FLEXPART is a Lagrangian particle dispersion model designed for both operational emergency response and research applications. It simulates the long-range transport, diffusion, dry and wet deposition and radioactive decay of air pollutants released from point, line, area or volume sources. The model can be used in forward mode to simulate the dispersion of pollutants released at given locations, or in backward mode to determine potential source contributions for a given receptor. The backward mode application is new at the Hungarian Meteorological Service.
FLEXPART is an off-line model that uses meteorological fields (analyses or forecasts) in Gridded Binary (GRIB) format from the ECMWF numerical weather prediction model on a latitude/longitude grid and on native ECMWF model levels as input.
The Monin-Obukhov similarity approach is used for the physical parameterization of the boundary layer parameters. The height of the mixing layer is calculated using the bulk Richardson number concept with the critical value of 0.25.
For the parameterization of boundary layer parameters, the surface sensible heat fluxes and surface stresses are essential. Accumulated surface sensible heat fluxes and surface stresses are available from ECMWF forecasts.
Results of a simulation with FLEXPART
The set up of the simulation
Start of the simulation: 15.06.2004. 12UTC.
Time of release: 2 hours
Height of release: 120-125m
Simulation is calculated for 60 hours.
Total mass emitted: 1.0 kg
Total number of particles released: 1000
The figures shows the surface level concentrations (ng m-3) and the deposition fields (ng m-2)(the isolines have logarithmic scale).
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Background air pollution measurements 
