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PREPUBLICATION COPY â Uncorrected Proofs 101 7 Conclusion Since lead was phased out of automotive gasoline more than 30 years ago, the leaded aviation gasoline (avgas) used by piston-engine aircraft has become the predominant source of lead pollution in the United States. Lead exposure can result in an array of negative health effects in humans and there are no known safe levels of lead exposure, as measured by blood lead concentrations. For example, exposure to low concentrations of lead, including prenatal exposure, has been linked to decreased cognitive performance in children, because of the susceptibility of the developing nervous system. The importance of reducing lead pollution motivates the development and implementation of mitigation measures to reduce or eliminate lead emissions from general aviation (GA) aircraft. Today, nearly all avgas is formulated to contain between 0.28 and 0.56 grams of lead per liter. Lead is added to avgas in the form of tetraethyl lead (TEL). The reason for adding TEL to avgas is to boost its octane to levels that will enable the reliable operation of high-compression piston engines at the wide range of altitudes and climates in which they operate. Without leaded avgas, tens of thousands of piston-engine aircraft, used for a wide range of beneficial GA purposes, could not be safely flown. Decades of research on octane-enhancing additives have failed to find an alternative to lead that performs in an operationally safe manner for all GA aircraft in use today. Hence, eliminating lead from avgas is a highly desirable public health goal, but one that has been difficult to achieve. As understanding of the adverse effects of lead pollution has grown, the U.S. Environmental Protection Agency (EPA), the Federal Aviation Administration (FAA), the National Institute of Health Sciences (NIEHS), the GA community, and other organizations have been working to identify where important environmental exposures occur and find ways for reducing lead emissions from piston-engine aircraft. Other researchers have examined how operations and practices at airports, including pre- flight checks, refueling practices, and aircraft maintenance activities, contribute to lead emissions and human exposures. FAA has been collaborating with fuel suppliers and the GA industry, through the Piston Aviation Fuels Initiative (PAFI), to find an unleaded avgas that can satisfy the entire piston-engine fleet. Some fuel suppliers have been working independently to develop avgas alternatives, resulting in at least one grade of unleaded avgas that can satisfy a portion of the piston-engine fleet that does not require fuel with high octane and a grade of avgas that has a lower lead content, which can be used by all piston-engine aircraft. Meanwhile, advancements continue in the development of lead-free propulsion technologies for small aircraft, including diesel, turbine, and electric-powered systems. As a result of those efforts, it has become increasingly clear that significantly reducing, and ultimately eliminating, the lead added to avgas and the sources of lead exposures at and near airports is a multi-faceted problem requiring multiple mitigation strategies. Forecasted long-term reductions in GA activity are likely to result in declining avgas use and lower lead emissions over time, but only marginallyâon the order of 10 percent over the next 20 years. Consequently, additional actions would be needed to reduce lead emissions faster and further. Because the piston-engine fleet, consisting of about 170,000 aircraft, serves many important purposes, any actions that risk major disruptions in the use of these aircraft would be impractical and
PREPUBLICATION COPY â Uncorrected Proofs 102 undesirable. Only a small number of new aircraft are added to the fleet each year and very few aircraft are retired, meaning that transitioning to a fleet that consists exclusively, or even predominantly, of aircraft not requiring high-octane avgas would take decades. Major technical challenges have slowed the development of a high-octane unleaded avgas that can serve all of the aircraft in this existing piston-engine fleet. Moreover, the fleet operates from more than 13,000 airports, including many smaller facilities that have limited fuel storage and dispensing capacity and few incentives and resources to offer both leaded and unleaded grades of avgas to satisfy specific segments of the fleet. All piston-engine aircraft, including those that do not require high-octane fuel, can operate safely using the leaded avgas available for purchase today. Many small airports, therefore, are inclined to supply only this grade of avgas, and fuel suppliers are likewise incentivized to offer only this grade because the total demand for avgas is already relatively small and expected to decline. Under the requirements of the Clean Air Act (CAA), if EPA were to determine that lead emissions from the use of leaded avgas cause or contribute to air pollution, which may reasonably be anticipated to endanger public health or welfare, the agency would need to develop regulations for controlling lead emissions from piston-engine aircraft. No such regulations are currently in place. In 2006, the Friends of the Earth (FOE) filed a petition requesting that EPA issue a finding that lead emissions from