Reducing the impact of lead emissions at airports

2. Leaded Gasoline Issues

This chapter summarizes information regarding issues with Pb directly and indirectly related to airport lead emissions. The information in this chapter is intended to be integrated into the airport guidance document and the public outreach materials that will be developed.

1. Health Impacts from Lead Exposure

Exposure to Pb can lead to a variety of adverse health impacts, including neurological effects in children that lead to behavioral problems, learning deficits, and lowered IQ.¹ Pb accumulates in the body in blood, bone, and soft tissue because it is not readily excreted. Pb affects the kidneys, liver, nervous system, and blood-forming organs; the U.S. Environmental Protection Agency (EPA) also considers Pb to be a probable human carcinogen.
Human exposure to Pb occurs primarily through inhalation and ingestion, with the health effects being same regardless of the route of exposure. People can be exposed to aircraft Pb emissions from the inhalation pathway and potentially through ingestion of deposited lead.
The concentration of Pb in blood (PbB) is the metric generally used to define exposure to Pb. Research^2,3 has shown that PbB is significantly associated with mean ambient Pb concentrations. Other studies^4,5 have shown that the use of leaded gasoline accounted for more than 50 percent of PbB in children and that the concentration of Pb in gasoline is directly proportional to PbB. The Centers for Disease Control (CDC) and the World Health Organization (WHO) have previously identified PbB concentrations of 10 micrograms per deciliter or higher as a “level of concern” to human health.^6,7

CDC no longer uses the “level of concern”, however, and instead now uses a new “reference level” to identify children with blood levels that are above normal levels. This reference level is based on the highest 2.5% of the U.S population of children (ages 1-5 years). The reference level has been set at 5 micrograms per deciliter.¹

2. U.S. Standards for Airborne Lead Concentrations

Concerns regarding adverse health effects associated with exposure to airborne Pb resulted in its classification as an air pollutant pursuant to the Clean Air Act in 1976. This was followed in 1978 by EPA’s requisite enactment of a health-based National Ambient Air Quality Standard (NAAQS) for Pb, which was set at 1.5 microgram per cubic meter based on a quarterly-average concentration.
In October 2008, EPA promulgated a revised Pb NAAQS that lowered the acceptable level by an order of magnitude, to 0.15 micrograms per cubic meter based on a rolling three-month average concentration. In December 2014, EPA issued a proposed rulemaking in which it reaffirmed its position that the existing Pb NAAQS of 0.15 micrograms per cubic meter is set appropriately to protect public health.²

3. Addition of Lead to Gasoline

The use of Pb as a gasoline additive, primarily in the form of tetraethyl lead (TEL), began in the 1920s. TEL increases the octane rating of gasoline.³ The availability of higher octane gasoline allows for the design of high compression ratio engines which provide greater power and fuel efficiency compared to engines with lower compression ratios. Use of TEL as a gasoline additive was transformative to the transportation engine and fuel industries during the twentieth century.⁴

4. Elimination of Lead from Motor Gasoline

Concerns regarding ambient Pb concentrations and the adoption of vehicle emission standards necessitating the use of catalytic converters which are poisoned by Pb resulted in EPA’s promulgation of regulations requiring the phase-out of Pb from gasoline used in on-road vehicles, referred to as motor gasoline (MOGAS), beginning in the mid-1970s. These regulations required major gasoline retailers to begin selling at least one grade of unleaded MOGAS by July 1, 1974.¹
In order to accommodate the elimination of Pb from gasoline, vehicle engines required redesign, and special gasoline nozzle and vehicle fill-pipe designs were needed to prevent the introduction of Pb-containing gasoline into vehicles designed for use with unleaded fuel.
By 1988, the amount of Pb consumed in MOGAS in the United States was reduced by 99 percent compared to peak levels in the 1970s.² Leaded MOGAS was completely phased out by 1990 in Canada and by 1996 in the U.S.³

5. Use of Lead in Aviation Gasoline

Key design considerations for piston-engines used in aircraft include maximizing the work performed per volume of fuel consumed and optimizing the power to weight ratio of the engine—both of which are facilitated by higher compression ratio engines, which in turn necessitate the use of high octane gasoline. As a result, aviation gasolines (AVGAS) have long contained relatively high levels of TEL. In addition, due to aircraft safety concerns,⁴ aircraft engines have not been subject to government emission standards that require the use of catalytic convertors. Therefore, there has not been the same impetus to remove Pb from AVGAS as there was to remove Pb from MOGAS. For perspective, the FAA has reported that about 99.4% of U.S. Registered Piston-Engine aircraft in 2010 used a grade of AVGAS.
Despite the continued use of leaded AVGAS, Pb emissions related to AVGAS use have declined over time for two reasons. The first reason was the introduction of 100 octane “low-lead” (100 LL) fuel, which halved the maximum allowable lead content from 4.22 to 2.11 grams of lead per gallon. The second reason is the decline in AVGAS consumption over time. This decline is shown in Figure 1, which illustrates the trend in domestic AVGAS consumption product supplied (i.e., consumption) as reported by the
Figure 1
U.S. Aviation Gasoline Consumption

Source: U.S. Energy Information Administration. www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=pet&s=mgaupus2&f=a

EIA.¹ While these data show a 61 percent reduction in AVGAS consumption since 1981, EIA forecasts AVGAS consumption will remain at approximately 4.4 million barrels per year for the foreseeable future.²

Research focused on the development of unleaded AVGAS has been going for years. Currently, the FAA is continuing with an evaluation program to identify a suitable lead-free replacement for 100LL that addresses both gasoline quality and flight safety needs.³ Multiple phases of aircraft testing are proposed, and a 2018 timeframe for publishing American Society for Testing Materials (ASTM) specifications for the unleaded replacement gasoline is estimated. Although there are specifications for a 100 octane “very low lead” (VLL) AVGAS that lowers the allowable lead content by about 20% relative to 100LL, it appears that 100LL will be the dominant AVAGS until if and when an unleaded AVGAS becomes commercially available.

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