Document ID: ./input/supremecourt_opinions/opinions/23pdf/23a349_0813.pdf
Page Number: 8.0

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

5 

Opinion of the Court 

bilit[y]’ ”  and  different  state  approaches,  EPA  now  appar-
ently took the view that “[e]ffective policy solutions to the 
problem of interstate ozone transport” demanded that kind 
of “uniform framework” and “[n]ationwide consistency.”  87 
Fed. Reg. 9841; see 87 Fed. Reg. 20073.  The FIP the agency 
proposed set as its target the reduction of the emissions of 
one ozone precursor in particular:  nitrous oxide.  See id., at 
20038.    And  it  sought  to  impose  nitrous  oxide  emissions-
control  measures  that  “maximized  cost-effectiveness”  in 
achieving “downwind ozone air quality improvements.”  Id., 
at 20055; see also id., at 20043. 
  In broad strokes, here is how EPA’s proposed rule worked 
to  eliminate  a  State’s  “significant  contribution”  to  down-
wind ozone problems.  First, the agency identified various 
emissions-control  measures  and,  using  nationwide  data, 
calculated how much each typically costs to reduce a ton of 
nitrous-oxide  emissions.    Id.,  at  20076;  see,  e.g.,  id.,  at 
20077–20081.  Next, the agency sought to predict how much 
each  upwind  State’s  nitrous-oxide  emissions  would  fall  if 
emissions-producing  facilities  in  the  State  adopted  each 
measure.  Id., at 20076; see, e.g., id., at 20088–20089; EPA, 
Ozone Transport Policy Analysis Proposed Rule TSD 22–23 
(EPA–HQ–OAR–2021–0668, 2022) (Proposed Ozone Analy-
sis).    In  making  those  predictions,  EPA  often  considered 
data  specific  to  the  emissions-producing  facilities  in  the 
State, and fed “unit-level and state-level” values into its cal-
culations.  See id., at 9–10, 13.  Then, the agency estimated 
how much, on average, ozone levels would fall in downwind 
States  with  the  adoption  of  each  measure.    87  Fed.  Reg. 
20076;  see,  e.g.,  id.,  at  20092–20093,  20096–20097;  Pro-
posed Ozone Analysis 51–52.  In making those estimations, 
too,  EPA  calibrated  its  modeling  to  each  State’s  features, 
“determin[ing]  the  relationship  between  changes  in  emis-
sions and changes in ozone contributions on a state-by-state 
. . . basis.”  Id., at 33; see also id., at 40, 42. 
  To  pick  which  measures  would  “maximiz[e]  cost-