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Where: 

E$_{ij }$ = emissions of pollutant i, expressed in pounds, produced by the APU model installed on aircraft type j for one LTO cycle 

T = operating time per LTO cycle, expressed in minutes 

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FF$_{j }$= fuel flow, for each APU used on aircraft type j, expressed in pounds per minute 

EF$_{ij }$= emission factor for pollutant i, expressed in pounds of pollutant per one thousand pounds of fuel, for each APU used on aircraft type j 

Total APU emissions are estimated by applying Equation A2-2 ( Total APU Emissions ), which multiples the APU emissions per LTO for a given aircraft type and operating time (determined using Equation A2-1 , APU Emissions from a Single LTO ) by the number of corresponding LTOs, then sums the emissions over all aircraft types. 

Where: 

i = pollutant type (e.g., HC, CO, NO$_{x}$, SO$_{2, }$etc.) 

j = aircraft type (e.g., B-737, MD-11, etc.) 

<img src='content_image/611540.jpg'>

ET$_{i }$ = total APU emissions of pollutant i, expressed in pounds, produced by all aircraft types in question 

E$_{ij }$ = emissions of pollutant i, expressed in pounds, produced by the APU model installed on aircraft type j for one LTO cycle 

LTO$_{j }$= number of landing and takeoff cycles for aircraft type j during the inventory period 

## A2.2.1 Data Inputs 

The data inputs required to estimate APU emissions and the likely sources of obtaining this information are listed in Table A2-1 ( Data Inputs for Estimating Emissions from APU ). 

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