This work is motivated by the question: how much complexity is appropriate for a cloud parameterization used in general circulation models (GCM). To approach this question, cloud parameterizations across the complexity range are explored using general circulation models and theoretical Monte-Carlo simulations. Their results are compared with high-resolution satellite observations and simulations that resolve the GCM subgrid-scale variability explicitly. A process-orientated evaluation is facilitated by GCM forecast simulations which reproduce the synoptic state. For this purpose novel methods were develop to a) conceptually relate the underlying saturation deficit probability density function (PDF) with its saturated cloudy part, b) analytically compute the vertical integrated liquid water path (LWP) variability, c) diagnose the relevant PDF-moments from cloud parameterizations, d) derive high-resolution LWP from satellite observations and e) deduce the LWP statistics by aggregating the LWP onto boxes equivalent to the GCM grid size. On this basis, this work shows that it is possible to evaluate the sub-grid scale variability of cloud parameterizations in terms of cloud variables. Differences among the PDF types increase with complexity, in particular the more advanced cloud parameterizations can make use of their double Gaussian PDF in conditions, where cumulus convection forms a separate mode with respect to the remainder of the grid-box. Therefore, it is concluded that the difference between unimodal and bimodal PDFs is more important, than the shape within each mode. However, the simulations and their evaluation reveals that the advanced parameterizations do not take full advantage of their abilities and their statistical relationships are broadly similar to less complex PDF shapes, while the results from observations and cloud resolving simulations indicate even more complex distributions. Therefore, this work suggests that the use of less complex PDF shapes might yield a better trade-off. With increasing model resolution initial weaknesses of simpler, e.g. unimodal PDFs, will be diminished. While cloud schemes for coarse-resolved models need to parameterize multiple cloud regimes per grid-box, higher spatial resolution of future GCMs will separate them better, so that the unimodal approximation improves.

An Airborne Mobile Aerosol Lidar (AMALi) was constructed and built at Alfred-Wegener-Institute for Polar and Marine Research (AWI) in Potsdam, Germany for the lower tropospheric aerosol and cloud research under tough arctic conditions. The system was successfully used during two AWI airborne field campaigns, ASTAR 2004 and SVALEX 2005, performed in vicinity of Spitsbergen in the Arctic. The novel evaluation schemes, the Two-Stream Inversion and the Iterative Airborne Inversion, were applied to the obtained lidar data. Thereby, calculation of the particle extinction and backscatter coefficient profiles with corresponding lidar ratio profiles characteristic for the arctic air was possible. The comparison of these lidar results with the results of other in-situ and remote instrumentation (ground based Koldewey Aerosol Raman Lidar (KARL), sunphotometer, radiosounding, satellite imagery) allowed to provided clean contra polluted (Arctic Haze) characteristics of the arctic aerosols. Moreover, the data interpretation by means of the ECMWF Operational Analyses and small-scale dispersion model EULAG allowed studying the effects of the Spitsbergens orography on the aerosol load in the Planetary Boundary Layer. With respect to the cloud studies a new methodology of alternated remote AMALi measurements with the airborne in-situ cloud optical and microphysical parameters measurements was proved feasible for the low density mixed-phase cloud studies. An example of such approach during observation of the natural cloud seeding (feeder-seeder phenomenon) with ice crystals precipitating into the lower supercooled stratocumulus deck were discussed in terms of the lidar signal intensity profiles and corresponding depolarisation ratio profiles. For parts of the cloud system characterised by almost negligible multiple scattering the calculation of the particle backscatter coefficient profiles was possible using the lidar ratio information obtained from the in-situ measurements in ice-crystal cloud and water cloud. / Das Airborne Mobile Aerosol Lidar (AMALi) wurde am Alfred-Wegener-Institut für Polar- und Meeresforschung in Potsdam für die Untersuchung arktischer Aerosole und Wolken der unteren Troposphäre entwickelt und gebaut. Das AMALi wurde erfolgreich in zwei AWI Flugzeugmesskampagnen, der ASTAR 2004 und der SvalEx 2005, die in Spitzbergen in der Arktis durchgeführt wurden, eingesetzt. Zwei neue Lidar Datenauswertungsmethoden wurden implementiert: die Two-Stream Inversion und die Iterative Airborne Inversion. Damit erwies sich die Berechnung der Profile der Teilchen Rückstreu- und Extinktionskoeffizienten mit einem entsprechenden Lidar Verhältnis, das charakteristisch für arktische Luft ist, als möglich. Der Vergleich dieser Auswertungen mit den Resultaten, die mit verschiedenen Fernerkundungs- und In-situ Instrumenten gewonnen worden waren (stationäres Koldewey Aerosol Raman Lidar KARL, Sonnenphotometer, Radiosondierung und Satellitenbilder) ermöglichten die Interpretation der Lidar-Resultate und eine Charakterisierung sowohl der reinen als auch der verschmutzten Luft. Außerdem konnten die Lidardaten mit operationellen ECMWF Daten und dem kleinskaligen Dispersionsmodel EULAG verglichen werden. Dadurch konnte der Einfluss der Spitzbergener Orographie auf die Aerosolladung der Planetaren Grenzschicht untersucht werden. Für Wolkenmessungen wurde eine neue Methode der alternativen Fernerkundung mit dem AMALi und flugzeuggetragenen In-situ Messgeräten verwendet, um optische und mikrophysikalische Eigenschaften der Wolken zu bestimmen. Diese Methode wurde erfolgreich implementiert und auf Mixed-Phase Wolken geringer optischen Dicke angewendet. Ein Beispiel hier stellt das Besamen der Wolken (sogenannte Feeder-Seeder Effekt) dar, bei dem Eiskristalle in eine niedrige unterkühlte Stratokumulus fallen. Dabei konnten Lidarsignale, Intensitätsprofile und die Volumendepolarisation gemessen werden. Zusätzlich konnten in den weniger dichten Bereichen der Wolken, in denen Vielfachstreuung vernachlässigbar ist, auch Profile des Teilchen Rückstreukoeffizienten berechnet werden, wobei Lidarverhältnisse genommen wurden, die aus In-situ Messungen für Wasser- und Eiswolken ermittelt wurden.

