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  • Pirazzini, Roberta (Helsingin yliopisto, 2008)
    Polar Regions are an energy sink of the Earth system, as the Sun rays do not reach the Poles for half of the year, and hit them only at very low angles for the other half of the year. In summer, solar radiation is the dominant energy source for the Polar areas, therefore even small changes in the surface albedo strongly affect the surface energy balance and, thus, the speed and amount of snow and ice melting. In winter, the main heat sources for the atmosphere are the cyclones approaching from lower latitudes, and the atmosphere-surface heat transfer takes place through turbulent mixing and longwave radiation, the latter dominated by clouds. The aim of this thesis is to improve the knowledge about the surface and atmospheric processes that control the surface energy budget over snow and ice, with particular focus on albedo during the spring and summer seasons, on horizontal advection of heat, cloud longwave forcing, and turbulent mixing during the winter season. The critical importance of a correct albedo representation in models is illustrated through the analysis of the causes for the errors in the surface and near-surface air temperature produced in a short-range numerical weather forecast by the HIRLAM model. Then, the daily and seasonal variability of snow and ice albedo have been examined by analysing field measurements of albedo, carried out in different environments. On the basis of the data analysis, simple albedo parameterizations have been derived, which can be implemented into thermodynamic sea ice models, as well as numerical weather prediction and climate models. Field measurements of radiation and turbulent fluxes over the Bay of Bothnia (Baltic Sea) also allowed examining the impact of a large albedo change during the melting season on surface energy and ice mass budgets. When high contrasts in surface albedo are present, as in the case of snow covered areas next to open water, the effect of the surface albedo heterogeneity on the downwelling solar irradiance under overcast condition is very significant, although it is usually not accounted for in single column radiative transfer calculations. To account for this effect, an effective albedo parameterization based on three-dimensional Monte Carlo radiative transfer calculations has been developed. To test a potentially relevant application of the effective albedo parameterization, its performance in the ground-based retrieval of cloud optical depth was illustrated. Finally, the factors causing the large variations of the surface and near-surface temperatures over the Central Arctic during winter were examined. The relative importance of cloud radiative forcing, turbulent mixing, and lateral heat advection on the Arctic surface temperature were quantified through the analysis of direct observations from Russian drifting ice stations, with the lateral heat advection calculated from reanalysis products.
  • Donadini, Fabio (Helsingin yliopisto, 2007)
    The geomagnetic field is one of the most fundamental geophysical properties of the Earth and has significantly contributed to our understanding of the internal structure of the Earth and its evolution. Paleomagnetic and paleointensity data have been crucial in shaping concepts like continental drift, magnetic reversals, as well as estimating the time when the Earth's core and associated geodynamo processes begun. The work of this dissertation is based on reliable Proterozoic and Holocene geomagnetic field intensity data obtained from rocks and archeological artifacts. New archeomagnetic field intensity results are presented for Finland, Estonia, Bulgaria, Italy and Switzerland. The data were obtained using sophisticated laboratory setups as well as various reliability checks and corrections. Inter-laboratory comparisons between three laboratories (Helsinki, Sofia and Liverpool) were performed in order to check the reliability of different paleointensity methods. The new intensity results fill up considerable gaps in the master curves for each region investigated. In order to interpret the paleointensity data of the Holocene period, a novel and user-friendly database (GEOMAGIA50) was constructed. This provided a new tool to independently test the reliability of various techniques and materials used in paleointensity determinations. The results show that archeological artifacts, if well fired, are the most suitable materials. Also lavas yield reliable paleointensity results, although they appear more scattered. This study also shows that reliable estimates are obtained using the Thellier methodology (and its modifications) with reliability checks. Global paleointensity curves during Paleozoic and Proterozoic have several time gaps with few or no intensity data. To define the global intensity behavior of the Earth's magnetic field during these times new rock types (meteorite impact rocks) were investigated. Two case histories are presented. The Ilyinets (Ukraine) impact melt rocks yielded a reliable paleointensity value at 440 Ma (Silurian), whereas the results from Jänisjärvi impact melts (Russian Karelia, ca. 700 Ma) might be biased towards high intensity values because of non-ideal magnetic mineralogy. The features of the geomagnetic field at 1.1 Ga are not well defined due to problems related to reversal asymmetries observed in Keweenawan data of the Lake Superior region. In this work new paleomagnetic, paleosecular variation and paleointensity results are reported from coeval diabases from Central Arizona and help understanding the asymmetry. The results confirm the earlier preliminary observations that the asymmetry is larger in Arizona than in Lake Superior area. Two of the mechanisms proposed to explain the asymmetry remain plausible: the plate motion and the non-dipole influence.
