is necessary to address a fundamentally regional pollution problem. In other words, the States can show an improvement in Cincinnati air quality due to less inflow of particulate matter from sources outside the nonattainment area. We think that the statutory context alone is sufficiently ambiguous for EPA to clear the first step of Chevron. Cf. Nat’l Ass’n of Home Builders v. Defenders of Wildlife, 551 U.S. 644, 666, 127 S.Ct. 2518, 168 L.Ed.2d 467 (2007) (finding a “fundamental ambiguity” from potential inferences across statutory sections). At least three times, appellate courts have vacated EPA rules that ignored explicit, area-specific mandates in assessing emission reductions under other sections of the CAA. See Natural Res. Def. Council v. EPA, 571 F.3d 1245, 1256 (D.C.Cir.2009) (<HOLDING>); North Carolina v. EPA, 53.1 F.3d 896, 907
holding that the phrase reductions in emission from existing sources in the area  7502c1 excluded regional source reductions attributable to nox sip call holding that the possibility of a mistaken understanding of the phrase preponderance of the evidence on the part of the jury is too remote to constitute plain error when counsel gave the jury an accurate explanation of the legal meaning of the phrase in his closing argument and that meaning is consistent with the common understanding of the words in the phrase holding that there is nothing inherent in the phrase that requires the action working the deprivation to come from the state holding that epa violated the mandate of  7511ablb which requires calculation of baseline emissions  from all anthropogenic sources in the area holding phrase based upon or attributable to is not ambiguous and rejecting secondary suit construction