Liliane Janssen

Computational Aspects of Air Quality Modelling in Urban Regions Using an Optimal Resolution Approach (AURORA)

An integrated model system for the evaluation of urban air qualityis presented. Various modules in the system have been designed and refined, resulting in an air quality management tool that can provide reliable answers to policy makers and traffic planners. In order to minimise the computational burden, careful attention has been paid to the computational aspects of the AURORA model, in particular with respect to the advection-diffusion scheme and the chemistry module. The AURORA model has been applied for the Antwerp region, focussing in detail on benzene concentrations at street level. The model results for benzene can represent accuratelythe measured trends in benzene concentrations as averaged over 5 dayp eriods for the entire city of Antwerp

Modelling changes of aerosol compositions over Belgium and Europe

Seasonal changes in aerosol compositions over Belgium and Europe are simulated with an extended version of the EUROS model. EUROS is capable of modelling mass and chemical composition of aerosols in two size fractions (PM2.5 and PM10-2.5). The chemical composition is expressed in terms of seven components: ammonium, nitrate, sulphate, primary inorganic compounds, elementary carbon, primary organic compounds and Secondary Organic Compounds (SOA). A comparison of modelled and measured aerosol concentrations showed that modelled concentrations are generally consistent with observed concentrations. The chemical composition of the aerosol showed a strong dependence on the season. High aerosol concentrations during the summer were mainly due to high concentrations of the secondary components nitrate, ammonium, sulphate and SOA in the size fraction PM2.5. In contrast, during autumn and winter, increased PM-concentrations were mainly due to higher concentrations of primary components, especially in the size fraction PM10-2.5.

Evaluation of Aurora Simulated Benzene Concentrations for the Urban Area of Antwerp

Urban air quality is a major topic in the European environmental policy because more than 70 % of the European inhabitants and a major part of the working places are located inside an urbanized area. This leads to increased levels of human exposure to harmful air pollutants such as ground-level ozone, nitrogen dioxide, volatile organic components and fine particles. In particular, the road traffic emitted BTEX-aromatics (Benzene-Toluene-Ethylbenzene and Xylene) are characteristic for local urban air pollution. Moreover, benzene is highly carcinogenic and therefore an annual averaged limit value of 5 μg m-3 has been set in the framework of the Air Quality Framework Directives 96/62/EC and 2000/69/EC (WHO, 2000). This limit value should be obtained in 2010. Traffic related benzene concentrations are controlled by the petrol composition, the car park composition and traffic speed as well as the atmospheric conditions.

Combining Models for Assessment of Local Air Quality

Assessing local air quality can be a challenging task. Indeed, local air quality is strongly dependent on local factors but also regional and in some cases even global effects have to be taken into account when assessing local air pollution concentrations. Furthermore, large gradients in pollutant concentrations can be present in the urban environment. In order to assess the local air quality for the city of Antwerp, a combination of an Eulerian dispersion model, a measurement interpolation tool, a Gaussian plume model and a simplified version of the OSPM street canyon model have been coupled to each other, taking into account double counting effects of local emissions. The coupled model which combines the regional, urban and street canyon scale has been applied for the city centre of Antwerp and its harbour. This results in detailed maps with a resolution up to 30 m for four pollutants: PM10, PM2.5, EC (elementary carbon) and NO2. Furthermore, several abatement measures have been assessed in order to improve the urban air quality. It has been shown that local (traffic) measures only have a small effect on total mass PM10 and PM2.5 concentrations, but exhibit a larger effect on EC and NO2-concentrations.

Modelling of Airborne Primary and Secondary Particulate Matter with the EUROS-Model

We used the Eulerian Chemistry-Transport Model EUROS to simulate the concentrations of airborne fine particulate matter above Europe. Special attention was paid to both primary as well as secondary particulate matter in the respirable size range up to 10 μm diameter. Especially the small particles with diameters up to 2.5 μm are often formed in the atmosphere from gaseous precursor compounds. Comprehensive computer codes for the calculation of gas phase chemical reactions and thermodynamic equilibria between the compounds in the gas phase and those ones in the solid phase had been implemented into the EUROS-model. Obtained concentrations of PM10for the year 2003 are compared to measurements. Additionally, calculations were carried out to assess the contribution of emissions derived from the sector agriculture in Flanders, the northern part of Belgium. The obtained results demonstrate the importance of ammonia emissions in the formation of secondary particulate matter. Hence, future abatement policy should consider more the role of ammonia in the formation of secondary particles.

The Emission Inventory Water: A Planning Support System for Reducing Pollution Emissions in the Surface Waters of Flanders

The Emission Inventory Water (EIW) is an important policy instrument enabling a better insight into the pressures and impacts of point and diffuse emissions caused by different sectors on the surface waters of Flanders in Belgium. It is a spatially explicit computer-based information system developed to support the Flemish Environmental Agency (VMM) in its monitoring and reporting obligations vis-à-vis the Flemish, Belgian and European authorities. In addition to this function of providing an up-to-date technical database, it enables the design and assessment of alternative policies and spatially explicit (alongside technical) measures targeted at particular sectors and aimed at improving the quality of the surface waters in different river basins and administrative entities of Flanders. It supports to that effect ‘what if’ analyses in an interactive context. Such exercises are propelled by the obligation imposed on the Member States by the European Union to treat all waste waters by 2012. It is, therefore, an important tool in helping to meet water quality standards as well as evaluating and prioritizing measures (Crouzet and Bogestrand 1999; Fuchs et al. 2002; emissieregistratie.nederland). The core of the EIW is an advanced MS Excel/Visual Basic module (Microsoft 2008) intimately linked to an ArcGIS module (ESRI 2008). The latter was only recently developed as part of the new version of the EIW-PSS (Engelen et al. 2006) delivered as an operational prototype in December 2006. As far as its GIS module is concerned, specific attention went into the emissions of metals caused by the building sector. In particular, the heavy metals lead, zinc, copper and, to a lesser degree, aluminium, chromium and nickel released by corrosion in the outer shell of the buildings as well as in the plumbing systems, are considered. Literature research and Chapter 7 The Emission Inventory Water: A Planning Support System for Reducing Pollution Emissions in the Surface Waters of Flanders

