Document ID: ./input/supremecourt_opinions/opinions/23pdf/23a349_0813.pdf
Page Number: 10

Cite as:  603 U. S. ____ (2024) 

7 

Opinion of the Court 

have consequences for the proposed FIP.  If the FIP did not 
wind up applying to all 23 States as EPA envisioned, com-
menters argued, the agency would need “to conduct a new 
assessment and modeling of contribution and subject those 
findings to public comment.”  E.g., Comments of Air Stew-
ardship Coalition 13–14 (June 21, 2022); Comments of Port-
land Cement Association 7 (June 21, 2022).  Why?  As noted 
above,  EPA  assessed  “significant  contribution”  by  deter-
mining what measures in  upwind  States  would maximize 
cost-effective ozone-level improvements in the States down-
wind of them.  Supra, at 5–6.  And a different set of States 
might mean that the “knee in the curve” would shift.  After 
all,  each  State  differs  in  its  mix  of  industries,  in  its  pre- 
existing  emissions-control  measures,  and  in  the  impact 
those measures may have on emissions and downwind air 
quality.  See 87 Fed. Reg. 20052, 20060, 20071–20073; EPA, 
Technical  Memorandum,  Screening  Assessment  of  Poten-
tial Emissions Reductions, Air Quality Impacts, and Costs 
from  Non-EGU  Emissions  Units  for  2026,  pp.  12–13 
(2022).4 
  As  it  happened,  ongoing  litigation  over  the  SIP  disap- 

—————— 

4 Commenters pointed out the variance among emissions-producing fa-
cilities too.  See, e.g., Comments of Indiana Municipal Power Agency 9 
(June 20, 2022) (the “cost effectiveness” of one tool “will be highly varia-
ble” across different power plants); Comments of Lower Colorado River 
Authority 21 (June 21, 2022) (power plants that “have already invested” 
in one emissions-control tool “have already undertaken significant costs 
to  achieve  [nitrous  oxide]  reductions  and  have  less  to  gain  from  addi-
tional control installation”); Comments of Air Stewardship Coalition 27 
(June 21, 2022) (noting that the knee in the curve appeared to be at a 
different  cost  depending  on  which  mix  of  industries  were  considered); 
Comments of Wisconsin Paper Council 2 (June 21, 2022) (the air-quality 
benefits  from  controlling  one  industry—pulp  and  paper  mills—had  a 
“maximum estimated improvement” in ozone levels in downwind States 
of just 0.0117 parts per billion).