piston-engine aircraft endanger public health and welfare, or conduct a study of lead emissions from the aircraft if there was insufficient information to make a determination.1,2 During the 14 years since that petition, EPA sought public comment twice on various issues related to lead emissions from aircraft and has completed several field monitoring and air quality modeling studies to help address open questions.3,4,5 EPA had planned to issue a proposed endangerment finding (either positive or negative) by 2017, but the agency did not meet its target date.6 The uncertainty surrounding a proposed endangerment finding from EPA complicates assessments of the array of policy options that are, or may become, available to mitigate aviation lead pollution. Given that uncertainty, the committee did not consider regulatory tools that might be issued by EPA under the CAA. However, if those tools were to become available, they would almost certainly have a prominent role in a lead mitigation strategy and be high among the candidate policy options for lead mitigation. An update published by EPA on the status of its endangerment assessment, along with identifying any open issues and any additional information needs, would be helpful for parties who are interested in the outcome of EPAâs endangerment assessment. While a formal EPA determination is not a prerequisite for introducing measures to mitigate lead emissions, it would add more clarity about the array of regulatory and non- regulatory means available for this purpose. 1 Endangerment finding is often used as a short-hand reference to a judgment as to whether lead emissions from aircraft engines resulting from the use of avgas cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare. 2 Friends of the Earth. 2006. Petition for Rulemaking Seeking the Regulation of Lead Emissions from General Aviation Aircraft Under Â§ 231 of the Clean Air Act. October 3. See https://www.epa.gov/sites/production/files/2016-09/documents/foe-20060929.pdf. 3 See 72 FR 64570 (November 16, 2007) and 75 FR 22440 (April 28, 2010). 4 These comments are also available in EPA docket EPAâHQâOARâ2007â0294. 5 See https://www.epa.gov/regulations-emissions-vehicles-and-engines/epas-data-and-analysis-piston-engine- aircraft-emissions. 6 Letter, Gina McCarthy EPA to Deborah Behles, Golden Gate University, and Marianne Lado, Earthjustice, January 23, 2015. See https://www.epa.gov/sites/production/files/2016-09/documents/ltr-response-av-ld-foe-psr- oaw-2015-1-23.pdf.
PREPUBLICATION COPY â Uncorrected Proofs 103 RECOMMENDED RESEARCH TO INFORM MITIGATION EFFORTS As discussed above, the challenges associated with reducing lead emissions and human exposures resulting from the use of leaded avgas are formidable. However, the evidence of lead pollutionâs hazard demands that those challenges not become an excuse for inaction, but instead become the subject of concerted, sustained, and multi-pronged efforts to find and implement mitigation measures. While development of a âdrop-inâ unleaded fuel that can satisfy the entire piston-engine fleet is a highly desirable goal, attainment of that goal is not assured, and a singular focus on achieving it risks the neglect of other opportunities to reduce lead emissions from GA aircraft and subsequent human exposures. Assessing the feasibility and effectiveness of the airport-specific application of potential mitigation measures in mitigating hot spots for ambient lead concentrations would benefit from an improved understanding of individual airport characteristics. The airports that serve piston- engine aircraft differ in traffic activity, layouts, and proximity to the local population. They serve as bases for different types and numbers of aircraft that provide different functions within the community. Therefore, additional analyses are needed that account for airport-specific conditions and attributes, including the geographic distribution of lead around the airport. Such analyses would inform the selection, design, and effectiveness assessment of lead mitigation efforts at individual airports. EPA should conduct more targeted monitoring and enhanced computational modeling of airborne lead concentrations at airports of potential concern, as indicated by its recent screening study, to evaluate aircraft operations that are main contributors to lead hot spots and design airport-specific mitigation measures. (Hot spots often refer to a spatial zone of emissions impact where the airborne lead concentration is significantly elevated above background.) In addition to airports found to have airborne lead concentrations exceeding the concentration of the lead National Ambient Air Quality Standards (NAAQS), additional monitoring and modeling should include airports found to have lead concentrations that are lower, but approaching, the NAAQS concentration (Recommendation 3.1). Lead in piston-engine aircraft exhaust has been observed to occur in the form of beads about 4 nanometers (nm) in diameter embedded in particles with diameters less than 20 nm. Those particles are smaller than the lead particles observed in automobile exhaust. Smaller particles may deposit and distribute in the body differently than larger-sized particles that have been the subject of more research in the past. Thus, it is important to understand the particle size properties of lead emitted from aircraft and how those properties affect atmospheric transport and deposition as well as human exposureâresponse relationships. EPA and NIEHS should sponsor research to improve the understanding of the physical state of the lead-containing particulate matter emitted from various types of GA-aircraft piston engines, including turbocharged engines, using fuel formulations of different lead content, including an existing grade of avgas with a lower lead content (100VLL), to inform future studies of atmospheric transport and deposition, human exposure, and health risks of lead emissions form GA aircraft (Recommendation 3.3).
