**The Best of Creative Computing Volume 1 (published 1976)**

Let's take an average residential district, composed of a mixture of apartments and single family dwellings, as the subject of our first air pollution model. Suppose that the residential district is square with one mile sides and that we are concerned with the air over the district up to an elevation of 500 feet. Moreover, we will assume that no air passes in or out of our residential district and that any pollutants created are uniformly distributed through the air up to our "ceiling" of 500 feet. These assumptions are typical of the ones we will be making continually. Certainly they are crude, and you may be in complete disagreement. However, experience shows that it is a valid approach to start with a very crude model and then refine it. EXERCISE 1 _ Estimating Number of Cars How many automobiles would you expect to find in our residential area? How many automobiles would you expect to find running at some arbitrary time? You will have to make some assumptions explicitly your answer. Be sure and state these assumptions explicitly. Compare your assumptions to those of other students. Do your assumptions stand up well under close examination? Now that you have estimated the number of cars, we will structure our first model. Let P stand for the number of cubic feet of pollutants at any time, R for the number of cubic feet of pollutants produced per hour by each car, and N for the number of cars operating at any given time. The simplest model we could construct would be Pnew=Pold+(R)(N). (1) Pnew is the amount of pollutants at the end of any hour.Pold is the end of the previous hour. [image] COMPUTER ALERTS CONNECTICUT T0 AIR POLLUTION LEVELS Connecticut's Department of Environmental Protection (DEP) is counting on a computer and electronic sensors to help fight air pollution. The IBM System/7 in Hartford, automatically records analyzes and informs DEP of air pollution levels gathered by mobile trailers filled with electronic monitoring equipment. If pollutants rise beyond normal ranges the computer triggers a bell alarm to alert the air compliance director. Stage 2 Alerts are issued when people with heart or respiratory conditions might be affected by the air pollution. (Photo State of Connecticut) 224