  • Soininen, Aleksi (Helsingin yliopisto, 2001)
  • Kangas, Kaisa (Helsingin yliopisto, 2015)
    The starting point for this dissertation is whether the concept of Zariski geometry, introduced by Hrushovski and Zilber, could be generalized to the context of non-elementary classes. This leads to the axiomatization of Zariski-like structures. As our main result, we prove that if the canonical pregeometry of a Zariski-like structure is non locally modular, then the structure interprets either an algebraically closed field or a non-classical group. This is a counterpart to the result by Hrushovski and Zilber which states that an algebraically closed field can be found in a non locally modular Zariski geometry. It demonstrates that the concept of a Zariski-like structure captures one of the most essential features of a Zariski geometry. Finally, we give a non-trivial example by showing that the cover of the multiplicative group of an algebraically closed field of characteristic zero is Zariski-like. We define a Zariski-like structure as a quasiminimal pregeometry structure that has certain properties. Instead of assuming underlying topologies, we formulate the axioms for a countable collection C of Galois definable sets that have some of the properties of irreducible closed sets from the Zariski geometry context. Quasiminimal classes are abstract elementary classes (AECs) that arise from a quasiminimal pregeometry structure. They are uncountably categorical, and have both the amalgamation property (AP) and the joint embedding property (JEP), and thus also a model homogeneous universal monster model, which we denote by M. To adapt Hrushovski's and Zilber's proof to our setting, we first generalize Hrushovski's Group Configuration Theorem to the context of quasiminimal classes. For this, we develop an independence calculus that has all the usual properties of non-forking and works in our context. We then prove the group configuration theorem and apply it to find a 1-dimensional group, assuming that the canonical pregeometry obtained from the bounded closure operator is non-trivial. A field can be found under the further assumptions that M does not interpret a non-classical group and the canonical pregeometry is non locally modular. Finally, we show that the cover of the multiplicative group of an algebraically closed field, studied by e.g. Boris Zilber and Lucy Burton, provides a non-trivial example of a Zariski-like structure. Burton obtained a topology on the cover by taking sets definable by positive, quantifier-free first order formulae as the basic closed sets. This is called the PQF-topology, and the sets that are closed with respect to it are called the PQF-closed sets. We show that the cover becomes Zariski-like after adding names for a countable number of elements to the language. The axioms for a Zariski-like structure are then satisfied if the collection C is taken to consist of the PQF-closed sets that are definable over the empty set.
  • Sahlsten, Tuomas (Helsingin yliopisto, 2012)
    The main goal of this dissertation is to study the local distribution and irregularities of measures in mostly Euclidean setting. The research belongs to the field of Geometric Measure Theory. The thesis consists of an overview and three refereed research articles. The first article concerns the relationship between Hausdorff- and packing dimensions of measures and the local distribution of measures. There are many ways to quantify local distribution and here we consider local homogeneity, conical densities and porosity. Historically, there have already been many results for these notions of local distribution, but our contribution is to generalize and simplify many of the earlier results, and most importantly, provide a unified framework where such results could be proved. This framework is based on local entropy averages, a recently introduced way to calculate dimensions of measures inspired by dynamical systems. In the second and third articles we consider another notion that describes the local irregularities of measures: tangent measures. Tangent measures were rigorously defined and studied by D. Preiss in 1987 and they provided a powerful tool in the study of rectifiability. In this thesis we consider the possible relationship between tangent measures and the original measure. Our motivation is to strengthen the heuristics that it is not in general possible to deduce information from just the tangent measures of the underlying measure without further assumptions from the measure. In the second paper we construct a highly singular measure, a non-doubling measure, for which every tangent measure is equivalent to Lebesgue measure. The existence of such a measure provides a natural extension to a previous result by Preiss and it also provides a direct counterexample to the characterisation of porosity with tangent measures for general measures, which was previously unknown. In the third paper we prove that for a typical measure in the Euclidean space, in the sense of Baire category, the set of tangent measures consists of all non-zero measures at almost every point with respect to the underlying measure. This result was already proved by T. O'Neil in this PhD thesis from 1994, but we provide another self-contained proof using different techniques. Moreover, we record previously unknown corollaries and sharpen the result by T. O'Neil. Furthermore, we are able to use similar ideas in the setting of micromeasures, which are a symbolic way to define tangent measures in trees, and prove an analogous result in this setting.
