Act means the Clean Air Act as codified at 42 U.S.C. 7401-7671q (2003).

Additional feasible measure is any control measure that otherwise meets the definition of “best available control measure” (BACM) but can only be implemented in whole or in part beginning 4 years after the date of reclassification of an area as Serious and no later than the statutory attainment date for the area.

Additional reasonable measure is any control measure that otherwise meets the definition of “reasonably available control measure” (RACM) but can only be implemented in whole or in part during the period beginning 4 years after the effective date of designation of a nonattainment area and no later than the end of the sixth calendar year following the effective date of designation of the area.

Applicable annual standard is the annual PM_2.5 NAAQS established, revised, or retained as a result of a particular PM_2.5 NAAQS review.

Applicable attainment date means the latest statutory date by which an area is required to attain a particular PM_2.5 NAAQS, unless the EPA has approved an attainment plan for the area to attain such NAAQS, in which case the applicable attainment date is the date approved under such attainment plan. If the EPA grants an extension of an approved attainment date, then the applicable attainment date for the area shall be the extended date.

Applicable 24-hour standard is the 24-hour PM_2.5 NAAQS established, revised, or retained as a result of a particular PM_2.5 NAAQS review.

Attainment projected inventory for the nonattainment area means the projected emissions of direct PM_2.5 and all PM_2.5 precursors on the projected attainment date for the area. This projected inventory includes sources included in the base year inventory for the nonattainment area revised to account for changes in direct PM_2.5 and all PM_2.5 precursors through implementation of the plan and any additional sources of such emissions expected within the boundaries of the nonattainment area by the projected attainment date for the area.

Average-season-day emissions means the sum of all emissions during the applicable season divided by the number of days in that season.

Base year inventory for the nonattainment area means the actual emissions of direct PM_2.5 and all PM_2.5 precursors from all sources within the boundaries of a nonattainment area in one of the 3 years used for purposes of designations or another technically appropriate year.

Best available control measure (BACM) is any technologically and economically feasible control measure that can be implemented in whole or in part within 4 years after the date of reclassification of a Moderate PM_2.5 nonattainment area to Serious and that generally can achieve greater permanent and enforceable emissions reductions in direct PM_2.5 emissions and/or emissions of PM_2.5 plan precursors from sources in the area than can be achieved through the implementation of RACM on the same source(s). BACM includes best available control technology (BACT).

Date of designation means the effective date of a PM_2.5 area designation as promulgated by the Administrator.

Date of reclassification means the effective date of a PM_2.5 area reclassification from Moderate to Serious as promulgated by the Administrator.

Direct PM_2.5 emissions means solid or liquid particles emitted directly from an air emissions source or activity, or reaction products of gases emitted directly from an air emissions source or activity which form particulate matter as they reach ambient temperatures. Direct PM_2.5 emissions include filterable and condensable PM_2.5 emissions composed of elemental carbon, directly emitted organic carbon, directly emitted sulfate, directly emitted nitrate, and other organic or inorganic particles that exist or form through reactions as emissions reach ambient temperatures (including but not limited to crustal material, metals, and sea salt).

Implemented means adopted by the state, fully approved into the SIP by the EPA, and requiring expeditious compliance by affected sources with installation and/or operation of any equipment, control device, process change, or other emission reduction activity.

Major stationary source means any stationary source of air pollutant(s) that emits, or has the potential to emit 100 tons per year or more of direct PM_2.5 or any PM_2.5 precursor in any Moderate nonattainment area for the PM_2.5 NAAQS, or 70 tons per year or more of direct PM_2.5 or any PM_2.5 precursor in any Serious nonattainment area for the PM_2.5 NAAQS.

Mobile source means mobile sources as defined by 40 CFR 51.50.

Most stringent measure (MSM) is any permanent and enforceable control measure that achieves the most stringent emissions reductions in direct PM_2.5 emissions and/or emissions of PM_2.5 plan precursors from among those control measures which are either included in the SIP for any other NAAQS, or have been achieved in practice in any state, and that can feasibly be implemented in the relevant PM_2.5 NAAQS nonattainment area.

Nonpoint source means nonpoint sources as defined by 40 CFR 51.50.

PM_2.5 design value (DV) for a PM_2.5 nonattainment area is the highest of the 3-year average concentrations calculated for the ambient air quality monitors in the area, in accordance with 40 CFR part 50, appendix N.

PM_2.5 NAAQS are the fine particulate matter National Ambient Air Quality Standards codified at 40 CFR part 50.

PM_2.5 plan precursors are those PM_2.5 precursors required to be regulated in the applicable attainment plan and/or NNSR program.

PM_2.5 precursors are Sulfur dioxide (SO₂), Oxides of nitrogen (NO_X), Volatile organic compounds (VOC), and Ammonia (NH₃).

Point source means point sources as defined by 40 CFR 51.50.

Precursor demonstration means an optional set of analyses provided by a state that are designed to show that emissions of a particular PM_2.5 precursor do not contribute significantly to PM_2.5 levels that exceed the relevant PM_2.5 standard in a particular nonattainment area. The three types of precursor demonstrations provided in this rule are the comprehensive precursor demonstration, the major stationary source precursor demonstration, and the NNSR precursor demonstration.

Reasonable further progress (RFP) means such annual incremental reductions in emissions of direct PM_2.5 and PM_2.5 plan precursors as are required for the purpose of ensuring attainment of the applicable PM_2.5 NAAQS in a nonattainment area by the applicable attainment date.

Reasonably available control measure (RACM) is any technologically and economically feasible measure that can be implemented in whole or in part within 4 years after the effective date of designation of a PM_2.5 nonattainment area and that achieves permanent and enforceable reductions in direct PM_2.5 emissions and/or PM_2.5 plan precursor emissions from sources in the area. RACM includes reasonably available control technology (RACT).

RFP projected emissions means the estimated emissions for direct PM_2.5 and PM_2.5 plan precursors by source category or subcategory for the years in which quantitative milestones are due for a nonattainment area.

Subpart 1 means subpart 1 of part D of title I of the Act.

Subpart 4 means subpart 4 of part D of title I of the Act.