1. Introduction

The decades of the 1960s and 1970s reflected an awakening of an environmental consciousness in America and increasing efforts to reduce the uncontrolled or poorly controlled releases into the natural environment that had characterized past human activity. It is perhaps hard to understand today the common belief that the air, soil and water were effectively limitless and therefore appropriate for largely uncontrolled disposal of our wastes. It is also hard to imagine that during the 1940s through the 1960s there were acute air pollution episodes in various cities around the globe that led to the premature deaths of people at a rate that was easily observable. More than 4,000 excess deaths occurred during a “killer smog” episode in London in 1952 due to the combination of normal air emissions and adverse atmospheric conditions. These acute episodes helped galvanize public opinion, leading ultimately to regulations such as the Clean Air Act amendments of 1970. Following passage of these regulations, air quality improvements were rapid in many areas although we continue to work to manage the more difficult air pollution problems.