  • Kesälä, Meeri (Helsingin yliopisto, 2006)
    The research in model theory has extended from the study of elementary classes to non-elementary classes, i.e. to classes which are not completely axiomatizable in elementary logic. The main theme has been the attempt to generalize tools from elementary stability theory to cover more applications arising in other branches of mathematics. In this doctoral thesis we introduce finitary abstract elementary classes, a non-elementary framework of model theory. These classes are a special case of abstract elementary classes (AEC), introduced by Saharon Shelah in the 1980's. We have collected a set of properties for classes of structures, which enable us to develop a 'geometric' approach to stability theory, including an independence calculus, in a very general framework. The thesis studies AEC's with amalgamation, joint embedding, arbitrarily large models, countable Löwenheim-Skolem number and finite character. The novel idea is the property of finite character, which enables the use of a notion of a weak type instead of the usual Galois type. Notions of simplicity, superstability, Lascar strong type, primary model and U-rank are inroduced for finitary classes. A categoricity transfer result is proved for simple, tame finitary classes: categoricity in any uncountable cardinal transfers upwards and to all cardinals above the Hanf number. Unlike the previous categoricity transfer results of equal generality the theorem does not assume the categoricity cardinal being a successor. The thesis consists of three independent papers. All three papers are joint work with Tapani Hyttinen.
  • Uusi-Simola, Jouni (Helsingin yliopisto, 2009)
    Boron neutron capture therapy (BNCT) is a form of chemically targeted radiotherapy that utilises the high neutron capture cross-section of boron-10 isotope to achieve a preferential dose increase in the tumour. The BNCT dosimetry poses a special challenge as the radiation dose absorbed by the irradiated tissues consists of several dose different components. Dosimetry is important as the effect of the radiation on the tissue is correlated with the radiation dose. Consistent and reliable radiation dose delivery and dosimetry are thus basic requirements for radiotherapy. The international recommendations for are not directly applicable to BNCT dosimetry. The existing dosimetry guidance for BNCT provides recommendations but also calls for investigating for complementary methods for comparison and improved accuracy. In this thesis the quality assurance and stability measurements of the neutron beam monitors used in dose delivery are presented. The beam monitors were found not to be affected by the presence of a phantom in the beam and that the effect of the reactor core power distribution was less than 1%. The weekly stability test with activation detectors has been generally reproducible within the recommended tolerance value of 2%. An established toolkit for epithermal neutron beams for determination of the dose components is presented and applied in an international dosimetric intercomparison. The measured quantities (neutron flux, fast neutron and photon dose) by the groups in the intercomparison were generally in agreement within the stated uncertainties. However, the uncertainties were large, ranging from 3-30% (1 standard deviation), emphasising the importance of dosimetric intercomparisons if clinical data is to be compared between different centers. Measurements with the Exradin type 2M ionisation chamber have been repeated in the epithermal neutron beam in the same measurement configuration over the course of 10 years. The presented results exclude severe sensitivity changes to thermal neutrons that have been reported for this type of chamber. Microdosimetry and polymer gel dosimetry as complementary methods for epithermal neutron beam dosimetry are studied. For microdosimetry the comparison of results with ionisation chambers and computer simulation showed that the photon dose measured with microdosimetry was lower than with the two other methods. The disagreement was within the uncertainties. For neutron dose the simulation and microdosimetry results agreed within 10% while the ionisation chamber technique gave 10-30% lower neutron dose rates than the two other methods. The response of the BANG-3 gel was found to be linear for both photon and epithermal neutron beam irradiation. The dose distribution normalised to dose maximum measured by MAGIC polymer gel was found to agree well with the simulated result near the dose maximum while the spatial difference between measured and simulated 30% isodose line was more than 1 cm. In both the BANG-3 and MAGIC gel studies, the interpretation of the results was complicated by the presence of high-LET radiation.