PREPUBLICATION COPY â Uncorrected Proofs 104 Based on the nature of the workplace activities involving piston-engine aircraft, lead exposures are expected to occur for flight line and maintenance shop workers, including those employed by the airport itself, fixed base operators (FBOs), and repair and overhaul facilities. Workplace lead exposures include not only inhalation of airborne emissions, but also inhalation, ingestion, and dermal absorption of the fuels additives TEL and the fuel additive ethylene dibromide, as a result of aircraft refueling and maintenance activities. Occupational Safety and Health Administration (OSHA) regulations, including permissible exposure limits and related requirements, apply for each of those contaminants. EPA and NIEHS should sponsor research to enhance the understanding of lead exposure routes and their relative importance for people living near airports and working at them. The research should include studies, such as observations of blood lead levels among children, in communities representing a variety of geographic settings and socioeconomic conditions that are designed to examine the effectiveness of the lead mitigation strategies over time (Recommendation 3.2). Airborne lead, which is usually in the form of particulate matter, can be inhaled by people in communities surrounding airports. In addition, particles containing lead can deposit onto soil and other surfaces and be ingested through activities, such as hand-to-mouth contact with surfaces where the particles have deposited. Deposited lead also can be resuspended into the air as dust and inhaled. Therefore, past emissions from piston-engine aircraft that deposited to soil and other surfaces can contribute to present-day lead exposures at some locations within and near airports. Lead exposures to workers at airports present another area of concern warranting possible mitigation. For example, the practices and protections of some airport personnel and aircraft technicians may need to be modified to reduce occupational and take-home exposures, for instance, from lead deposits and residue in aircraft engines, oil, and spark plugs. POTENTIAL MITIGATION PATHWAYS Previous chapters of this report identify candidate mitigation pathways that could result in a more holistic approach to addressing lead emissions from piston-engine aircraft and possibly eliminate the problem in the future. Table 7-1 presents the pathways in three categories: airport operations and practices, existing specified fuels and fleet, and new lead-free technologies (fuels and propulsion systems). The table also provides various considerations associated with each pathway. As indicated in Table 7-1, the advent of an unleaded drop-in fuel could greatly reduce or even eliminate aviation lead. However, the formidable technical challenges and associated uncertainties about whether and when such a fuel could be developed and deployed suggest that it should not be relied upon as the sole mitigation measure. This suggests that a multi-pathway approach that pursues lead emission and exposure reductions is needed in which the development of a drop-in fuel proceeds as a part of broader mitigation pathway focused on the development and deployment of lead-free fuels and new propulsion technologies, in combination with mitigation pathways focused on airport operations and practices and on existing fuels and aircraft. Pursued simultaneously, these pathways would differ in their potential to yield near-term reductions in lead emissions and exposures and present different implementation requirements
PREPUBLICATION COPY â Uncorrected Proofs 105 and levels of certainty about effectiveness. However, such a multi-pathway approach that pursues lead reductions in combination is more likely to produce tangible and sustained results. Each of the mitigation pathways considered in Table 7-1 would require the adoption of a range of policies to prompt the participation of pilots; airport owners, managers and personnel; fuel suppliers; and aircraft engine, propulsion, and airframe manufacturers. For some pathways, candidate policy options are easy to identify while, for others, the most suitable policies are difficult to define because they could involve combinations of financial assistance and incentives, regulatory requirements, support for technology research and development, and other potential interventions to motivate and enable the desired response. The steps recommended in this report that are intended to further each mitigation pathway are given next, while recognizing that important differences in the timing of when each will reduce aviation lead and the magnitude and certainty of those reductions are reasons for pursuing them simultaneously.