Im Rahmen der Arbeit wurden Lidar- und Wolkenradarmessungen von troposphärischen Schichtwolken durchgeführt und ausgewertet, um den Zusammenhang zwischen Vertikalwinden und Eisbildung in diesen Wolken zu untersuchen. Der Eis- und Flüssigwassergehalt von Schichtwolken wurde mit einer Kombination aus Raman-Lidar und Wolkenradar untersucht. Die vertikalen Windbewegungen an der Wolkenunterkante wurden mit einem Doppler-Lidar aufgezeichnet. Durch die Auswertung vorangegangener Messkampagnen konnte die Vertikalwindstatistik in mittelhohen Schichtwolken zwischen den Standorten Leipzig und Praia (Kap Verde) verglichen werden. Messverfahren für die Vertikalwindmessung mit Doppler-Lidar wurden im Rahmen dieser Arbeit weiterentwickelt. In Zusammenarbeit mit dem Deutschen Wetterdienst wurde außerdem die Kombination von Doppler-Lidar, Wolkenradar und Wind-Profiler getestet. Die Eisbildungseffizienz in der Troposphäre wurde im Temperaturbereich zwischen 0 und -40°C für den Standort Leipzig untersucht und sowohl mit vorangegangenen Lidarmessungen, als auch mit aktuellen Satellitenmessungen verglichen. Zum ersten Mal wurde außerdem die statistische Verteilung von Vertikalwinden an der Basis von Mischphasenwolken dargestellt. Es wurde festgestellt, dass sich bei einer Temperatur von (-9 +/- 3)°C bereits in 50% der Schichtwolken über Leipzig Eis bildet. Zwischen -15 und 0°C wurden Verhältnisse zwischen Eis- und Flüssigwasserpfad zwischen 0,1 und 0,0001 abgeschätzt. Im Rahmen der Messgenauigkeit wurden zwischen den Standorten Leipzig und Praia keine Unterschiede in der Vertikalwindstatistik festgestellt.

This work is motivated by the question: how much complexity is appropriate for a cloud parameterization used in general circulation models (GCM). To approach this question, cloud parameterizations across the complexity range are explored using general circulation models and theoretical Monte-Carlo simulations. Their results are compared with high-resolution satellite observations and simulations that resolve the GCM subgrid-scale variability explicitly. A process-orientated evaluation is facilitated by GCM forecast simulations which reproduce the synoptic state. For this purpose novel methods were develop to a) conceptually relate the underlying saturation deficit probability density function (PDF) with its saturated cloudy part, b) analytically compute the vertical integrated liquid water path (LWP) variability, c) diagnose the relevant PDF-moments from cloud parameterizations, d) derive high-resolution LWP from satellite observations and e) deduce the LWP statistics by aggregating the LWP onto boxes equivalent to the GCM grid size. On this basis, this work shows that it is possible to evaluate the sub-grid scale variability of cloud parameterizations in terms of cloud variables. Differences among the PDF types increase with complexity, in particular the more advanced cloud parameterizations can make use of their double Gaussian PDF in conditions, where cumulus convection forms a separate mode with respect to the remainder of the grid-box. Therefore, it is concluded that the difference between unimodal and bimodal PDFs is more important, than the shape within each mode. However, the simulations and their evaluation reveals that the advanced parameterizations do not take full advantage of their abilities and their statistical relationships are broadly similar to less complex PDF shapes, while the results from observations and cloud resolving simulations indicate even more complex distributions. Therefore, this work suggests that the use of less complex PDF shapes might yield a better trade-off. With increasing model resolution initial weaknesses of simpler, e.g. unimodal PDFs, will be diminished. While cloud schemes for coarse-resolved models need to parameterize multiple cloud regimes per grid-box, higher spatial resolution of future GCMs will separate them better, so that the unimodal approximation improves.

Diese Dissertation beschäftigt sich mit regionaler Klimamodellierung über Südamerika, der Analyse von Modellsensitivitäten bezüglich Wolkenparametrisierungen und der Entwicklung neuer Methoden zur Modellevaluierung mithilfe von Klimanetzwerken. Im ersten Teil untersuchen wir Simulationen mit dem COnsortium for Small scale MOdeling model in CLimate Mode (COSMO-CLM) und stellen die erste umfassende Evaluierung dieses dynamischen regionalen Klimamodells über Südamerika vor. Dabei untersuchen wir insbesondere die Abhängigkeit simulierter tropischer Niederschläge von Parametrisierungen subgitterskaliger cumuliformer und stratiformer Wolken und finden starke Sensitivitäten bezüglich beider Wolkenparametrisierungen über Land. Durch einen simultanen Austausch der entsprechenden Schemata gelingt uns eine beträchtliche Reduzierung von Fehlern in klimatologischen Niederschlags- und Strahlungsmitteln, die das COSMO-CLM über tropischen Regionen für lange Zeit charakterisierten. Im zweiten Teil führen wir neue Metriken für die Evaluierung von Klimamodellen bezüglich räumlicher Kovariabilitäten ein. Im Kern bestehen diese Metriken aus Unähnlichkeitsmaßen für den Vergleich von simulierten mit beobachteten Klimanetzwerken. Wir entwickeln lokale und globale Unähnlichkeitsmaße zum Zwecke der Darstellung lokaler Unähnlichkeiten in Form von Fehlerkarten sowie der Rangordnung von Modellen durch Zusammenfassung lokaler zu globalen Unähnlichkeiten. Die neuen Maße werden dann für eine vergleichende Evaluierung regionaler Klimasimulationen mit COSMO-CLM und dem Statistical Analogue Resampling Scheme über Südamerika verwendet. Dabei vergleichen wir die sich ergebenden Modellrangfolgen mit solchen basierend auf mittleren quadratischen Abweichungen klimatologischer Mittelwerte und Varianzen und untersuchen die Abhängigkeit dieser Rangfolgen von der betrachteten Jahreszeit, Variable, dem verwendeten Referenzdatensatz und