  • Isavnin, Alexey (Helsingin yliopisto, 2014)
    A lot of modern ground-based and space systems, such as navigation satellites, electric power grids, and telecommunication frameworks, can be affected by the changes in the near-Earth space environment, i.e., space weather. The main driver of the space weather is the Sun, which provides a supersonic flow of plasma, known as the solar wind. Coronal mass ejections (CMEs) are the most prominent feature of solar activity. They result from the eruptions on the Sun and propagate almost radially from it embedded into the solar wind. CMEs drive the strongest disturbances of the near-Earth space environment and cause the strongest geomagnetic storms when they encounter the magnetosphere of the Earth. A significant fraction of CMEs exhibit a specific configuration of twisted magnetic field lines, i.e., the flux rope configuration. The geoffectiveness of flux rope CMEs depends on their internal magnetic structure, morphological properties, speed, and the geometry of their propagation through the interplanetary space. In this thesis, the internal structure of flux rope CMEs and their three-dimensional evolution in the interplanetary space were investigated using the combination of white-light and extreme ultraviolet observations and in-situ measurements and modeling. The results of the analysis show that a typical flux rope CME consists of regions of physically different plasma with the flux rope occupying one of them. The methodology for studying the evolution of the individual flux rope in three-dimensional space is described. The presented technique is used to show that solar flux ropes experience significant deflections and rotations during their propagation from the Sun to the Earth's orbit that have to be taken into account for reliable space weather forecasting. These structures deflect predominantly towards the solar equatorial plane and their rotations are affected by the solar wind streams. It is discovered that 40% of the flux rope evolution happens after 30 solar radii. Flux-rope-like structures can also form in the magnetosphere during the periods of geomagnetic disturbances. They are generated in the magnetotail configurations with multiple reconnection sites and travel towards the Earth or away from it. Both types of these helical magnetic structures are addressed in this thesis as well. It is demonstrated that the properties of these structures help to get insight into the dynamics of the magnetosphere. The model of evolution of earthward-traveling flux ropes is presented, according to which they deteriorate and degrade into dipolarization fronts, another magnetic field configuration that is characteristic for geomagnetic disturbances. This thesis contributes both to the improvement of the flux rope analysis techniques as well as conducts a comprehensive analysis of solar and magnetospheric flux ropes and their evolution. The results of the research advance our understanding of the Sun-Earth coupling in one dynamical process and can be used for improving the space weather forecasting tools.
  • Muukkonen, Petteri (Helsingin yliopisto, 2006)
    In recent years, concern has arisen over the effects of increasing carbon dioxide (CO2) in the earth's atmosphere due to the burning of fossil fuels. One way to mitigate increase in atmospheric CO2 concentration and climate change is carbon sequestration to forest vegeta-tion through photosynthesis. Comparable regional scale estimates for the carbon balance of forests are therefore needed for scientific and political purposes. The aim of the present dissertation was to improve methods for quantifying and verifying inventory-based carbon pool estimates of the boreal forests in the mineral soils. Ongoing forest inventories provide a data based on statistically sounded sampling for estimating the level of carbon stocks and stock changes, but improved modelling tools and comparison of methods are still needed. In this dissertation, the entire inventory-based large-scale forest carbon stock assessment method was presented together with some separate methods for enhancing and comparing it. The enhancement methods presented here include ways to quantify the biomass of understorey vegetation as well as to estimate the litter production of needles and branches. In addition, the optical remote sensing method illustrated in this dis-sertation can be used to compare with independent data. The forest inventory-based large-scale carbon stock assessment method demonstrated here provided reliable carbon estimates when compared with independent data. Future ac-tivity to improve the accuracy of this method could consist of reducing the uncertainties regarding belowground biomass and litter production as well as the soil compartment. The methods developed will serve the needs for UNFCCC reporting and the reporting under the Kyoto Protocol. This method is principally intended for analysts or planners interested in quantifying carbon over extensive forest areas.