PREPUBLICATION COPY â Uncorrected Proofs 106 TABLE 7-1 Candidate Pathways for Aviation Lead Mitigation Measures Considerations Airport Operations and Practices Existing Specified Fuels and Fleet New Lead-Free Technologies (FuelsâPropulsion Systems) Aircraft Operations at Airports Pilot and Airport Personnel Practices 100VLL Used by All Aircraft or with Some Using UL94 UL94 Used by Low- Performance Aircraft UL94 in New Aircraft Including High- Performance Aircraft 100+UL in All Aircraft New Propulsion Systems (new aircraft and retrofit some legacy aircraft) Potential Reduction in Lead Exposuresa Small and Variable, depends on individual airport conditions, activity, and hot spots Small and Variable, but could be particularly important for aircraft technicians Up to 20% reduction (could exceed 40% if combined with UL94 use by low- performance aircraft) Up to 30% reduction (could exceed 40% if combined with 100VLL use by all other aircraft) ~0.5% reduction per year 100% reduction ~0.5% reduction per year Time Frame for Lead Reduction Benefits If Started Soon Near-term Near-term Near- to mid- term Mid-term Far-term for appreciable reductions and will require technical advances Unknown, may require technical breakthrough Far-term, pace of reduction depends on cost, rate of innovation, and extent of applicability to GA fleet Focus of Implementation Airport Management FAA Flight Standards, pilot instruction and training Fuel supply chain, especially refiners Fuel supply chain and airports, especially fuel storage and Engine and aircraft makers Fuel supply chain, especially fuel developers; Technology developers, aircraft manufacturers, aircraft owners
PREPUBLICATION COPY â Uncorrected Proofs 107 programs, GA community dispensing capacity engine and aircraft makers Possible Policy Actions for Facilitating Implementation Provide data and tools for analysis and identifying operations changes Provide training and education materials, engage in awareness campaigns Directives and/or incentives, perhaps focused on refiners Incentives and financial assistance for airports to add fueling capacity, eased FAA certification Directives and/or incentives applicable to GA industry Publicâprivate collaborative (PAFI-like) for R&D, testing, and certification R&D support, FAA certification, incentives for aircraft owners to incur expense Main Sources of Uncertainty in Achieving Effective Implementation Variability in airport- specific factors Potential to affect practices Refiner capacity to meet tighter lead specifications Feasibility of adding fuel supply chain (refiners and airports), certification Ability to design suitable engines for all high- performance aircraft Potential to meet fuel performance requirements Rate of innovation, certification challenge, cost and owner interest Ancillary Benefits and Concerns Greater lead awareness and interest in lead-free fuels and propulsion Greater lead awareness and interest in lead-free fuels and propulsion Environmental and health impacts related to other fuel components Changes in pollutants, including greenhouse gases over life cycle a Where percentages are given, they refer to estimates of reductions in lead from the total fuel consumed by the piston-engine fleet.
