Credits are earned by controlling pollutants to a greater degree than required by law. Credits can be sold to firms seeking an offset for new sources or can be used in the context of the EPA's netting, bubble, and banking programs. Netting allows a firm to add a new source of emissions at a plant if it can reduce emissions by as much, or more, from other sources in the plant. The bubble program allows several sources to be grouped together and treated as a unit. Some sources in the bubble can increase emissions as long as other sources decrease emissions by an equivalent or greater amount.
Banking allows firms to store emission reduction credits for subsequent use.
H. Prevention of Significant Deterioration 1. The SIP, approved by the EPA, details how these standards are to be met.