Klimanetzwerktyp. / This dissertation is about regional climate modeling over South America, the analysis of model sensitivities to cloud parameterizations, and the development of novel model evaluation techniques based on climate networks. In the first part we examine simulations with the COnsortium for Small scale MOdeling weather prediction model in CLimate Mode (COSMO-CLM) and provide the first thorough evaluation of this dynamical regional climate model over South America. We focus our analysis on the sensitivity of simulated tropical precipitation to the parameterizations of subgrid-scale cumuliform and stratiform clouds. It is shown that COSMO-CLM is strongly sensitive to both cloud parameterizations over tropical land. Using nondefault cumulus and stratus parameterization schemes we are able to considerably reduce long-standing precipitation and radiation biases that have plagued COSMO-CLM across tropical domains. In the second part we introduce new performance metrics for climate model evaluation with respect to spatial covariabilities. In essence, these metrics consist of dissimilarity measures for climate networks constructed from simulations and observations. We develop both local and global dissimilarity measures to facilitate the depiction of local dissimilarities in the form of bias maps as well as the aggregation of those local to global dissimilarities for the purposes of climate model intercomparison and ranking. The new measures are then applied for a comparative evaluation of regional climate simulations with COSMO-CLM and the STatistical Analogue Resampling Scheme (STARS) over South America. We compare model rankings obtained with our new performance metrics to those obtained with conventional root-mean-square errors of climatological mean values and variances, and analyze how these rankings depend on season, variable, reference data set, and climate network type.

The ubiquitous abundance of organic compounds in natural and anthorpogenically influenced eco-systems has put these compounds into the focus of atmospheric research. Organic compounds have an impact on air quality, climate, and human health. Moreover, they affect particle growth, secondary organic aerosol (SOA) formation, and the global radiation budget by altering particle properties. To investigate the multiphase chemistry of organic compounds and interactions with the aqueous phase in the troposphere, modelling can provide a useful tool. The oxidation of larger organic molecules to the final product CO2 can involve a huge number of intermediate compounds and tens of thousands of reactions. Therefore, the creation of explicit mechanisms relies on automated mechanism construction. Estimation methods for the prediction of the kinetic data needed to describe the degradation of these intermediates are inevitable due to the infeasibility of an experimental determination of all necessary data. Current aqueous phase descriptions of organic chemistry lag behind the gas phase descriptions in atmospheric chemical mechanisms despite its importance for the multiphase chemistry of organic compounds. In this dissertation, the gas phase mechanism Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) has been advanced by a protocol for the description of the oxidation of organic compounds in the aqueous phase. Therefore, a database with kinetic data of 465 aqueous phase hydroxyl radical and 129 aqueous phase nitrate radical reactions with organic compounds has been compiled and evaluated. The database was used to evaluate currently available estimation methods for the prediction of aqueous phase kinetic data of reactions of organic compounds. Among the investigated methods were correlations of gas and aqueous kinetic data, kinetic data of homologous series of various compound classes, reactivity comparisons of inorganic radical oxidants, Evans-Polanyi-type correlations, and structure-activity relationships (SARs). Evans-Polanyi-type correlations have been improved for the purpose of automated mechanism self-generation of mechanisms with large organic molecules. A protocol has been designed based on SARs for hydroxyl radical reactions and the improved Evans-Polanyi-type correlations for nitrate radical reactions with organic compounds. The protocol was assessed in a series of critical sensitivity studies, where uncertainties of critical parameters were investigated. The advanced multiphase generator GECKO-A was used to generate mechanisms, which were applied in box model studies and validated against two sets of aerosol chamber experiments. Experiments differed by the initial compounds used (hexane and trimethylbenzene) and the experimental conditions (UV-C lights off/on and additional in-situ hydroxyl radical source no/yes). Reasonable to good agreement of the modelled and experimental results was achieved in these studies. Finally, GECKO-A was used to create two new CAPRAM version, where, for the first time, branchingratios for different reaction pathways were introduced and the chemistry of compounds with up to four carbon atoms has been extended. The most detailed mechanism comprises 4174 compounds and 7145 processes. Detailed investigations were performed under real tropospheric conditions in urban and remote continental environments. Model results showed significant improvements, especially in regard to the formation of organic aerosol mass. Detailed investigations of concentration-time profiles and chemical fluxes refined the current knowledge of the multiphase processing of organic compounds in the troposphere, but also pointed at current limitations of the generator protocol, the mechanisms created, and current understanding of aqueous phase processes of organic compounds. / Das zahlreiche Vorkommen organischer Verbindungen in natürlichen und anthropogen beeinflussten Ökosystemen hat diese Verbindungen in den Fokus