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27 CO2, with Section 3.4.4 discussing the methodology for the ger category, vehicles can be further identified by the mode of Level 2 and Level 3 pollutants for GAV. travel--private vehicle, taxi, shared van, etc. For many air- ports, data of this nature are not available. Thus, sources of data that the inventory developer might consult could include: 3.4.1 GAV Method 1 total airport activity characteristics (passenger, operations, Method 1 calculations involving the determination of GHG and cargo including the FAA's Terminal Area Forecast), air- emissions from GAVs basically determine fuel consumption port parking revenue (for vehicles accessing the airport park- values for use with the appropriate emission factors. This is ing lots), passenger surveys (for modes of travel and distance the general method described under both Tiers 1 and 2 of the traveled), metropolitan planning organization (MPO is re- emissions section in Volume 2, Chapter 3 (IPCC 2006). How- sponsible for regional surface traffic analysis) traffic analysis ever, unlike using the IPCC tiers, national fuel consumption for the area, airport employee parking and badge office in- data specific to an airport and the vehicles that use an airport formation (concerning employees and their travel), airport are not available. Therefore data surrogates are used to pro- master plans and environmental analysis (for ground travel vide an indication of the distance that vehicles travel and the information), rental car revenue data (to identify rental car fuel economy of those vehicles. The overall method for airport companies and percentage of market shares), etc. GAV emissions is presented in Figure 3-7. In order to calculate GAV fuel consumption, fuel econ- The first step in calculating GAV emissions is to collect omy data would need to be obtained from sources such as VMT data for all vehicles. The total origin-destination distance the USEPA (USEPAb 2005), FHWA (FHWA 2002), and DOE should be included to allow proper accounting of GHG emis- (DOE 2007). For national averages, some typical values are sions based on the influence of the airport. Such data could as follow: potentially be derived from passenger surveys or estimates of Passenger cars = 23.9 mpg (USEPAb 2005), passenger trip distances. Although passenger vehicles will tend Passenger cars = 22.1 mpg (FHWA 2002), and to account for the biggest portion of GAV emissions, other Cars (2005) = 22.9 mpg (DOE 2007). vehicles, such as those used by airport employees and shuttle buses, should also be included. Each of these vehicles should Any of these example fuel economy values could be used also be categorized by fuel type (e.g., gasoline, diesel, etc.). since they are all from reputable sources. The inventory devel- In the simplest form, the vehicles using an airport can be cat- oper needs to clearly document the sources and should consider egorized by passengers, employees, cargo, and service delivery. the potential need for consistency with previous inventories If specific vehicle data are not available, the inventory devel- when choosing which values to use. If more specific fuel oper will be required to estimate the number of vehicles and economy data are available (i.e., more specific to airport distance traveled of the various vehicle types. In the passen- GAVs), they should be used instead of the national averages. Although the data could be segregated into categories (e.g., cars and trucks), the purpose of this method is to conduct a rela- Total VMT or by a tively "simple" assessment using average values. Using these Few Major Vehicle Fuel Categories Economy Data national averages, fuel consumption would be calculated as exemplified below. The following sample calculation is for one round trip: Calculate Fuel consumption = ( 40 mi ) ( 23.9 mpg fuel economy ) = 1.67 gal fuel. To calculate GHG emissions, emission factors can be ob- GAV Fuel Emission Consumption Factors tained from the following variety of sources: Motor gasoline = 19.564 lbs CO2/gal fuel (EIA 2008), Diesel = 22.384 lbs CO2/gal fuel (EIA 2008), Calculate LPG = 12.805 lbs CO2/gal fuel (EIA 2008), Gasoline = 8.81 kg CO2/gal fuel (USEPAa 2005), On-road diesel fuel = 10.15 kg CO2/gal fuel (USEPAa 2005), GAV GHG LPG = 5.79 kg CO2/gal fuel (USEPAa 2005), Emissions LNG = 4.46 kg CO2/gal fuel (USEPAa 2005), and Gasoline = 19.4 lbs CO2/gal fuel (USEPAb 2005 and CFR Figure 3-7. Overview of GAV Method 1. 2003).