17.8.804    AMBIENT AIR INCREMENTS

(1) In areas designated as Class I, II, or III, increases in pollutant concentration over the baseline concentration shall be limited to the following:

Pollutant

Maximum allowable increase (micrograms per cubic meter)

CLASS I

Particulate matter:
           PM-2.5, annual arithmetic mean.................................................................................1
           PM-2.5, 24-hr maximum..............................................................................................2
           PM-10, annual arithmetic mean..................................................................................4
           PM-10, 24-hr maximum...............................................................................................8
Sulfur dioxide (SO₂):
           Annual arithmetic mean...............................................................................................2
           24-hr maximum.............................................................................................................5
           3-hr maximum.............................................................................................................25
Nitrogen dioxide (NO₂):
           Annual arithmetic mean...............................................................................................2.5

CLASS II

Particulate matter:
           PM-2.5, annual arithmetic mean.................................................................................4
           PM-2.5, 24-hr maximum..............................................................................................9
           PM-10, annual arithmetic mean................................................................................17
           PM-10, 24-hr maximum.............................................................................................30
Sulfur dioxide (SO₂):
           Annual arithmetic mean.............................................................................................20
           24-hr maximum...........................................................................................................91
           3-hr maximum...........................................................................................................512
Nitrogen dioxide (NO₂):
           Annual arithmetic mean.............................................................................................25

CLASS III

Particulate matter:
           PM-2.5, annual arithmetic mean.................................................................................8
           PM-2.5, 24-hr maximum............................................................................................18
           PM-10, annual arithmetic mean................................................................................34
           PM-10, 24-hr maximum.............................................................................................60
Sulfur dioxide (SO₂):
           Annual arithmetic mean.............................................................................................40
           24-hr maximum.........................................................................................................182
           3-hr maximum............................................................................................................700
Nitrogen dioxide (NO₂):
           Annual arithmetic mean..............................................................................................50

(2) For any period other than an annual period, the applicable maximum allowable increase may be exceeded during one such period per year at any one location.

History: 75-2-111, 75-2-203, MCA; IMP, 75-2-202, 75-2-203, 75-2-204, MCA; NEW, 1993 MAR p. 2919, Eff. 12/10/93; AMD, 1994 MAR p. 2829, Eff. 10/28/94; TRANS, from DHES, 1996 MAR p. 2285; AMD, 2011 MAR p. 2134, Eff. 10/14/11.