Particles versus gases

[sahil.bhandari]

Can the flow of gases be simulated reasonably using HYSPLIT? Why would we expect the gases to follow these trajectories? I would have thought they would deviate easily from the plume line. It's easier to imagine solid aerosols actually following the plume line.

[alicec]

The computational particles in HYSPLIT represent fluid parcels. The Lagrangian framework for fluid dynamics uses a frame of reference from the viewpoint of fluid parcels.
HYSPLIT is very accurate for a gas as long as it is not a dense gas - that is as long as it will follow the flow of the rest of the gas that makes up the atmosphere. The meteorological data provides the mean flow field. The trajectory basically provides the path of a fluid parcel if the mean flow field represented all the motions of the atmosphere.
The dispersion calculation takes into account turbulent motions not represented by the mean flow field.