der Atmosphärenforschung gerückt. Organische Verbindungen beeinträchtigen die Luftqualität, die menschliche Gesundheit und das Klima. Weiterhin werden Partikelwachstum und -eigenschaften, sekundäre organische Partikelbildung und dadurch der globale Strahlungshaushalt durch sie beeinflusst. Um die troposphärische Multiphasenchemie organischer Verbindungen und Wechselwirkungen mit der Flüssigphase zu untersuchen, sind Modellstudien hilfreich. Die Oxidation großer organischer Moleküle führt zu einer Vielzahl an Zwischenprodukten. Der Abbau erfolgt in unzähligen Reaktionen bis hin zum Endprodukt CO2. Bei der Entwicklung expliziter Mechanismen muss deshalb für diese Verbindungen auf computergestützte, automatisierte Methoden zurückgegriffen werden. Abschätzungsmethoden für die Vorhersage kinetischer Daten zur Beschreibung des Abbaus der Zwischenprodukte sind unabdingbar, da eine experimentelle Bestimmung aller benötigten Daten nicht realisierbar ist. Die derzeitige Beschreibung der Flüssigphasenchemie unterliegt deutlich den Beschreibungen der Gasphase in atmosphärischen Chemiemechanismen trotz deren Relevanz für die Multiphasenchemie. In dieser Arbeit wurde der Gasphasenmechanismusgenerator GECKO-A (“Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere”) um ein Protokoll zur Oxidation organischer Verbindungen in der Flüssigphase erweitert. Dazu wurde eine Datenbank mit kinetischen Daten von 465 Hydroxylradikal- und 129 Nitratradikalreaktionen mit organischen Verbindungen angelegt und evaluiert. Mit Hilfe der Datenbank wurden derzeitige Abschätzungsmethoden für die Vorhersage kinetischer Daten von Flüssigphasenreaktionen organischer Verbindungen evaluiert. Die untersuchten Methoden beinhalteten Korrelationen kinetischer Daten aus Gas- und Flüssigphase, homologer Reihen verschiedener Stoffklassen, Reaktivitätsvergleiche, Evans-Polanyi-Korrelationen und Struktur-Reaktivitätsbeziehungen. Für die Mechanismusgenerierung großer organischer Moleküle wurden die Evans-Polanyi-Korrelationen in dieser Arbeit weiterentwickelt. Es wurde ein Protokol für die Mechanismusgenerierung entwickelt, das auf Struktur-Reaktivitätsbeziehungen bei Reaktionen von organischen Verbindungen mit OH-Radikalen und auf den erweiterten Evans-Polanyi-Korrelationen bei NO3-Radikalreaktionen beruht. Das Protokoll wurde umfangreich in einer Reihe von Sensitivitätsstudien getestet, um Unsicherheiten kritischer Parameter abzuschätzen. Der erweiterte Multiphasengenerator GECKO-A wurde dazu verwendet, neue Mechanismen zu generieren, die in Boxmodellstudien gegen Aerosolkammerexperimente evaluiert wurden. Die Experimentreihen unterschieden sich sowohl in der betrachteten Ausgangssubstanz (Hexan und Trimethylbenzen) und dem Experimentaufbau (ohne oder mit UV-C-Photolyse und ohne oder mit zusätzlicher partikulärer Hydroxylradikalquelle). Bei den Experimenten konnte eine zufriedenstellende bis gute Übereinstimmung der experimentellen und Modellergebnisse erreicht werden. Weiterhin wurde GECKO-A verwendet, um zwei neue CAPRAM-Versionen mit bis zu 4174 Verbindungen und 7145 Prozessen zu generieren. Erstmals wurden Verzweigungsverhältnisse in CAPRAM eingeführt. Außerdem wurde die Chemie organischer Verbindungen mit bis zu vier Kohlenstoffatomen erweitert. Umfangreiche Untersuchungen unter realistischen troposphärischen Bedingungen in urbanen und ländlichen Gebieten haben deutliche Verbesserungen der erweiterten Mechanismen besonders in Bezug auf Massenzuwachs des organischen Aerosolanteils gezeigt. Das Verständnis der organischen Multiphasenchemie konnte durch detaillierte Untersuchungen zu den Konzentrations-Zeit-Profilen und chemischen Flüssen vertieft werden, aber auch gegenwärtige Limitierungen des Generators, der erzeugten Mechanismen und unseres Verständnisses für Flüssigphasenprozesse organischer Verbindungen aufgezeigt werden.

No description available.

No description available.

The ubiquitous abundance of organic compounds in natural and anthorpogenically influenced eco-systems has put these compounds into the focus of atmospheric research. Organic compounds have an impact on air quality, climate, and human health. Moreover, they affect particle growth, secondary organic aerosol (SOA) formation, and the global radiation budget by altering particle properties. To investigate the multiphase chemistry of organic compounds and interactions with the aqueous phase in the troposphere, modelling can provide a useful tool. The oxidation of larger organic molecules to the final product CO2 can involve a huge number of intermediate compounds and tens of thousands of reactions. Therefore, the creation of explicit mechanisms relies on automated mechanism construction. Estimation methods for the prediction of the kinetic data needed to describe the degradation of these intermediates are inevitable due to the infeasibility of an experimental determination of all necessary data. Current aqueous phase descriptions of organic chemistry lag behind the gas phase descriptions in atmospheric chemical mechanisms despite its importance for the multiphase chemistry of organic compounds. In this dissertation, the gas phase mechanism Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) has been advanced by a protocol for the description of the oxidation of organic compounds in the aqueous phase. Therefore, a database with kinetic data of 465 aqueous phase hydroxyl radical and 129 aqueous phase nitrate radical reactions with organic compounds has been compiled and evaluated. The database was used to evaluate currently available estimation methods for the prediction of aqueous phase kinetic data of reactions of organic compounds. Among the investigated methods were correlations of gas and aqueous kinetic data, kinetic data of homologous series of various compound classes, reactivity comparisons of inorganic radical oxidants, Evans-Polanyi-type