Opinion ID: 501652
Heading Depth: 2
Heading Rank: 1

Heading: Multi-Point Rollback

Text: 164 NRDC argued in a footnote in its opening brief that a system of calculating emissions limitations known as multi-point rollback (MPR) is a form of intermittent control system (ICS), and is therefore unlawful under the statute. Sec. 123(b) states that dispersion techniques include any intermittent ... control of air pollutants varying with atmospheric conditions. 165 MPR in fact involves calculating emission limits in light of the fact that a certain proportion of days will involve relatively high dispersion; it allows the source to emit more on an equivalent proportion of days. But the days of higher emission need not correspond with the actual days of higher dispersion. We think that under Chevron U.S.A. Inc. v. NRDC, 467 U.S. 837, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984), EPA was entitled to read the statutory language as referring only to control systems that varied output with the time of actual weather changes. We join the Ninth Circuit in upholding the agency's reading. See Kamp v. Hernandez, 752 F.2d 1444, 1451-52 (9th Cir.1985). 166