  • Flender, Samuel (Helsingin yliopisto, 2014)
    One of the most important aspects of cosmology is the theory of structure formation, which describes the transition from the early, homogeneous Universe to the inhomogeneous Universe we observe today, i.e. the formation of stars, galaxies and clusters of galaxies. In this thesis, we study structure formation using the Newtonian theory of gravity within an expanding Friedmann-Robertson-Walker spacetime. We use this simple framework in order to learn for instance about the order of structure formation, which is a bottom-up evolution. Further, we introduce relativistic cosmological perturbation theory. We show that the Newtonian and relativistic descriptions of linear perturbations coincide on scales that are well inside the horizon. On larger scales however, we find differences between the two theories, in particular in the obtained linear matter power spectra. Observations indicate that the Universe is today in a phase of accelerated expansion. In the standard model of cosmology, the LCDM model, the accelerated expansion is explained by the existence of dark energy in form of a cosmological constant. Here, we focus on the integrated Sachs-Wolfe effect as a probe of the dynamical effects of dark energy. In particular, this effect causes an imprint of the local large-scale structure into the temperature anisotropies of the cosmic microwave background (CMB). We discuss how this effect arises in theory and how it can be measured in practice. The statistical properties of the temperature fluctuations in the CMB can be remarkably well described within the LCDM model. However, on the largest angular scales some features have been found that are difficult to explain within the standard model, the so-called CMB anomalies. Here, we discuss these anomalies from a statistical point of view. We focus on one particular anomaly, the hemispherical power asymmetry, and explore its connection to the initial conditions of the Universe. In particular, this asymmetry can be related to primordial non-Gaussianity in certain inflation models.
  • Jokinen, Tuija (Helsingin yliopisto, 2015)
    We live in a world full of aerosols and witness their existence constantly. Changes in visibility, road dust and pollen filling the air in the spring time and even dosing some medicines are all related to aerosols. The most important aspect for this thesis is however, the formation of aerosol precursor molecules and clusters and their possible effects on aerosol properties. Different types of aerosols e. g. organic and inorganic, ice and pollen, biogenic and anthropogenic, when acting as cloud condensation nuclei (CCN), can change the optical properties of clouds and thus have different climate effects via changes in precipitation or cloud cover. Also the mechanism how the small cloud seeds are formed can have a major effect on the cloud properties. Clouds reflect and scatter radiation cooling the atmosphere but to this day aerosol effects still form the largest uncertainty in estimates of the climate of the future. Low-volatility compounds in the ambient air are the most important components in both aerosol formation and their growth to sizes that can affect cloud properties such as their reflectivity. The vapours in the atmosphere form around half of the first precursors of aerosol particles via nucleation, still molecular in size. The rest is released directly into the air e.g. by the traffic or from the oceans as sea salt. Neutral molecular size precursor substituents are difficult to detect because they lack electric charge and their concentrations rarely exceed the detection limits of the used measurement instruments. This is one of the reasons why the first steps of nucleation process are still partly unsolved after decades of research. This thesis concentrates first in development of selective methods and ultrasensitive instrumentation for the detection of acidic aerosol precursor molecules and clusters. These compounds include sulphuric acid, which is known to be highly important precursor for new particle formation. This thesis presents the first ambient measurements with the new instrumentation and even though sulphuric acid was detected in relative high concentrations during a particle formation event, no ambient cluster formation was yet observed. The same instrumentation was further used in an ultraclean chamber experiment were sulphuric acid and dimethyl amine formed growing clusters and they were detected from the smallest clusters all the way up to ~2 nm size. These compounds are likely to dominate the new particle formation with low-volatility organic compounds. Tens of thousands of volatile organic compounds (VOC) are emitted in the atmosphere by terrestrial vegetation, marine environments and anthropogenic sources, making the search for the meaningful compounds for new particle formation extremely difficult. In this thesis a new group of extremely low-volatility organic compounds (ELVOC) from terpene oxidation are introduced. They form a large source of secondary organic aerosol (SOA) and might help explaining the former big gap between the measured and the modelled SOA loads in the atmosphere. Formation of these compounds from RO2 radicals via rapid autoxidation process to stable molecules is also studied in details in laboratory experiments. This thesis also utilizes a global modelling framework, where the measurement results are applied. According to this thesis, ELVOC in particular are in crucial role when estimating SOA and CCN formation in the air. All together this thesis is a comprehensive study of both organic and inorganic low-volatility precursor molecules and clusters in the atmosphere, from their origin, formation mechanisms, and measurement techniques to their possible effects on climate now and in the future.
