Background Even though air quality in Europe has improved in recent decades, many areas still fail to meet standards set in the European Air Quality Directive (2008/50/EC). This is particularly the case in so-called air pollution hot-spot regions, which are characterised by markedly higher-than-average atmospheric pollution levels, mostly caused by the high density of human activities. Examples of hot spots in Europe are the Flanders-Randstad-Ruhr region, the Italian Po Valley, and the urban agglomerations of London, Madrid and Paris. A significant proportion of the population in these areas is exposed to unhealthy levels of pollutants such as particulate matter (PM) and nitrogen dioxide (NO2). Objectives The objective of the ATMOSYS project was to set up, evaluate and demonstrate an advanced air quality modelling system and associated web-based service, containing novel elements specifically designed for air pollution policy support in hot spot regions. The system was designed around advanced technology, including prognostic 3-D atmospheric computer models. The project aimed to cover multiple scales, with a coherent approach to forecasts, assessments and scenario studies. Rather than establish a centralised service for users, the goal was to establish a demonstration project that could be replicated throughout Europe. The key requirements were easy accessibility through a web-based interface; a high level of usability and a focus on relevant spatial scales, air quality forecasts and human exposure estimates; a high degree of reliability in terms of performance and operational stability; and the sustainability necessary to guarantee its continued use in Flanders. Results To achieve the objective of demonstrating an advanced air quality modelling system, the project’s coordinating beneficiary, the Flemish Research and Technology Organisation (VITO), collaborated closely with the key end-user partners, the Belgian Interregional Environment Agency (IRCEL-CELINE) and the Flemish Environment Agency (VMM). Project activities were conducted in four core stages. Firstly, the project partners designed the architecture of the ATMOSYS web-based system and its various functionalities, and also prepared the air quality modelling tools. The implementation stage involved the development of these functionalities and the generation of various air quality data through specific urban measurement campaigns, emission inventory development and multi-spatial model simulations. During the third stage, the project evaluated the functionalities and the air quality services. The final demonstration stage involved the implementation of the website (www.atmosys.eu) to host the air quality system and its various applications. This operated both as a test platform for potential users to explore air quality information and to disseminate the various findings. The final ATMOSYS demonstration system is essentially an Air Quality Management Dashboard that the project team developed to help Environmental Protection Agencies (EPAs) predict, assess and plan air quality. This will support EPAs in their role of making policy decisions to improve air quality and to inform the public on the status of air quality. The dashboard provides three main services: forecasting, assessing and planning. In each case, ATMOSYS offers different possible solutions to provide the most relevant information, with a strong emphasis on quality and usability. The ATMOSYS dashboard is constructed in a modular fashion, with a number of building blocks that can be applied according to the specific needs and air quality conditions of the region of implementation. Once the building blocks have been selected and configured, ATMOSYS enables experts and policy-makers to monitor, assess, validate, analyse and improve the air quality situation. Users can assess air quality, for example, using annual high-resolution air quality maps, including AQ Directive indicators, time series data, a model evaluation tool and an exposure calculation. This can inform decisions to implement smog warnings, reduce traffic speed, implement low-emission zones, and other air pollutant mitigation measures in hot spot regions. The demonstration system was set up for the European hot spot region of Flanders (Belgium). Near real-time monitoring data and modelling results, including data assimilation techniques, were made available by means of INSPIRE-compliant ICT technology to offer a multitude of data about local air pollution. The ATMOSYS website demonstrated the building blocks incorporated into the air quality management system in Flanders. However, the system can be customised when deployed in other regions, for example, by changing the air quality models used or the associated web-based services. There are basically three major parts in the demonstration system: a front-end interface for experts with a web-based visualisation/control system for air quality management; a public information interface that is also a valuable tool for raising public awareness; and the back-end components that provide most of the modelling, validation, analysis and reporting functionality. The core back-end components comprise a system database, which integrates all data sources required for air quality management; modelling components that enable current and near-future air quality to be calculated; and decision-support components for helping decide which measures to take when air quality problems occur. The monitoring and modelling of elemental carbon (EC) in Flanders was pioneered in this LIFE project. Its monitoring is not yet required under the Air Quality Directive and it is currently undertaken in few EU Member States. EC is a more suitable indicator of traffic pollution than PM, however, and the ATMOSYS measurement campaigns provided valuable information on the EC component of PM, as well as black carbon concentrations near a highway. Innovative 3-D atmospheric computer models were also used during the project to model air pollutants at street level to benefit urban planning. Taken together, measures to improve air quality can improve the general state of health of the population and help to reduce healthcare costs. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).