GRAL

GRAL has been developed since 1999 at the Institute of Thermodynamics and Sustainable Propulsion Systems at Graz University of Technology.¹ Lagrangian means it follows the paths of many individual particles of pollutant. With its companion model GRAMM it forms the GRAMM/GRAL system.¹ The institute says the system is used both in research and in regulatory assessments of urban air quality.¹ The model was first built for the frequent low-wind conditions of inner-Alpine basins in Austria, where wind is below 1.5 m/s for up to 90 per cent of the time.¹ It handles dispersion across the full range of wind speeds and stability conditions.²

It simulates chemically non-reactive pollutants in built-up areas and complex terrain.^1,2 Its features include:²

• a micro-scale flow model that accounts for buildings and building downwash, the air pulled down behind a building
• stack emissions with temperature and exit velocity
• dispersion from road tunnel portals, meeting the Austrian guideline RVS 04.02.12
• dry and wet deposition and sedimentation
• decay, such as bacteria die-off
• flow within vegetation layers.²

For smell it computes odour hours from a concentration-variance model.² Runs can be steady-state or transient, for instance for puff releases.²

The model system is freeware, downloaded from the TU Graz site after registering with some basic details.^1,3 It comes with no warranty of completeness or correctness, and the risk of correct application is the user's.³ The institute offers trainings.¹