To date, the only practical "in vivo" method for assessing odors is olfactometry; however, sampling is only effective directly at the source and not in the area of ​​immission. In such cases, the use of dispersion models is helpful – this is the only way to determine odor pollution in a defined target area. Furthermore, computer-aided dispersion models can be used to determine the contribution of different sources to the overall pollution level.

The GRAL model under investigation is a complex numerical model (Lagrange model) with a moving coordinate system. In conjunction with the upstream flow model GRAMM (Graz Mesoscale Model), through special algorithms for dispersion conditions at low wind speeds and the input of various source types and groups, as well as complex terrain and buildings, this program is increasingly used to calculate pollution levels caused by pollutants. National and international validation datasets exist for nitrogen oxides (NOx ₎ and tracer gas simulations; however, a standards-compliant comparison of the predicted odor levels and the actual perception of test subjects in the field is still lacking.

Odor surveys are a recognized method for evaluating odor dispersion models; these must be carried out in accordance with EN 16841-1:2016 (Outdoor air – Determination of odor emission by surveys – Part 1: Grid measurement). The result of an odor survey is annual odor hours for specific, predefined areas (grid) or for designated points. These results can be directly compared with the values ​​from computer-aided odor emission calculations.