The following restrictions apply for using emission credits:

(a) Averaging sets. Emission credits may be exchanged only within an averaging set. For emission credits generated by Tier 4 engines, there are two averaging sets—one for engines at or below 560 kW and another for engines above 560 kW.

(b) Emission credits from earlier tiers of standards.

(1) For purposes of ABT under this subpart, you may not use emission credits generated from engines subject to emission standards under 40 CFR part 89, except as specified in §1039.102(d)(1) or the following table:

(2) Emission credits generated from marine engines certified under the provisions of 40 CFR part 89 may not be used under this part.

(3) See 40 CFR part 89 for other restrictions that may apply for using emission credits generated under that part.

(4) If the maximum power of an engine generating credits under the Tier 2 standards in 40 CFR part 89 is at or above 37 kW and below 75 kW, you may use those credits for certifying engines under the Option #1 standards in §1039.102.

(c) NOX and NOX + NMHC emission credits. You may use NOX emission credits without adjustment to show compliance with NOX + NMHC standards. You may use NOX + NMHC emission credits to show compliance with NOX standards, but you must adjust the NOX + NMHC emission credits downward by twenty percent when you use them, as shown in the following equation:

NOX emission credits = (0.8) × (NOX + NMHC emission credits).

(d) Other restrictions. Other sections of this part specify additional restrictions for using emission credits under certain special provisions.

[69 FR 39213, June 29, 2004, as amended at 70 FR 40464, July 13, 2005; 81 FR 74140, Oct. 25, 2016]