Aircraft and Airport-Related Hazardous Air Pollutants: Research Needs and Analysis (2008)

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45 9.1 Dependence of HAP Emissions from Idling Aircraft on Ambient Conditions AIRPORT COOPERATIVE RESEARCH PROGRAM PROBLEM STATEMENT I. PROBLEM TITLE Dependence of HAP emissions from idling aircraft on ambient conditions II. RESEARCH PROBLEM STATEMENT Frequently, commercial airport operators are asked to estimate the magnitude of toxic emissions from air- port-related sources. These requests may come from government officials, courts, or concerned commu- nity groups. One of the key categories of potentially toxic emissions is Hazardous Air Pollutant (HAP) emissions—and the most important source of airport related HAPs compounds at most commercial air- ports is idling jet engines. This is because the HAPs emissions of modern jet engines are very small at power settings greater than idle. It is therefore critical to understand the rate of HAPs emissions at low power settings. These emissions will vary as a function of thrust setting, environmental variables (especially temperature), and engine type. In order to properly estimate airport HAP emissions it is necessary to bet- ter understand the aircraft engine emission factors as a function of these variables. III. OBJECTIVE The goal of this project would be to improve our quantitative understanding of the largest aviation- related HAPs emission source—jet engines operating at low power. Emissions data for commercial aircraft are only available in the narrow temperature range (8 to 35 degrees Celsius [°C], 46–95 degrees Fahren- heit [°F]), and show that HAP emissions increase greatly with decreasing temperatures. The lack of knowledge regarding the temperature dependence of HAP emissions, and how it depends on engine tech- nology, currently results in uncertainties of more than a factor of 2 in modeled HAP concentrations and risk. This is especially important for airports located in cold environments. IV. RESEARCH PROPOSED This project would measure the emission rates of var- ious HAPs compounds from commercial aircraft as a function of thrust level near idle and as a function of environmental variables such as temperature, humid- ity and pressure. The project should quantify HAPs emissions from a wide variety of in-service commer- cial aircraft under a wide variety of environmental conditions while operating in idle mode. It is envi- sioned that this will require making measurements during summer and winter to achieve as wide a tem- perature range as possible. Measurements at more than one airport are desirable. It is essential that the engine type and thrust setting be determined during these measurements to separate their effects from those of the environmental variables. V. ESTIMATE OF THE PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $500,000 Research Period: 18 to 24 months VI. URGENCY AND PAYOFF POTENTIAL This research will provide a detailed and quantitative understanding of jet aircraft HAPs emissions as a function of environmental and operational factors. The results will likely be incorporated in the U.S. S E C T I O N 9 Problem Statements

airport emissions modeling tool—Emissions and Dis- persion Modeling System (EDMS). This will allow airport operators to utilize the latest scientific findings to construct HAPs emission estimates tailored to their specific airport. These estimates will be more defensi- ble and better able to withstand litigation since they will be based on the latest scientific findings regarding jet engine HAPs emissions and the variables that affect them. VII. RELATED RESEARCH See ACRP 02-03 report. VIII. PERSON(S) DEVELOPING THE PROBLEM ACRP Project 02-03, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). IX. PROCESS USED TO DEVELOP PROBLEM STATEMENT ACRP Project 02-03 X. DATE AND SUBMITTED BY ACRP Project 02-03, December 20, 2007, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). 9.2 Characterization of Operational Thrust Levels AIRPORT COOPERATIVE RESEARCH PROGRAM PROBLEM STATEMENT I. PROBLEM TITLE Characterization of operational thrust levels II. RESEARCH PROBLEM STATEMENT The International Civil Aviation Organization estab- lished and maintains the databank of engine certifica- tion data for all engines currently in commercial aviation use. The emissions component of the certification process defines four engine conditions and the associated thrust levels: idle (7%); approach (30%); climb-out (85%); and take-off (100%). Air- port emission inventories for CO, NOx, unburned hydrocarbons (UHC), and “smoke number” are rou- tinely constructed using the certification emission indices, fuel flow rate, and time-in-mode data. While the overall time-in-mode is often known to some degree, there is significant evidence