# Exercise #16

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• Problem #1 - In the previous example, a customized EMITIMES file was created with three 12-h emission time groups. Edit the file so that only one time group is defined for the 36-h emission period.

• Hint - Start with the EMITIMES and CONTROL files that were created in the previous example and should still be found in /hysplit4/working directory.

• Solution - After editing the EMITIMES and CONTROL files, simply rerun the model ..\exec\hycs_std and graphics display program ..\exec\parxplot -iPARDUMP -k1 -z80 from the command prompt. Although the particle plots look almost identical, the new single emission cycle simulation shows 6716 particles at the end while the previous three-cycle simulation showed 17157 particles. Why are there three times fewer particles in the single cycle simulation?

• Problem #2 - Just using the information given for the calculation in problem #1, estimate the depth of the deposition layer in the region a few hundred kilometers downwind of the volcano.

• Hint - Add the deposition layer and use a finer concentration grid, use more particles (you may want to limit the duration for a faster calculation), and estimate the conversion factor required to convert ug/m2 to cm by assuming a lower density than the particle value used in the calculation.

• Solution - The concentration display menu may take a little manipulation to get a nice looking graphic and correct labels require the creation of a LABELS.CFG file. The maximum value of 0.0038 cm just downwind is only a crude estimate because of the short duration calculation, uncertainty in the emission rate1, and particles larger than 20 um were not included in the calculation.

1In contrast, the emission rate for the Mt. St. Helens eruption was around 10^13 g/h or 10^19 ug/h, 1000 times larger than the emission rate used in this example. The result would be deposition totals on the order of several cm.