correlations, and structure-activity relationships (SARs). Evans-Polanyi-type correlations have been improved for the purpose of automated mechanism self-generation of mechanisms with large organic molecules. A protocol has been designed based on SARs for hydroxyl radical reactions and the improved Evans-Polanyi-type correlations for nitrate radical reactions with organic compounds. The protocol was assessed in a series of critical sensitivity studies, where uncertainties of critical parameters were investigated. The advanced multiphase generator GECKO-A was used to generate mechanisms, which were applied in box model studies and validated against two sets of aerosol chamber experiments. Experiments differed by the initial compounds used (hexane and trimethylbenzene) and the experimental conditions (UV-C lights off/on and additional in-situ hydroxyl radical source no/yes). Reasonable to good agreement of the modelled and experimental results was achieved in these studies. Finally, GECKO-A was used to create two new CAPRAM version, where, for the first time, branchingratios for different reaction pathways were introduced and the chemistry of compounds with up to four carbon atoms has been extended. The most detailed mechanism comprises 4174 compounds and 7145 processes. Detailed investigations were performed under real tropospheric conditions in urban and remote continental environments. Model results showed significant improvements, especially in regard to the formation of organic aerosol mass. Detailed investigations of concentration-time profiles and chemical fluxes refined the current knowledge of the multiphase processing of organic compounds in the troposphere, but also pointed at current limitations of the generator protocol, the mechanisms created, and current understanding of aqueous phase processes of organic compounds.:1 Introduction and motivation 2 Theoretical background 2.1 General overview of the tropospheric multiphase chemistry of organic compounds 2.1.1 Gas phase chemistry 2.1.2 Phase transfer 2.1.3 Aqueous phase chemistry 2.2 Tropospheric multiphase chemistry mechanisms 2.2.1 Gas phase mechanisms 2.2.2 Aqueous phase mechanisms 2.2.3 The multiphase mechanism MCMv3.1-CAPRAM 3.0n 2.2.3.1 MCMv3.1 2.2.3.2 CAPRAM 3.0n 2.3 Multiphase chemistry box models 2.3.1 Overview 2.3.2 The model SPACCIM 2.3.2.1 Overview 2.3.2.2 The microphysical scheme 2.3.2.3 The chemical and phase transfer scheme 2.3.2.4 The coupling scheme 2.4 Prediction of aqueous phase kinetic data 2.4.1 Simple correlations 2.4.2 Evans-Polanyi-correlations 2.4.3 Structure-activity relationships 2.5 The generator GECKO-A 3 Evaluation of kinetic data and prediction methods 3.1 Compilation and evaluation of aqueous phase kinetic data 3.2 Extrapolation of gas phase rate constants to the aqueous phase 3.3 Homologous series of compound classes 3.4 Radical reactivity comparisons 3.5 Evans-Polanyi-type correlations 3.5.1 OH rate constant prediction 3.5.2 NO3 rate constant prediction 3.5.3 Development of an advanced Evans-Polanyi-type correlation 3.6 Structure-activity relationships 3.7 Conclusions from the evaluation process 4 Development of the new aqueous phase protocol and its implementation into GECKO-A 4.1 Initialisation and workflow of GECKO-A 4.2 Estimation of phase transfer data 4.3 OH reactions of stable compounds 4.4 NO3 reactions of stable compounds 4.5 Hydration of carbonyl compounds 4.6 Hydrolysis of carbonyl nitrates 4.7 Dissociation of carboxylic acids 4.8 Degradation of radical compounds 4.8.1 RO2 recombinations and cross-reactions 4.8.2 HO2 elimination of ff-hydroxy peroxy radicals 4.8.3 Degradation of acylperoxy radicals 4.8.4 Degradation of fi-carboxyl peroxy radicals 4.8.5 Degradation of alkoxy radicals 4.8.6 Degradation of acyloxy radicals 5 Investigation and refinement of crucial parameters in GECKO-A and CAPRAM mechanism development 5.1 Formation and degradation of polycarbonyl compounds in the protocol 5.2 Influence of the mass accommodation coefficient on the organic multiphase chemistry and composition 5.3 Influence of the cut-off parameter for minor reaction pathways 5.4 Influence of the chosen SAR in the protocol 5.5 Processing of organic mass fraction in the protocol 5.5.1 Parameterisations for radical attack of the overall organic mass fraction 5.5.2 Detailed studies of organic nitrate sinks and sources 5.5.3 Phase transfer of oxygenated organic compounds in the protocol 5.5.4 Decay of alkoxy radicals in the protocol 5.5.5 Revision of the GROMHE thermodynamic database 5.6 Influence of the nitrate radical chemistry 5.7 The final protocol for aqueous phase mechanism self-generation 5.8 CAPRAM mechanism development 5.8.1 CAPRAM 3.0 5.8.2 CAPRAM 3.5 5.8.3 CAPRAM 4.0 6 Model results and discussion 6.1 Comparisons of model results with aerosol chamber experiments 6.1.1 Design of the aerosol chamber experiments 6.1.1.1 Hexane oxidation experiment 6.1.1.2 Trimethylbenzene oxidation experiment 6.1.2 Mechanism generation and model setup 6.1.2.1 Hexane oxidation experiment 6.1.2.2 Trimethylbenzene oxidation experiment 6.1.3 Evaluation of the model versus aerosol chamber results 6.1.3.1 Hexane oxidation experiment 6.1.3.2 Trimethylbenzene oxidation experiment 6.2 Simulations with a ‘real atmosphere’ scenario 6.2.1 Model setup 6.2.2 Meteorological and microphysical parameters 6.2.3 Influence of the extended organic scheme on the particle acidity and SOA formation 6.2.3.1 Particle acidity 6.2.3.2 Particle mass 6.2.4 Influence of the extended organic scheme on inorganic radical oxidants 6.2.4.1 OH chemistry 6.2.4.2 NO3 chemistry 6.2.4.3 Comparison of OH and NO3 chemistry 6.2.4.4 HO2/O2- chemistry 6.2.5 Influence of the extended organic scheme on inorganic non-radical oxidants 6.2.5.1 H2O2 chemistry 6.2.5.2 O3 chemistry 6.2.6 Influence of the extended organic scheme on inorganic particulate matter 6.2.6.1 Sulfate