An interactive atmospheric dispersion model for simulation and visualisation of industrial plant emissions. Written in JavaScript.
LIVE EXAMPLE can be found here: https://joshua.nu/really-simple-dispersion/example
In the live example above, the properties of the industrial source and the weather conditions can be tweaked to see the effect on dispersion. Each change will plot average concentrations for a single hour. The Simulate button can be used to run a simulation for the specified number of hours of random weather conditions, which builds up a picture of how concentrations may look time-averaged over a longer period with varied conditions.
This project has also been implemented in Wasm (compiled from Rust) in order to compare performance - see https://github.com/joshuanunn/really-simple-dispersion-wasm for more information.
This is Gaussian based dispersion model, which is a mathematical simulation of how air pollution disperses in the atmosphere. The form of the plume exiting a stack at a given height is derived from the overall Gaussian plume equation below, which describes the pollutant concentration at a single position (x,y,z) in a plume referenced coordinate system. The sigma plume formulas ฯy and ฯz are power-law or logarithmic functions which vary with meteorological conditions. Briggs plume rise formulas are used to add an additional plume rise due to the buoyancy or momentum of the plume. A typical schematic of a plume is shown below (centre).
The plume is visualised by mapping concentrations onto a regular gridded areas, which are effectively 2D slices through a 3D plume. Typical outputs showing simulated ground level emissions over a 5km x 5km area centred on an industrial facility time-averaged over 20 hours is shown below (left). The corresponding side elevation profile of the plume average cross-section with height up to 1km altitude (right). These are contoured on a log scale (each contour is 10x lower/higher than the next).
NOTE that while this simulation can help with understanding and visualising how Gaussian plume dispersion models work, the ISC-3 model on which it is based has long-since been replaced by modern atmospheric dispersion models such as AERMOD (US) and ADMS (UK).
Most of the core functionality and program state is encapsulated in an RSDM class. The concentration maps are held in two internal arrays for each plot - one to hold running raw concentrations and another to build a contour map. The default "High" image quality is based on a 500 x 500 element array for the plan view (5km @ 10m pixel spacing) and a 500 x 200 element array for the height profile (5 km @ 10m horizontal spacing and 1km @ 5m vertical spacing). These are converted to png images and rendered in the browser.
Simple unit tests can be run by simply loading the following page in a browser and checking the console output (refresh page with console open): https://joshua.nu/really-simple-dispersion/example/runtests.html
This software is released under the MIT license MIT.
This software is based upon equations derived from the Industrial Source Complex (ISC-3) atmospheric dispersion model developed by the US EPA. More details can be found in the ISC-3 user guide: http://www.epa.gov/scram001/userg/regmod/isc3v2.pdf.
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