Synergetic or Non-Linear Effects in PM10 and PM2.5 Scenario Calculations for 2015 in Belgium

We applied the extended version of the EUROS model to evaluate the impact of emission reductions on PM10 and PM2.5 concentrations in Flanders and Belgium for 2015. Individual sector contributions were assessed and the current and future changes in aerosol concentrations and compositions over Belgium and Europe were investigated. Contributions from anthropogenic sources in Flanders were found to be responsible for 34.3% of the annual averaged PM10 concentrations in Flanders in 2003. In 2015 this contribution is estimated to be 35.0%. For PM2.5 these contributions are 29.1% in 2003 and 27.8% in 2015 respectively. Results show that non-linear effects can not be neglected. Because of the non-linear processes that take place when secondary aerosols are formed, a small reduction in a gaseous compound (e.g. SO2) does not necessarily lead to the same amount of reduction of the secondary compound (e.g. sulphate). Another “non-linear” aspect is the formation of aerosols by contributions from two compounds that are delivered by two individual sectors. The synergetic effect of these “non-linear” contributions was found to be an additional 2.1% for PM10 and 3.7% for PM2.5, representing an increase of 6–13%, which is not negligible and might become relevant in abatement policies.

Chapter 5.4 Modelling seasonal changes of aerosol compositions over Belgium and Europe

Abstract The EUROpean Smog model (EUROS) was extended with two special modular algorithms for atmospheric particles. The first module is the Caltech Atmospheric Chemistry Mechanism (CACM) which describes in a mechanistic way the formation of precursors of secondary organic aerosols. The second module is the Model of Aerosol Dynamics, Reaction, Ionization and Dissolution (MADRID 2), which describes the formation of secondary aerosols by means of an equilibrium between the gas phase and the aerosol phase. It includes inorganic as well as hydrophilic and hydrophobic organic compounds. Through this extension, the EUROS model was able to model mass and chemical composition of aerosols in two size fractions (PM 2.5 and PM 10-2.5 ). The model was validated for 3 seasonal episodes in 2002 and 2003. A comparison between modelled and observed aerosol concentrations showed that the trends in PM 10 concentrations are well captured. A strong seasonal dependency was found in the chemical composition of the aerosols. Large contributions of secondary inorganic components were found for summer episodes with high aerosol concentrations, whereas during autumn/winter episodes the concentrations of secondary aerosol were less abundant.

Assessment of different land use development scenarios in terms of traffic flows and associated air quality

Compact and polycentric city forms are associated with minimal consumption of land and energy, and are often promoted as the more sustainable and hence preferred mode of urban development. In this context, a series of numerical simulations was performed to evaluate the impact of two urban development scenarios on air quality and related human exposure. The area that was selected consists of a highly urbanised region in the Ruhr area, located in the north-western part of Germany in central North Rhine-Westphalia with a total population in excess of 5.5 million. The choice for this particular area was mainly motivated by its size and importance, as well as its conversion potential. Two distinct scenarios were selected. The first is referred to as ‘urban sprawl’ and is characterized by a significant increase in built-up surface. This scenario supposes a continuation of the current process of people leaving the highly occupied central part of the study area to settle in the greener surroundings. In the second scenario, referred to as ‘satellite cities’, persons and jobs were displaced to five existing towns located near the core of the urban area. Models dealing with land use, traffic flows, and atmospheric dispersion were applied, first under conditions representative of the urbanised area as it is today. Subsequently, the urban development scenarios were implemented using spatial modelling techniques, and the impact of the scenarios with respect to air quality was evaluated, including an estimate of human exposure to air pollution and the associated external costs.

Environmental impact assessment of air quality in street canyons related to council directives 1999/30/EC and 2000/69/EC

Council directive 96/62/EC on ambient air quality assessment and management requires the development of action plans for zones where concentrations of pollutants in ambient air exceed limit values. The directive also recognises air quality models as assessment tools. We discuss the application of an integrated air quality model, Air quality modelling in Urban Regions using an Optimal Resolution Approach (AURORA), to evaluate the concentration levels of NOx, SO2, PM10 (1999/30/EC), CO and benzene (2000/69/EC) in street canyons. Air quality modelling in Urban Regions using an Optimal Resolution Approach (AURORA) is applied to 11 selected streets in the City of Antwerp. Comparisons with a measurement station in one of the streets show agreements that are within the uncertainty range given by the guidelines in the EU directives. An analysis of the measured and modelled concentrations and percentiles shows that concentrations of NOx, CO and benzene vary widely from street to street, whereas for SO2 and PM10 the model results show less variation between individual streets, indicating a more important contribution from the urban and regional background. The result for PM10 is not confirmed by the measured higher percentiles.