The previous step only showed the concentration integral of the accumulated mass as the single particle passed through the computational domain. To illustrate the temporal contributions, the averaging time should be reduced.
- To examine the details of the calculation we need to eliminate the temporal averaging. Open the Concentration / Setup menu and the open the grids menu and change the last line from 00 12 00 to 01 01 00. This changes the particle mass accumulation from a 12 hour average to a snapshot value once an hour. The term "now" equals a one-time-step accumulation.
- Save the change, run the model, and open the display menu. There will now be 12 frames in the graphic, one for each hour, the first frame shows the concentration pattern after one hour. Note the concentration grid cell size is represented by the red square and although it looks like the pattern covers several grid cells, a single particle calculation can only be contributing to one cell during a time step. The bleeding of the concentration contours into adjacent cells is just an artifact of the smoothing and contouring process.
- To see all the frames in a single animated graphic, similar to a trajectory, press the Concentration / Utilities / Postscript to Image menu tab to open the ImageMagick conversion menu. Select the Animate and crop radio-buttons, and move the slider bar to a higher resolution (140) for a better quality image. After executing the conversion, the window closes with no message, but you will find the animated GIF, concplot.gif in the working directory. The animation is a little jumpy due to the atmospheric turbulence affecting this single particle trajectory.
- Save the control file to conc_test_control.txt and the namelist file to
conc_test_setup.txt for future reference.
The results shown here illustrate how a particle trajectory is used to compute air concentrations. This particular example, using one particle, is insufficient for a realistic simulation. These issues will be explored in more detail in the following sections.