Models of the dispersion of gases are useful for planning the response to an accidental or deliberate harmful gas release in a populous city environment. Heavier-than-air gases in particular will tend to not disperse safely away upwards into the atmosphere.
Cambustion's fast gas analysers, especially the fast FID (for hydrocarbons) are often used in gas dispersion experiments (for example in wind tunnels) where their fast response allows high temporal and spatial resolution in plotting gas concentrations.
A nice paper has just been published from authors at Bundesanstalt für Materialforschung und -prüfung (BAM) and the Meteorological Institute, University of Hamburg in this area. Researchers produced a model of the dispersion of "heavy" gases in a complex urban area. They then validated their model using a Cambustion Fast FID in a wind tunnel to make concentration measurements at various positions and times after release, and found good agreement.
Here is a link to the paper: A Modified k-ε Turbulence Model for Heavy Gas Dispersion in Built-Up Environment