Why Avgas is so BAD

The Problem with Aviation Lead Pollution

Why Aviation Gas is Poisoning Us: The Hidden Dangers of Leaded Fuel

Every day flights take off from various airfields all over the US. These aircraft are incredible, some of them still airworthy from as long ago as 1909! Aviation is one of the most tremendous innovations in transportation in the last 200 years and it shows. We rely on these aircraft to carry supplies all over the world and without them we would be in serious trouble.

In order to make this form of travel safer, the FAA (Federal Aviation Administration) worked to reduce the chance of engine failure by imposing strict standards regarding the characteristics of our operated aircraft. These rules were drafted at a time before many of our modern inventions, and improvements. Focusing on the engine, the FAA worked to keep the system as simple and bullet proof as possible, to reduce chance of failure and increase the ability to service units out in remote locations. In order to guarantee safety these engines required very stable fuel.

Aviation gasoline (Avgas) 100LL (Low Lead) is a type of fuel primarily used in piston-engine aircraft. It was introduced in the 1970s as a lower-lead alternative to the earlier 100/130 aviation gasoline, which contained higher levels of tetraethyl lead (TEL) as an octane enhancer.

The "100" in 100LL refers to the octane rating, indicating that the fuel has a higher resistance to preignition in aircraft engines. The "LL" denotes "Low Lead," as it contains less lead than previous formulations to reduce environmental and health risks.

Despite its reduced lead content, Avgas 100LL is still considered hazardous and is targeted for eventual phase-out. Efforts have been ongoing to develop unleaded alternatives to reduce the reliance on leaded fuel in aviation. However, Avgas 100LL remains widely used due to its compatibility with existing aircraft engines and infrastructure.

  • 100LL Contains Tetraethyl Lead at 0.27 Min/0.53 Max grams Pb/litre [1,2]

    • The EPA ruled that lead exposure from aviation fuel is a serious health risk. [3,4,5]

    • The use of leaded aviation gasoline (avgas) in small aircraft is an outdated practice contributing to widespread pollution. Check out this article from NBC [6]

    • The danger is compounded by proximity to small airports, where communities experience chronic exposure. [6,7]

What Is the Problem with Leaded Aviation Gasoline?

It’s everywhere!

Aircrafts are everywhere. It’s easier to list towns without airports-airstrips than those with, as even the smallest communities frequently have some form of airfield within a short drive.

Everywhere you go, there will be at least some exposure to the emissions generated by this fuel. [10]
This capture was taken from https://globe.adsbexchange.com/ on 3/6/2025 and limited to flights under 10,000 feet.

In addition these aircraft have manual engine fuel mixture controls. [9]

This means that the pilot of each respective aircraft controls the ratio of fuel added to the engine. In a perfect world, pilots would run their engines with the least amount of fuel possible to save gas, but this is not always the case. Some pilots choose to run their engines with more fuel, under the impression that fuel is cheap and the safety margin is worth the extra cost. This means that some aircraft spew significantly more lead emissions than others, making it more difficult to calculate the exact amount of pollutants by each flight.

Some even increase fuel over factory full rich settings during takeoff, increasing the emissions at low altitude [11]

Not all HEPA Filters Will Protect You

Why not all HEPA Filters Can Stop Leaded Dust from Aviation

EPA and the vast majority of outlets state to use a HEPA filter to clean up lead dust. [12]
This method is insufficient to clean up lead dust generated by aircraft! [13]

  • Key Points:

    • Lead Dibromide Particles found in aircraft exhaust are incredibly small and difficult to capture. This study states

      ”High angle annular detector dark field scanning EM revealed irregular particles with a mean diameter of 13 nm consisting of a 4 nm microcrystal of lead dibromide surrounded by a halo of hydrocarbons. In contrast, exhaust particles from an automobile burning leaded fuel averaged 35 nm in diameter and contained 5–10, 4 nm lead beads. Of significant concern, the smaller aircraft particles could penetrate mucosal barriers in the lung and be readily taken up by epithelial cells.”

    • These particles, are 13 nanometers with a 4 nanometer lead crystal.

    • HEPA standard filters filter out “99.97% of particles in the 0.3-micron range” [14]

    • 1 Micron is 1000 Nanometers. HEPA’s rating of 0.3 Micron is 300 Nanometers. This means that a HEPA filter is rated with particles 23X larger than the mean diameter of the emissions from aircraft.

    • Why is this a problem? It is extraordinarily difficult to find specifications on filter standard penetration below 0.3-0.1 microns, as in most applications this is not a noted concern. Some manufacturers state the filter becomes more efficient at lower particle sizes, and other places say the opposite.

    • Even aggressive filters like ULPA Ultra low Particulate Air filters, which capture 99.999% of particles in the 0.1-0.3 micron range, struggle with this as the lowest rating for UPLA appears to be around 100 Nanometers. Still larger than the particles [15] with variable information depending on the specific brand as to the efficiency below this standard.

  • Clarify Misconceptions:
    Many people assume that vacuuming with a HEPA vacuum will eliminate aviation lead dust, but it can actually spread it into the air as it may easily pass through your filter.

The Cost of Changeover: Why We Can’t Ignore It

Unleaded Aviation Gas: The Cost of Switching vs. Keeping the Status Quo

There is no specific universal cost to switching from leaded gas.

