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prior to main engines start up on departure and the run time after the aircraft engines are shut down on arrival and, if available, connected to ground power at an airport. Notably, if ground power and pre-conditioned air is not available, an APU may be used the entire time an aircraft is at an airport’s gate. 

## B.2.2.2 Conversion Factors 

The required input data for obtaining an estimate of HAP emission for an APU includes: (i) the fuel flow rate for the specific APU model, (ii) the APU run time (for a complete landing-takeoff cycle), (iii) a THC emission index specific to the APU model, (iv) a factor that converts the estimated level of THC to TOG, and (v) a HAPs speciation profile. Equation B-5 ( HAP Emissions – APU ) demonstrates how to derive HAP emissions for an APU. 

Where: 

## B.2.3 Ground Support Equipment 

A = Fuel flow rate (kg/sec) 

B = Time in operation (sec) 

D = THC emission index (g/kg fuel consumed) 

F = THC to TOG conversion factor (unitless) 

H= Speciation profile for HAP of interest (mass fraction) 

1/1000 = Converstion factor from grams to kilograms 

I= Mass of HAP of interest (kg) 

<img src='content_image/536090.jpg'>

GSE provide service to aircraft while at an airport terminal and are generally classified as either “on-road” vehicles or trucks (e.g., an airline employee shuttle bus) and other similar vehicles or “non-road” vehicles/equipment such as tugs, tractors, loaders, etc. The fleet of GSE utilized at an airport, their operating times and fuel types (gasoline or diesel) varies by aircraft (commercial, commuter, GA, military), by airline, and by airport. 

## B.2.3.1 Methodology 

GSE emissions are calculated either using a total GSE population- based approach (i.e., an accounting of all the equipment and vehicles on the airport) or using an aircraft LTO approach (i.e., based on the type and number of GSE servicing each aircraft type for an LTO) (see Appendix A.3 , Ground Support Equipment Emissions Inventory for Criteria Pollutants ). 

## B.2.3.2 Emission Factors 

For GSE, the input data used determine the amount of HAP emission include: (i) the brake horsepower of the equipment, (ii) the load factor, (iii) equipment usage (equipment operating time), (iv) THC emission indices, (v) a THC to TOG conversion factor specific to the equipment fuel type, and (vi) a HAPs speciation profile that is also specific to the fuel type. 

