Model evaluation studies are essential for determining model performance as well as assessing model deficiencies, and are the focus of the Air Quality Model Evaluation International Initiative (AQMEII). The chemistry-transport model system COSMO-MUSCAT participates in this initiative. In this paper the robustness and variability of the model results against changes in the model setup are analyzed. Special focus is given to the formation of secondary particulate matter and the ability to reproduce unusually high levels of PM10 in Central Europe caused by long-range transported smoke of widespread agricultural burning and forest fires in western Russia. Seven different model configurations are investigated in this study. The COSMO-MUSCAT results are evaluated in comparison with ground-base measurements in Central Europe. The analysis is performed for two selected periods in April/ May and October 2006 which are characterized by elevated concentrations of PM. The model sensitivity is studied against changes in the used grid resolution, the meteorological forcing and the applied aerosol module. Possible reasons for differences in model results will be discussed.

Der Bericht Unter kunftigen ‚Normalbedingungen‘ zu erwartende chemische, grosenfraktionierte Aerosol- und Feinstaub-Charakteristik einschlieslich Herkunft, Transport, reprasentiert das REGKLAM-Produkt 2.2c. Auf der Grundlage von Feldmessungen wurde die heutige Situation analysiert sowie verschiedene Anderungsszeanarien betrachtet. Die Untersuchung der Zusammenhange zwischen Meteorologie und Atmospharenchemie stellen eine wichtige Voraussetzung fur die Abschatzung der im Rahmen des Klimawandels sich andernden Luftbelastung dar (unabhangig von Emissionsszenarien). In Zusammenarbeit mit TP 2.2b (TROPOS, Leipzig) wurden im Zeitraum von vier Jahren im urba-nen und regionalen Hintergrund der Stadt Dresden grosenaufgeloste reprasentative Stichproben von PM10 wahrend haufig auftretender Wettersituationen gewonnen (Produktbericht TP 2.2b). Zudem wurden an einem Standort des regionalen Hintergrunds im Osterzgebirge weitere kontinuierliche und ereignisbezogene Messkampagnen von Gasen und Aerosolen zur Charakterisierung des Messstandorts vorgenommen. Besonderes Augenmerk lag bei der Auswertung auf den gesundheitsrelevanten Metallen und dem sogenannten Krustenanteil (aufgewirbelte Bodenstaube). Insbesondere werden mogliche Quellen und die Deposition von Nahr- und Schadstoffen betrachtet. Die Auswertung einer 10jahrigen Zeitreihe in Abhangigkeit von grosraumigen Zirkulationssystemen wird zusatzlich herangezogen.

Der Bericht "Abschatzung der grosenaufgelosten Partikelkonzentration und -zusammensetzung anhand wetterlagenorientierter experimenteller Messungen" reprasentiert das REGKLAM-Produkt 2.2b. Auf der Grundlage von Experimenten wurde die heutige Situation analysiert und Szeanarien fur einen Temperaturanstiegt sowie fur eine Anderung der Anstromcharakteristik erarbeitet. Da die PM10-Massenkonzentrationen bereits heute Grenzwerte uberschreiten und im Rahmen der klimatischen Veranderung nicht mit einer wesentlichen Abnahme zu rechnen ist, bleibt es auch zukunftig eine wichtige Herausforderung, die Emissionen von Partikeln und deren Vorlaufersubstanzen sowohl in der Stadt als auch in der grosraumigen Umgebung zu vermeiden.

Model evaluation studies are essential for determining model performance as well as assessing model deficiencies, and are the focus of the Air Quality Model Evaluation International Initiative (AQMEII). The chemistry-transport model system COSMO–MUSCAT participates in this initiative. In this paper the robustness and variability of the model results against changes in the model setup are analyzed. Special focus is given to the formation of secondary particulate matter and the ability to reproduce unusually high levels of PM10 in Central Europe caused by long-range transported smoke of fires in western Russia. Seven different model configurations are investigated in this study. The COSMO–MUSCAT results are evaluated in comparison with ground-based measurements in Central Europe. The analysis is performed for two selected periods in April/May 2006 and October 2006 which are characterized by elevated concentrations of PM. Furthermore, the sensitivity of the results is studied against the used grid resolution and the meteorological forcing. Here, COSMO–MUSCAT is applied with different horizontal grid sizes and, alternatively, forced by reanalysis data with finer resolution. The use of finer grid resolutions in COSMO–MUSCAT has direct consequences on the meteorological forcing as well as on the calculated emission and deposition rates. The presented results suggest a large impact of the meteorological effects on the PM concentrations. The more accurate spatial appointment of the emissions and deposition fluxes seems to be of little consequence compared to the meteorological forcing.

