7.6 Display Particle Positions




Although the air concentration calculation results are typically represented by a grid cell integral representing a pre-defined layer in the atmosphere, it is possible to display snapshots (an instantaneous view) of the individual particle positions in three-dimensional space using the simulation parameters of the previous example and reruning the simulation with additional output. If not continuing from the previous section, retrieve cpart_control.txt and cpart_setup.txt.

  1. To illustrate the nature of the particle-trajectory calculation, we can output the individual particle positions in addition to the air concentrations by opening the Advanced / Configuration Setup / Concentration / Input and Output of Particle Files menu #9 and change the First Output and Repeat Interval from 0 to 3. This will create a special output file called PARDUMP which will contain all the particle information every three hours. This is a more complex file than the ASCII trajectory endpoints file. It is binary and in addition to the particle position, it contains all the information needed to restart the model. Save to exit, close all menus, and then run the model.

  2. A different program is used to display the contents of the particle endpoints file. Press the Concentration / Display / Particle menu tab to open the particle display menu. Accept the cross-section (X-Sect) defaults, perhaps increasing the zoom if desired, and Execute Display to open the graphic. In addition to the horizontal plane view, the vertical cross-section is shown in the lower panel. Other display options include plane or vertical projection views as well as map projection optimized for global particle distributions.

  3. To speed up the creation and display of the graphics, try plotting every 5th particle.

The particle display results clearly show why a single particle trajectory is insufficient to simulate the pollutant distribution. Particles that mixed to the upper-levels of the boundary layer travel at faster speeds. Winds aloft also tend to be more clockwise than those at the surface.