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26 equipment, specific engine, date manufactured, horsepower emissions for HFC and PFC based on default parameters of the equipment, and annual hours of use. Then, specific emis- related to mobile air conditioning. Designated as a screen- sion factors can be obtained from the respective model. These ing method, both the USEPA Climate Leaders and TCR have data represent the GSE vehicle mix-use data. adopted this method. The inventory developer will need to For those airports that have not conducted a GSE inventory determine if this method is justifiable and the corresponding (for either their owned equipment or their tenants' equip- data are appropriate for the airport. ment), estimates of such vehicle use can be prepared. For For the other pollutants in Level 3 (beyond the six Kyoto pol- airport-owned equipment, it is best to survey the airport staff lutants), NONROAD2005 or similar models like OFFROAD- responsible for that equipment. However, in most cases, GSE 2007 can be used to obtain emission factors. The pollutants Method 1 is recommended for airport-owned equipment (fuel include various gases and PM. Emissions of H2O and SOx can dispensed to these vehicles). For airline GSE, AEDT/EDMS potentially be estimated using fuel composition data with provides default GSE-use based on the aircraft fleet mix con- mass balance as indicated in Appendix C. sidered. This information will provide types of equipment, horsepower setting, and annual hours of use. Once the GSE vehicle mix-use data are obtained, the 3.4 Ground Access Vehicles NONROAD model can be accessed to obtain emission fac- When preparing inventories of GAV, care must be exer- tors that are generally representative of the vehicle mix. cised in evaluating travel for on-airport, as well as off-airport, NONROAD can be run for the nation as a whole or for a state roadways. Most airports have data concerning on-airport or county. Given the general nature of the data, it is at the travel; large airports are likely to have actual vehicle count discretion of the user as to whether national averages, state data; small airports may have more limited datasets. A review averages, or county local data are used. In many cases, exact of the available inventories prepared to date indicates that the vehicle matches are not possible and therefore, estimates of evaluation of GAV emissions may require approximations of equipment may be made based on knowledge of the specific vehicle counts and travel. GSE used at the airport. Alternatively, emission factors could Due to the scale differences between the national inventories potentially be obtained directly from the manufacturers of developed under the IPCC methods and airport inventories, the GSEs. Although this is a less likely source of information the calculation methods for GAVs presented herein do not and would be time consuming, it would provide improved correlate directly with the tiers used by IPCC. However, they estimates of GSE emissions. Potentially, manufacturer spec- share common components that are consistent. The follow- ification sheets (if they do not have emission factors) could ing methods are presented in this Guidebook for GAVs: also provide useful information in matching a GSE to an ap- propriate equipment type in NONROAD. Method 1: Use average vehicle miles traveled (VMT) es- The following provides a sample calculation assuming 120 timates with appropriate emission factors for an average annual hr of 112 hp Bobtail GSE activity, where the Bobtail vehicle. generates 871.4 g/hp-hr: Method 2: Use vehicle-specific VMT data with appropriate CO2 emissions = (120 h ) ( 871.4 g CO2 h ) vehicle-specific emission factors. = 104, 568 g CO2 or 0.1046 metric tons Method 3: Use vehicle-specific VMT data with models of CO2 ( converting the grams to such as MOBILE6.2 to calculate vehicle-specific emission metric tons, by multiplying the grams factors. of CO 2 by 0.000001 g metric ton ). Although Method 3 is preferred, few airports have data at this level for the entire set of GAV that are suggested for in- 3.3.3 Other Pollutants clusion in the GHG inventory. Therefore, it may be appro- Emission factors of CH4 and N2O are provided by both the priate to use Method 3 for some subset of GAVs, such as the USEPA's Climate Leaders (USEPAa 2008) and IPCC Volume 2, on-airport movement, and a lower method for the off-airport Chapter 3 of their guidelines (IPCC 2006) for a variety of non- movement. It is within the GAV category of sources that highway mobile sources (e.g., small utility, large utility, etc.). data availability is likely to represent the greatest difficulty Since IPCC data represent international defaults, USEPA data for most airports. The documentation that accompanies the are preferred. It is up to the inventory developer to determine inventory should clearly document the data sources and the appropriateness of this information in estimating GSE their use. emissions for those pollutants. Based on the availability of data, inventory developers are For GSE that has air conditioning, IPCC Volume 3, Chap- encouraged to use the highest method for the data available. ter 7 of their guidelines (2006) provides a method to derive The following three subsections discuss the calculation of