The transport and transformation of PM is mainly forced by meteorological processes. Therefore, an appropriate description of these processes is of essential interest in chemistry transport modelling. In the paper, the influence of two different meteorological drivers on the simulated particle concentrations is analyzed. For this purpose, the chemistry transport code MUSCAT was online-coupled with WRF as well as with the COSMO model of the German Weather Service. Furthermore, WRF-Chem simulations are also considered in the model comparison. The combination of two meteorological and two chemistry-transport models has a great potential for a detailed analysis of the meteorological dependencies and its impact on the aerosol processes. The simulation results were compared with a comprehensive set of ground-based and profile measurements. The influence of several meteorological parameters (e.g., PBL height, humidity, precipitation) on the simulated concentration fields was analyzed. Main differences are caused by deviations in PBL and cloudiness.

The building effect parameterization (BEP) module [3] was implemented in a high resolution version of the COSMO model (DWD) in order to take into account the urban impact on the airflow and the radiation budget. Based on urban structure data of Dresden, relevant input parameters of the BEP module were developed. By means of this model setup it is possible to investigate the interactions between the city structure and the meteorological variables with different types of artificial cities, ranging from densely built-up areas to suburban areas in order to illuminate the impact of the city type on the dynamical and thermal properties of the atmosphere.

The application of suitable time integration schemes is especially important for highly dynamical problems like atmospheric aerosol processes. Usually, classical time integrators take the same time step over the complete domain and for all components. Consequently, the model regions and the components with the strictest time step restrictions dictate this global time step. Opposed to this, multirate schemes are employed to adapt the time step locally, so that slower components take longer and fewer time steps, which can reduce the computational costs substantially. In the paper, a new class of time integration schemes is proposed which combines the multirate approach with implicit-explicit (IMEX) methods. These schemes are applied for block-structured grids with different horizontal resolutions as well as the coupling between aerosol dynamical and gas phase chemical processes in the chemistry-transport model COSMO-MUSCAT.

Regional simulations of sulfate, nitrate and ammonium aerosols were performed by a nested application of the online-coupled three-dimensional Eulerian model system COSMO-MUSCAT. This was done in a domain covering the northern part of Germany and surrounding regions for the full month of May and a 6-week period in August/September 2006 with the primary focus on secondary inorganic aerosol levels caused by ammonia emissions from domesticated animals and agricultural operations.The results show that in situations with westerly winds ammonium nitrate dominates with concentrations of about 5-10 mu g m(-3) whereas the ammonium sulfate concentrations are about 5 mu g m(-3). In situations with winds mainly from the East characterized by warmer and dryer air the ammonium sulfate concentrations have their maximum at about 10 mu g m(-3) whereas at the same time no ammonium nitrate is present.A reduction of agricultural NH3 emissions by 50% in a regional scale reduces the ammonium nitrate concentrations to a maximum of 30%, while the ammonium sulfate concentrations are unchanged. The reduction of NH3 emissions in a more limited area (here in the Federal state of Germany Niedersachsen) does have no noticeable effect neither on ammonium sulfate nor on ammonium nitrate. (C) 2010 Elsevier Ltd. All rights reserved.

The fraction of ambient PM10 that is due to the formation of secondary inorganic particulate sulfate and nitrate from the emissions of two large, brown-coal-fired power stations in Saxony (East Germany) is examined. The power stations are equipped with natural-draft cooling towers. The flue gases are directly piped into the cooling towers, thereby receiving an additionally intensified uplift. The exhausted gas-steam mixture contains the gases CO, CO2, NO, NO2, and SO2, the directly emitted primary particles, and additionally, an excess of ‘free’ sulfate ions in water solution, which, after the desulfurization steps, remain non-neutralized by cations. The precursor gases NO2 and SO2 are capable of forming nitric and sulfuric acid by several pathways. The acids can be neutralized by ammonia and generate secondary particulate matter by heterogeneous condensation on preexisting particles.

Ammonia (NH3) is the most abundant gaseous base and responsible for neutralizing a large fraction of acidic gases promoting the formation of atmospheric particles. Therefore, the contribution of ammonia to the formation of secondary particles (PM2.5and PM10) in a regional scale is examined. The aerosols result from SO2 and NOx via sulfuric and nitric acid formation in the gas- and the liquid-phase and following subsequent reactions with ammonia.A period in May and a period in August/September 2006 were simulated by a nested application of the model system LM-MUSCAT.

