WP7: Integrated tools and implementation

Overview and background

Processes involving nonlinear interactions and feedbacks between emissions, chemistry and meteorology require coherent and robust approaches using integrated/online methods. This is particularly important where multiple spatial and temporal scales are involved with a complex mixture of pollutants from large sources, as in the case of megacities. The impacts of megacities on the atmospheric environment are tied directly to anthropogenic activities as sources of air pollution. These impacts act on urban, regional and global scales. Currently, there are only limited attempts to integrate this wide range of scales for regional and global air quality and climate applications. Indeed, progress on scale and process interactions has been limited because of the tendency to focus mainly on issues arising at specific scales. However the inter-relating factors between megacities and their impacts on the environment rely on the whole range of scales and thus should be considered within an integrated framework bringing together the treatment of emissions, chemistry and meteorology in a consistent modelling approach. Numerical weather and air pollution prediction models are now able to approach urban-scale resolution, as detailed input data are becoming more often available. As a result the conventional concepts of down- (and up-) scaling for air pollution prediction need revision along the lines of integration of multi-scale meteorological and chemical transport models. MEGAPOLI aims at developing a comprehensive integrated modelling framework usable by the research community which will be tested and implemented for a range of megacities within Europe and across the world to increase our understanding of how large urban areas and other hotspots affect air quality and climate on multiple scales.

Methodology and advancement beyond the state-of-the-art

The integration strategy in MEGAPOLI will not be focused on any particular meteorological and/or air pollution modelling system. The approach will consider an open integrated framework with flexible architecture (module/interface structure) and with a possibility of incorporating different meteorological and chemical transport models. Such a strategy will be made possible through jointly agreed specifications to interface the modules for easy-to-use integration. The modules which have to be considered, include input data such as emissions, meteorological and chemical transport calculations. The structure of the framework will enable the coupling across the whole range of scales by minimizing the scale-dependence of the interfaces. This multi-scale approach is especially crucial for an efficient integration strategy. Indeed, atmospheric flows include frequently locally forced features, which interact with regional- and global-scale processes such as fronts and convection. Then, scale interaction is a challenge for both weather and air pollution predictions, especially at regional scales. Depending on both time and space scales, certain atmospheric processes can no longer be explicitly resolved or treated as sub-grid scale features and thus need to be parameterized. Furthermore, the interaction between these processes may be of considerable importance (e.g. Mandal et al. 2004), so that it is not sufficient to test individual components. The framework will contain methods for the aggregation of episodic and long term results, model downscaling as well as nesting. The activity will also address the requirements in terms of outputs from meteorological models suitable as inputs to chemical transport models (e.g. Seaman 2000). Thus, a timely and innovative field of activity will be to assess the integration of the modules and interfaces as well as to establish a strong basis for their harmonization.

Under most atmospheric conditions, the interaction of meteorology with pollution transport is important for air quality. At regional scales the decoupling between atmospheric dynamics and chemistry is questionable. The interaction of meteorology and pollution transport may become significant in the sense that feedbacks of atmospheric pollutants on meteorological processes need to be taken into account. Integrated physical and chemical parameterization schemes would need to be considered. For instance, effects of aerosols on atmospheric dynamics and climate are not usually considered in off-line meteorological and air pollution models. However, aerosol radiative forcing can result in significant changes in regional atmospheric dynamics. Also, re-circulating air masses can become large photochemical reactors that may feedback atmospheric dynamics at both regional and global scales. Therefore the impacts of the feedback processes have to be assessed in an integrated framework. Both off-line and on-line coupling of meteorological and air pollution models will then be considered in MEGAPOLI. The cornerstone is the quantification of air quality forcing and its impacts on meteorological processes.

A few initiatives for integrated tools do exist in Europe, e.g. ENVIRO-HIRLAM (see for instance Chenevez et al. 2004), PRISM (Valcke et al. 2006), UKCA (in development, http://www.ukca.ac.uk), COSMOS (in development, http://cosmos.enes.org), M-SYS (Trukenmüller et al., 2004) and would eventually be considered in MEGAPOLI. Similar frameworks are being developed in the USA, such as ESMF (e.g. Dickenson et al. 2002). The WRF-Chem model (Grell et al. 2005), which has been developed within the WRF collaborative framework, will also be considered. This integrated model has been successfully applied to the Mexico City metropolitan area in order to study the origin and evolution of ozone for a pollution event in May 2003 (Tie et al. 2007). The strategy adopted in MEGAPOLI will benefit from the existing integrated frameworks and eventually would be embedded within a European modelling strategy. With the application to megacities in mind, the ‘integration’ needs to be fully achieved down to urban scales (e.g. Baklanov et al. 2002). MEGAPOLI is thus expected to address the difficulties arising from the treatment of the multi-scale and multi-process nature of the integration procedure down to the city scale.

Task 1 will serve to integrate the research outcomes of the project related to improved emissions, coupling of meteorology and chemistry, improved parametrisation of megacity features and model developments with a view of developing a European integrated modelling framework in Task 2. The task will span most of the duration of the project and will involve close cooperation with other WPs ensuring that tools are developed which meet the over-riding scientific aims and user needs (e.g. in WP7 Task 4 and 5 and WP8). It will consider emissions, air quality and climate aspects on regional to global scales and formulate a framework for online coupled systems addressing multi-scales (urban to global), multi-pollutant (eg O3, PM, NO2) and air quality-climate feedback processes (e.g. for aerosols). Within Task 2, the integrated tools will be used to support the needs of mitigation and policy strategies considered in WP8 including supporting the thematic strategy on air pollution (CAFÉ). Based on the outcomes of Task 1 a framework to integrate air quality and climate models will be developed. It will be important to to build upon know-how gained from existing modelling systems and earlier and ongoing projects e.g. PRISM (DMI), COSMOS (DMI), FUMAPEX/CLEAR (DMI et al), GEMS (FMI), PROMOTE2 (FMI), M-SYS (UHam), and EUCAARI (UHel). It is not intended to develop new coupling approaches, but the focus will be on developing interfaces for coupling (direct links between emissions, chemistry and meteorology at every time step) and defining common formats for data exchange to ease the implementation and combination of the different models via agreed data exchange protocols. Task 3 will examine process requirements, operational aspects, levels of integration, interfaces between meteorological, air quality and climate models and formulate strategies for undertaking comparison of approaches according to different levels of integration and order of complexity. This will require interaction with all other WPs. Task 4 will apply the improved and integrated models to real megacity cases on multiple scales from city to global. The task will employ complex and simpler approaches highlighting their complementary nature. The cities will be selected according to emission source mix, intensity of emission rates, meteorological characteristics (orographic and weather patterns), future growth trends, local impact as well as potential to directly affect Europe. Task 5 will lead to recommendations on the main science questions related to megacities (see section 1.1).

FP7 EC MEGAPOLI, 2008-2011