Exhaust Emissions from In-Use General Aviation Aircraft (2016)

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Research Approach 7 Suppose an airport’s environmental manager wants to know how plans to construct a new runway will affect the total emissions from the airport. Emissions data tables such as those in Appendix P, when combined with some additional information about the airport, will allow the environmental manager to estimate current and future emissions. With these estimates in hand, an informed decision on the future of construction can then be made. So how do we get all the way from the exhaust pipe of an aircraft engine to the final airport emissions estimate? This sec- tion defines terms and explains the math needed. We start at the greatest level of detail with an emission index (EI). The EI is a measure of the amount of a pollutant (or “chemical species”) that is emitted per amount of fuel burned for a given engine type. EIs are expressed in terms of grams of pollutant per kilogram of fuel burned (g/kg fuel). In practice, an emission ratio (ER), the molar ratio of a measured species versus the sum of carbon-containing species, is determined experimentally for each chemical species of interest (see Appendix D for a discussion of ER calculation methods) and then combined with the known carbon content of the aircraft fuel to calculate the EIs. Appendix E details the math- ematics of this procedure. Tables of EIs (such as those in Appendix P) list EIs for many different engines and many different pollutants at many different power states. The power states, based on the operation of an aircraft, will be familiar to any pilot. The power states used in this report are idle, taxi, climb-out (C/O), cruise, approach (App), and take- off (T/O). The report defines the additional power state of final approach (Final App) with less power than approach, based on anecdotal evidence from pilots that the crosswind and upwind leg of the approach are distinct and different. The precise definitions of these power states vary depending on the emissions database in question. For example, Appendix C compares the power states defined by the ICAO, which has data for large commercial jets, to the Swiss FOCA, which has data for small piston engines. Throughout this report, power is usually plotted in terms of the percentage of the maximum fuel flow, because this is most indicative of thrust for piston engines. Depending on the size of an airport, the time that a typical aircraft spends in each power state can vary. These characteristic times are referred to as “times in mode.” In this report, the Nitrogen oxides = NO + NO2 Carbon Monoxide Par culate Maer Carbon Dioxide CO2 vola le vola le non- vola le non- vola le PM number mass Total Hydrocarbons = methane + ethane + … + benzene + … Figure 2-1. Important species in aircraft exhaust: nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbons (HC), and particulate matter (PM).