Lagrangian transport evaluation of atmospheric chemistry in the Mediterranean region

Global observations of the chemical composition of the atmosphere are essential for understanding and studying the present and future state of the earth's atmosphere. However, by analyzing field experiments the consideration of the atmospheric motion is indispensable, because transport enables different chemical species, with different local natural and anthropogenic sources, to interact chemically and so consequently influences the chemical composition of the atmosphere. The distance over which that transport occurs is highly dependent upon meteorological conditions (e.g., wind speed, precipitation) and the properties of chemical species itself (e.g., solubility, reactivity). This interaction between chemistry and dynamics makes the study of atmospheric chemistry both difficult and challenging, and also demonstrates the relevance of including the atmospheric motions in that context. In this doctoral thesis the large-scale transport of air over the eastern Mediterranean region during summer 2001, with a focus on August during the Mediterranean Intensive Oxidant Study (MINOS) measurement campaign, was investigated from a lagrangian perspective. Analysis of back trajectories demonstrated transport of polluted air masses from western and eastern Europe in the boundary layer, from the North Atlantic/North American area in the middle end upper troposphere and additionally from South Asia in the upper troposphere towards the eastern Mediterranean. Investigation of air mass transport near the tropopause indicated enhanced cross-tropopause transport relative to the surrounding area over the eastern Mediterranean region in summer. A large band of air mass transport across the dynamical tropopause develops in June, and is shifted toward higher latitudes in July and August. This shifting is associated with the development and the intensification of the Arabian and South Asian upper-level anticyclones and consequential with areas of maximum clear-air turbulence, hypothesizing quasi-permanent areas with turbulent mixing of tropospheric and stratospheric air during summer over the eastern Mediterranean as a result of large-scale synoptic circulation. In context with the latex knowledge about the transport of polluted air masses towards the Mediterranean and with increasing emissions, especially in developing countries like India, this likely gains in importance.

Surface-functionalized latex particles as additives in the mineralization of zinc oxide

Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and applied to control the crystallization of zinc oxide in aqueous medium. The effects of both latex structure and concentration on the crystal growth, morphology, crystalline structure, and properties of the resulting zinc oxide were analyzed. Depending on the latex additive used, micro- and submicrosized crystals with a broad variety of morphologies were obtained. Among the studied latexes, the carboxyl-derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the aspect ratio of the crystals decreases systematically. Latex particles are assumed to adsorb preferentially onto the fast growing {001} faces of ZnO, interacting with the growth centers and reducing the growth rate in [001]. When zinc oxide is precipitated in the presence of latex, the polymer particles become incorporated into the growing crystals and polymer–inorganic hybrid materials are obtained. These materials are composed of an inorganic and largely undisturbed crystalline matrix in which organic latex particles are embedded. Increasing amounts of latex become incorporated into the growing crystals at increasing overall concentration in the crystallizing system. Photoluminescence (PL) spectra were measured to obtain information on defect centers. Emission spectra of all samples showed a narrow UV peak and a broad band in the green-yellow spectral region. The former emission is attributed to exciton recombination, whereas the latter seems to be related with deep-level donors. Latex appears to be a quencher of the visible emission of zinc oxide. Thus, compared to pure zincite, ZnO–latex hybrid materials show a significantly lower PL intensity in the visible range of the spectrum. Under continuous photoexcitation, a noticeable dynamic behavior of the PL is observed, which can be related to a photodesorption of adsorbed oxygen. These surface-adsorbed oxygen species seem to play a crucial role for the optical properties of the materials and may mediate the tunneling of electrons from the conduction band to preexisting deep-level traps, probably related to intrinsic defects (oxygen vacancies or interstitial zinc). The polymer particles can block the sites where oxygen adsorbs, and the disappearance of the “electron-shuttle” species leads to the observed quenching of the visible emission. Electron paramagnetic resonance (EPR) provided additional information about crystal defects with unpaired electrons. Spectra of all samples exhibit a single signal at g ≈ 1.96, typical for shallow donors. Contrary to the results of other authors, no correlation was possible between the EPR signal and the visible range of PL spectra, which suggests that centers responsible for the visible emission and the EPR signal are different.