HYSPLIT Limitations

This HYSPLIT interface does not incorporate the effects of:

  • chemical reactions
  • dense gases
  • byproducts from fires, explosions, or chemical reactions
  • gases released that are not neutrally-bouyant
  • deposition - unless the user enters appropriate wet and dry deposition parameters
  • particulate transport - unless the user enters information about the particle (size, deposition rates, etc)
  • complex terrain - other than what is resolved by the meteorological model's terrain
  • varying emission rate with time (except for Controlled Burn simulation)
  • varying emission rate with height (except for volcanic ash simulation)

Other considerations:

  • HYSPLIT's minimum time step is 1 minute, so the model cannot be used for transport less than the distance it takes for the pollutant to move in 1 minute. However, keep in mind that the meteorology may not adequately represent the transport/dispersion at the point of release regardless of the model time step. For scales less than 1 km the CAMEO/ALOHA model is recommended.
  • For ground-based hazardous material releases, near-surface meteorological conditions, including the 10-meter winds, 2-m temperatures, and surface fluxes (which determine the stability and thus the vertical dispersion of material) are important determinants of the horizontal and vertical spread of the material. Numerical weather prediction (NWP) forecasts of these meteorological variables are inputs to the HYSPLIT model, but the NWP models are limited in a number of ways in their representation and forecast of near-surface conditions. Frequently, the meteorological forecast data available to run HYSPLIT has been spatially averaged, resulting in representativeness problems for modeling dispersion in, for example, areas of complex terrain.
  • Meteorological data used to force HYSPLIT is available at relatively coarse temporal resolution (1-6 hours), which can result in errors in rapidly changing conditions, even if the NWP model itself can faithfully emulate these conditions. NWP models also have limitations in their ability to accurately forecast the onset and spatial scales of phenomena that may affect dispersion, such as sea-breezes and mountain-valley circulations.
  • Finally, the meteorological data used by HYSPLIT is bi-linearly interpolated in space and linearly interpolated in time to the location and time of a pollutant release and during the forecast of the subsequent diffusion of materials. If important variations in the meteorological fields occur between grid points or between meteorological data output times, concentrations errors may result.

For further details on HYSPLIT, see the following sources: