Ill. Admin. Code tit. 35, § 204.900 – Ambient Air Increments

a) 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 Area
PM_2.5:
Annual arithmetic mean	1
24-hr maximum	2
PM₁₀:
Annual arithmetic mean	4
24-hr maximum	8
SO₂:
Annual arithmetic mean	2
24-hr maximum	5
3-hr maximum	25
NO₂:
Annual arithmetic mean	2.5
Class II Area
PM_2.5:
Annual arithmetic mean	4
24-hr maximum	9
PM₁₀:
Annual arithmetic mean	17
24-hr maximum	30
SO₂:
Annual arithmetic mean	20
24-hr maximum	91
3-hr maximum	512
NO₂:
Annual arithmetic mean	25
Class III Area
PM_2.5:
Annual arithmetic mean	8
24-hr maximum	18
PM₁₀:
Annual arithmetic mean	34
24-hr maximum	60
SO₂:
Annual arithmetic mean	40
24-hr maximum	182
3-hr maximum	700
NO₂:
Annual arithmetic mean	50

b) 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.