EPA Finalizes ‘Once In, Always In’ Rule for Emission Sources (1)

Facilities that have been downgraded to the EPA’s “area” source designation must still comply with “major” air pollution standards, according to a rule finalized on Wednesday.

The decades-old rule—colloquially known as “once in, always in"—preserves certain pollution control requirements for facilities that have stemmed their emissions and were reclassified as smaller area sources of hazardous air pollutants.

Under the final mandate, major sources that transition to area sources must still comply with federally enforceable emission limits regardless of their reclassification if they account for “90 percent of the aggregate emissions” of seven hazardous air pollutants under the Clean Air ...