In the Eulerian modeling approach, air concentrations
are computed for every grid cell by integrating the pollutant
fluxes at each grid cell interface due to diffusion and advection. In
the Lagrangian modeling approach, air concentrations
are computed by summing the contribution of each pollutant puff
that is advected through the grid cell as represented by its
trajectory. In a Lagrangian model, modeling the growth of the
pollutant puff’s 2nd moment or explicitly modeling the growth
of a cluster of particles can simulate dispersion. Contrary
to its acronym, HYSPLIT can simulate a pollutant
distribution starting with a single particle or puff, or by following
the dispersive motion of a large number of particles.
