In an article for Bloomberg BNA’s Daily Environment Report, NERA Vice President Scott Bloomberg explores the Environmental Protection Agency’s (EPA) use of “co-benefits” (beneficial impacts that are not the direct objective of regulation) when performing regulatory impact analyses. In his article, Mr. Bloomberg focuses on and questions the credibility of co-benefits from ambient fine particulate matter (PM-2.5). Mr. Bloomberg cites an article published in the journal Risk Analysis in which the author, NERA Senior Vice President Dr. Anne E. Smith, draws attention to inconsistencies in the EPA’s calculation of criteria pollutant benefits and co-benefits in its impact analyses. Dr. Smith notes—and Mr. Bloomberg concurs—that co-benefits estimates are exceptionally susceptible to credibility issues arising from these inconsistencies, pointing to the stated co-benefits of both the mercury and the climate rules for power plants as examples. The degree of overstatement in co-benefits estimates from one regulatory analysis to the next has been increasing over time and will continue to do so. Mr. Bloomberg concludes by observing that until the EPA’s method for assessing benefits in its regulatory impact analyses is made consistent with its own regulatory determinations, one can only expect criteria pollutant co-benefits to become even more overstated and unreliable over time, a phenomenon that will undoubtedly carry over to the regulatory impact analysis conducted on the EPA’s Clean Power Plan.