Forecasting Systems and Urban Air Quality Information

About 70% of the European population live in cities. A major share of anthropogenic sources of pollutants originate from conurbations. These pollutants not only have local effects (on human health, material, ecosystem), but also may impact all the way to the regional (acidification, euthrophication) and global scales (atmospheric composition, climate changes). Urban areas present a challenge to atmospheric scientists, both from the experimentalist and modeler point of view as typically urban areas have high roughness elements penetrating well above the surface layer, heterogeneous distribution of surface features with wide variation in surface fluxes of heat, moisture, momentum, and pollutants. Additionally, the structure of the conurbation may trigger local meteorological circulations and processes (e.g., heat island, enhanced production of condensation nuclei) as well as enhanced vertical motions resulting in longer residence time of atmospheric compounds. As model resolution is increasing toward a few kilometers or finer and various stakeholders and the public are expecting better-targeted meteorological forecasts and products, it has become a necessity to be able to account for, describe, and simulate urban effects and processes in various meteorological and air pollution models. On the other hand, this has brought new requirements for observations and measuring strategy in order to be able to describe, simulate, and forecast meteorological and concentration fields in urban areas. Integration of these aspects will greatly benefit the development of urban air quality information and forecasting systems (UAQIFS) for a variety of applications and end-users.

Modern numerical weather prediction (NWP) and meso-meteorological models (MetM), able to resolve urban-scale processes, are considered to be the main tools in future urban air pollution (UAP) forecasting and assessments because they allow for sufficiently high spatial and temporal resolution and can trace back the linkages between sources and impacts. The Cluster of European Urban Air Quality Research (CLEAR) considers improvements of meteorological data and models for urban areas as one of the targets, because most of the CLEAR projects (FUMAPEX, OSCAR, SAPPHIRE, URBAN AEROSOL, URBAN EXPOSURE, BOND, NEPAP, AIR4EU) need urban meteorological fields for their air quality studies. However, only the FUMAPEX project focuses on the evaluation and improvement of meteorological modeling and preprocessing specifically for urban areas. This work is a logical continuation of the COST Action 715.

The following urban features can influence the atmospheric flow, microclimate, turbulence regime and, consequently, the transport, dispersion, and deposition of atmospheric pollutants within urban areas:

1. local-scale nonhomogeneities, sharp changes of roughness and heat fluxes;

2. the building effect in reducing wind velocity;

3. redistribution of eddies, from large to small, due to buildings;

4. trapping of radiation in street canyons;

5. effect of urban soil structure on diffusivities of heat and water vapor;

6. anthropogenic heat fluxes, including the urban heat island effect;

7. urban internal boundary layers and the urban mixing height (MH);

8. different gas and particle deposition efficiencies for different types of the urban surfaces (walls, roofs, streets, etc.);

9. effects of pollutants (including aerosols) on urban meteorology and climate; and

10. urban effects on clouds and precipitation.

Accordingly, the following aspects of urban effects were considered by the FUMAPEX project in improved urban-scale NWP and meteorological models: higher spatial grid resolution and model downscaling, improved physiographic data and land-use classification, calculation of effective urban roughness and urban heat fluxes, urban canopy and soil submodels, MH in urban areas.

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