When analyzing air quality impacts from pollution sources, it may be important to understand which sources or groups of sources are contributing the most to the cumulative impact of all sources. Some air dispersion models have simple routines for grouping sources or analyzing individual source contributions, but it can be a challenge in some systems.
The CALPUFF air dispersion modeling system has a utility called CALSUM which is useful for analyzing cumulative impacts from multiple model runs. This allows modelers the flexibility to analyze contribution from one or more sources separately and still see the overall effects on air quality.
Using CALPUFF View, modelers have multiple tools at their disposal to carry out this type of analysis.
Step 1: Start by setting up your project in CALPUFF View. Include all sources of interest.
Step 2: Determine how many different sources (or groups of sources) you have from which you want to analyze contribution. For each contribution group of interest, create a project copy.
Step 3: In each project copy, go to the Sources window and uncheck the Active box for the unused sources. This can also be done via the Source List view.
Source List Showing 1 Active Source
Step 4:Run CALPUFF for each project. The results from these individual projects represent the contribution of each source or source group.
Step 5:Create a new project to store the combined results. The easiest way to do this is to create another project copy. Make sure it includes all sources. If you do not have a single run which contains all sources, you can use the Export | Sources command from the individual projects and Import the resulting spreadsheets to your cumulative project.
Step 6:Select Tools | CALSUM Wizard. Follow the Wizard steps to verify the species of interest, add the model output files (CONC.DAT, DFLX.DAT, or WFLX.DAT) from the individual projects, and scale output as necessary.
Step 7:Press the Run button to execute CALSUM.
The output from CALSUM can be processed through CALPOST to get the cumulative air quality impacts from the various sources. Source contribution information is derived from the individual source modeling projects.
Another benefit to following this setup is that the individual model run times can take much less time than a project containing all sources in a single run.
Note that CALSUM can only be used if:
The output files are of the same type (containing either concentrations, wet deposition fluxes, or dry deposition fluxes)
The time periods contained in the files are identical
The species are the same and in the same order
The receptors (e.g., sampling, discrete, etc.) are the same in terms of number, location, and order