that the four cer- tification thrust levels do not accurately mirror what is used during actual operation. Furthermore, emis- sions profiles are nonlinear with engine thrust set- tings. The emission rate of gas-phase HAPs at thrust levels less than 7% can be more than twice as high as the emission rate at the certification value (7% thrust). Variation in the thrusts used during take-off can greatly impact NOx emissions as well. Such dif- ferences in the emission rate with small changes in thrust level are sufficiently large to introduce large errors in emission inventories. Since airport operators use these emission inventories to evaluate mitigation strategies, the accuracy must be improved to reflect real-work thrust conditions. III. OBJECTIVE The principal objective of this research is to generate an input function for the Emissions Dispersion Mod- eling System that accurately reflects the distribution of thrusts used by aircraft at airports. Factors such as airport congestion, ambient conditions, and any effects of overall class of aircraft should be parame- terized for simple implementation. The knowledge gained from this research will greatly improve the accuracy of emissions inventories. IV. RESEARCH PROPOSED The development of the real-world thrust profile will require an analysis of recorded fuel flow rates, the recorded “N1” parameter or other electronic data from a statistically significant number of land- ing, take-off cycles. The research will collect data from cooperative aircraft operators and merge with other datasets generated via the airport or other sources. This program will develop operational thrust distributions to be used in conjunction with emissions profile. The research will investigate the influence of anticipated factors on the real-world thrust profile (e.g., LTO/hr). The research will iden- tify a simple approach to the parameterization of in- use thrust levels. V. ESTIMATE OF THE PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $50,000 to $75,000 Research Period: 12 months VI. URGENCY AND PAYOFF POTENTIAL This straightforward improvement to how invento- ries are constructed represents a very direct improve- ment to emissions management and understanding. As alternative emission mitigation strategies emerge, particularly those that target the ground idle and taxiing phases, an improved tool is mandatory to evaluate the benefits. This project would have a large payoff to airport emissions management and air qual- ity modeling. 46

VII. RELATED RESEARCH See ACRP 02-03 report. We are aware of some limited work in progress through the FAA/Partner research program. The product of that research we know of is an assessment of the impact of reduced thrust take-off on NOx emissions. We are unaware of an effort to apply real-world thrust profiles to the hazardous air pollutant emissions. VIII. PERSON(S) DEVELOPING THE PROBLEM ACRP Project 02-03, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). IX. PROCESS USED TO DEVELOP PROBLEM STATEMENT ACRP Project 02-03 X. DATE AND SUBMITTED BY ACRP Project 02-03, December 20, 2007, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). 9.3 HAP Emissions from General Aviation Aircraft AIRPORT COOPERATIVE RESEARCH PROGRAM PROBLEM STATEMENT I. PROBLEM TITLE HAP emissions from general aviation aircraft II. RESEARCH PROBLEM STATEMENT Frequently, general aviation airport operators are asked to estimate the magnitude of toxic emissions from airport-related sources. These requests may come from government officials, courts, or concerned com- munity groups. One of the key categories of potentially toxic emissions is Hazardous Air Pollutant (HAP) emissions. HAP emission from general aviation air- craft are currently difficult to estimate because they have not been well studied and because there is no engine emission certification requirement for most general aviation aircraft. This is due to the relatively small size of their engines. Hence, HAP emissions (with the exception of lead) from aircraft piston engines, turbojet engines, and low-bypass turbofan engines (such as business jets) are largely unknown and should be quantified. In order to properly estimate airport HAP emissions from general aviation aircraft it is nec- essary to study these emissions with in-service aircraft. III. OBJECTIVE The goal of this project would be to improve our quantitative understanding of HAP emissions from general aviation aircraft. This project would support HAP emissions measurements of general aviation aircraft such as those employing piston engines, turbo- jet engines, and low-bypass turbofan engines (such as business jets). This information will be most impor- tant at general aviation airports. IV. RESEARCH PROPOSED This project would measure the emission rates of various HAPs compounds from general