Retrieval
3.7.1 Raytracing
3.7.2 AMF matrix inversion
3.7.3 Errors of the inversion technique
3.7.4 Differential Onion Peeling technique
3.8 Modelling of SCDs
4 Results and Discussion of the LPMA/DOAS balloon flights
4.1 The sunset flight at León on November 23, 1996
4.1.1 BrO profile and SCD model comparison
4.1.2 OClO profile and SCD model comparison
4.2 The sunset flight at Kiruna on February 14, 1997
4.2.1 BrO profile and SCD model comparison
4.2.2 OClO profile model comparison
4.2.3 O3 profile model comparison
4.2.4 NO2 profile model comparison
4.2.5 Summary of the model comparison
4.3 The sunrise flight at Gap on June 20, 1997
4.3.1 BrO profile and SCD model comparison
4.4 The sunset flight at León on March 19, 1998
4.4.1 BrO profile and VCD comparison with GOME
4.5 The sunset and sunrise flight at Kiruna on August 19/20, 1998
4.5.1 BrO profile and SCD model comparison for the sunset
4.5.2 BrO SCD model comparison for the sunrise
4.6 The sunset flight at Kiruna on February 10, 1999
4.6.1 BrO profile and SCD model comparison
4.6.2 OClO profile and SCD model comparison
4.7 The sunrise flight at Gap on June 25, 1999
4.8 The sunset flight at Kiruna on February 18, 2000
4.8.1 BrO profile and SCD model comparison
4.8.2 OClO profile and SCD model comparison
4.9 Summary of BrO measurements during the eight LPMA/DOAS balloon flights
4.9.1 BrO profile measurements
4.9.2 BrO VCD comparisons with satellite and ground-based instruments
5 The first measurement of a BrO profile in the free troposphere
5.1 Methodology and Measurements
5.2 Discussion of the free tropospheric BrO measurements
6 Comparison of the inorganic and organic bromine budget for the Arctic lower stratosphere in winter 1998/1999
6.1 Methodology of the comparison
6.2 Discussion of the comparison
6.3 A recent history of total organic and inorganic stratospheric bromine
7 Lagrangian case studies for the interpretation of enhanced OClO measurements at mid and high latitudes
7.1 The Lagrangian trajectory box model LABMOS
7.2 Case study of the in-vortex flight at Kiruna on February 10, 1999
7.3 Case study of the out-of-vortex flight at León on November 23, 1996
8 Conclusions and Outlook
Research Objectives and Key Topics
This doctoral thesis investigates the stratospheric inorganic bromine budget between 1996 and 2000 using balloon-borne Differential Optical Absorption Spectroscopy (DOAS) measurements. The primary objective is to advance the understanding of stratospheric bromine chemistry, quantify the total inorganic bromine content, and compare these observational findings with 3-D Chemical Transport Models (CTM) and Lagrangian trajectory simulations to resolve discrepancies in bromine and chlorine partitioning.
- Measurement of BrO vertical profiles using balloon-borne DOAS in various geophysical conditions.
- Determination of the total stratospheric inorganic bromine budget and its comparison with organic bromine precursors.
- Detection and analysis of OClO as an indicator of chlorine activation in the Arctic and at mid-latitudes.
- Development and implementation of an improved DOAS evaluation algorithm and a Lagrangian trajectory box model (LABMOS).
- Investigation of free tropospheric BrO to close the gap between integrated balloon profiles and total atmospheric column measurements.
Excerpt from the Book
4.1 The sunset flight at León on November 23, 1996
The first flight of the LPMA/DOAS payload took part from León(Spain) on Nov. 23, 1996. Figure 4.1 shows the trajectory of the balloon and the probed airmass during the occultation of the sun, when the tangent points are floating away from the balloon trajectory towards the sun. That means during the solar occultation we are probing different airmasses and integrating the column over possible horizontal gradients while during the ascent of the flight the remote sensing instrument probes only airmasses within an area of less than 100x100km².
In Figure 4.2 the balloon height as a function of time as well as the SZA at the balloon position (latitude, longitude) is presented. As the balloon is flying in easterly direction the SZA is increasing faster than it would if the position of the balloon was fixed.
