It feels good to buy a chocolate bar with the Fair Trade label, signifying decent wages for the farm workers in developing countries who harvest the cocoa beans. But are you willing to pay more for that chocolate than for a regular chocolate bar? What about corn chips? And, to go beyond snack food, what about pollution?

Jay Corrigan looks into such questions with the eye of an economist who studies the complex world of economic interaction from the standpoint of how and why individual people make choices.

Corrigan likes to use hands-on exercises in the classroom. In his course on "Environmental Economics," for example, he asked students to voluntarily (and anonymously) donate money to buy a pollution allowance from the Environmental Protection Agency. The class actually purchased 497 pounds of sulfur dioxide emissions for 2005, through a nonprofit organization called the Acid Rain Retirement Fund, which buys the allowances so that they can't be used by power plants. The group reduces acid rain by buying the right to pollute with sulfur dioxide and then, in effect, choosing not to use that right.

The exercise addressed one of the problems inherent in teaching "Environmental Economics," which attracts a good many non-majors as well as economics majors. "It's an advanced course," notes Corrigan. "I want to make it appealing and useful to the non-majors who may lack some of the theoretical tools, while keeping it challenging for the majors."