Leaded emissions from piston engine aircraft pose a significant health threat

August 29, 2016 by Mark Dwortzan
Collectively, piston-engine aircraft like this Cirrus SR-22T constitute the nation’s largest remaining source of lead emissions. Credit: Travis Air Force Base/Flickr

They may seem innocuous enough, those small planes used for weekend getaways, flight training, small freight deliveries, and other civilian purposes. But collectively, the more than 167,000 piston-engine aircraft that comprise the majority of the U.S. general aviation (GA) fleet may pose a significant health threat. That's because these vehicles, which rely on leaded fuel to operate safely, constitute the nation's largest remaining source of lead emissions. Those exposed to low levels of lead, especially children, have been shown to suffer neurological and cognitive impairment, including IQ loss.

Unlike commercial airliners, which do not use leaded fuel, and automobiles, which went all-unleaded by 1995, piston-driven GA aircraft account for about half of anthropogenic lead emissions in U.S. skies. But just how much of an impact is this airborne lead having on the nation's public health and economy? To answer that question, a team of MIT researchers has conducted the first assessment of the nationwide annual costs of IQ losses that can be attributed to aviation lead emissions.

The team found that each year, these IQ losses result in about $1 billion in damages from lifetime earnings reductions, with an additional $0.5 billion in economy-wide losses due to decreases in labor productivity. Its findings appear in the journal Environmental Science and Technology.

"Regulations have brought about a dramatic reduction in lead exposure for the U.S. population over time, but childhood lead exposure is associated with decreased academic achievement and IQ loss even at low blood lead levels," says Philip Wolfe, a postdoc in the MIT Laboratory for Aviation and the Environment, and lead author of the paper. "This study not only provides an estimate of the costs of these effects, but also is the first to look at how these damages have feedback loops in the economy. It shows that emissions today will continue to have an impact for decades."

Conducted by researchers affiliated with the Joint Program on the Science and Policy of Global Change, the Center for Environmental Health Sciences and the Laboratory for Aviation and the Environment, the study is unique in its inclusion of lead emissions incurred not only on takeoff and landing, but also during the cruise phase of GA flights. Previous investigations of GA-based focused primarily on health impacts at local airports and regions, and did not explore economic damages.

"This study shows that even minor sources of toxic pollutants can have a major health and economic impact," says Noelle Selin, an associate professor in the MIT Institute for Data, Systems and Society and Department of Earth, Atmospheric and Planetary Sciences, and one of two faculty co-authors (along with associate professor of aeronautics and astronautics Steven Barrett) of the study. "Our results underscore the need to assess carefully the implications of exempting certain sectors or specific uses from regulations on harmful substances."

To obtain their results, the researchers developed an inventory of general aviation emissions across the continental U.S., and modeled its impact on atmospheric lead concentrations using the Community Multi-Scale Air Quality Model (CMAQ). Based on these GA-specific contributions to overall atmospheric levels, they quantified associated IQ deficits nationwide and their annual economic impacts. They estimated annual losses in lifetime earnings potential using earnings data from the U.S. Department of Labor's Bureau of Labor Statistics, and annual losses in labor productivity using a Joint Program computational general equilibrium model called USREP, which models the U.S. economy.

Efforts to curb leaded emissions from GA aircraft have been underway for at least a decade. Petitioned by the environmental nonprofit group Friends of the Earth (FoE) in 2006 to address the problem of leaded emissions from GA aircraft, the Environmental Protection Agency proposed limiting such emissions in 2010, but has yet to issue a ruling. The FoE claims that 70 percent of GA planes could switch to unleaded fuel without retrofitting. Toward that end, the Federal Aviation Administration aims to certify and distribute an unleaded replacement fuel by 2018.