  • Key Points:

    • Per this publication from Lycoming, approximately 60% of their engines can run on unleaded avgas without modification. [16]

    • The cost of modifying the remaining fleet varies based on the aircraft/engine combination that was used. This can include installing an electronic ignition system, which is more efficient than the existing fixed timing system and allows for lower grade/alternative fuels. In addition the replacement of fuel lines, seals, and the resealing of fuel tanks may be necessary as some are sealed with a material which is incompatible with alternative fuels. Yet another concern with switching to unleaded is the trouble with some engine’s exhaust valve seating surface, which appears to wear quicker with unleaded fuel. [17]

    • There will be an upfront cost to the modification of the existing fleet. This cost is far less than the cost to our economy and people’s health by continuing to poison. [18,19,20,21][22,23,24]

    • Currently, several companies are in the process of creating a drop in 100LL replacement, which may reduce the expected cost even further.

    • Communities and governments must weigh the cost of public health versus the cost of switching fuels.

    • Read more here: https://esassoc.com/news-and-ideas/2023/08/changing-course-on-aviation-emissions-the-transition-to-unleaded-aviation-gasoline/

Moving Toward Lead-Free Aviation

The ball is already rolling.

  • We must keep it rolling!

    • Unleaded aviation fuel alternatives do exist and are in use in some places.

    • Governments can introduce incentives and regulations that encourage the industry to adopt unleaded alternatives.

    • Local community action can reduce the amount of lead deposited in their community by speaking out and raising awareness.

    • In Alaska, our elected officials are railing against the EPA’s endangerment finding and working to mandate the continued use of this toxic fuel! Read This article on IPEN, and This article from ADN

Conclusion: The Need for Action

The reality of leaded aviation fuel's impact on public health is undeniable, and the consequences are far-reaching. As aircraft continue to fill our skies, the invisible cloud of lead pollution they leave behind is not only contaminating the air we breathe, but also harming all of us as the pollution accumulates. The particles emitted by aircraft engines are so small that even the most advanced filters struggle to capture them, making the situation even more dire. This ongoing exposure, especially near small airports, is a silent and growing crisis that cannot be ignored.

The fact that we still use leaded fuel in aviation, despite the known risks, is an outdated practice that has long outlived its necessity. We have the technology and the alternatives to make a change. The shift to unleaded aviation fuel is not just an environmental or economic issue it's a matter of public health, a matter of life and death. Communities, governments, and industries must weigh the cost of continuing this harmful practice against the health and well-being of billions. The changeover will take investment and time, but the cost of doing nothing is far greater.

It’s time for action. We have the power to protect our future, to ensure cleaner skies, and to safeguard the health of generations to come. The ball is already rolling, and we must keep pushing for a future where leaded aviation fuel is no longer a threat to our children or our own health. Let’s not wait until it’s too late.

1 https://www.exxonmobil.com/en/aviation/products-and-services/products/avgas-100ll
2 https://www.airport-suppliers.com/wp-content/uploads/2021/03/Aviatop-Def-Stan-91-090-Issue-4-2015-AVGAS.pdf
3 https://www.epa.gov/newsreleases/epa-determines-lead-emissions-aircraft-engines-cause-or-contribute-air-pollution
4 https://www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-lead-emissions-aircraft
5 https://www.federalregister.gov/documents/2023/10/20/2023-23247/finding-that-lead-emissions-from-aircraft-engines-that-operate-on-leaded-fuel-cause-or-contribute-to
6 https://www.nbcnews.com/business/business-news/leaded-gas-was-phased-out-25-years-ago-why-are-n1264970
7 https://qz.com/2158594/do-you-live-near-enough-to-a-small-airport-to-have-lead-exposure
8 https://globe.adsbexchange.com/
9 https://www.aopa.org/training-and-safety/students/solo/special/the-fuel-air-mixture
10 https://pmc.ncbi.nlm.nih.gov/articles/PMC5338738/
11 https://www.avweb.com/ownership/the-savvy-aviator-65-whats-your-fuel-flow-at-takeoff/
12 https://www.epa.gov/sites/default/files/2020-10/documents/module_2_key_messages.pdf
13 https://www.sciencedirect.com/science/article/pii/S1309104220301331
14 https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating
15 https://www.escolifesciences.com/news/why-ulpa-filters
16 https://www.lycoming.com/sites/default/files/attachments/SI1070AB%2520Specified%2520Fuels.pdf
17 https://aviationweek.com/business-aviation/safety-ops-regulation/slowly-surely-ga-moves-unleaded-avgas
18 https://www.vox.com/science-and-health/2017/4/27/15424050/us-underreports-lead-poisoning-cases-map-community
19 https://leadelimination.org/economic-productivity-lead-exposure/
20 https://pmc.ncbi.nlm.nih.gov/articles/PMC4984972/
21 https://pmc.ncbi.nlm.nih.gov/articles/PMC2717145/
22 https://www.aviationconsumer.com/uncategorized/unleaded-avgas-whats-this-gonna-cost/
23 https://generalaviationnews.com/2024/05/02/drop-in-unleaded-replacement-for-100ll-expected-to-be-approved-in-late-2025/
24 https://esassoc.com/news-and-ideas/2023/08/changing-course-on-aviation-emissions-the-transition-to-unleaded-aviation-gasoline/
25 Photo by - https://www.jetphotos.com/photo/10197015
26 https://ipen.org/news/lead-aviation-fuel-threatens-public-health