PREPUBLICATION COPY â Uncorrected Proofs 108 RECOMMENDATIONS Airport Operations and Practices The committeeâs review of FAA-related manuals and handbooks pertaining to flight training, aircraft maintenance, and airport management found scarce mention of lead emissions and exposures as an environmental risk or health hazard nor guidelines for refueling to avoid spills and emissions, ensuring the safe disposal of inspected fuel, and reducing exposures to lead residue when performing aircraft maintenance and repairs. FAA should coordinate its efforts to reduce lead pollution and exposures at airports with those of other federal agencies that have key responsibilities for protecting public health, safety, and the environment at airports, including OSHA as well as EPA. FAA should collaborate with these agencies to explore the regulatory and programmatic means within their respective jurisdictions that can be brought to bear and combined in a complementary manner to reduce lead emissions and exposures at airports (Recommendation 4.1). FAA, in partnership with prominent organizations within the GA community, should initiate an ongoing campaign for education, training, and awareness of avgas lead exposure that is targeted to GA pilots, aircraft technicians, and others who work at airports. Informed by research on the most effective approaches for reaching these audiences, the campaign should be multipronged by ensuring that information on lead risks and mitigation practices is prominent in relevant manuals, guidelines, training materials, and handbooks for pilots, airport managers, and aircraft technicians manuals, guidelines, training materials, and handbooks. Where appropriate, it should also be covered in relevant certification and licensure examinations. In addition, the information should be featured on FAA and GA organization websites and included in written materials distributed at GA industry conferences, tradeshows, and fly-ins (Recommendation 4.2). Airport lead air quality studies have shown that engine run-ups, whereby a pilot confirms shortly before takeoff that the engine is operating safely by briefly bringing the engine up to high power for system checks while the aircraft is stopped, can contribute to significant airborne lead concentrations at designated run-up areas. Maintenance personnel may also perform extensive engine tests at run-up areas. Run-up area planning guidance provided by FAA has not been updated to reflect the results of air quality studies that suggest it may be desirable for airports to move their run-up locations away from being close to where human activities occur (including activities both on-airport and in neighboring communities) and away from high-traffic locations such as runway ends where lead is also emitted from aircraft taking off. FAA should update its guidance on the location of run-up areas to reflect the results of research since the latest interim guidance was issued in 2013, including the need to account for both the emissions of engine run-ups and of takeoffs when analyzing the geographic distribution of lead emissions at the airport. This analysis should support decisions of whether to move run-up areas to reduce peopleâs exposure to lead emissions
PREPUBLICATION COPY â Uncorrected Proofs 109 while also accounting for other concerns including safety and aircraft noise (Recommendation 4.3). Existing Fuels and Fleet While the downward trend in GA activity should yield gradual reductions in lead emissions from avgas consumption, larger reductions will require lower-lead or unleaded fuel alternatives to 100LL. Because the activity of the piston-engine GA fleet has been declining by an average of 1.6 percent per year during the past four decades and is expected by FAA to continue to decline by 0.6 percent per year during the next two decades,1 total lead use by the GA sector is on a modest downward trajectory and projected to be 10 percent lower within 20 years. 100VLL is the only other currently ASTM-specified fuel other than 100LL that could be used by all GA piston-engine aircraft. Fleetwide use of 100VLL, therefore, offers a potential means of reducing total lead emissions from avgas by nearly 20 percent. However, 100VLL is not currently being produced, presumably because there are no regulatory requirements or apparent economic incentives for fuel producers to formulate fuel that can meet the tighter lead ranges in the ASTM standard. At least 57 percent, and perhaps as much as 68 percent, of the current piston-engine fleet could use UL94, which is the only existing grade of unleaded avgas. However, this outcome would require special FAA certifications for some of the aircraft. The eligible fleet consists mostly of smaller, lower-performance aircraft that are not used as frequently as the higher- performance fleet that requires leaded avgas. Therefore, the reduction in leaded fuel use from making UL94 widely available is not likely to be proportional to the large share of lower performance aircraft in the fleet. Nevertheless, if