  • Koivisto, Tomi (Helsingin yliopisto, 2006)
    Acceleration of the universe has been established but not explained. During the past few years precise cosmological experiments have confirmed the standard big bang scenario of a flat universe undergoing an inflationary expansion in its earliest stages, where the perturbations are generated that eventually form into galaxies and other structure in matter, most of which is non-baryonic dark matter. Curiously, the universe has presently entered into another period of acceleration. Such a result is inferred from observations of extra-galactic supernovae and is independently supported by the cosmic microwave background radiation and large scale structure data. It seems there is a positive cosmological constant speeding up the universal expansion of space. Then the vacuum energy density the constant describes should be about a dozen times the present energy density in visible matter, but particle physics scales are enormously larger than that. This is the cosmological constant problem, perhaps the greatest mystery of contemporary cosmology. In this thesis we will explore alternative agents of the acceleration. Generically, such are called dark energy. If some symmetry turns off vacuum energy, its value is not a problem but one needs some dark energy. Such could be a scalar field dynamically evolving in its potential, or some other exotic constituent exhibiting negative pressure. Another option is to assume that gravity at cosmological scales is not well described by general relativity. In a modified theory of gravity one might find the expansion rate increasing in a universe filled by just dark matter and baryons. Such possibilities are taken here under investigation. The main goal is to uncover observational consequences of different models of dark energy, the emphasis being on their implications for the formation of large-scale structure of the universe. Possible properties of dark energy are investigated using phenomenological paramaterizations, but several specific models are also considered in detail. Difficulties in unifying dark matter and dark energy into a single concept are pointed out. Considerable attention is on modifications of gravity resulting in second order field equations. It is shown that in a general class of such models the viable ones represent effectively the cosmological constant, while from another class one might find interesting modifications of the standard cosmological scenario yet allowed by observations. The thesis consists of seven research papers preceded by an introductory discussion.
  • Sottinen, Tommi (Helsingin yliopisto, 2003)
  • Tuusjärvi, Mari (Helsingin yliopisto, 2013)
    The metal mining industry has experienced a marked boom in Finland since the beginning of the 21st century, driven by the general rise in the price levels of base metals, iron and gold, in particular. The boom started with increased exploration and mine development activity, and from 2007 onwards has increased the mined ore levels to all-time highs. Before the current boom, the industry had been suffering a gradual downturn during the 1990s, and was considered as a minor branch in the economic structure of the country. Furthermore, the strong domestic metals industry started to lean increasingly on imported mineral raw materials. The rapid growth in exploration and mining activity in the country has now raised expectations of increased socio-economic benefits, but also fears of environmental degradation and negative effects on other lines of business, such as nature tourism. Reflecting this, the mining industry has already faced more intensive opposition than ever in its history in Finland. The opposition reflects the changed values of civil society in Finland in the 21st century, and the expectations towards the good environmental and socioeconomic performance of the mining industry. In this thesis study, the future directions of the Finnish metals mining industry and the related environmental and expected socio-economic effects were examined, as well as the trade of minerals to Finland and its environmental effects and governance context in origin countries. The focus was also on considering the environmental pressures and material flows of production chains of metals (e.g. life cycle assessment and material flow analysis), and on investigating the roles of governance, industry and academia in striving towards increased sustainability of the metal mining industry in Finland. The results suggest that in the context of international production chains of metals in Finland, the environmental pressures abroad related to mining and mineral processing are higher than domestic pressures. However, the domestic effects are increasing, as the mining industry in Finland will most probably continue to grow in the future. This growth has the potential to bring socio-economic prosperity to the country, but also increases in environmental pressures. In reaching towards a more sustainable mining industry, the co-operation between governance, industry and academia has to be profound. Environmental protection has to be strengthened and preventing further environmental accidents in mines needs to be the key goal. Further developments in environmentally sound mining and processing technologies will help to both steer environmental performance and enhance the competitiveness of the Finnish mining technology branch. Additionally, transparent CSR and communication strategies in mining companies will help to raise common knowledge and acceptance of mining. Finally, careful legislation and solid project feasibility planning support the continuation of mining activity in a climate of economic fluctuation.