aviation air- craft. The project should quantify HAP emissions from a wide variety of in-service general aviation air- craft. It will be important to make measurements as a function of engine type and operational mode (idle, taxi, take-off). It is envisioned that this will require making measurements at more than one airport. It is essential that the engine type and operational mode be determined during these measurements to allow these measurement results to be incorporated in models that airport operators can use to estimate their emissions. V. ESTIMATE OF THE PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $400,000 to $500,000 Research Period: 18 to 24 months VI. URGENCY AND PAYOFF POTENTIAL This research will provide much needed measure- ments of HAP emission from in-service general aviation aircraft. The results of this research will be used to produce more accurate emissions estimates for general avia- tion aircraft. These estimates will be more defensible and better able to withstand litigation since they will be based on the latest scientific findings regarding HAP emissions from general aviation aircraft. VII. RELATED RESEARCH See ACRP 02-03 report. VIII. PERSON(S) DEVELOPING THE PROBLEM ACRP Project 02-03, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). IX. PROCESS USED TO DEVELOP PROBLEM STATEMENT ACRP Project 02-03 X. DATE AND SUBMITTED BY ACRP Project 02-03, December 20, 2007, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). 47

9.4 Identification of the Emission Sources Most Important to On-Airport and Off-Airport Exposure AIRPORT COOPERATIVE RESEARCH PROGRAM PROBLEM STATEMENT I. PROBLEM TITLE Identification of the emission sources most important to on-airport and off-airport exposures II. RESEARCH PROBLEM STATEMENT Airports are an easily identified source of emissions within an urban or suburban setting. The emissions at airports come from jet engines, ground support ve- hicles, the airport facilities themselves and from ground access vehicles arriving at or departing from the airport grounds. Due to the high visibility of the airport and the activity it supports, it is frequently challenged to provide a self-assessment of its emis- sions and impact on the surrounding neighborhoods and environment. The emissions at airports are spa- tially inhomogenous, vary diurnally, and very likely have seasonal dependence. As a result, annual tabula- tion of net emissions, summing multiple sources is not adequate to understand what emissions sources influence exposure. III. OBJECTIVE The purpose of this project is to identify which emis- sion sources (aircraft, GSE, terminal traffic, etc.) most greatly affect potential receptors (e.g., nearby resi- dents, airport-based workers, passengers). This will include apportionment among the various airport sources (e.g., aircraft, GSE, GAV) and non-airport sources. Measurements used in conjunction with pre- dictive models will provide a quantitative evaluation of the accuracy of models. Models used to predict the concentrations of HAPs near airports have not been adequately tested. IV. RESEARCH PROPOSED This should be done using dispersion/chemistry models tested against complementary measurements. Conclusive deduction of source apportionment will require coordinated measurements of the main com- bustion gases (CO2, CO, NO, NO2), speciated HAPs (e.g., benzene, formaldehyde, etc.) and PM (charac- terized by number/size, mass, and chemical composi- tion). Source apportionment is required to evaluate proposed emissions mitigation strategies. This proj- ect will help airport operators to identify the “low- hanging fruit” with regards to minimizing the health risk presented by the various emission sources pres- ent at an airport. This research will necessarily involve the integration of measurements and models over multiple spatial and temporal scales. Different exposure groups being considered may require different model, inventory, and measurement demands. The exposure of a curb- side check-in worker is very different from that of ground support workers. The proposed research will identify the exposure groups to be evaluated and develop appropriate assessments for each. V. ESTIMATE OF THE PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $500,000-$750,000 Research Period: 24-36 months VI. URGENCY AND PAYOFF POTENTIAL Successful execution of the proposed work will gain a genuine understanding of how airport emissions affect different exposure groups. VII. RELATED RESEARCH See ACRP 02-03 report. VIII. PERSON(S) DEVELOPING THE PROBLEM ACRP Project 02-03, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). IX. PROCESS USED TO DEVELOP PROBLEM STATEMENT ACRP Project 02-03 X. DATE AND SUBMITTED BY ACRP Project 02-03, December 20, 2007, PI: David Nelson (ddn@aerodyne.com, 978-663-9500). 48