chemistry 6.2.6.2 Nitrate chemistry 6.2.6.3 TMI chemistry 6.2.7 Detailed investigations of selected organic subsystems 6.2.7.1 Monofunctional organic compounds 6.2.7.2 Carbonyl compounds 6.2.7.3 Dicarboxylic acids and functionalised monocarboxylic acids 7 Conclusions References Glossary Acronyms List of symbols List of Figures List of Tables Acknowledgements Curriculum Vitae List of relevant publications Peer-reviewed publications Oral conference contributions Poster conference contributions Appendix A Overview of selected compound classes of tropospheric relevance B Detailed description of the function of SARs C The kinetic database C.1 Reactions of hydroxyl radicals with organic compounds C.2 Reactions of nitrate radicals with organic compounds D Detailed information about the evaluation of prediction methods D.1 Rate data used for the derivation and evaluation of gas-aqueous phase correlations D.2 Explanation of the use of box plots D.3 Additional correlations of homologous series of various compound classes D.4 Additional information of Evans-Polanyi-type correlations D.5 Additional information of structure-activity relationships E Additional information for the development of the protocol of GECKO-A E.1 Investigations on the decay of acylperoxy radicals E.2 Additional information about the sensitivity of mass accomodation coefficients E.3 Additional information about the sensitivity studies concerning the decay of polycarbonyls E.4 Additional information about the sensitivity studies concerning the omission of minor reaction pathways E.5 Additional information about the sensitivity studies concerning the processing of the organic mass fraction E.6 Additional information about the influence of the nitrate radical chemistry F Additional information about the mechanism generation and model initialisation F.1 List of primary compounds used for the generation of CAPRAM 3.5 F.2 List of primary compounds used for the generation of CAPRAM 4.0 F.3 Model initialization of the ‘real atmosphere’ scenarios G The CAPRAM oxidation scheme G.1 Photolysis processes G.2 Inorganic chemistry G.2.1 Phase transfer processes G.2.2 Chemical conversions G.3 Organic chemistry G.3.1 Phase transfer processes G.3.2 Chemical conversions H Detailed information about the model validation with chamber experiments H.1 Additional information about the initialisation of the hexane oxidation experiment H.2 Additional model results from the hexane oxidation experiment H.3 Additional information about the sensitivity runs used in the trimethylbenzene oxidation experiment H.4 Additional results from the TMB oxidation experiment I Additional results from the ‘real atmosphere’ scenario I.1 Particle acidity and SOA formation I.2 Radical oxidants I.3 Organic compounds References of the Appendix / Das zahlreiche Vorkommen organischer Verbindungen in natürlichen und anthropogen beeinflussten Ökosystemen hat diese Verbindungen in den Fokus der Atmosphärenforschung gerückt. Organische Verbindungen beeinträchtigen die Luftqualität, die menschliche Gesundheit und das Klima. Weiterhin werden Partikelwachstum und -eigenschaften, sekundäre organische Partikelbildung und dadurch der globale Strahlungshaushalt durch sie beeinflusst. Um die troposphärische Multiphasenchemie organischer Verbindungen und Wechselwirkungen mit der Flüssigphase zu untersuchen, sind Modellstudien hilfreich. Die Oxidation großer organischer Moleküle führt zu einer Vielzahl an Zwischenprodukten. Der Abbau erfolgt in unzähligen Reaktionen bis hin zum Endprodukt CO2. Bei der Entwicklung expliziter Mechanismen muss deshalb für diese Verbindungen auf computergestützte, automatisierte Methoden zurückgegriffen werden. Abschätzungsmethoden für die Vorhersage kinetischer Daten zur Beschreibung des Abbaus der Zwischenprodukte sind unabdingbar, da eine experimentelle Bestimmung aller benötigten Daten nicht realisierbar ist. Die derzeitige Beschreibung der Flüssigphasenchemie unterliegt deutlich den Beschreibungen der Gasphase in atmosphärischen Chemiemechanismen trotz deren Relevanz für die Multiphasenchemie. In dieser Arbeit wurde der Gasphasenmechanismusgenerator GECKO-A (“Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere”) um ein Protokoll zur Oxidation organischer Verbindungen in der Flüssigphase erweitert. Dazu wurde eine Datenbank mit kinetischen Daten von 465 Hydroxylradikal- und 129 Nitratradikalreaktionen mit organischen Verbindungen angelegt und evaluiert. Mit Hilfe der Datenbank wurden derzeitige Abschätzungsmethoden für die Vorhersage kinetischer Daten von Flüssigphasenreaktionen organischer Verbindungen evaluiert. Die untersuchten Methoden beinhalteten Korrelationen kinetischer Daten aus Gas- und Flüssigphase, homologer Reihen verschiedener Stoffklassen, Reaktivitätsvergleiche, Evans-Polanyi-Korrelationen und Struktur-Reaktivitätsbeziehungen. Für die Mechanismusgenerierung großer organischer Moleküle wurden die Evans-Polanyi-Korrelationen in dieser Arbeit weiterentwickelt. Es wurde ein Protokol für die Mechanismusgenerierung entwickelt, das auf Struktur-Reaktivitätsbeziehungen bei Reaktionen von organischen Verbindungen mit OH-Radikalen und auf den erweiterten Evans-Polanyi-Korrelationen bei NO3-Radikalreaktionen beruht. Das Protokoll wurde umfangreich in einer Reihe von Sensitivitätsstudien getestet, um Unsicherheiten kritischer Parameter abzuschätzen. Der erweiterte Multiphasengenerator GECKO-A wurde dazu verwendet, neue Mechanismen zu generieren, die in Boxmodellstudien gegen Aerosolkammerexperimente evaluiert wurden. Die Experimentreihen unterschieden sich sowohl in der betrachteten Ausgangssubstanz (Hexan und Trimethylbenzen) und dem Experimentaufbau (ohne oder mit UV-C-Photolyse und ohne oder mit zusätzlicher partikulärer Hydroxylradikalquelle). Bei den Experimenten konnte eine zufriedenstellende bis gute Übereinstimmung der experimentellen und