all these aircraft were to use UL94, lead emissions would be reduced by an estimated 30 percent. In addition, if higher-performance aircraft were to use 100VLL, reductions in lead emissions could exceed 40 percent. An unleaded fuel, such as UL94, approved for only part of the piston-engine fleet would require creating a second supply chain and fuel distribution system across the nation. Such a fragmentation of avgas supplies into two grades that are each produced in lower volumes could also lead to higher avgas prices due to the loss of scale economies. Furthermore, the cost for airports to add storage and distribution facilities for a second fuel could be significant and potentially prohibitive, especially for small airports. Consequently, widespread availability of UL94 might be overly optimistic, and more likely to be restricted to a portion of airports that have or can afford to add the required fueling facilities. Automotive gasoline formulations are no longer a viable option for reducing lead emissions from the piston-engine fleet. Thousands of piston-engine aircraft were approved during the 1980s to use automotive gasoline formulationsâloosely called MOGASâthat were then deemed to be safe substitutes for low octane avgas grades (80/87 MON) permitted by the aircraftâs original TCs. However, the composition of automotive gasoline has changed considerably during the past 30 years, particularly including ethanol blends that are not compatible with almost all aircraft engines. 1 See Table 31 of âFAA Aerospace Forecast FY 2020-2040â at https://www.faa.gov/data_research/aviation/aerospace_forecasts.
PREPUBLICATION COPY â Uncorrected Proofs 110 FAA should research public policy options, which could be implemented as quickly as possible at the federal and state levels as well as by Congress, for motivating refiners to produce and airports to supply 100VLL. The objective would be to reduce lead emissions from the entire piston-engine fleet while unleaded alternatives are being pursued for fleetwide use (Recommendation 5.1). FAA should research public policy options that will enable and encourage greater use of available unleaded avgas by the portion of the piston-engine fleet that can safely use it. Possible options include (a) issuing a Special Airworthiness Information Bulletin that will permit such use and (b) providing airports with incentives and means to supply unleaded fuel, particularly airports that are eligible for FAA-administered federal aid as part of the National Plan for Integrated Airport Systems (Recommendation 5.2). A mechanism should be established for facilitating the increased availability of existing grades of unleaded avgas across the fleet of piston-engine aircraft,. Fulfilling that need would likely require congressional involvement, such as by providing incentives for pilots to use existing unleaded avgas and for more small airports to add requisite fuel storage and dispensing capacity (Recommendation 5.3). Future Lead-Free Fuels and Propulsion Systems While a lead-free, high-octane (100+ MON) avgas to fully replace leaded avgas for the entire fleet without requiring changes to aircraft engines would be ideal, it faces many challenges that more than 25 years of research into hundreds of fuel formulations has not been able to address. While several fuel suppliers are actively trying to develop such a fuel, their prospects for success could not be assessed directly in this study because the fuel formulations and testing results are proprietary. It is uncertain when such a fuel can be developed, tested, and accepted, and the costs associated with its adoption and use are not known. The FAA-industry PAFI collaborative represents a systematic and holistic approach for screening, evaluating, and selecting an acceptable unleaded replacement for leaded avgas for fleetwide use, as well as for overcoming certification and other obstacles to the commercialization and widespread introduction of a lead-free alternative. Although it has not yet yielded a viable replacement, PAFI has led to the development of a fuel testing and evaluation process, prompted supplier interest in developing replacement fuels, and sought solutions to the many regulatory, economic, and other practical challenges associated with developing, introducing, and broadly supplying an unleaded replacement fuel. FAA should continue to collaborate with the GA industry, aircraft users, airports, and fuel suppliers in the search for and deployment of an acceptable and universally usable unleaded replacement fuel. The collaboration should be carried out through the Piston Aviation Fuels Initiative PAFI or an alternate holistic process for evaluating all the properties and conditions necessary for production, distribution, and safe use of the fuel, including the use of common test protocols and procedures and by making available the needed testing facilities for the development of the data required to support FAA approvals for the fuel to be used by existing piston-engine aircraft (Recommendation 6.1).
