Methods for Setting Limits for Acute and Chronic Toxic Ambient Air Contaminants

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Abstract
Over the past 10 years there has been increasing interest in understanding the amount of emissions of nonpriority pollutants to the ambient air and the degree of control needed to achieve acceptable (safe) levels of exposure. These chemicals, which have often been called air toxics, are present as a result of combustion, various fugitive and point source emissions, and mobile sources. In an attempt to understand the airborne concentrations at which some chemicals might pose a health hazard, a number of approaches have been proposed and used. These safe concentrations are often called ambient air limits (AALs). This article presents the ten different methods by which AALs have been or could be calculated. Historically, the vast majority of AALs established by regulatory agencies have been derived from occupational exposure limits, such as the American Conference of Governmental Industrial Hygienists Threshold Limit Values® (TLV®) and the Occupational Safety and Health Administration's Permissible Exposure Limits. The advantages and disadvantages of the various approaches are discussed. About 50 references are cited.