Article Summaries

The FAA's webpage titled "Environment & Airports" provides information on the toxicity of Tetraethyllead (TEL) and measures for airport mitigation regarding lead emissions. According to the FAA, all forms of lead, including TEL, are toxic and can have adverse effects on human health, particularly on the nervous system, red blood cells, cardiovascular system, and immune system. Infants and young children are especially vulnerable to even low levels of lead exposure, which can lead to behavioral problems, learning difficulties, and lower IQ due to their developing nervous systems. In terms of airport mitigation, the FAA outlines short-term strategies to reduce lead emissions from piston-engine aircraft, with the goal of phasing out leaded aviation fuels by the end of 2030. These measures include offering unleaded fuel options, minimizing engine idling and run-up times, increasing awareness among airport personnel and pilots, and relocating run-up areas to reduce public exposure to lead emissions ("Environment & Airports," FAA, 7 Oct. 2022).

Source: "Environment & Airports." FAA, 7 Oct. 2022, https://www.faa.gov/about/initiatives/avgas/env_airports.

=====================================================================================

A Proposed Rule by the Environmental Protection Agency on 10/17/2022

Aircraft in the U.S. predominantly operate on either turbine or piston engines, with the latter mostly utilizing leaded aviation gasoline (avgas). The use of lead, in the form of tetraethyl lead, is crucial for enhancing fuel octane, preventing engine knock, and maintaining compression in engines without hardened valves. There are several types of leaded avgas, such as 100 Octane, 100 Octane Low Lead (100LL), and 100 Octane Very Low Lead (100VLL), with 100LL being the most commonly used. The first introduction of tetraethyl lead in aircraft was in 1927, and it continued to be an essential component in aviation fuel, especially for piston-engine aircraft like Cessna 172 and the Beechcraft Baron G58, until alternatives started gaining prominence. The Department of Energy and FAA provide annual data on avgas supply and consumption, indicating fluctuations and projecting a decrease in leaded avgas consumption by three percent from 2026 to 2041.

Regarding the aircraft themselves, as of 2019, there were around 171,934 piston-engine aircraft in the U.S., including single-engine, twin-engine, and rotorcraft. The activity of these aircraft is mainly centered around general aviation, involving personal, recreational, business, and instructional flying, as well as aerial application in agriculture. From 2012 to 2019, total hours flown by piston-engine aircraft increased by nine percent. While the national consumption of leaded avgas is projected to decrease, the FAA anticipates varied activity across airports, with some experiencing an increase in general aviation activities. The projections for 2045, based on the Terminal Area Forecast, suggest varying levels of increase in general aviation activity at different airports, reflecting the evolving dynamics of aviation activities and fuel consumption in the U.S.

This section focuses on the emissions of lead from piston-engine aircraft and its various forms and impacts. Lead is added to aviation gasoline (avgas) in the form of tetraethyl lead, which is oxidized to form lead oxide during combustion. The lead oxide can accumulate on engine components and damage the engine if it becomes excessive. However, ethylene dibromide in the fuel reacts with lead oxide, forming brominated lead and lead oxybromides, which are emitted with other combustion by-products. Upon cooling, these brominated compounds convert to particulate matter, and lead dibromide particles are confirmed to be the primary form of lead emitted by these engines. In addition, alkyl lead is likely present in the exhaust, and tetraethyl lead, a volatile compound, can partition into the vapor phase. The particle emissions from piston-engine aircraft are comparable to those from diesel passenger car engines and are primarily in the submicron size range, with a mean diameter reported to be 13 nanometers consisting of lead dibromide surrounded by hydrocarbons.

Lead emissions from piston-engine aircraft are significant, being the largest single source of lead to the air in the U.S. since 2008, contributing over 50% of lead emissions to air. In 2017, approximately 470 tons of lead were emitted by piston-powered aircraft engines, accounting for 70% of the annual emissions of lead to air. The EPA has detailed estimations and inventory regarding lead emissions at different administrative levels, from state to county, and airport-specific emissions. At the state level, emissions range from 0.3 to 50.5 tons, and among the approximately 20,000 airports in the U.S., lead inventories range from 0.00005 tons per year to 0.9 tons per year. The EPA's National Emissions Inventory reports estimates of lead emitted in-flight, and these are allocated to states based on the fraction of piston-engine aircraft activity estimated for each state. The contribution of aircraft engine emissions to the total lead emissions in counties with multiple sources of lead ranges from 0.0065 to 99.98 percent. The EPA projects that airport-specific inventories may range from 0.00003 tons to 1.28 tons of lead by 2045, with 656 airports estimated to have inventories above 0.1 tons. Since 1930, piston-engine aircraft have consumed around 38.6 billion gallons of leaded avgas in the U.S., emitting approximately 113,000 tons of lead to the air, excluding the military aircraft usage.