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General Conformity

General Conformity Training Modules: Glossary

Term Definition

Clean Air Act (CAA)

The basis of clean air programs in the United States. The original CAA passed in 1970 and was amended in 1977 and 1990. It is comprised of nine sections or Titles that cover, in order, the National Ambient Air Quality Standards, mobile sources, hazardous air pollutants, acid-deposition control, stationary source operating permits, stratospheric ozone and global climate protection, enforcement, miscellaneous provisions, and clean air research.

Continuing Program Responsibility

Means a Federal agency has responsibility for emissions caused by:

  1. Actions it takes itself; or
  2. Actions of non-Federal entities that the Federal agency, in exercising its normal programs and authorities, approves, funds, licenses or permits, provided the agency can impose conditions on any portion of the action that could affect the emissions.

Criteria Pollutant

Any pollutant for which there is established a NAAQS at 40 CFR part 50.

De Minimis

When the total direct and indirect emissions resulting from a federal action are below the listed de minimis level, the action is not subject to a conformity determination. The creation of de minimis emission levels limited the need to conduct conformity determinations for federal actions that create minimal air pollution increases.

Direct Emissions

Those emissions of a criteria pollutant or its precursors that are caused or initiated by the Federal action and originate in a nonattainment or maintenance area and occur at the same time and place as the action and are reasonably foreseeable.


A situation where extremely quick action on the part of the Federal agencies involved is needed and where the timing of such Federal activities makes it impractical to meet the requirements of this subpart, such as natural disasters like hurricanes or earthquakes, civil disturbances such as terrorist acts and military mobilizations.

Federal Action

Any activity engaged in by a department, agency, or instrumentality of the Federal government, or any activity that a department, agency or instrumentality of the Federal government supports in any way, provides financial assistance for, licenses, permits, or approves, other than activities related to transportation plans, programs, and projects developed, funded, or approved under title 23 U.S.C. or the Federal Transit Act (49 U.S.C. 1601 et seq. ). Where the Federal action is a permit, license, or other approval for some aspect of a non-Federal undertaking, the relevant activity is the part, portion, or phase of the non-Federal undertaking that requires the Federal permit, license, or approval.

Federal Agencies

A Federal department, agency, or instrumentality of the Federal government.

Federal Facilities

Facilities owned by the federal agencies or facilities subject to routine federal actions such as airports and seaports.

Federal Implementation Plan

In the absence of an approved State Implementation Plan (SIP), a plan prepared by the EPA which provides measures needed to meet the requirements of the Clean Air Act.

Indirect Emissions

Those emissions of a criteria pollutant or its precursors:

  1. That are caused or initiated by the Federal action and originate in the same nonattainment or maintenance area but occur at a different time or place as the action;
  2. That are reasonably foreseeable;
  3. That the agency can practically control; and
  4. For which the agency has continuing program responsibility.

For the purposes of this definition, even if a Federal licensing, rulemaking or other approving action is a required initial step for a subsequent activity that causes emissions, such initial steps do not mean that a Federal agency can practically control any resulting emissions.

Maintenance Area

An area that was designated as nonattainment and has been re-designated in 40 CFR part 81 to attainment, meeting the provisions of section 107(d)(3)(E) of the Act and has a maintenance plan approved under section 175A of the Act.

Metropolitan Planning Organization (MPO)

The policy board of an organization created as a result of the designation process in 23 U.S.C. 134(d).

National Ambient Air Quality Standards (NAAQS)

Those standards established pursuant to section 109 of the Act and include standards for carbon monoxide (CO2), lead (Pb), nitrogen dioxide (NO2), ozone, particulate matter (PM–10 and PM2.5), and sulfur dioxide (SO2).

Nonattainment Area

An area designated as nonattainment under section 107 of the Act and described in 40 CFR part 81.

Precursor Pollutants


  1.  For ozone, nitrogen oxides (NOx), unless an area is exempted from NOx requirements under section 182(f) of the Act, and volatile organic compounds (VOC).
  2.  For PM–10, those pollutants described in the PM–10 nonattainment area applicable SIP as significant contributors to the PM–10 levels.
  3.  For PM2.5:
    • (i) Sulfur dioxide (SO2) in all PM2.5 nonattainment and maintenance areas,
    • (ii) Nitrogen oxides in all PM2.5 nonattainment and maintenance areas unless both the State and EPA determine that it is not a significant precursor, and
    • (iii) Volatile organic compounds (VOC) and ammonia (NH3) only in PM2.5 nonattainment or maintenance areas where either the State or EPA determines that they are significant precursors.

Practicably Controllable

The ability of the federal agency to regulate in some way the emissions caused by the federal action.

Reasonably Foreseeable Emissions

Projected future direct and indirect emissions that are identified at the time the conformity determination is made; the location of such emissions is known and the emissions are quantifiable as described and documented by the Federal agency based on its own information and after reviewing any information presented to the Federal agency.

State Implementation Plan (SIP)

A plan developed by a State, including a set of programs and regulations designed to assure that the NAAQS are attained and maintained.

Total of Direct and Indirect Emissions

The sum of direct and indirect emissions increases and decreases caused by the Federal action; i.e., the “net” emissions considering all direct and indirect emissions. The portion of emissions which are exempt or presumed to conform under §93.153 (c), (d), (e), or (f) are not included in the “total of direct and indirect emissions.” The “total of direct and indirect emissions” includes emissions of criteria pollutants and emissions of precursors of criteria pollutants.

Transportation Conformity

Transportation conformity applies to transportation plans, transportation improvement programs, or Federal Highway Administration or Federal Transit Administration projects in areas that do not meet air quality standards for the NAAQS.

Transportation Plan

A plan developed by the Metropolitan Planning Organization.

Tribal Implementation Plan (TIP)

A plan to implement the national ambient air quality standards adopted and submitted by a federally recognized Indian tribal government determined to be eligible under 40 CFR 49.9 and the plan has been approved by EPA.