Explore further: NASA charges toward greener aviation with novel concepts

More information: Philip J. Wolfe et al. Costs of IQ Loss from Leaded Aviation Gasoline Emissions, Environmental Science & Technology (2016). DOI: 10.1021/acs.est.6b02910

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MR166
2.9 / 5 (9) Aug 29, 2016
Where is the empirical evidence? Atmospheric and environmental lead and mercury levels have plummeted since the 50s yet the collective IQ of the US appears to have gone down during the same period. If the IQs have not gone down certainly general ignorance has gone up.
tinitus
Aug 29, 2016
This comment has been removed by a moderator.
MR166
4 / 5 (1) Aug 29, 2016
Tinitus I think that the power to weight ratio of diesel vs gas is the deciding answer.
F111F
3.9 / 5 (7) Aug 29, 2016
MR166 has a valid point. This source: http://www.gama.a...wRes.pdf Shows the vast majority, about 99% of GA aircraft, are not flying in any given hour. (13,206,000 hours flown in 2012 / 143,160 GA aircraft X 365 X 24). It does mean, on average, about 1,507 hours are being flown every hour of every day by piston aircraft. Given the sheer size of the United States and the volume of air above it, not sure how the (comparatively) miniscule addition of lead from piston exhaust could even be measurable.
Edit: I can't say 1,507 aircraft are flying each hour, on average, because some are two piston engine aircraft...so somewhere just south of 1,500 probably.
krundoloss
3.3 / 5 (7) Aug 29, 2016
This article is speculation upon speculation, yet we should find a way to remove lead from any fuel that is used near populated areas.

The slow reduction in IQ Worldwide is thought to be the result of more relaxed school standards in the USA and Russia since the cold war era, in addition to the tendency of less intelligent people to have more children, and more intelligent people to have less children.

Who needs a high IQ when you can just google everything?
antialias_physorg
3.3 / 5 (7) Aug 29, 2016
it, not sure how the (comparatively) miniscule addition of lead from piston exhaust could even be measurable.

Wow, you didn't even read the article and then made a pronouncement. Way to go. You, sir, are truly a scholar amongst scholars.
MR166
3.2 / 5 (6) Aug 29, 2016
What unadulterated BS! It is the diminishing IQs and standards of our teachers that is of 1000x more troubling than anything caused by leaded aviation fuel.
MR166
3 / 5 (6) Aug 29, 2016
The sad fact is that the socialist welfare state has eliminated Darwinian selection. The US is plunging headlong towards the prediction made by the movie "Idiocrasy" .

http://www.imdb.c...0387808/

This movie is a must see for anyone curious about our future society.
skystare
4 / 5 (4) Aug 29, 2016
Tinitus and MR166, Diesels can and have been built lightly enough for aircraft use and are a terrific idea, with excellent fuel consumption and long life. General Aviation is however, a very conservative industry (understandably, re safety) and the amount of engineering and certification expense for a new class of engine is almost prohibitive, especially for a market this small.
Fortunately, three-quarters of lightplane engines will run happily on unleaded regular autofuel and a fair number of the rest can use unleaded premium, so the sooner the FAA can mandate this, the better.
MR166
5 / 5 (3) Aug 29, 2016
"What unadulterated BS! It is the diminishing IQ and standards of our teachers that is 1000x more troubling than anything caused by leaded aviation fuel.

( What could be more humiliating than a grammatical error in a sentence criticising teachers? )
RichManJoe
2.6 / 5 (5) Aug 29, 2016
Plus, they are a major source of noise polution.
MR166
3 / 5 (6) Aug 29, 2016
This article really does reflect poorly upon our academic system. Since when has worrying about nothing become a noteworthy accomplishment?
MR166
3 / 5 (4) Aug 29, 2016
I am just guessing here, but I am willing to bet that there is some sort of FAA rule that requires the use of leaded gas. Change the rule and pilots would be more than happy to use the much cheaper automotive fuel if it is suitable for their aircraft.

I suppose that the ethanol added to automotive gas could be a real problem also.
Eikka
4.2 / 5 (5) Aug 29, 2016
it, not sure how the (comparatively) miniscule addition of lead from piston exhaust could even be measurable.

Wow, you didn't even read the article and then made a pronouncement. Way to go. You, sir, are truly a scholar amongst scholars.


