Document ID: ./input/supremecourt_opinions/opinions/23pdf/23a349_0813.pdf
Page Number: 17.0

14 

OHIO v. EPA 

Opinion of the Court 

27 (quoting 88 Fed. Reg. 36693).  In support of its severa-
bility provision, EPA cited, among other things, its intent 
to  address  “ ‘important  public  health  and  environmental 
benefits”  and  encourage  reliance  by  others  “on  th[e]  final 
rule in their planning.’ ”  Ibid. 
  None of this, however, solves the agency’s problem.  True, 
the  severability  provision  highlights  that  EPA  was  aware 
of  the  applicants’  concern.   But  awareness is not itself  an 
explanation.  The severability provision highlights, too, the 
agency’s desire to apply its rule expeditiously and “ ‘to the 
greatest  extent  possible,’ ”  no  matter  how  many  States  it 
could cover.  Ibid.  But none of that, nor anything else EPA 
said  in  support  of  its  severability  provision,  addresses 
whether  and  how  measures  found  to  maximize  cost  effec-
tiveness in achieving downwind ozone air-quality improve-
ments with the participation of 23 States remain so when 
many fewer States, responsible for a much smaller amount 
of the originally targeted emissions, might be subject to the 
agency’s plan.  Put simply, EPA’s response did not address 
the applicants’ concern so much as sidestep it.11 

—————— 

11 As the applicants conceded at oral argument, see Tr. of Oral Arg. 25–
26,  EPA  did  not  need  to  address  every  possible  permutation  when  it 
sought to adopt a multi-State FIP.  Our conclusion is narrower:  When 
faced  with  comments  like  the  ones  it  received,  EPA  needed  to  explain 
why  it  believed  its  rule  would  continue  to  offer  cost-effective  improve-
ments in downwind air quality with only a subset of the States it origi-
nally intended  to  cover.    To be  sure,  after  this  Court  heard  argument, 
EPA issued a document in which it sought to provide further explana-
tions for the course it pursued.  See 89 Fed. Reg. 23526 (2024).  But the 
government  has  not  suggested  that  we  should  consult  this  analysis  in 
assessing the validity of the final rule.  See Letter from E. Prelogar, So-
licitor General, to S. Harris, Clerk of Court 1 (Mar. 28, 2024).  Nor could 
it, since the Clean Air Act prevents us (and courts that may in the future 
assess  the  FIP’s merits)  from  consulting  explanations  and  information 
offered  after  the  rule’s  promulgation.    See  42  U. S. C.  §§7607(d)(6)(C) 
(“The promulgated rule may not be based (in part or whole) on any infor-
mation or data which has not been placed in the docket as of the date of