The physical and chemical processes that determine the distribution of air pollutants occur on a wide range of temporal and spatial scales. Multiscale models can provide finer resolution in certain key regions, e.g. around large sources. The paper focuses on some numerical aspects of modelling urban and regional scale interactions as well as on requirements on the used parameterisations in this context. Multiblock grid techniques ("two-way nesting") and implicit-explicit time integration schemes are suitable for an efficient numerical treatment of such scale interactions. In the online coupled model system LM-MUSCAT, both approaches are implemented for the chemistry-transport code. Gas phase processes, especially the formation of photooxidants, as well as the transport and the transformation of particulate matter, can be investigated. The advantages of the multiblock technique to establish the interactions between different scales in a natural way are demonstrated for one selected scenario in the Saxony area. The influence of grid resolutions on the simulation results is discussed.

Five three-dimensional chemical transport models of different complexity were applied to Central Europe to assess the ability of models to reproduce PM10 concentrations under highly polluted conditions. The participating models were the French CHIMERE model, the Dutch LOTOS-EUROS model, as well as the REM-CALGRID, the EURAD and the LM–MUSCAT models from Germany. In the selected 80-day period, observed PM10 daily mean concentrations reached values well above 50μgm−3 on many days in large parts of Northern Germany. This model evaluation shows that there is an increasing underestimation of primary and secondary species with increasing observed PM10. The high PM levels were observed under stagnant weather conditions, which are difficult to simulate with either prognostic or diagnostic, interpolation-based meteorological models. Thus, it is quite likely that uncertainties in PM emissions and incomplete process sub-modules each separately account for only a portion of the underestimation of high PM. Uncertainties in key boundary layer parameters, which can differ by a factor of two or more between the models, represent an additional source of error—both as direct sources of error through the transporting meteorological fields and indirect sources of error through the physico-chemical modules which rely on key boundary layer parameters.

The multiscale model system LM-MUSCAT consists of two online coupled codes: the operational forecast model LM (Local Model) of the German Weather Service and the chemistry transport model MUSCAT (Multi-Scale Atmospheric Transport Model). The coupler provides MUSCAT with meteorological fields like temperature, humidity and density from LM. An improved coupling scheme was developed to optimize the parallel efficiency of the model system.

The interaction of gases and aerosol particles with clouds entails a number of key environmental processes. On the one hand, they directly influence the life cycles of trace constituents and facilitate conversions of these trace constituents. On the other hand, multiphase transformations strongly influence cloud formation. Over a long time, the complexities of the cloud processes involved have discouraged investigators from simultaneously treating all aspects of multiphase chemistry and microphysics with equal rigor. Many recently available models focus either on complex multiphase chemistry only in a few aggregated drop classes (Ervens et al., 2003; Herrmann et al., 2000), or detailed microphysics for strongly simplified chemical mechanisms (Bott, 1999).

Directly after the release of stack emissions into the atmosphere, particle size and number concentrations change depending on surrounding conditions. Coagulation and condensation are identified as the main aerosol dynamic processes in the plume. High resolution numeric calculations were carried out to predict plume conditions and resulting particle dynamic effects for different plant types, such as heating plants (<1KW) and power stations (>> 10MW). The model results are compared with measurements at different locations in the flue gas tract and in the plume for two different plants. The simulation results show a general dependence of the particle evolution on volume flow and mixing conditions. In priciple, for small plants only small effects are quantified; for larger power plant plumes the predicted effects are more significant.

Regional modelling of atmospheric trace gases and particulate matter is of major importance for air pollution studies as well as climate considerations. In this context, the chemistry transport model system LM-MUSCAT is applied for several air quality studies and the investigation of local climate effects. Two selected applications from diff erent objects of research are presented in the paper. The first study enables a detailed quantificatio n of the contributions of cooling tower emissions to particle concentration levels in specifi c Saxonian urban areas. In the sec- ond project, the influence of Saharan dust emissions on radia tive forcing and, hence, on the meteorology is quantified. These regional effects are also r elevant for climate change studies. Regional scale models are well suited for simulation of individual dust storm events, or for comparisons with in-situ observations made during field experiments. Improvements i n the pa- rameterisation of dust processes which are obtained by such regional model investigations can help to improve parameterisations in global scale models. Both applications require a detailed process description as well as a high spatial resolution. Su ch simulations are very expensive in terms of computing time and demand the use of powerful parallel computers.