PREPUBLICATION COPY â Uncorrected Proofs 111 Retrofitting current aircraft to enable fleetwide use of currently available unleaded fuels and other lead-free means of propulsion would require incentives to develop new technologies for those aircraft where retrofits do not currently exist. Incentives also would need to motivate large and potentially prohibitive investments by aircraft owners in systems, such as anti- detonation injection, replacing engines along with other critical components, and undergoing costly recertification processes. Tangible success is being demonstrated by aircraft engine makers in creating high- performance gasoline engines that can run on existing unleaded avgas, and innovations (such as diesel, electric, and gas turbine) are showing increasing potential for GA aircraft. Implementing these new technologies can result in the phasing in of aircraft that do not use leaded gas and are not subject to the uncertainty of when fuel alternatives alone can eliminate GA lead emissions, albeit limited by the slow turnover rate in the fleet barring new incentives to change. A clear goal should be established that all newly certified gasoline-powered aircraft after a certain point in time (e.g., within 10 years) are approved to operate with at least one ASTM-specified unleaded fuel. Also, an additional amount of time should be identified by which all newly produced gasoline-powered aircraft, including those currently produced with older type certificates, would attain that same goal. Congressional action to establish the goal and timeframes would ensure achievement of those important results. For example, that congressional action would promote the development of new engine variants compatible with existing unleaded fuels, which could possibly yield prescriptions to support the eventual retrofit of some legacy aircraft and engines as they reach required overhaul milestones (Recommendation 6.2). FAA initiativesâincluding collaborations with industry and other government agencies such as the National Aeronautics and Space Administrationâshould be used to promote the development, testing, and certification of safe and environmentally desirable lead-free emerging propulsion systems (such as, diesel, electric, and jet fuel turbine engine) for use in GA aircraft, including the requisite airport refueling and recharging infrastructure. Congressional encouragement and the provision of resources as required would ensure the success of those initiatives (Recommendation 6.3). Over the coming decades, efforts to reduce GHG emissions from the production and use of transportation fuels may influence the availability and composition of petroleum-based aviation fuels and hasten the introduction of aviation propulsion systems that do not require petroleum. It will be important that the transition to using avgas with lower or no lead content also coordinate with efforts seeking to reduce or eliminate GHG emissions, given the shared concerns with developing and certifying new aircraft technology, the supply and distribution systems for GA aircraft fuels, and broad awareness within the GA community. CONCLUDING COMMENTS There are no known safe lead exposures as measured by blood lead levels; leadâs adverse effects on human health, and particularly on the development of children, are well established. While the elimination of lead pollution has been a U.S. public policy goal for decades, the GA sector
PREPUBLICATION COPY â Uncorrected Proofs 112 continues to be a major source of lead emissions, largely because of the complex challenge of eliminating those emissions that is documented in this report. However, the evidence of lead pollutionâs hazard demands that those challenges not become an excuse for inaction, but instead become the subject of concerted, sustained, and multipronged efforts to find and implement mitigations. It is important to note that EPA has been studying airborne lead concentrations at airports for the past decade to determine whether lead emissions endanger public health or welfare. However, the agency has not yet proposed such a formal determination, positive or negative. Given the uncertainty of this development, CAA-specific regulatory tools were not considered in this study, but if they were to become available, they would almost certainly have a prominent role in a lead mitigation strategy. A key message of this report is that a lead mitigation strategy focused almost entirely on developing an unleaded drop-in fuel that would eliminate aviation lead emissions has a high degree of uncertainty of success given the formidable technical challenges. Additional mitigation measures are available that could be applied in the near and mid-terms to make progress in reducing lead emissions and exposures while other approaches having the potential for much larger impacts are being pursued.