Atmospheric Dispersion Modelling

Atmospheric Dispersion Models

Contact
Silvia Trini Castelli

MILORD

MILORD is a 3-D long-range Lagrangian particle model. Transport and dispersion of pollutants or tracers are simulated by following the trajectories of virtual particles, each representing a finite mass and/or activity of the substance considered, in a three dimensional wind field (ECMWF analyses). Diffusion due to turbulence is prescribed by integrating the Langevin equation for displacement. Depletion of the mass particle by dry and wet deposition and radioactive decay or chemical transformation are accounted for by exponential reduction equations. A post-processing analysis package allows calculating concentration and deposition over specific locations or over a grid. The model is designed to work requiring the minimum information available from typical data sets: topography, 3-D wind at standard pressure levels and precipitation. It can use any kind of gridded input data, having any time and space resolution and source configuration. It is able to treat area, line or point sources, time and space depending emissions, where a plume rise can be assigned.

SPRAY

SPRAY is a three dimensional model designed to simulate the airborne pollutant dispersion, able to take into account the spatial and temporal inhomogeneities of both the mean flow and turbulence. Concentration fields generated by point, areal or volume sources can be simulated by the model. The trajectory of the airborne pollutant is simulated through virtual particles: the mean motion is defined by the local wind and the dispersion is determined solving the Langevin stochastic differential equations for the velocity fluctuations, reproducing the statistical characteristics of the turbulent flow. Different portions of the emitted plumes can therefore experience different atmospheric conditions, allowing realistic reproductions of complex phenomena, such as low wind-speed conditions, strong temperature inversions, flow over topography, landuse and terrain variability. ISAC-Torino has a long-term collaboration with Arianet srl in Spray development: Spray is now a commercial model licensed by Arianet. Spray can be driven by a diagnostic mass-consistent model (SWIFT, developed at Aria Technologies, Paris) and by the atmospheric model RAMS (in the modelling suite RMS developed at ISAC-Torino).

RMS and MicroRMS

RMS and MicroRMS are modelling suites composed by the known atmospheric model RAMS, the boundary-layer parameterization code MIRS and the Lagrangian particle model (Micro)Spray. MIRS (Model for Interfacing RAMS and SPRAY) processes the meteorological RAMS output fields or, alternatively, other kinds of data fields deriving by observations or diagnostic models, then calculates the boundary-layer quantities and the Lagrangian turbulence fields. In our suites, RAMS has been modified including alternative turbulence closure schemes, also for specific simulations at the microscale (RAMS6_Mod). MicroRMS is the microscale version of RMS suitable for the simulation of the flow and dispersion at high spatial resolution (order of 1 m) in presence of obstacles and buildings. In MicroRMS, MIRS is specifically modified to process and transfer the information about the presence of the obstacles as used in RAMS to the approach implemented in MicroSPRAY

MicroSpray

MicroSpray is a microscale Lagrangian particle model derived from SPRAY code and able to take into account the presence of obstacles. Microspray is especially oriented to deal with gas dispersion in urban environment and industrial sites. It is a flexible tool including the treatment of several features: plume without initial momentum and with initially arbitrarily oriented momentum, negative or positive buoyancy, elevated and ground level emissions, instantaneous and continuous emissions, time varying sources, cloud spread at the ground due to gravity, bouncing against obstacles and particle reflection at the domain bottom in presence of a dense cloud. Modules treating the phase changes liquid – vapour that may occur at the source, and the latent heat processes in the dispersing cloud, such as aerosol evaporation, have been recently implemented. MicroSPRAY is applied in the frames of MSS (MicroSwift-Spray) and MicroRMS (RAMS-MIRS-SPRAY) modelling systems.

SPRAY-WEB

SPRAY-WEB is the research-version of the Lagrangian particle model SPRAY. A consortium has been established and the partners consider of general utility that the model SPRAY could be made available to a wider researcher community, which contributes to its development, update and to a more disseminated use for environmental problems. SPRAY-WEB is particularly suitable for studying the atmospheric pollution processes under complex meteorological and orographic conditions (typical of the Italian regions), avoiding the impact assessment errors obtained by more simplified models, which are not able to reproduce the dispersion under non-stationary and non-uniform conditions. The model can then be effectively used both in the impact assessment of plants and infrastructures and in the analysis of very severe configurations in terms of air quality alteration (e.g., urban centres, industrial sites, …). The complexity of the atmospheric dispersion makes necessary the continuous improvement of the algorithms implemented. The partners  (called “developers”) are responsible for intervening and maintaining the code;  they have personnel suitable for orienting and verifying the developments which might be useful and necessary. SPRAY-WEB site is at http://sprayweb.isac.cnr.it/

SMART

SMART – Spray-Moloch Atmospheric Regional Tool

A new modelling system, SMART, is under development for the simulation of the dispersion by accidental releases of pollutant in the atmosphere. It can be applied also for the assessment of continuous releases from known sources. In the new modelling suite SMART, the non-hydrostatic atmospheric model MOLOCH and the Lagrangian stochastic dispersion model SPRAY are interfaced by the boundary-layer and turbulence parameterization code ARAMIS (Atmospheric Regional Algorithm for Moloch Interfaced to Spray).

Based on the MOLOCH meteorological forecasts, ARAMIS and SPRAY models can be run to simulate the pollutant dispersion and to forecast affected areas and ground-level concentration patterns.

SMART is planned to be adopted as a tool for emergency response purposes in any part of the Italian territory at any time.

References

MILORDLong range simulation of transport, dispersion and deposition (radioactive decay or first order chemical reactions are included) of tracers for continuous or accidental releases. Typical simulations cover regional to long-range area scale, from hundreds to thousand kilometres, and time period ranging from one day to months

SPRAYSimulation of the dispersion of airborne pollutants through the stochastic motion of virtual particles in the turbulent atmospheric flow in complex topography, from the local scale (1 to 5 km) to the mesoscale (100 km).

MicroSPRAYSimulation of the dispersion of airborne pollutants trough the stochastic motion of virtual particles in the turbulent atmospheric flow in complex topography and presence of obstacles at the microscale (100 m, up to 1 km), for buoyant or non-buoyant release.

RMS and MicroRMS: Simulation of the atmospheric circulation and dispersion of any type of airborne pollutants, passive, buoyant or non-buoyant, in the turbulent atmospheric flow in complex topography and presence of obstacles at all scales, microscale (up to 1 km, MicroRMS), local scale (1-5 km, RMS) and mesoscale (100 km, RMS).

SMARTSimulation of the atmospheric circulation and dispersion of any type of airborne pollutants, passive, buoyant or non-buoyant, in the turbulent atmospheric flow in complex topography; aimed at potential emergency response tool over Italy.