a) The requirements of this Part, other than Subpart R, shall apply to the construction of any new major stationary source (as defined in Section 203.1230) or major modification (as defined in Section 203.1220) that is major for the pollutant for which the area is designated nonattainment under section 107(d)(1)(A)(i) of the CAA (42 U.S.C. 7407(d)(1)(A)(i)), if the stationary source or modification would locate anywhere in the designated nonattainment area. Different pollutants, including individual precursors, are not summed to determine applicability of a major stationary source or major modification.

b) No new major stationary source or major modification to which the requirements of Sections 203.1410, 203.1420, 203.1430, 203.1440, 203.1800, 203.1810, 203.1820, 203.1830, or 203.2000 apply shall begin actual construction without a permit that states that the major stationary source or major modification will meet those requirements. The Agency has authority to issue any such permit.

c) The requirements of this Part will be applied in accordance with subsections (c)(1) through (c)(6).

1) Except as otherwise provided in subsection (e) and in Sections 203.1220(d) through (e), and consistent with the definition of major modification contained in Section 203.1220, a project is a major modification for a regulated NSR pollutant if it causes two types of emissions increases: a significant emissions increase (as defined in Section 203.1380), and a significant net emissions increase (as defined in Section 203.1260 and Section 203.1370). The project is not a major modification if it does not cause a significant emissions increase. If the project causes a significant emissions increase, then the project is a major modification only if it also results in a significant net emissions increase.

2) The procedure for calculating (before beginning actual construction) whether a significant emissions increase (i.e., the first step of the process) will occur depends upon the type or types of emissions units involved in the project, according to subsections (c)(3) through (c)(5). The procedure for calculating (before beginning actual construction) whether a significant net emissions increase will occur at the major stationary source (i.e., the second step of the process) is contained in the definition in Section 203.1260. Regardless of any such preconstruction projections, a major modification results if the project causes a significant emissions increase and a significant net emissions increase.

3) Actual-to-Projected-Actual Applicability Test for Projects That Only Involve Existing Emissions Units. A significant emissions increase of a regulated NSR pollutant is projected to occur if the sum of the difference between the projected actual emissions (as defined in Section 203.1320) and the baseline actual emissions (as defined in Section 203.1070), for each existing emissions unit, equals or exceeds the significant amount for that pollutant (as defined in Section 203.1370).

4) Actual-to-Potential Test for Projects That Only Involve Construction of a New Emissions Unit or Units. A significant emissions increase of a regulated NSR pollutant is projected to occur if the sum of the difference between the potential to emit (as defined in Section 203.1290) from each new emissions unit following completion of the project and the baseline actual emissions (as defined in Section 203.1070) of these units before the project equals or exceeds the significant amount for that pollutant (as defined in Section 203.1370).

5) Hybrid Test for Projects That Involve Multiple Types of Emissions Units. A significant emissions increase of a regulated NSR pollutant is projected to occur if the sum of the difference for all emissions units, using the method specified in subsections (c)(3) and (c)(4) as applicable with respect to each emissions unit, equals or exceeds the significant amount for that pollutant (as defined in Section 203.1370).

6) The "sum of the difference" as used in subsections (c)(3) through (c)(5) shall include both increases and decreases in emissions calculated in compliance with those subsections.

d) Except as otherwise provided in Section 203.1700(f)(2), the provisions of Section 203.1700 apply with respect to any regulated NSR pollutant emitted from projects involving existing emissions units at a major stationary source (other than projects at a source with a PAL) in circumstances in which there is a reasonable possibility, within the meaning of Section 203.1700(f), that a project that is not a part of a major modification may result in a significant emissions increase of such pollutant, and the owner or operator elects to use the method specified in Section 203.1320(b)(1) through (b)(3) for calculating projected actual emissions.

e) For any major stationary source with a PAL for a regulated NSR pollutant, the major stationary source shall comply with requirements under Section 203.2100 through Section 203.2420.

(Source: Added at 49 Ill. Reg. 6237, effective April 23, 2025)