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3.5 - (1.346 x Million Annual Passengers + 0.0194 x General Aviation & Air Taxi LTOs) < 0
Equation 1: Dispersion Modeling Threshold
If the above equation is not true, a NAAQS assessment does not have to be considered.
Otherwise, a NAAQS assessment (including dispersion modeling) should be considered. To
determine if a NAAQS assessment should be performed, the nature of the project should be
considered in consultation with state or regional air quality regulatory staff. The nature of the
project must be considered since special project concerns and characteristics or high background
levels of CO may suggest that a NAAQS assessment is indicated at lower activity levels or not at
all.
Figure 4. Airport Activity Threshold For NAAQS Assessment
4 Operations based on an LTO cycle. One landing and one takeoff equal 1 LTO.
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2.3.5 NAAQS Assessment - Roadway Intersection Analysis
If a project has the potential to adversely affect the air quality at a roadway intersection (e.g. by
significantly increasing traffic volume), CO emissions may exceed the NAAQS. In such cases, a
comparison with the NAAQS should be considered. Intersections with the highest traffic
volumes and lowest Level-of-Service (LOS) ratings are considered and selected for modeling.
LOS ratings measure the operating conditions at the intersection and how these conditions affect
traffic volume, signal timing, and related congestion delays. There are six LOS rankings: LOS
A through LOS F. LOS A is the highest ranking relating to delays of less than 5.0 seconds per
vehicle. LOS F is the lowest, describing operations with delays greater than 60.0 seconds per
vehicle. If the top intersections selected for modeling do not show an exceedance of the
NAAQS, it is assumed that none of the other intersections will exceed either. Intersections that
should be considered for modeling are called Critical intersections. Critical intersections have
LOS ratings of D, E, or F or are intersections that have dropped to those levels due to increased
traffic volumes or to construction related to a new project in the vicinity.
Intersection modeling may be required based on other special considerations or indications.
State or regional air quality regulatory staff or the regional transportation planning staff
should be consulted. For EPA guidance on a methodology for evaluating air quality impacts
at one or more roadway intersections where vehicle traffic will cause or contribute to increased
emissions of carbon monoxide (CO), please refer to EPA’s Guideline For Modeling Carbon
Monoxide From Roadway Intersections (Reference 74).
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3. EMISSIONS ASSESSMENT
3.1 Introduction
After defining a proposed project and any alternatives, creating an emission inventory is an
important step in assessing air quality. An emissions inventory provides a first indication of the
magnitude of a proposed project’s potential environmental impact. An emissions inventory
provides the total amount or mass of pollutants generated by emission sources during a specified
period of time (e.g., tons per year). To determine the emission inventory of an airport or air base,
emissions are calculated for all relevant sources and operators and then totaled. Potential sources
of emissions at airports and air bases include aircraft, ground support equipment, ground access
vehicles, stationary sources, and construction activities5. Examples of potential operators include
the FAA, the Air Force, the airport authority, airlines, fixed base operators (FBOs), rental car
agencies, or individual passengers or employees.
The emissions inventory can be created for various purposes. It can be used to compare various
proposed project alternatives (e.g., “build” and “no-build” alternatives), a proposed project’s
emissions to the total emissions of the local air quality area, or a proposed project’s emissions to
regulatory thresholds (e.g., general conformity thresholds). The inventory may also be used as
part of the State Implementation Plan (SIP) emission inventory.
An inventory may include both direct and indirect emissions. Direct emissions are those
emissions that are caused or initiated by a Federal action and occur at the same time and place as
the action. Indirect emissions are those that are caused by a Federal action, but may occur later
in time and/or may be farther removed in distance from the action itself but are still reasonably
foreseeable. Under conformity, indirect emissions are further limited to those that the Federal
agency can practicably control and will maintain control over due to a continuing program
responsibility of the Federal agency. Motor vehicle emission that result from passengers or
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