ATMoS-4.0 is a dispersion model that generates source-receptor transfer matrix that is used for the SIM-air model.
In the SIM-air tool, all the calculations, including the conversion of emissions to concentrations, are conducted in Excel, using the source-receptor transfer matrix (SRTM). The transfer matrix, which enables the conversion of emissions to concentrations, is based on a dispersion model, which is not included the Excel analytical tool. This part of the calculations (generating the SRTM) is conducted outside the SIM-air tool and then transferred into Excel to enable further analysis to health impacts and optimization.
A number of dispersion models are available to support the development of SRTM; some are free for use with some technical support and some are available at commercial level. As usual, the dispersion models are very data intensive and need substantial training, before using the models for analysis.
At training events, the one question that is asked repeatedly is “How does one access a dispersion model, when the data available is minimum, experience is limited, and yet there is need for some rapid assessment”. While we supplemented the need for a dispersion model with SRTM concept, the generation of the SRTM based on a dispersion model is now available through a simplified dispersion model ATMoS-4.0 to generate SRTM using minimum data inputs for direct use in SIM-air for urban applications.
Source-Receptor Transfer Matrix
The source-receptor transfer matrix presents the incremental change in concentrations due to an incremental change in emissions and defined as “change in concentrations in a receptor grid per ton/year change in emissions in the source grid”. For the scenario analysis in urban cases, when the only variable changing is emissions, this methodology helps with the rapid assessment.
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Mathematically, it is represented as 
where
· Eb = base case emission rate of used to generate the transfer matrix (3,000 tons/yr)
- Eij = actual emission rate at the source cell (i, j)
- Ckl = calculated mass concentration of the pollutant at the receptor cell (k, l)
· Cbkl = modeled mass concentration at the receptor cell (k, l) due to “Eb”
- l, i = maximum number of horizontal cells
- k, j = maximum number of vertical cells
One matrix doesn’t fit all. This should be developed separately for each city, using local meteorological conditions. All the matrix calculations need calibration and validation before using for multiple scenario analysis. The output of the ATMoS-4.0 model is a source-receptor transfer matrix and for use in the SIM-air tool ONLY.
An example Excel file is included along with the dispersion model.
Limitations
- This is a model and needs calibration, like any other model.
- User can play with the deposition and reaction rates using appropriate and available literature.
- The dispersion depends on the meteorological data. The model is set-up to use only one meteorological data point, hence applicable for a city level analysis only.
The output is 8 files containing grid-grid source-receptor matrix using a dummy emission of 3,000 tons/yr for each grid. The output must be divided by 3,000 and follow the equation presented in Page 2 (of the full report) and the example excel file.
This is a first cut analysis to demonstrate how the dispersion calculations can be conducted and an alternative for rapid analysis. If more detailed modeling is required, for example, adding ozone analysis to the model, then ATMoS-4.0 is not capable of doing so.
User is responsible for the final results.
ATMoS-4.0 Model Installation & Requirements
The model and the test run results are available for download
Please follow the installation and running steps as explained in this document
The complete paper explaining the methodology and uses can be accessed on SIM Working Paper Series No. 30.