Even according to the article's figures, the lifetime impact for the average American from the loss of IQ and productivity is about $5.

That's such a small number that it's very very doubtful that any such effect can actually be measured empirically. Even if you followed everyone to the second of their lives, you couldn't tell the difference whether their performance over a lifetime was five dollars better or worse.

$1.5 Billion over a lifetime in an economy with a GDP of $18 Trillion a year is truly a small number. It's approximately one part per million.
24volts
3.5 / 5 (4) Aug 29, 2016
Shut down a large cargo ship for a couple of days and you have taken out more pollution out of the air than all the small airplanes put out in a year. If people really want to reduce pollution then the large cargo ships should be nuclear powered.

I know a couple of pilots and they would be very happy to be able to use regular gas in their small planes. Aviation gas is really overpriced.
nilbud
1 / 5 (2) Aug 29, 2016
Look at the amount of ammo being bought in the US and calculate how much atomised lead is being inhaled from that source. Compared to that it doesn't matter in the slightest about a few planes.
googol
3.7 / 5 (3) Aug 29, 2016
MR166, average IQ has risen over the last 50 years due to the Flynn Effect, the causes of which are heavily debated and contentious, but there's certainly not strong evidence that this rise has stopped on average, let alone reversed and declined.
MR166
3.7 / 5 (3) Aug 29, 2016
"MR166, average IQ has risen over the last 50 years due to the Flynn Effect......."

Well I suppose that that is open to debate.

http://www.huffin...846.html
Eikka
5 / 5 (2) Aug 29, 2016
"MR166, average IQ has risen over the last 50 years due to the Flynn Effect......."

Well I suppose that that is open to debate.

http://www.huffin...846.html


" Reaction time reflects a person's mental processing speed, and so is considered an indication of general intelligence."

That's patently absurd, because reflex reactions don't have anything to do with cognitive effort. They're automated responses, and anyone with the need to can train themselves to it without any sort of intelligence required. Consider, if reaction time were indicative of intelligence, martial artists and twitch gamers would all be members of Mensa.

As far as intelligence goes, working memory (not rote memory) is a better indicator.
ab3a
5 / 5 (3) Aug 29, 2016
It's not quite clear for me, why the https://en.wikipe...l_engine aren't already widely used in avionic industry.


Certification costs are a big part of the equation. Maintenance costs are another. Also most small airports do not offer Jet-A for sale, never mind the cold weather anti-gel additives. Furthermore, these engines cost more. Jet-A is not significantly cheaper than AvGas, and it is possible to rebuild a gasoline engine, but not the Diesel engines.

Are those reasons enough for you?
ab3a
5 / 5 (4) Aug 29, 2016
It is also worth noting that unleaded AvGas is being certified now. The FAA has spent an eternity working on it because

1. It should not destroy gasket materials currently in use
2. It should provide sufficient detonation margins so that turbocharged aircraft can use it. Leaded gas provides Motor Octane ratings of 130 or more.
3. It should be able to tolerate a wide temperature and altitude changes without gelling up or boiling off additives.
4. The price should be reasonable.

In other words, they're looking for a good substitutes. A substitute has been found, and is undergoing certification tests.

I would love to see something replace TetraEthylLead. I hate cleaning spark plugs and valve guides. But if it eats the sealants and gaskets of the aircraft engine, that's a non-starter.
Telekinetic
not rated yet Aug 29, 2016
"What unadulterated BS! It is the diminishing IQ and standards of our teachers that is 1000x more troubling than anything caused by leaded aviation fuel.

( What could be more humiliating than a grammatical error in a sentence criticising teachers? )

If you're not from England, then you misspelled "criticizing".
Eikka
5 / 5 (1) Aug 30, 2016
never mind the cold weather anti-gel additives


There's scant few additives that prevent clouding/gelling if you got wax in the diesel. That's why automotive diesel isn't really suitable for airplanes - it's been formulated for better lubricity for the high pressure injection pumps in car engines, and for low cost, rather than cold weather performance. If you put aviation kerosene in a modern car diesel engine, it seizes up the injection system.

