Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Historical Climatology In Europe – The State Of The Art

This paper discusses the state of European research in historical climatology. This field of science and an overview of its development are described in detail. Special attention is given to the documentary evidence used for data sources, including its drawbacks and advantages. Further, methods and significant results of historical-climatological research, mainly achieved since 1990, are presented. The main focus concentrates on data, methods, definitions of the “Medieval Warm Period” and the “Little Ice Age”, synoptic interpretation of past climates, climatic anomalies and natural disasters, and the vulnerability of economies and societies to climate as well as images and social representations of past weather and climate. The potential of historical climatology for climate modelling research is discussed briefly. Research perspectives in historical climatology are formulated with reference to data, methods, interdisciplinarity and impacts.     

European Surface Pressure Patterns for Months with Outstanding Climatic Anomalies During the Sixteenth Century

Monthly mean surface pressure patterns in the European area are reconstructed for those winter and summer seasons of the 16th century with outstanding climatic anomalies being either widespread over Europe or remarkably intensive in some European regions. From the available documentary information about weather characteristics and their sequences, it proved possible to infer prevalent processes of lower tropospheric advection of typical air masses and to assess the position and strength of major surface pressure centres on a monthly scale. For comparison with modern pressure patterns, monthly mean sea level pressure (SLP) grids from the 20th century have been selected for seasons with similar climatic anomalies. There are broad coincidences between these pressure patterns of the 16th and the 20th centuries except for cold summer seasons. Finally, results from the 16th century are discussed in terms of circulation dynamics (different phases of the North Atlantic Oscillation (NAO) in winter, decreasing frequency of anticyclonic ridging in summer).     

Interdecadal modulation of the relationship between ENSO,IPO and precipitation: insights from tree rings in Australia

Australian climate-proxy reconstructions based on tree rings from tropical and subtropical forests have not been achieved so far due to the rarity of species producing anatomically distinct annual growth rings. Our study identifies the Australian Red Cedar (Toona ciliata) as one of the most promising tree species for tree-ring research in Australasia because this species exhibits distinct annual tree rings, a prerequisite for high quality tropical dendroclimatology. Based on these preliminary studies, we were able, for the first time in subtropical and tropical Australia, to develop a statistically robust, precisely dated and annually resolved chronology back to AD1854. We show that the variability in ring widths of T. ciliata is mainly dependent on annual precipitation. The developed proxy data series contains both high- and low-frequency climate signals which can be associated with the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). A comparison of different data sets (Brisbane precipitation, tree rings, coral luminescence record from the Great Barrier Reef, ENSO and IPO) revealed non-stationary correlation patterns throughout the twentieth century but little instability between the new tree-ring chronology and Brisbane precipitation.     

Winter-to-spring temperature dynamics in Turkey derived from tree rings since AD 1125

In the eastern Mediterranean in general and in Turkey in particular, temperature reconstructions based on tree rings have not been achieved so far. Furthermore, centennial-long chronologies of stable isotopes are generally also missing. Recent studies have identified the tree species Juniperus excelsa as one of the most promising tree species in Turkey for developing long climate sensitive stable carbon isotope chronologies because this species is long-living and thus has the ability to capture low-frequency climate signals. We were able to develop a statistically robust, precisely dated and annually resolved chronology back to AD 1125. We proved that variability of δ¹³C in tree rings of J. excelsa is mainly dependent on winter-to-spring temperatures (January–May). Low-frequency trends, which were associated with the medieval warm period and the little ice age, were identified in the winter-to-spring temperature reconstruction, however, the twentieth century warming trend found elsewhere could not be identified in our proxy record, nor was it found in the corresponding meteorological data used for our study. Comparisons with other northern-hemispherical proxy data showed that similar low-frequency signals are present until the beginning of the twentieth century when the other proxies derived from further north indicate a significant warming while the winter-to-spring temperature proxy from SW-Turkey does not. Correlation analyses including our temperature reconstruction and seven well-known climate indices suggest that various atmospheric oscillation patterns are capable of influencing the temperature variations in SW-Turkey.     

MTBE in Drinking Water Production – Occurrence and Efficiency of Treatment Technologies

In Germany, the gasoline additive methyl tert‐butyl ether (MTBE) is almost constantly detected in measurable concentrations in surface waters and is not significantly removed during riverbank filtration. The removal of MTBE from water has been the focus of many studies that mostly were performed at high concentration levels and centred in understanding the mechanisms of elimination. In order to assess the performance of conventional and advanced water treatment technologies for MTBE removal in the low concentration range further studies were undertaken. Laboratory experiments included aeration, granulated activated carbon (GAC) adsorption, ozonation and advanced oxidation processes (AOP). The results show that the removal of MTBE by conventional technologies is not easily achieved. MTBE is only removed by aeration at high expense. Ozonation at neutral pH values did not prove to be effective in eliminating MTBE at all. The use of ozone/H₂O₂ (AOP) may lead to a partly elimination of MTBE. However, the ozone/H₂O₂ concentrations required for a complete removal of MTBE from natural waters is much higher than the ozone levels applied nowadays in waterworks. MTBE is only poorly adsorbed on activated carbon, thus GAC filtration is not efficient in eliminating MTBE. A comparison with real‐life data from German waterworks reveals that if MTBE is detected in the raw water it is most often found in the corresponding drinking water as well due to the poor removal efficiency of conventional treatment steps.     

Wind and temperature profile prediction for diabatic surface layers including strong inversion cases

The micrometeorological research program in Antarctica has provided extensive data on wind and temperature profile structure under strong to extreme inversion conditions (Dalrymple et al., 1966; Lettau et al., 1977). The basic similarity hypotheses and limiting conditions for prediction of diabatic surface layer profiles are summarized. The model by Businger et al. (1971) for dimensionless shear and temperature gradients is revised to conform with the new results for strong stability. A novel similarity hypothesis is introduced to complete the step from shear and gradient prediction to prediction of absolute wind speed, wind energy, and temperature on the basis of prescribed external factors of surface layer structure. The physics of interactions between predicted profile tilting and curving are discussed and used to explain several micrometeorological paradoxes, including that of the elevated minimum of air temperature observed occasionally near the active surface when the energy budget is of the nocturnal type.     

Using regional regression within index flood procedures and an empirical Bayesian estimator

Studies have illustrated the performance of at-site and regional flood quantile estimators. For realistic generalized extreme value (GEV) distributions and short records, a simple index-flood quantile estimator performs better than two-parameter (2P) GEV quantile estimators with probability weighted moment (PWM) estimation using a regional shape parameter and at-site mean and L-coefficient of variation (L-CV), and full three-parameter at-site GEV/PWM quantile estimators. However, as regional heterogeneity or record lengths increase, the 2P-estimator quickly dominates. This paper generalizes the index flood procedure by employing regression with physiographic information to refine a normalized T-year flood estimator. A linear empirical Bayes estimator uses the normalized quantile regression estimator to define a prior distribution which is employed with the normalized 2P-quantile estimator. Monte Carlo simulations indicate that this empirical Bayes estimator does essentially as well as or better than the simpler normalized quantile regression estimator at sites with short records, and performs as well as or better than the 2P-estimator at sites with longer records or smaller L-CV.