  • Makkonen, Risto (Helsingin yliopisto, 2012)
    Atmospheric aerosol particles influence everyday life through their adverse health effects. Aerosols also affect the Earth's climate, directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei (CCN) and modifying cloud properties. The net effect of aerosols on climate is cooling. Although only a small fraction of atmospheric aerosol mass is of direct human origin, the anthropogenic aerosol climate forcing can be of same magnitude, but opposite in sign, as the anthropogenic forcing via CO2. As aerosols are short-lived and respond rapidly to changes in emissions, they are an important factor in determining the future climate change. Aerosols are either emitted as primary particles or they are formed from gas-phase precursors. Atmospheric new particle formation is observed around the world. In this thesis, new particle formation is studied with a global aerosol-climate model. Several thermodynamic and semi-empirical parameterizations of nucleation are investigated. It is shown that in addition to the thermodynamic models, semi-empirical parameterizations are needed to explain the observed aerosol number concentrations. Volatile organic compounds (VOCs) can contribute to particle number, particle growth, and total aerosol mass. It was shown that biogenic VOCs have an important role in growing the freshly-nucleated particles to sizes capable of acting as CCN. It was also shown that the current atmospheric concentrations of nitric acid can greatly affect cloud droplet activation and increase the number of cloud droplets, making a large contribution to the indirect aerosols effect. With current scenarios for anthropogenic SO2 emissions, the formation of new particles will diminish significantly by the year 2100. Together with the predicted reductions in primary particles, the future cloud droplet number concentrations were shown to decrease close to pre-industrial levels. As a result, the anthropogenic aerosol forcing decreased close to zero. Several possible counteracting processes were studied. It was shown that an increase in either oceanic dimethyl sulfide (DMS) or biogenic VOC emission could provide more CCN and cooling in the future. Also, the differences in the predicted future trend of NOx and SO2 emissions indicate an increasingly important role for the indirect effects via nitric acid.
  • Tonttila, Juha (Helsingin yliopisto, 2015)
    Clouds, aerosols and the interactions between them are some of the most important uncertainties in climate modelling. The scales of spatial variability related to clouds are generally too small to be resolved using a typical climate model grid resolution. This work comprises studies about the small-scale variability of the vertical wind component, which significantly contributes to the process of cloud droplet formation. In addition, more elaborate methods for describing the small-scale variability of cloud properties in climate models are developed. The key questions that are investigated include: 1) What are the statistical properties of the turbulent vertical wind variability in the boundary layer and can they be represented accurately by atmospheric models? 2) How does parameterizing the small-scale variability in cloud microphysical processes affect the simulated cloud properties in climate models? 3) How does accounting for the small-scale variability in cloud properties affect the model-based estimates of the aerosol indirect radiative effects? The most important tool used in this work was the ECHAM5-HAM2 aerosol-climate model. The model simulates not only the atmospheric circulation and thermodynamics, but also the global distribution of aerosols and the physical processes between particles that affect the aerosol particle population. This allows the model to represent the interactions between clouds and aerosols. In addition, parts of this work also make use of measurement data based on remote sensing methods as well as high-resolution output from a numerical weather prediction model. The results show that the small-scale variability of the vertical wind associated with cloud droplet formation must be parameterized even in models with relatively high grid resolution. This highlights especially the importance of such methods for lower-resolution climate models. The variability of vertical wind can be described using a probability density function (PDF), the shape of which may vary significantly depending on the atmospheric conditions. The intricacies of the PDF include many uncertainties which can only be reduced by more extensive observations. With a simplified representation of the vertical velocity PDF, a new version of the climate model is constructed in this work, which can be used to study the climate effects due to the small-scale variability in vertical wind and clouds. It is noted that earlier methods that try to account for the variability in vertical velocity and cloud formation are somewhat insufficient. More attention should be paid on treating the small-scale variability self-consistently for entire chains of processes rather than separately for individual processes. This was accomplished in this work with the newly developed method, comprising the chain of processes from cloud formation to radiative transfer. The new method has a strong impact on the number of cloud droplets and drizzle formation as compared to the default model version, where the small-scale variaiblity of clouds is not as accurately accounted for. Moreover, the response of the model-simulated cloud properties to anthropogenic changes in aerosol emissions is found to be considerably weaker in the new model version than in the default model version. In effect, when compared with the default model version, the aerosol indirect radiative effect estimated with the new model version is closer to the best observation-based estimate. The results of this work contribute to improving our understanding of the aerosol-cloud interactions and to guide the work towards further reducing the uncertainties related to modelling clouds and climate.