The winter/arctic quality diesel is an entirely different formulation that shouldn't be blended with summer diesel because the waxes still come out of solution at low temperature. It's a perennial problem when the weather turns cold and people are left with blocked fuel filters.

and it is possible to rebuild a gasoline engine, but not the Diesel engines.


Why not? Sounds dubious.
Eikka
5 / 5 (1) Aug 30, 2016
One actual problem with diesel engines in aviation is that if you get air in the fuel lines, the whole fuel system should be purged before starting the engine again. It won't just run rough for a moment, it will cut the whole engine and fail to start.

If the air bubble reaches the injection pumps, it will cause havoc because the pump will try to compress the air and that can make it ignite within the fuel line.
antialias_physorg
5 / 5 (1) Aug 30, 2016
Plus, they are a major source of noise polution.

Is it really that bad? Maybe close to an airport...but it's a long time since I thought "man, that tiny plane is really disturbing my peace and quiet"

average IQ has risen over the last 50 years

Average IQ is always 100. That's how IQ is defined. People may get smarter or dumber - but average IQ always stays the same.
ab3a
not rated yet Aug 30, 2016
and it is possible to rebuild a gasoline engine, but not the Diesel engines.


Why not? Sounds dubious.


I'm not really sure, but I suspect liability is a significant factor. Similar rules exist for smaller marine diesels too.

A runaway diesel on the ground is an expensive nuisance. However in boats and aircraft the risk of fire or sinking from damage is significant. In aircraft, the propeller is usually attached directly to the drive shaft or perhaps with a gearbox, but there is no clutch. Overspeeding a propeller can easily tear the blades off of the hub, and the resulting imbalance could tear the aircraft engine off of its mounts.

This would result in a severely imbalanced airplane that probably will not be able to fly.

Thus, I suspect a hard and fast one-time limit is the only way that lawyers and engineers can arrive at a liability agreement.
Eikka
not rated yet Sep 01, 2016
A runaway diesel on the ground is an expensive nuisance.


A runaway diesel is usually caused by oil leaks through the crankcase breathing tube that is connected to the intake, which enables the engine to ingest its own oil and run on that. The breathing tube is there for emissions reasons and to keep a slight negative pressure in the sump to stop oil leaks and scavenge piston ring blowby gasses etc.

Another common cause is a leaking turbo that spills oil in the intake.

In an airplane engine the tube doesn't necessarily need to be there, and in trucks and other equipment that are in danger of running off, there's a special choke flap or a "hunger bung" that blocks the intake and starves the engine.
Shootist
1 / 5 (1) Sep 04, 2016
Leaded emissions from piston engine aircraft pose a significant health threat


Cow pies. The number of piston driven aircraft are insignificant.
ThomasQuinn
1 / 5 (1) Sep 04, 2016
Plus, they are a major source of noise polution.

Is it really that bad? Maybe close to an airport...but it's a long time since I thought "man, that tiny plane is really disturbing my peace and quiet"

average IQ has risen over the last 50 years

Average IQ is always 100. That's how IQ is defined. People may get smarter or dumber - but average IQ always stays the same.


Median IQ = 100. Not average.
Eikka
not rated yet Sep 09, 2016
Median IQ = 100. Not average.


Median is an average. With IQ, the median and the mean are the same by definition because the scores are normalized to a gaussian distribution.

To say that average IQ has risen is meaningless. You can only compare the raw scores between different times of measurement, and say that e.g. the cohort of 30 year olds get higher raw scores than the same cohort ten years ago. That means you're taking old raw scores and seeing what IQ score they would produce in comparison to all the tested 30-year-olds of today.

The issue with IQ tests is that they test cultural assumptions almost as much as they test any supposed intelligence, so the Flynn effect is more plausibly explained by the fact that more people are getting academic education and taught to think alike the people who design the test and designate the "right" answers.

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