The Best of Creative Computing Volume 1 (published 1976)

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The Automobile and Air Pollution (closing freeways, time-dependent model, political questions)

graphic of page

EXERCISE 11 – Closing Down Freeways
Use the program from Exercise 8 and any wind velocity you desire. What happens
to C if the freeways are shut down at some particular instant?  Sketch a rough
graph of the program printout.

We still have serious flaws in our automobile air pollution model.  We have been
assuming constant values of N, W, and R2. Clearly, this isn't realistic.  It is
common experience that there are morning and afternoon traffic rush hours, and
that very little traffic is on the street in the middle of the night.  Also, the
wind rarely blows with constant velocity.  Finally, the dissipation rate R2 is
certainly not constant.  As we discussed previously, photochemical smog is the
result of organics, oxides or nitrogen and sunlight.  It stands to reason that
R2 should be smaller during hours of sunlight than during hours of darkness.

It will be fairly easy to take these ideas into account and make our model much
more realistic.  The key is to assume maximum values of N, W, and R2, then take
hourly decimal parts of the maximum values.  Thus we can set up one list of 24
factors to be applied to N, another list for W, and so on.  Each of these lists
constitutes a time profile of each factor. Now, the model is

Pnew = Pold + XiN – YiWPold/50 – ZiR2Pold.     (4)

Xi is the traffic profile factor (applied to N), Yi is the wind profile factor,
and Zi is the dissipation profile factor.  The subscript i is the hour number (1
to 24).  So we can compare results, let's agree that hour number 1 in any day is
from midnight to 1 a.m.

EXERCISE 12 – A Time Dependent Model
Write a BASIC program to evaluate the model given by (4) applied to the freeway
example in Exercise 8.  Assume reasonable sets of values for X, Y, and Z.  Print
out C every hour.  Sketch your result in a simple graph.

EXERCISE 13 – Political Questions
Use the model developed in Exercise 12 on a system whose characteristics are
specified by you.  Run the program to get a feel for the pollutant
concentrations that come out of the model.  Now, suppose that the edict has come
down to cut down on pollution.  Use your model and program to investigate the
question.  Make realistic suggestions as to how the pollution concentration from
automobiles might be cut down.


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