[reactordev]

It states that half of aircraft pollution is from contrails made of aircraft soot.

I’d like to see the literature and discovery of aircraft soot.

As an engineer who has built aircraft, I find this fascinating. I would like to measure my amount of soot. How does one go about measuring how much soot I have?

Obviously if my exhaust ports are black that’s bad but I’m genuinely curious about this as I’ve always assumed “black smoke bad, white smoke ok”. As for contrails, disturbing the atmosphere is going to cause some freezing (clouds) at that altitude, at that temperature. How do you suggest we mitigate that? Fly lower and burn more fuel? Fly less and tell people to take the train or that their package will arrive next week?

[spuz]

It does not state that half of aircraft pollution is from contrails. It says half of the climate impact of aviation is from contrails. Soot can have other effects and cause pollution in other ways such as reducing air quality but I suspect that is very minimal compared to other industries.

The guide presented by the map gives a very good explanation on how contrail formation can be mitigating by altering the course of flights to reduce the formation in areas where it will have the most impact. This is based on a recent study that showed contrail avoidance could be one of the most cost-effective methods of reducing warming that we know of.

https://iopscience.iop.org/article/10.1088/2634-4505/ad310c

Simon Clark did a good video on this recently:

https://www.youtube.com/watch?v=QoOVqQ5sa08

[reactordev]

>The CO2 emitted by aircraft only causes about half the climate impact of aviation. The other half comes from contrails— artificial clouds that are created by soot in the engine exhaust.

Then what does that mean?

I find it strange. Clouds happen naturally. Contrails are mini clouds (literally a cloud chamber), are we saying that all those “chemtrails” are pollution?

Or are we saying the unspent fuel particulate inside that they formed around is?

This is where this bizarro science is going off the deep end for me. As any object traveling through the atmosphere at that altitude, disrupting air, is going to form condensation and cloud trails. The more moisture in the atmosphere, the more trails. Sure there’s a little bit of unspent kerosene particles but hardly enough to even be a glycerin on a well working engine.

Are we suggesting changing flight routes and wasting more fuel (which pollutes more) to protect the ground from these 0.0000001% reduction in light cloud trails? Seriously. I want to know the science behind how this plays out.

I’m all for shutting down the black exhaust engines and cleaning up how we produce thrust. I’m all for that. This argument that clouds cause pollution is just wacky.

What about wingtips. Those cause trails (though not as pronounced as the engines turning at 12,000rpm), those contain no particulates and yet, they exist. Atmospheric science can explain a lot of what you see at 30,000ft (10,000m). This all sounds like NIMBY science posturing and pseudo-science to me.

[counters]

> I find it strange. Clouds happen naturally. Contrails are mini clouds (literally a cloud chamber), are we saying that all those “chemtrails” are pollution?

Estimating radiative forcing is about measuring relative to a baseline. Here, the baseline is a world with no contrails. When you introduce contrails, you're introducing cloudy volumes predominantly made of ice crystals and occurring very high in the atmosphere. On the balance, these clouds re-emit more long-wave radiation (e.g. what' emitted by the Earth's surface) than they allow to escape the atmosphere.

Hence, these clouds have a small but positive net radiative forcing - meaning that aviation, by the way it leads to contrail formation, has at least this small radiative forcing on climate.

> As any object traveling through the atmosphere at that altitude, disrupting air, is going to form condensation and cloud trails. The more moisture in the atmosphere, the more trails.

Actually - it won't. We rigorously started studying contrail formation back in WWII when meteorologists tried to anticipate when bomber flights returning from mainland Europe might induce contrails and leave a path for intercept fighters to follow and shoot them down. As the science and understanding of vertical atmosphere thermodynamic structure and cloud microphysical structure has advanced in the ensuing 80 years, we have a much better understanding of when contrails are likely to form, versus when they aren't.

But don't take my word for it. Look up at the sky any time you hear an aircraft - sometimes you'll see a contrail, sometimes you won't. Contrails aren't a given when a jet flies high in the atmosphere.

(that's actually the entire basis for the Contrails/DeepMind team's work - avoid areas where contrails _are_ likely to form, to avoid that radiative forcing from the first part of this comment)

> Are we suggesting changing flight routes and wasting more fuel (which pollutes more) to protect the ground from these 0.0000001% reduction in light cloud trails? Seriously. I want to know the science behind how this plays out.

The science is pretty well developed at this point. You'd probably hit it in an undergraduate-level physical meteorology class. The missing detail that the Contrails team helped solve was improving forecasts of the key parameters involved here from weather models.

The whole point is that this is _another_ lever that flight planners could use to optimize their route planning. It's just one factor. It has trade-offs - although those trade-offs aren't always net negative (e.g. it's not a given that the "less contrail-y" route is also the "more fuel burn-y" one).

