Sec.  163.  (a) In  the case  of  sulfur oxide  and particulate
matter,  each   applicable  implementation  plan   shall  contain
measures assuring that maximum  allowable increases over baseline
concen-trations of, and maximum allowable concentrations of, such
pol-lutant  shall not  be exceeded.  In the  case of  any maximum
allowable increase  (except an allowable increase specified under
section 165(d)(2)(C)(iv)) for a pollutant based on concentrations
per-mitted under  national ambient air quality  standards for any
period other than an annual period, such regulations shall permit
such maximum allowable  increase to be  exceeded during one  such
period per year.
  (b)(1)  For any class I area, the maximum allowable increase in
concentrations of sulfur dioxide  and particulate matter over the
baseline concentration  of such  pollutants shall not  exceed the
following amounts:
                    Maximum allowable increase
                  [ Micrograms per cubic meter ]
     Pollutant
Particulate matter:
  Annual geometric mean . . . . . . . . . . . . . . . . . . . . 5
     Pollutant
  Twenty-four-hour maximum  . . . . . . . . . . . . . . . . .  10
Sulfur dioxide:
  Annual arithmetic mean  . . . . . . . . . . . . . . . . . . . 2
  Twenty-four-hour maximum  . . . . . . . . . . . . . . . . . . 5
  Three-hour maximum  . . . . . . . . . . . . . . . . . . . .  25
  (2)  For any class II  area, the maximum  allowable increase in
concentrations of sulfur dioxide  and particulate matter over the
baseline concentration  of such  pollutants shall not  exceed the
following amounts:
                    Maximum allowable increase
                  [ Micrograms per cubic meter ]
     Pollutant
Particulate matter:
  Annual geometric mean . . . . . . . . . . . . . . . . . . .  19
  Twenty-four-hour maximum  . . . . . . . . . . . . . . . . .  37
Sulfur dioxide:
  Annual arithmetic mean  . . . . . . . . . . . . . . . . . .  20
  Twenty-four-hour maximum  . . . . . . . . . . . . . . . . .  91
  Three-hour maximum  . . . . . . . . . . . . . . . . . . . . 512
  (3) For any class  III area, the maximum allowable  increase in
concentrations of sulfur dioxide  and particulate matter over the
baseline concentration  of such  pollutants shall not  exceed the
following amounts:
                    Maximum allowable increase
                  [ Micrograms per cubic meter ]
     Pollutant
Particulate matter:
  Annual geometric mean . . . . . . . . . . . . . . . . . . .  37
  Twenty-four-hour maximum  . . . . . . . . . . . . . . . . .  75
Sulfur dioxide:
  Annual arithmetic mean  . . . . . . . . . . . . . . . . . .  40
  Twenty-four-hour maximum  . . . . . . . . . . . . . . . . . 182
  Three-hour maximum  . . . . . . . . . . . . . . . . . . . . 700
  (4) The maximum allowable concentration of any air pollutant in
any area to which this part applies shall not exceed a concentra-
tion for such pollutant for each period of exposure equal to - 
       (A) the concentration permitted under the national second-
     ary ambient air quality standard, or
       (B) the concentration permitted under the national primary
     ambient  air  quality standard,  whichever  concentration is
     lowest for such pollutant for such period of exposure.
  (c)(1) In  the case of any  State which has a  plan approved by
the Administrator  for purposes  of carrying  out this part,  the
Governor  of such  State may,  after notice  and opportunity  for
public hearing,  issue orders or promulgate  rules providing that
for purposes of determining compliance with the maximum allowable
increases  in ambient  concentrations  of an  air pollutant,  the
following  concentrations of  such pollutant  shall not  be taken
into account:
       (A)  concentrations of such  pollutant attributable to the
     increase  in emissions  from stationary  sources which  have
     converted  from the  use of  petroleum products,  or natural
     gas, or both, by reason of an order which is in effect under
     the  provisions  of sections  2 (a)  and  (b) of  the Energy
     Supply and
     Environmental Coordination  Act of  1974 (or any  subsequent
     legislation  which  supersedes  such  provisions)  over  the
     emissions  from such  sources before  the effective  date of
     such order.
       (B) the  concentrations of such pollutant  attributable to
     the increase in emissions from stationary sources which have
     converted  from using natural gas by reason of a natural gas
     curtailment pursuant  to a  natural gas curtailment  plan in
     effect pursuant to the Federal Power Act over the  emissions
     from such sources before the effective date of such plan,
       (C)  concentrations of particulate  matter attributable to
     the increase in emissions  from construction or other tempo-
     rary emission-related activities, and
       (D)  the  increase in  concentrations attributable  to new
     sources outside  the United  States over the  concentrations
     attributable to  existing sources which are  included in the
     baseline concentration determined in accordance with section
     169(4).
  (2)  No action taken with  respect to a  source under paragraph
(1)(A)  or  (1)(B) shall  apply more  than  five years  after the
effec-tive date of the  order referred to in paragraph  (1)(A) or
the  plan   referred  to   in  paragraph  (1)(B),   whichever  is
applicable. If both such  order and plan are applicable,  no such
action shall apply more  than five years after the later  of such
effective dates.
  (3)  No action under  this subsection shall  take effect unless
the  Governor  submits  the  order  or  rule  providing  for such
exclusion to the  Administrator and the Administrator  determines
that such order  or rule is in compliance with  the provisions of
this subsection.
[42 U.S.C. 7473]