Modellergebnisse erreicht werden. Weiterhin wurde GECKO-A verwendet, um zwei neue CAPRAM-Versionen mit bis zu 4174 Verbindungen und 7145 Prozessen zu generieren. Erstmals wurden Verzweigungsverhältnisse in CAPRAM eingeführt. Außerdem wurde die Chemie organischer Verbindungen mit bis zu vier Kohlenstoffatomen erweitert. Umfangreiche Untersuchungen unter realistischen troposphärischen Bedingungen in urbanen und ländlichen Gebieten haben deutliche Verbesserungen der erweiterten Mechanismen besonders in Bezug auf Massenzuwachs des organischen Aerosolanteils gezeigt. Das Verständnis der organischen Multiphasenchemie konnte durch detaillierte Untersuchungen zu den Konzentrations-Zeit-Profilen und chemischen Flüssen vertieft werden, aber auch gegenwärtige Limitierungen des Generators, der erzeugten Mechanismen und unseres Verständnisses für Flüssigphasenprozesse organischer Verbindungen aufgezeigt werden.:1 Introduction and motivation 2 Theoretical background 2.1 General overview of the tropospheric multiphase chemistry of organic compounds 2.1.1 Gas phase chemistry 2.1.2 Phase transfer 2.1.3 Aqueous phase chemistry 2.2 Tropospheric multiphase chemistry mechanisms 2.2.1 Gas phase mechanisms 2.2.2 Aqueous phase mechanisms 2.2.3 The multiphase mechanism MCMv3.1-CAPRAM 3.0n 2.2.3.1 MCMv3.1 2.2.3.2 CAPRAM 3.0n 2.3 Multiphase chemistry box models 2.3.1 Overview 2.3.2 The model SPACCIM 2.3.2.1 Overview 2.3.2.2 The microphysical scheme 2.3.2.3 The chemical and phase transfer scheme 2.3.2.4 The coupling scheme 2.4 Prediction of aqueous phase kinetic data 2.4.1 Simple correlations 2.4.2 Evans-Polanyi-correlations 2.4.3 Structure-activity relationships 2.5 The generator GECKO-A 3 Evaluation of kinetic data and prediction methods 3.1 Compilation and evaluation of aqueous phase kinetic data 3.2 Extrapolation of gas phase rate constants to the aqueous phase 3.3 Homologous series of compound classes 3.4 Radical reactivity comparisons 3.5 Evans-Polanyi-type correlations 3.5.1 OH rate constant prediction 3.5.2 NO3 rate constant prediction 3.5.3 Development of an advanced Evans-Polanyi-type correlation 3.6 Structure-activity relationships 3.7 Conclusions from the evaluation process 4 Development of the new aqueous phase protocol and its implementation into GECKO-A 4.1 Initialisation and workflow of GECKO-A 4.2 Estimation of phase transfer data 4.3 OH reactions of stable compounds 4.4 NO3 reactions of stable compounds 4.5 Hydration of carbonyl compounds 4.6 Hydrolysis of carbonyl nitrates 4.7 Dissociation of carboxylic acids 4.8 Degradation of radical compounds 4.8.1 RO2 recombinations and cross-reactions 4.8.2 HO2 elimination of ff-hydroxy peroxy radicals 4.8.3 Degradation of acylperoxy radicals 4.8.4 Degradation of fi-carboxyl peroxy radicals 4.8.5 Degradation of alkoxy radicals 4.8.6 Degradation of acyloxy radicals 5 Investigation and refinement of crucial parameters in GECKO-A and CAPRAM mechanism development 5.1 Formation and degradation of polycarbonyl compounds in the protocol 5.2 Influence of the mass accommodation coefficient on the organic multiphase chemistry and composition 5.3 Influence of the cut-off parameter for minor reaction pathways 5.4 Influence of the chosen SAR in the protocol 5.5 Processing of organic mass fraction in the protocol 5.5.1 Parameterisations for radical attack of the overall organic mass fraction 5.5.2 Detailed studies of organic nitrate sinks and sources 5.5.3 Phase transfer of oxygenated organic compounds in the protocol 5.5.4 Decay of alkoxy radicals in the protocol 5.5.5 Revision of the GROMHE thermodynamic database 5.6 Influence of the nitrate radical chemistry 5.7 The final protocol for aqueous phase mechanism self-generation 5.8 CAPRAM mechanism development 5.8.1 CAPRAM 3.0 5.8.2 CAPRAM 3.5 5.8.3 CAPRAM 4.0 6 Model results and discussion 6.1 Comparisons of model results with aerosol chamber experiments 6.1.1 Design of the aerosol chamber experiments 6.1.1.1 Hexane oxidation experiment 6.1.1.2 Trimethylbenzene oxidation experiment 6.1.2 Mechanism generation and model setup 6.1.2.1 Hexane oxidation experiment 6.1.2.2 Trimethylbenzene oxidation experiment 6.1.3 Evaluation of the model versus aerosol chamber results 6.1.3.1 Hexane oxidation experiment 6.1.3.2 Trimethylbenzene oxidation experiment 6.2 Simulations with a ‘real atmosphere’ scenario 6.2.1 Model setup 6.2.2 Meteorological and microphysical parameters 6.2.3 Influence of the extended organic scheme on the particle acidity and SOA formation 6.2.3.1 Particle acidity 6.2.3.2 Particle mass 6.2.4 Influence of the extended organic scheme on inorganic radical oxidants 6.2.4.1 OH chemistry 6.2.4.2 NO3 chemistry 6.2.4.3 Comparison of OH and NO3 chemistry 6.2.4.4 HO2/O2- chemistry 6.2.5 Influence of the extended organic scheme on inorganic non-radical oxidants 6.2.5.1 H2O2 chemistry 6.2.5.2 O3 chemistry 6.2.6 Influence of the extended organic scheme on inorganic particulate matter 6.2.6.1 Sulfate chemistry 6.2.6.2 Nitrate chemistry 6.2.6.3 TMI chemistry 6.2.7 Detailed investigations of selected organic subsystems 6.2.7.1 Monofunctional organic compounds 6.2.7.2 Carbonyl compounds 6.2.7.3 Dicarboxylic acids and functionalised monocarboxylic acids 7 Conclusions References Glossary Acronyms List of symbols List of Figures List of Tables Acknowledgements Curriculum Vitae List of relevant publications Peer-reviewed publications Oral conference contributions Poster conference contributions Appendix A Overview of selected compound classes of tropospheric relevance B Detailed description of the function of SARs C The kinetic database C.1 Reactions of hydroxyl radicals with organic compounds C.2 Reactions of nitrate radicals with organic compounds D Detailed information about the evaluation of prediction methods D.1 Rate data used for the derivation and evaluation of gas-aqueous phase correlations D.2 Explanation of the use of