Acid rain probably raises a number of questions in your mind: What exactly is an acid, and how acidic is the rain? What makes rain acidic? How does acid rain damage trees, fish, and marble statues? And perhaps most importantly, how do emissions into the atmosphere contribute to acid rain? These are primarily scientific questions, and in the pages that follow we will provide information that can help you answer them.

We begin by considering acids and bases and their properties, then look at acidic and basic solutions to find the ions responsible for these properties. The concept of pH is introduced as a measure of acidity, so that we can discuss the pH of rain. Precipitation with low pH values (high acidity) generally falls in regions where the atmospheric concentrations of sulfur oxides and nitrogen oxides are high. These gases are traced back to their sources: coal-burning power plants and gasoline-burning automobiles, respectively. Then, we turn to the effects of acid precipitation on materials, visibility, human health, lakes and streams, and trees and forests.

Interwoven with these largely scientific issues are the social and political factors that have made the public debate over acid rain as sour as the rain itself. Controversy surrounds the interpretation of the effects of acid rain and the best ways to deal with these effects. We consider several strategies, each with its own price tag. The financial impact of acid rain and the money required to curtail it introduce important economic dimensions. One nationwide pollution solution is that offered by the 1990 federal Clean Air Act Amendments. This legislation and its amendments have already reduced the concentrations of the acidifying oxides. A discussion of this legislation and its current and potential impact brings the chapter to a close.