Megacities need mega-models to assess their environmental impact

Assessing the impact of large urban areas on air quality and climate change needs an integrated approach with a range of spatial and temporal scales, according to researchers. The EU-funded MEGAPOLI project considers time scales from seconds to decades and spatial scales from local to global.

Populations have been gathering in larger and larger settlements and currently there are about 20 cities worldwide with a population of 10 million citizens or more. Urban areas with more than 5 million people are usually called megacities; in Europe there are at least 6 such megacities or urban agglomerations: London, Paris, the Rhine-Ruhr region, the Po Valley, Moscow and Istanbul.

The MEGAPOLI¹ project aims to investigate the interactions among megacities, air quality and climate change. It is researching how megacities affect air quality and health on regional and global scales, as well the key feedback systems between air quality, local climate and global climate. MEGAPOLI is also evaluating the available policy options that can influence emissions of air pollutants and greenhouse gases (GHG) in megacities.

Due to the size and scope of the project - it involves 23 partners - MEGAPOLI has so far focused on methodology and developing tools on a number of scales. For example, time scales of seconds and hours are needed to understand the chemical interaction of air pollutants and emissions, whilst scales of years and decades are needed for climate effects. Similarly, spatial resolutions from a very local to a global scale are required. The project is organised into several 'work packages' in which there have been the following developments:

• The project has integrated emission inventories from local administrations into larger datasets. This has built connections between existing information and bridges between the air quality and climate change research communities.
• Researchers have developed a classification of megacity features, such as land use, and features of the atmosphere above the city.
• Using measurements from Paris, the project has characterised different aerosols (tiny airborne particles) and their behaviour above megacities. Results indicate that a large cloud of pollution is still well-defined more than 100km from its source in Paris, providing a spatial framework for future study of aerosols.
• New methods have been developed to model local and urban scale impacts of megacity emissions on air quality and on the feedback loops between air quality and climate change. The results indicate that urban aerosols affect several weather conditions, such as temperature and rainfall.
• Progress has been made in developing modelling tools at the continental and global scale and findings indicate that megacities contribute about 2 to 5 per cent to the total global fluxes of emissions caused by humans.
• Finally, the results of modelling are being used to estimate the financial impact of megacity emissions on human health, ecosystems and climate change. Using this information, various mitigation options will be evaluated.

MEGAPOLI is running until the end of 2011. By using reliable integrated tools on multiple scales and for multiple pollutants, it will be able to assess the impact of the largest urban centres and hotspots in Europe and globally.

1. MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) is supported by the European Commission under the Seventh Framework Programme. See: http://megapoli.dmi.dk/
   

Source: Baklanov, A., Lawrence, M., Pandis, S. et al. (2010) MEGAPOLI: concept of multi-scale modelling of megacity impact on air quality and climate. Advances in Science & Research. 4:115-120.

Contact: alb@dmi.dk