---
id: engines/gral
about:
  depiction: engines/gral.jpg
  label: GRAL
  description: >-
    The Graz Lagrangian Model from Graz University of Technology; simulates the
    dispersion of pollutants and odour in built-up areas and complex terrain,
    including low-wind conditions and road tunnel portals.
  tags:
    - air quality
    - odour
    - dispersion
    - pollution
    - freeware
tool:
  form: Free dispersion model
  group: Sensory landscape
  homepage: 'https://gral.tugraz.at/'
open:
  source: unknown
  data: unknown
  api: unknown
  participation: unknown
  licence: freeware
  note: >-
    The model system is a free download after registration on the TU Graz site,
    with no warranty; the pages read do not say whether the source code is
    published.
domains:
  - sensory
relations:
  - predicate: answers
    target: questions/sensory-landscape
provenance:
  origin: agent
  sources:
    - title: Home - GRAL - Graz Lagrangian Model
      url: 'https://gral.tugraz.at/'
    - title: Features - GRAL - Graz Lagrangian Model
      url: 'https://gral.tugraz.at/features.html'
    - title: Welcome - GRAL - Graz Lagrangian Model
      url: 'https://gral.tugraz.at/download.html'
  created: '2026-10-18'
  reviewed: '2026-10-18'
  reviewed_by: 'Claude, from the sources listed'
  status: draft
---
GRAL, the Graz Lagrangian Model, is a dispersion model developed since 1999 at the Institute of Thermodynamics and Sustainable Propulsion Systems at Graz University of Technology. With its companion wind-field model GRAMM it forms the GRAMM/GRAL system, which the institute says is used both in research and in regulatory assessments of urban air quality. It 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, and it handles dispersion across the full range of wind speeds and stability conditions.

It simulates chemically non-reactive pollutants in built-up areas and complex terrain, with a micro-scale flow model that accounts for buildings and building downwash; 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; and flow within vegetation layers. For smell it computes odour hours from a concentration-variance model. Runs can be steady-state or transient, for instance for puff releases.

The model system is freeware. It is downloaded from the TU Graz site after registering with some basic details; the download page gives no warranty of completeness or correctness and puts the risk of correct application on the user. The pages read do not name a source licence or a public repository. The institute offers trainings.

Status: in use; the download site was renewed in November 2022, and the home page gives no later date.