  • Valtola, Lauri (Helsingin yliopisto, 2014)
    The main objectives of the present research were the synthesis and characterization of organosoluble semifluorinated copolymers from various monomers. Polymers were synthesized either by free radical solution polymerization yielding random copolymers or by atom transfer radical polymerization to build up block structures. Both block and random copolymers bearing CF3 showed high surface activity in toluene and had critical micellization concentration (CMC) below 0.5 wt%. Above the CMC aggregates with sizes ranging from 10 nm to 100 nm were observed by dynamic, (DLS), and static light scattering, (SLS). Combined LS and TEM studies showed that due to the rigidity of fluorinated blocks the aggregates were ellipsoidal when dispersed without heating but shrunk to spherical aggregates upon heating. Fluorinated surfaces and particles of the block copolymers were made by solvent casting, electrospinning or breath figure templating (BF). All produced surfaces were hydrophobic (contact angle of water, CAwater >100°). When the surface roughness was increased e.g. by electrospinning or breath figure templating, it was possible to turn some surfaces superhydrophobic (CAwater >150°) and their lipophobic properties were enhanced. Such films with enhanced hydro- or oleophobic characteristics may find application for example as dirt repelling surfaces or bringing anticorrosive properties to coatings. One of the studied block copolymers, polystyrene-block-polypentafluorostyrene (PS-b-PFS) was modified with glucose or carboxylic acid moieties via thiol Click -reaction. These polymers were then prepared as porous BF films or made to nanoparticles with varying sizes (diameter 100 to 360 nm) utilising solvent exchange or aerosol technique. The introduction of glucose or carboxylic acid functionalities rendered the porous surfaces made of these polymers hydrophilic while the films with PS-b-PFS were hydrophobic. It was shown that the sugar residues in the pores of BF films or on the nanoparticles are capable of binding fluorescent markers, lectin ConA-FITC and rhodamine B isothiocyanate (RITC) either via biorecognition or chemical reactions enabling the use of these materials for example in diagnostics applications.
  • Soto, Tomás (Helsingin yliopisto, 2015)
    The homogeneous Besov spaces B(s,p,q) and the homogeneous Triebel-Lizorkin spaces F(s,p,q) are two scales of function spaces on the Euclidean space that include the standard and fractional-order Sobolev spaces, and arise naturally in the contexts of e.g. partial differential equations and interpolation theory. In the first article presented in this thesis (joint work with H. Koch, P. Koskela and E. Saksman), we characterize the homeomorphisms of the Euclidean space that induce bounded composition operators on the Besov spaces whose norms are invariant under a scaling change of variable, i.e. where sp equals the dimension of the underlying space, for most indices in the smoothness range 0 < s < 1. We also establish similar results in the setting of certain more general metric measure spaces. In the second article (joint work with M. Bonk and E. Saksman), we present a new characterization of the Triebel-Lizorkin spaces for most indices in the smoothness range 0 < s < 1 in the setting of doubling metric measure spaces, and use the characterization to expand on an earlier result by Koskela, Yang and Zhou concerning the bounded composition operators on the scaling invariant Triebel-Lizorkin spaces. We also establish results concerning general Sobolev-type embeddings and complex interpolation for these function spaces in the generality of doubling metric measure spaces. In the third article, we establish several characterizations of certain larger scales of function spaces on the Euclidean space introduced by Yang and Yuan. One of these characterizations can in particular be applied in the setting of more general metric measure spaces.