I.J. Ackermann

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.

Modal aerosol dynamics model for Europe: development and first applications

Abstract The Modal Aerosol Dynamics model for Europe (MADE) has been developed as an extension to mesoscale chemistry transport models to allow a more detailed treatment of aerosol effects in these models. Due to the complexity of the atmospheric aerosol system an approach has been chosen which is, on the one hand, fast enough for this application and, on the other, provides sufficient information on the particle size distribution. In MADE, which is developed from the regional particulate model (RPM) the particle size distribution of the submicrometer aerosol is represented by two overlapping lognormal modes. The chemical composition is currently treated in the sulfate–nitrate–ammonium and water system. Sources for aerosol particles are modelled through nucleation and emission. Coagulation, condensation, transport and deposition are considered as processes modifying the aerosol population in the atmosphere. Aerosol dynamics calculations are performed on-line within the chemistry-transport model. Process studies with a one-dimensional version of the model system are used to investigate the relative importance of the individual aerosol dynamic processes and the important links between between the gas and aerosol phase as well as meteorological parameters. Results from a first three-dimensional application of the fully coupled system of MADE and the European Air Pollution Dispersion model system (EURAD) are presented, showing the suitability of MADE as an aerosol dynamics model even within complex air quality models. The application of the new aerosol model provides information on particle number, size and surface area in addition to the chemical concentration fields, which can be used to study a variety of aerosol-related air pollution issues in subsequent studies.

Contribution of road traffic emissions to the atmospheric black carbon burden in the mid-1990s

We developed a global inventory for black carbon (BC) emissions from road traffic for 1993. Global emissions of 2.4 TgC were found in this year. The inventory was implemented in the atmosphere general circulation model ECHAM4.L39(DLR), together with inventories for BC emissions from fossil fuel combustion, biomass burning, and air traffic. The transport of BC particles and the concentration changes due to these emissions were investigated. Particularly, we focused on the contributions of road traffic emissions from North America, Europe, and Asia to the atmospheric BC burden. The sink of BC was parameterized as an exponential decay process with a half-lifetime depending on altitude. Because of the simplified BC cycle, the current investigation should be regarded as a pilot study. However, it is the first study dealing specifically with global road traffic BC emissions. The model results indicate that less than 20% of the BC mass concentrations predicted to be in the planetary boundary layer of the northern midlatitudes arise from road traffic. The road traffic fraction of BC concentrations over North America, Europe, and Asia originated mostly from emissions in the respective region. However, road traffic BC particles from Asia also significantly influence the tropopause region. In July their relative contribution is about 10%. A very rough estimate of the globally averaged direct radiative forcing of BC particles from global and Asian road traffic is given. As road traffic and its emissions in Asia are expected to rise in the near future, their relative importance will also grow and may, eventually, become a significant factor in anthropogenic climate change, unless the specific emissions are drastically reduced.

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.

Aerosol Dynamics Modelling in the Regional Chemistry Transport Model System Eurad

The particulate matter suspended in the atmosphere is strongly linked to numerous air pollution problems. These include the -direct and indirect- influences on the radiative budget of the atmosphere, the potential for adverse health effects, the influence of particles on the long-range transport of air pollutants and the interaction of aerosol particles with clouds. Therefore air quality models have to take into account particle formation, transport and deposition with respect to aerosol chemistry as well as aerosol dynamics. Due to the strong interactions between the gas phase and the aerosol phase, the aerosol model has to be fully coupled to a gas phase model. The Modal Aerosol Dynamics modelling technique as a time and memory efficient method provides a suitable approach to realise that purpose even in complex three-dimensional Eulerian models.