The first step in understanding the nature of the air concentration dispersion calculation will be to modify the test example, gradually reduce the simulation down to its most basic component, a single particle trajectory, which we will then enhance step-by-step until the calculation is optimized to represent a realistic concentration simulation.
- First from the main menu press the Reset button to set the menu variables for the test calculation and then press the Concentration / Setup Run menu tab to open the concentration setup menu to set all the concentration run parameters. Change the starting time to 83 09 25 17, the run duration to 12 hours, and the starting location to the tracer release point 39.90 -84.22 10.0. Clear the meteorology files and then add captex2_wrf27uw.bin from the Tutorial/captex directory. When finished with the changes, Save to close the menu window.
- Then go ahead and press the Run Model tab under the Concentration tab. If the SETUP.CFG namelist file found! message appears, select Delete file and then Run because we have not yet created a namelist file for this example and it is probably left over from a previous calculation. When complete, Exit and continue to the next step.
- To create the concentration graphic, press the Concentration / Display / Concentration / Contours
menu tab to open the display menu, where you should just accept the defaults, press Execute Display to open the plume graphic which shows color filled contours of 12-hour average air concentrations at factor of 10 intervals ranging from 10-12 to 10-15 mass units per cubic meter. This calculation is identical to the original test case except we moved the location and time to be consistent with CAPTEX release number two.
The results shown here illustrate the first step in changing the configuration of the test case simulation to match the details of the CAPTEX experiment. In the test calculation, one unit of mass was divided over 2500 pollutant particles released over a one hour duration. The concentration pattern represents the average particle mass in each grid cell divided by the cell volume. For instance, if one particle (mass = 1/2500) were contained in a grid cell of volume 5x5x1 km (2.5E+10 m3), then the air concentration would be about 1E-14 units m-3, a number comparable to the lower end of the range shown in the calculations. Because the output is time‐averaged, the even smaller values reflect the particle's reduced residence time.