a) "Net emissions increase" means, with respect to any regulated NSR pollutant emitted by a major stationary source, the amount by which the sum of the following exceeds zero:

1. 1) The increase in emissions from a particular physical change or change in the method of operation at a stationary source as calculated under Section 204.800(d); and
2. 2) Any other increases and decreases in actual emissions at the major stationary source that are contemporaneous with the particular change and are otherwise creditable. Baseline actual emissions for calculating increases and decreases under this subsection (a)(2) shall be determined as provided in Section 204.240, except that Section 204.240(a)(3) and (b)(4) shall not apply.

b) An increase or decrease in actual emissions is contemporaneous with the increase from the particular change only if it occurs between:

1. 1) The date five years before construction on the particular change commences; and

2) The date that the increase from the particular change occurs.

1. 3) An increase or decrease in actual emissions is creditable only if the reviewing authority has not relied on it in issuing a permit for the source under 40 CFR 52.21 or this Part, which permit is in effect when the increase in actual emissions from the particular change occurs.
2. c) An increase or decrease in actual emissions of SO₂, PM, or NO_X that occurs before the applicable minor source baseline date is creditable only if it is required to be considered in calculating the amount of maximum allowable increases remaining available.
3. d) An increase in actual emissions is creditable only to the extent that the new level of actual emissions exceeds the old level.

4. e) A decrease in actual emissions is creditable only to the extent that:

   1. 1) The old level of actual emissions or the old level of allowable emissions, whichever is lower, exceeds the new level of actual emissions;
   2. 2) It is enforceable as a practical matter at and after the time that actual construction on the particular change begins; and
   3. 3) It has approximately the same qualitative significance for public health and welfare as that attributed to the increase from the particular change.
5. f) An increase that results from a physical change at a source occurs when the emissions unit on which construction occurred becomes operational and begins to emit a particular pollutant. Any emissions unit that replaces an existing emissions unit that requires shakedown becomes operational only after a reasonable shakedown period, not to exceed 180 days.
6. g) Section 204.210(b) shall not apply in determining creditable increases and decreases.