AN emission standard is a limit on the amount or concentration of a pollutant emitted from a source. The concentration of pollutant in the effluent may be stated subjectively in terms of its appearance to the eye or its odor, as determined by the nose; or objectively in terms of its weight or volume. Emission standards may be derived from process and equipment considerations, air quality considerations, or both. Emission standards sometimes reflect economic, sociological, and political considerations in addition to those which are technological. In some cases, we have the technological ability to control certain pollutants, but are not doing so for economic, sociological, or political reasons. However, despite considerable economic, sociological, and political pressure to regulate certain other emissions more stringently, we are not doing so because we lack an adequate technological ability for their more widespread control.