The Environmental Protection Agency (EPA) has been the target in recent years of growing criticism that its pollution control requirements are in many instances unnecessarily rigid and excessively expensive. These pressures, in combination with EPA's developing interest in economically based alternatives to traditional regulatory approaches to pollution abatement,¹ have led the Agency to take several steps toward a regime that will, in its view, reconcile improved environmental quality with economic growth at the lowest possible cost. In this vein, the Agency is now making a major effort to encourage the development and use of alternative emission reduction strategies which are less costly and more flexible than current regulatory approaches. The basic aim of all these measures is to allow sources in certain circumstances the freedom to adopt more economically efficient pollution controls.

As a central component of this effort, EPA recently promulgated² its final policy on the use of the "bubble" concept by existing sources to abate air pollution emissions. The concept is so named because it treats a source with multiple emission points as if an imaginary bubble with a single vent had been placed over it. The focal point for regulation under this approach is the aggregate of all emissions from the source. Provided that increases and decreases in emissions from plant components offset one another, theoperator would be free to adopt a different set of controls on stacks and other emission points as long as the alternative control strategy does not delay compliance with statutory deadlines or have an adverse impact on air quality. Emission reduction thus may be lessened on those plant components that are most expensive to control and correspondingly maximized on those emission points that are least costly to clean up.