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G2.10 Region ______________________________________________________________ 13
LIST OF TABLES
Table G-1 : Types Of Evaporative-Related Emissions _________________________________________6
LIST OF EQUATIONS
Equation G-1: GAV Exhaust Emissions _____________________________________________________6
Equation G-2: Crankcase or Running Losses ________________________________________________8
Equation G-3: Refueling Losses ___________________________________________________________8
Equation G-4: Hot Soak _________________________________________________________________8
Equation G-5: Diurnal (Partial/Full-Day or Multiple-Day of Rest) _______________________________8
Equation G-6: Resting Losses ____________________________________________________________9
G-4
G-5
Appendix G: Ground Access Vehicles Emission Methodology
G1. METHODOLOGY
Ground access vehicles (GAVs) produce exhaust, evaporative and idling emissions. The activity
of GAVs is separated into two categories: roadway and parking lot. In general, roadway activity
consists of the segment of GAV operations that occur on roadways (both on- and off-airport).
Parking lot activity refers to the segment of GAV operations that occur in airport and air base
parking lots. Parking lot activity does not include vehicles that enter parking lots but are not
customers and do not stop (e.g., parking lot and rental car shuttle buses).
The general guidance for calculating emissions from on-road or highway vehicles is provided in
EPA’s Procedures for Emission Inventory Preparation, Volume IV, Chapter 3 (Reference 81).
The EPA specifies that the MOBILE and PART5 motor vehicle emissions models be used to
develop highway vehicle emission indices and emission inventories. The user guides for EPA
motor vehicle emission models (References 72 and 88) also provide additional guidance. Many
factors influence motor vehicle emissions including vehicle age, vehicle travel speed and
distance, vehicle operating mode, fuel characteristics, control programs, and local ambient
conditions. The influence of these factors is constantly changing as technology continues to
evolve.
Due to the complex process of determining emission indices, simplified descriptions of the
exhaust, evaporative-related, and idling emissions calculation methodologies are provided below.
It is possible to estimate both exhaust and evaporative-related emissions using just the exhaust
calculation methodology if “combined” emission indices (i.e., combined exhaust and evaporative
emission indices) are used. An emission estimate based on combined emission indices will not be
as accurate since default assumptions are used in the emission index development. The EPA’s
Procedures for Emission Inventory Preparation should be consulted for a more detailed
description of the methodologies. For air bases, the USAF document Calculation Methods for
Criteria Air Pollutant Emission Inventories (Reference 23) also should be consulted for further
guidance.
G1.1 Emissions
G1.1.1 Exhaust Emissions
The exhaust emission calculation methodology can be simply described as multiplying the
pollutant emission index for a desired average speed and the designated study year against the
distance traveled against the volume of traffic. Emissions must be calculated separately for
different years of interest, since emission indices change by year. This calculation can be
performed for each EPA vehicle category or for all vehicles using composite inputs. This
calculation can be used to determine emissions for any time period (e.g., day, week, month, year)
by adjusting the number of trips. Equation G-1 shows the simplified description of the exhaust
emissions calculation methodology. As mentioned above, motor vehicle emissions vary based on
local ambient conditions (e.g., CO is high in colder weather). If the time period of interest
includes both warm and cold weather seasons, the emissions should be calculated for each season
to obtain accurate emission estimates.
G-6
Ei = EIisy x D x T x CF
Equation G-1: GAV Exhaust Emissions
Where: Ei - emissions of pollutant i, in pounds, produced by the vehicles of interest in
the given time period
EIisy - emission index, in grams per mile, for pollutant i and a specified speed s and
year y
D - distance traveled, in miles, by the vehicles of interest
T - number of vehicle trips of interest
i - pollutant type (e.g., HC)
s - average vehicle speed, in miles per hour
y - designated study year
CF - 0.0022046 unit conversion factor from grams to pounds
Note: Distance traveled (D) times number of vehicle trips (T) also is known as
vehicle miles traveled (VMT)
　
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