1. A. As used in this section:

   "Data center" means the same as that term is defined in subdivision A 43 of § 58.1-3506.

   "Diesel oxidation catalyst" means a flow-through exhaust device that contains a honeycomb structure covered with a layer of chemical catalyst containing small amounts of precious metal such as platinum or palladium that interact with and oxidize pollutants, including carbon monoxide and unburned hydrocarbons, in the exhaust stream, thereby reducing carbon monoxide emissions.

   "Diesel particulate filter" means an emission control technology that reduces particulate matter emissions by trapping the particles in a flow filter substrate and periodically removes the collected particles by either physical action or by oxidizing or burning off the particles in a process called regeneration.

   "Engine-generator set" or "gen-set" means the combination of an electrical generator and an engine mounted together to form a single piece of equipment.

   "Selective catalytic reduction" means a control device that reduces the exhaust gas concentration of nitrogen oxides by injecting an ammonia solution or urea into the exhaust gas stream, which in the presence of a catalyst, reacts with the nitrogen oxides to form nitrogen gas and water vapor.

   "Tier 4 equivalent" means a gen-set with a selective catalytic reduction system or equivalent for nitrogen oxides control, a diesel oxidation catalyst system or equivalent for carbon monoxide control, and a diesel particulate filter or equivalent for particulate matter control.

2. B. For any application submitted for a data center on or after July 1, 2026, for a permit issued by the Department pursuant to this chapter, including coverage under any general permit, the Department shall not issue such permit unless the emission limit for each gen-set established by such permit is equal to or less than the emissions achieved by a Tier 4 equivalent gen-set.
3. C. Nothing in this section shall be construed to prevent the Department from (i) determining the Best Available Control Technology, Lowest Achievable Emission Rate, Reasonably Available Control Technology, any New Source Performance Standard, or any National Emission Standards for Hazardous Air Pollutants or (ii) establishing in a permit issued by the Department pursuant to this chapter more stringent emission limits than those achieved by a Tier 4 equivalent gen-set.

2026, c. 397.