Document ID: ./input/supremecourt_opinions/opinions/23pdf/23a349_0813.pdf
Page Number: 9

6 

OHIO v. EPA 

Opinion of the Court 

effectiveness” in achieving “downwind ozone air quality im-
provements,” 87 Fed. Reg. 20055, EPA focused on what it 
called the “ ‘knee in the curve,’ ” or the point at which more 
expenditures  in  the  upwind  States  were  likely  to  produce 
“very little” in the way of “additional emissions reductions 
and air quality improvement” downwind, id., at 20095 (hy-
phenation omitted).  EPA used this point to select a “uni-
form level” of cost, and so a uniform package of emissions-
reduction tools, for upwind States to adopt.  Id., at 20076.  
And EPA performed this analysis on two “parallel tracks”—
one for power plants, one for other industries.  Ibid.  Pursu-
ant  to  the  Clean  Air  Act,  §§7607(d)(1)(B),  (d)(3)–(6),  the 
agency published its proposed FIP for notice and comment 
in April 2022, 87 Fed. Reg. 20036. 
  Immediately, commenters warned of a potential pitfall in 
the  agency’s  approach.    EPA  had  determined  which  
emissions-control measures were cost effective at address-
ing downwind ozone levels based on an assumption that the 
FIP would apply to all covered States.  But what happens if 
some or many of those States are not covered?  As the com-
menters portrayed the SIPs, this was not an entirely spec-
ulative  possibility.    Many  believed  EPA’s  disapprovals  of 
the SIPs were legally flawed.  See, e.g., Comments of Mis-
souri Dept. of Natural Resources 3 (June 17, 2022) (refer-
encing “all the technical, legal, and procedural issues” with 
the proposed SIP disapproval); see also, e.g., Comments of 
Louisiana  Dept.  of  Environmental  Quality  1–3  (June  21, 
2022);  Comments  of  Texas  Comm’n  on  Environmental 
Quality 2–4 (June 21, 2022); EPA, Response to Public Com-
ments on Proposed Rule 9–11 (EPA–HQ–OAR–2021–0668).  
They added that EPA’s FIP was “inextricably linked” to the 
SIP disapprovals.  E.g., Comments of Missouri Dept. of Nat-
ural Resources, at 4.  Without a SIP disapproval or missing 
SIP, after all, EPA could not include a State in its FIP.  See, 
e.g., id., at 3; supra, at 3. 
  Commenters added that failing to include a State could