Clean Air Act
CLEAN AIR ACT
Since the time of the Industrial Revolution, air pollution has been a major public health problem. In 1948, in Donora, Pennsylvania, an air pollution episode resulted in the deaths of nineteen people in a community of 14,000; 43 percent of the population were adversely effected. The cause was industrial emissions of combustion products combined with a thermal inversion. Today, air pollution still causes extensive rates of morbidity and mortality, and it poses a particular risk for children and those with chronic lung disease. Air pollution is a complex mixture of substances discharged into the air in a myriad of ways. Incinerators and combustion sources, including motor vehicles, emit large quantities of carbon dioxide, carbon monoxide, nitrous oxides, and sulfur dioxide; as well as more complex combustion by-products such as polycyclic aromatic hydrocarbons (PAHs), dioxins, furans, and benzo[a]pyrene. Feedstock materials (e.g., wastes that are included in incineration) that do not burn, such as cadmium, lead, chromium, mercury, and other metals also contribute to air pollution. Toxic-air contaminants may be emitted as products of incomplete combustion or in consequence of their manufacture, processing, use, or disposal.
In 1970, Senator Edmund Muskie led the effort to enact the Clean Air Act (CAA). It was a very ambitious statute in scope, technical detail, and in terms of precise timetables for compliance. Amendments in 1977 set new goals for attaining CAA standards, which had not been met in many parts of the United States. Amendments enacted in 1990 were directed to a number of areas that had not previously been addressed, including acid rain, ground-level ozone, stratospheric ozone depletion (by implementing the Montreal Protocol), and air toxics (control of toxic contaminants in air).
PRIORITY AIR POLLUTANTS
The CAA act established six "priority air pollutants": ozone, sulfur dioxide, respirable particulate matter, nitrogen dioxide (NO2), carbon monoxide (CO), and lead. Priority air pollutants are
The CAA led eventually to the phaseout of leaded gasoline in the United States, which in turn resulted in the lowering of blood-lead levels across the nation. The act also succeeded in attaining large reductions in sulfur dioxide and carbon monoxide release levels in nearly every area of the country. An innovative pollution trading program for sulfur dioxides has played an important role in reducing acid rain and in creating new mechanisms for environmental protection.
More challenging have been efforts to reduce pollution from two sectors: motor vehicles (cars and trucks) and coal-fired utilities. Difficulties in these areas have been compounded by Congessionally mandated delays in evaluation and tightening of fuel economy standards, the increased demand for energy in a growing economy, and the increased numbers of vehicle miles driven by an expanding population. These pressures have in turn created pressures to change the standards for priority pollutants to include the consideration of costs as well as public health benefits.
HAZARDOUS AIR POLLUTANTS
Hazardous air pollutants (HAPs) developed a higher public profile in 1985, due to the catastrophic release of methyl isocyanate (MIC) at a pesticide production facility in Bhopal, India. Prior to 1990, HAPs were regulated based on complex risk determinations, and standards had been promulgated for only six of them. Frustrated by the slow progress, Congress, in 1990, directed the EPA to establish standards for nearly two hundred HAPs, listed by name in the statute. These standards are called the National Emissions Standards for Hazardous Air Pollutants (NESHAPs). Congress directed the EPA to establish these standards based on the maximum achievable control technology (MACT). This strategy has resulted in a 90 percent decrease in emissions of toxic air contaminants from regulated industry. In a later phase, the EPA must conduct "residual risk" analyses and tighten the MACT standards if they provide inadequate in protecting the public health. It remains to be seen whether this very complex risk analysis will be successful. Congress directed two studies that are to direct the EPA in the methodology for this effort.
LYNN R. GOLDMAN
Committee of the Environmental and Occupational Health Assembly of the American Thoracic Society (1996). "Health Effects of Outdoor Air Pollution. State of the Art." American Journal of Respiratory and Critical Care Medicine 153:3–50; 477–498.
National Research Council (1994). Science and Judgment in Risk Assessment. Washington, DC: National Academy Press.
Presidential/Congressional Commission on Risk Assessment and Risk Management (1997) Framework for Environmental Health Risk Management. Washington, DC.