B. Schell

Modeling the formation of secondary organic aerosol within a comprehensive air quality model system

The Secondary Organic Aerosol Model (SORGAM) has been developed for use in comprehensive air quality model systems. Coupled to a chemistry-transport model, SORGAM is capable of simulating secondary organic aerosol (SOA) formation including the production of low-volatility products and their subsequent gas/particle partitioning. The current model formulation assumes that all SOA compounds interact and form a quasi-ideal solution. This has significant impact on the gas/particle partitioning, since in this case the saturation concentrations of the SOA compounds depend on the composition of the SOA and the amount of absorbing material present. Box model simulations have been performed to investigate the sensitivity of the model against several parameters. Results clearly show the importance of the temperature dependence of saturation concentrations on the partitioning process. Furthermore, SORGAM has been coupled to the comprehensive European Air Pollution and Dispersion/Modal Aerosol Dynamics Model for Europe air quality model system, and results of a three-dimensional model application are presented. The model results indicate that assuming interacting SOA compounds, biogenic and anthropogenic contributions significantly influence each other and cannot be treated independently.

Regional modelling of particulate matter with MADE

Describes the development and application of an aerosol model for regional air quality simulations. The aerosol model MADE is based on a modal concept and describes the chemical composition and the size distribution of atmospheric particulate matter. Primary as well as secondary aerosol components are considered in the model, which is fully integrated into the photochemical transport model EURAD. The model system has been applied to a European domain with different resolutions, using a one‐way nesting procedure. Simulations show the potential importance of secondary organics of anthropogenic and biogenic origin for the tropospheric particle loading. In addition it is shown that a reduction in precursor emissions for the inorganic ion fraction of PM (sulphate, nitrate and ammonium) does not necessarily lead to an equivalent reduction in PM2.5 mass concentrations, as for example a reduction in sulphate aerosol caused by reduced SO2 emissions might be compensated by enhanced formation of nitrate aerosols in certain regions.

Particulate Air Quality over Europe in the Growing Season of 1995 and 2010 as Simulated with the MADE/EURAD Model

MADE (Modal Aerosol Dynamics Model for Europe) provides detailed information on the size distribution, primary and secondary contributions, as well as the chemical composition of atmospheric particles. Coupled to the three-dimensional Eulerian gas-phase air quality model EURAD (European Air Pollution and Dispersion Model) it is applied to simulate particle formation, transport and deposition during a long-term simulation over essentially the whole growing season in the year 1995 and 2010. To take account of regional difference the model domain covers Europe in a sufficiently fine horizontal resolution (grid resolution: 27 km). The results of the results of the base case simulation are compared to available measurements during the modeled period.

Regional Modelling of Atmospheric Aerosols

Atmospheric particles are comprised of a complex mixture of a variety of organic and inorganic substances that can be of primary or secondary nature, the size distribution of which particles can span several orders of magnitude in diameter. This complexity, together with significant gaps in knowledge of the formation and transformation processes, provides an ambitious task for the development of atmospheric particles for particulate matter. However potential impacts of these particles and the new standards for these particulate matter require the development and application of sophisticated Air Quality Models for particles.

Aerosol Modelling Within the Eurad Model System: Developments and Applications

In order to fullfill their scientific tasks state-of-the-art air quality models should be capable of predicting particulate matter in addition to the gas-phase concentrations. A suitable aerosol model for the application in complex regional transport models has to provide sufficient information on the chemical composition as well as on the size distribution of the particles. Furthermore it has to be coupled to a photochemical model in order to be able to represent the interactions between the gas-phase and the particle-phase.

Effects of Initial and Boundary Values of Reactive Nitrogen Compounds and Hydrocarbons on the Ozone Concentration in the Free Troposphere

The initialisation and the treatment of the boundary conditions of a mesoscale chemistry-transport-model, covering a limited area, are of great importance. The choice of the initial and boundary values can significantly influence the results of a simulation, so that they should be determined as well as possible (NAPAP, 1991). For this reason it is important to provide realistic conditions, if possible derived from current measurements. Unfortunately trace species in the troposphere, especially in the middle and upper free troposphere, are not observed continuously so that relatively little is known about background concentrations. Usually there are no current observations available which can be used as input data for episodic simulations. The available measurements show a high variability in the concentrations of the trace species. To analyse and to quantify the effects of a variation of the initial and boundary values for model results sensitivity studies were carried out with the European Air Pollution Dispersion modeling system (EURAD) using different initial and boundary scenarios. Therefore the literature has been reviewed and a set of initial and boundary values were derived based on available observation data. With regard to the formation of ozone the focus was set on reactive nitrogen species and hydrocarbons, which are important photooxidant precursor species. First a set of simulations with different scenarios representing free tropospheric conditions is calculated with a boxmodel version of the EURAD model in order to determine the non-linear dependencies of the gas phase chemistry. Furthermore a sensitivity study with the full three dimensional model is performed for a summersmog episode.