Air Quality Models

Assessment Models

(Source: IRCELINE We thank the Interregional Environmental Cell for its valuable collaboration in disseminating the interpolation and modeling maps for Wallonia)

RIO-IFDM Model

RIO is an "intelligent" interpolation technique that normalizes the stations based on emission information and land use in order to ensure they have the same spatial representativeness. The measurement values thus obtained can be interpolated using a standard method (ordinary kriging). Then, the local characteristics of each interpolated measurement point are considered in the final step of the procedure. The RIO interpolation technique provides results at a spatial resolution of 4x4 km². Its temporal resolution is the same as that of telemetric measurement networks (hourly).

The RIO-IFDM model results from coupling the RIO interpolation method with an IFDM dispersion model based on knowledge of the pollutant emission sources. The latter calculates the impact of atmospheric pollutant emissions from point and linear sources on air quality in the immediate vicinity of the sources. Unlike the RIO interpolation method, the IFDM model does not rely on measurements but assesses atmospheric pollutant concentrations based on emission data and meteorological data such as wind speed, wind direction, and temperature. The combination of these two approaches allows the production of high-resolution spatial maps across the entire Belgian territory and is particularly useful for representing air pollution related to road traffic on the main network (motorways and national roads).

ATMO-Street Model

ATMO-Street simulates the dispersion of pollutants (PM₁₀, PM_2.5, BC, and NO₂) from their main emission sources, which are large industries and the road network, taking into account weather conditions. The concentrations of these pollutants are then calculated at various points of the studied area and subsequently interpolated across the entire zone. ATMO-Street resulted from the coupling between the IFDM model (presented above) and the OSPM (Operational Street Pollution Model) by VITO.

For the industry, only the most polluting industrial sources within the municipal perimeter are considered by the IFDM model, with the impact of the overall industrial fabric being accounted for in the background concentrations.

For the road network, pollutant emissions are assigned to each road segment based on measured traffic. Each vehicle is associated with an emission factor depending on its category (light or heavy vehicle, engine type, Euro standard) and driving mode (urban, rural, or motorway). The emission factors are based on a large compilation of measurements and comparative analyses of emission models and take into account several measurements made under real driving conditions.

The model also considers the configuration of streets. In the case of urban canyons, which are narrow roads with tall buildings, the IFDM model is replaced by the OSPM model. The latter allows distinguishing the direct contribution of traffic emissions from the one due to recirculation caused by vortex presence. Inside these streets, there is usually poor dispersion, leading to a local accumulation of pollutants.

Predictive Model

CHIMERE is a deterministic model that simulates the physico-chemical processes occurring within the atmosphere. It relies on weather forecasts, pollutant emissions into the ambient air, and land use. The spatial resolution used in this version of CHIMERE is about 50x50 km², meaning that concentrations are representative of average values over large areas, and real concentrations can be locally higher (in industrial zones, near road axes, etc.).