EPA Acknowledges the “Piston Effect”
EPA has commented on the effects of the "piston" effect. In its October 5, 1998 report "Use of Models and Other Analyses in Attainment Demonstrations for the 8-Hour ozone NAAQS," the Agency noted
"Analyses of regional modeling results suggest that relative reduction factors tend to have lower values (i.e., greater reductions occur) if the starting concentrations are higher (ECR, 1998; Meyer et al., 1997). Lefohn, et al., (1998) report similar findings in their review of recent trend data."