For a criteria pollutant emissions inventory, EDMS/AEDT uses static times in mode (TIM) for ground-based aircraft movements (i.e. taxi times) but these times often do not capture airport- specific operating parameters such as ground delay, airfield configuration, ramp locations , variation in aircraft speed, and other important factors. So, users are allowed to modify taxi times on a per-aircraft basis to account for these airport -specific operating conditions. Appendix F ( Data and Information Sources ) presents resources available to obtain actual taxi times, simulated taxi times, and to apportion/estimate airfield delay. 

## Ground Support Equipment (GSE) 

GSE criteria pollutant emissions inventories using EDMS/AEDT capture two distinct sets of utilization at an airport: (i) GSE servicing gated aircraft on the apron, and (ii) other activities of the GSE population not tied to gate service operations. An example of a gate service operation is a baggage tractor visiting an aircraft at the apron to drop off baggage; an example of a population activity is a deicing truck driving back and forth to a deicing area during the deicing season. 

To compute GSE emissions, EDMS/AEDT applies emissions factors (in grams per horsepower hour [g/hp-hr]) specific to the make/model, year of manufacture, approximate horsepower , and fuel type of a given equipment to annual hours of operation for that equipment. These emissions calculations are further adjusted using the observed horsepower of the equipment and equipment’s average percentage of full throttle (i.e., load factor). EDM S/AEDT offer “default” values for many of these parameters and affords a user to override them to the extent information on an airport’s GSE fleet is known. 

For GSE population activities, users need only specify the make/model, model year, horsepower, fuel type, and annual hours of operation for a given piece of equipment (or accept EDMS’s default information). This approach also applies to the gate service GSE. EDMS/AEDT computes annual hours of operation for gate service GSE by considering number of aircraft LTOs for which GSE service is provided and the total running time of the GSE per LTO. 

Calculation steps and input data necessary to compute GSE emissions in EDMS/AEDT further explained in Appendix A3 ( Ground Support Equipment Emission Inventory for Criteria Pollutants ). 

## Auxiliary Power Units (APUs) 

When input to EDMS/AEDT, most large commercial and cargo aircraft are automatically assigned a representative make and model of APU if agency/industry documentation indicates that an APU is used on that aircraft.$^{$_{43}$, $_{44 }$}$Annual APU emissions are a function of the number of LTOs performed by the equipped aircraft, the time the assigned APU operates per LTO, and the emissions factors assigned to the APU. When assigning APU operating times per infrastructure considerations such as the availability of fixed electrical ground power and pre- conditioned air, as well as meteorological conditions such as the annual temperature in the area, 