For the DOAS fit - see Figure 4.3 - reference spectra measured in the laboratory of O3(-80°C) and NO2(-70°C) were used. The O4 reference spectrum is not an absolute cross section but a collision pair absorption cross section. Only the BrO absorption cross section is an absolute cross section taken from [Wahner et al. 1988] and adapted to the spectrograph resolution by laboratory reference measurements. The reference spectra were aligned with the Fraunhofer reference and fitted altogether to the measured spectra. The respective shifts and squeezes of the reference spectra ensemble during the flight are shown in Figure 4.12 and Figure 4.13.
Summary of Chapters
1 Introduction: Provides a comprehensive overview of the chemical composition and dynamics of the atmosphere, highlighting the ozone depletion problem and the motivation for investigating the bromine budget.
2 Halogen species and their importance in atmospheric chemistry: Describes the fundamental stratospheric chemistry, catalytic cycles, and the specific role of bromine, chlorine, and nitrogen species in ozone depletion.
3 Measurement Technique : Direct Sunlight Balloon Borne DOAS (Differential Optical Absorption Spectroscopy): Details the DOAS measurement technique, the balloon-borne instrumentation, data retrieval algorithms, and error sources.
4 Results and Discussion of the LPMA/DOAS balloon flights: Presents and discusses the data obtained from eight successful balloon flights, including detailed comparisons with model results.
5 The first measurement of a BrO profile in the free troposphere: Documents the pioneering measurement of free tropospheric BrO, providing evidence for its presence based on inter-comparison of balloon and satellite data.
6 Comparison of the inorganic and organic bromine budget for the Arctic lower stratosphere in winter 1998/1999: Analyzes the bromine budget by comparing inorganic bromine inferred from balloon measurements with organic precursor measurements.
7 Lagrangian case studies for the interpretation of enhanced OClO measurements at mid and high latitudes: Utilizes the LABMOS model to study OClO enhancements and validate the interpretation of chlorine activation.
8 Conclusions and Outlook: Summarizes the major scientific findings and suggests future directions for atmospheric research and instrument validation.
Keywords
Stratosphere, Ozone depletion, Bromine budget, BrO, OClO, DOAS, Balloon-borne measurements, Atmospheric chemistry, Lagrangian modelling, PSCs, Tropospheric bromine, Stratospheric dynamics, Photolysis, Chemical Transport Models, Trace gas detection
Frequently Asked Questions
What is the primary scientific focus of this dissertation?
The thesis investigates the stratospheric inorganic bromine budget from 1996 to 2000 using balloon-borne DOAS measurements to understand its role in catalytic ozone depletion.
Which chemical species are central to this research?
The main species studied are Bromine monoxide (BrO), Chlorine dioxide (OClO), Nitrogen dioxide (NO2), Ozone (O3), and various organic bromine and chlorine source gases.
What is the core research objective of the study?
The primary goal is to accurately quantify the stratospheric inorganic bromine content and resolve the differences between observational data and current photochemical models.
Which methodology is employed to retrieve concentration data?
The work utilizes Differential Optical Absorption Spectroscopy (DOAS) from balloon platforms, applying raytracing and matrix inversion techniques to retrieve vertical profiles from slant column density (SCD) measurements.
What topics are covered in the main body of the work?
The main body covers the atmospheric halogen budget, measurement techniques, detailed analysis of eight balloon flights, comparisons with CTM models (like SLIMCAT), and Lagrangian case studies to interpret OClO measurements.
How can this research be characterized by its keywords?
It is best characterized by keywords such as stratosphere, bromine budget, BrO, OClO, DOAS, balloon-borne measurements, and atmospheric chemical modelling.
Why is the measurement of tropospheric BrO significant?
It provides crucial evidence to explain discrepancies between integrated stratospheric balloon profiles and total atmospheric column measurements obtained by satellites.
What do the Lagrangian case studies reveal about OClO?
The case studies demonstrate that observed OClO enhancements, often interpreted as chlorine activation, require detailed Lagrangian modelling of airmass history to be reconciled with standard photochemical theory.
- Quote paper
- Richard Fitzenberger (Author), 2000, Investigation of the stratospheric inorganic bromine budget for 1996-2000: balloon-borne measurements and model comparisons, Munich, GRIN Verlag, https://www.grin.com/document/3169