box plots D.3 Additional correlations of homologous series of various compound classes D.4 Additional information of Evans-Polanyi-type correlations D.5 Additional information of structure-activity relationships E Additional information for the development of the protocol of GECKO-A E.1 Investigations on the decay of acylperoxy radicals E.2 Additional information about the sensitivity of mass accomodation coefficients E.3 Additional information about the sensitivity studies concerning the decay of polycarbonyls E.4 Additional information about the sensitivity studies concerning the omission of minor reaction pathways E.5 Additional information about the sensitivity studies concerning the processing of the organic mass fraction E.6 Additional information about the influence of the nitrate radical chemistry F Additional information about the mechanism generation and model initialisation F.1 List of primary compounds used for the generation of CAPRAM 3.5 F.2 List of primary compounds used for the generation of CAPRAM 4.0 F.3 Model initialization of the ‘real atmosphere’ scenarios G The CAPRAM oxidation scheme G.1 Photolysis processes G.2 Inorganic chemistry G.2.1 Phase transfer processes G.2.2 Chemical conversions G.3 Organic chemistry G.3.1 Phase transfer processes G.3.2 Chemical conversions H Detailed information about the model validation with chamber experiments H.1 Additional information about the initialisation of the hexane oxidation experiment H.2 Additional model results from the hexane oxidation experiment H.3 Additional information about the sensitivity runs used in the trimethylbenzene oxidation experiment H.4 Additional results from the TMB oxidation experiment I Additional results from the ‘real atmosphere’ scenario I.1 Particle acidity and SOA formation I.2 Radical oxidants I.3 Organic compounds References of the Appendix

This thesis is devoted to the experimental quantitative characterization of the shape and orientation distribution of ice particles in clouds. The characterization is based on measured and modeled elevation dependencies of the polarimetric parameters differential reflectivity and correlation coefficient. The polarimetric data is obtained using a newly developed 35-GHz cloud radar MIRA-35 with hybrid polarimetric configuration and scanning capabilities. The full procedure chain of the technical implementation and the realization of the setup of the hybrid-mode cloud radar for the shape determination are presented. This includes the description of phase adjustments in the transmitting paths, the introduction of the general data processing scheme, correction of the data for the differences of amplifications and electrical path lengths in the transmitting and receiving channels, the rotation of the polarization basis by 45°, the correction of antenna effects on polarimetric measurements, the determination of spectral polarimetric variables, and the formulation of a scheme to increase the signal-to-noise ratio. Modeling of the polarimetric variables is based on existing backscattering models assuming the spheroidal representation of cloud scatterers. The parameters retrieved from the model are polarizability ratio and degree of orientation, which can be assigned to certain particle orientations and shapes. In the thesis the first quantitative estimations of ice particle shape at the top of liquid-topped clouds are presented. Analyzed ice particles were formed in the presence of supercooled water and in the temperature range from -20 °C to -3 °C. The estimation is based on polarizability ratios of ice particles measured by the MIRA-35 with hybrid polarimetric configuration, manufactured by METEK GmbH. For the study, 22 cases observed during the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign were used. Polarizability ratios retrieved for cloud layers with cloud-top temperatures of about -5, -8, -15, and -20 °C were 1.6, 0.9, 0.6, and 0.9, respectively. Such values correspond to prolate, quasi-isotropic, oblate, and quasi-isotropic particles, respectively. Data from a free-fall chamber were used for the comparison. A good agreement of detected shapes with well-known shape{temperature dependencies observed in laboratories was found.:1 Introduction 2 Formation and development of ice particles: Laboratory studies and remote observations 2.1 Heterogeneous ice formation in the atmosphere 2.2 Laboratory investigations of ice crystal development 2.3 Polarimetric radar observations of ice microphysics 2.3.1 Polarimetry in weather radar networks 2.3.2 Polarimetry in cloud radars 2.3.3 Polarization coupling 2.4 Aims and scientific questions 3 Effects of antenna patterns on cloud radar polarimetric measurements 3.1 Measurements of complex antenna patterns 3.1.1 Problem definition 3.1.2 Measurement description 3.1.3 Results of antenna pattern measurements 3.2 Correction of LDR measurements 3.3 Discrimination between insects and clouds 4 Cloud radar MIRA-35 with hybrid mode 4.1 Implementation and phase adjustment 4.2 Processing of the coherency matrix 4.3 Correction of the coherency matrix for differences of channels 4.4 The coherency matrix in the slanted basis 4.5 Correction for the antenna coupling 4.6 Spectral polarimetric variables 4.7 Sensitivity issue 5 Shape and orientation retrieval 5.1 Backscattering model 5.2 Retrieval technique 5.3 Case study 6 Shape-temperature relationship of pristine ice crystals 6.1 Instrumentation and data set 6.2 Examples of the shape retrieval 6.2.1 Case 1: 12 October 2014, 15:00-16:00 UTC 6.2.2 Case 2: 18 October 2014, 01:00-02:00 UTC 6.2.3 Case 3: 20 October 2014, 18:00-19:00 UTC 6.2.4 Case 4: 10 November 2014, 02:00-03:00 UTC 6.2.5 Case 5: 7 November 2014, 20:00-21:00 UTC 6.3 Comparison of shape with laboratory studies 6.4 Orientation of pristine ice crystals 7 Summary and outlook Bibliography List of Abbreviations List of Symbols