# Exercise #7

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• Problem #1 - The multiple particle release tutorial showed that when the particle number was increased from 100 to 1000 and then again from 1000 to 10000, each time the maximum concentration decreased by half during the last sampling time period (0500). The 100,000 particle simulation was not shown, but the maximum concentration only decreased by 10% from the 10000 particle simulation, suggesting that the 10,000 particle release was sufficient. What particle number would be sufficient if the concentration grid was increased from 0.05 to 0.10 degrees?

• Hint - Retrieve conc_test_control.txt and conc_test_setup.txt and reconfigure.

• Solution - The 1000 particle 0.10 deg grid result is similar to the previous 10,000 particle 0.05 deg grid simulation. An explanation for this result might be inferred from this illustration.

• Problem #2 - From the previous problem, can you explain the changes to the minimum concentration?

• Hint - For example, the minimum value shown from concplot in the previous graphic 3.5E-19 cannot be used because it is the result of interpolation by the contouring program. Instead use gridplot to determine the minimum values for the 100, 1000, and 10,000 particle number simulations.

• Solution - You should get values of 2.1E-14, 2.1E-15, and 2.1E-16, respectively, with each factor of 10 increase in particle number! The minimum value is directly proportional to the particle number. Using a calculator, how would you compute the expected mimumum concentration for the 10,000 particle simulation?