[reactordev]

Finally some science, ok cool. So we're basing this on the baseline of no contrails what-so-ever. We measure the radiative photons? of the light refracting? through it and see it's long-wave radiation channeling properties scatter it rather than allow it through to relieve the earth's heat?

As for contrails, if they're likely to form in certain areas and not others, what's that coefficient? is it the moisture content? is it the jet fuel mixture? Since you say the Contrails program helps predict when these might occur, is that data being used to alter cruise paths?

It's been 20 years since I was a student at College so forgive me when I ask these questions. My grandfather flew bombers and my father flew fighters so I've known about exhaust and pollution from aircraft for a long time. I know the older aircraft pollute and the contrails from bombers (my grandfather had some stories) were an awful mix of frozen water vapor and diesel exhaust. Modern commercial jets are a lot more efficient.

Any route (with the exception of the SIDS and STARS) is charted across airways to the most direct route possible. Right?

[spuz]

The link to the paper I gave is the latest research on contrails and the potential effect of contrail mitigation and answers all the questions you have asked here. The video I gave boils all that information down into an easily digestible format. It honestly baffles me that you start your reply with "Finally some science" when the very same information was already provided to you. If you want to reply to my comment without digging into the links I shared then you should specify that you haven't had a chance to look into them.

[counters]

> Finally some science, ok cool. So we're basing this on the baseline of no contrails what-so-ever. We measure the radiative photons? of the light refracting? through it and see it's long-wave radiation channeling properties scatter it rather than allow it through to relieve the earth's heat?

There are many different avenues you could pursue to estimate this, with different degrees of complexity and they all boil down to a radiative transfer calculation. You could start with an idealized, single-column model using a very simple approximation like a 2-stream approach, crudely parameterizing how a few bulk properties of a cloud in the column would influence the estimate of radiative balance at the top of the atmosphere. Such a model would let you explore a huge variety of factors.

To get more into the world of "real climate", you'd eventually scale up to an atmosphere model with a more complex 3D radiative transfer scheme, probably with more complex cloud microphysical representation and interactions with radiation. This still lets you do idealized experiments.

The next step up, you'd do what the DeepMind and Contrails teams have done, which is to use a standard Earth System Model ("climate model"). That just builds the complexity, and allows you to study realistic scenarios with counterfactuals (e.g. with or without additional contrail formation due to aviation). It's still going to be parameterized in some sense.

Ultimately, we'd look at real-world data top-of-atmosphere radiative estimates, which we conveniently measure from a variety of satellites (CERES would be the most well-known one). The problem is that we can't study the counter-factual very easily in the real world. We get a few isolated cases (like the aviation pause over CONUS after 9/11, or the global decrease in aviation during COVID), but there's so much inherent noise (from weather) that it's hard to infer any causality; you'd likely end up using that climate model from the last part to simulate the counterfactual in a weather scenario nudged to reproduce the real-world observations you have.

This would make a great Masters thesis, or maybe a slice of a PhD, but it's not much more complex than that.

> As for contrails, if they're likely to form in certain areas and not others, what's that coefficient? is it the moisture content? is it the jet fuel mixture? Since you say the Contrails program helps predict when these might occur, is that data being used to alter cruise paths?

It's the ambient thermodynamic and kinematic parameters. Namely, background water vapor and temperature, combined with local kinetic energy in the form of turbulence that you need to drive very local supersaturation. Given those parameters, different distributions of gases and particulates emitted from a jet engine may be more or less effective at nucleating ice - if the conditions are even right to do so.

It's worth pointing out that it's _very_ hard to capture these background conditions in weather models, hence why a major part of the DeepMind/Contrails project have been to use machine learning to try to constrain background circulation patterns most consistent with contrail develop as evidenced by high-resolution remote sensing and imagery. Some of the earliest work they did was to use these types of tools to generate data that allow us to better parameterize contrail formation in numerical weather/climate models, which is why they're able to turn this into a predictive and actionable problem.

Otherwise, there's an 80-year literature on this topic. I encourage you to read it. Kärcher's review paper in Nature in 2018 is a good starting point (https://www.nature.com/articles/s41467-018-04068-0).

> Any route (with the exception of the SIDS and STARS) is charted across airways to the most direct route possible. Right?

I'm not an expert in aviation route planning, but from personal experience I know that many other factors come into play with routing (namely avoiding weather, limiting time spent extremely remote / far away from airport or other infrastructure, traffic / network congestion, etc).

[reactordev]

This is why I love HN. My god man, thank you. I’ll have to look into this more.

[roxolotl]

Fly less. Is waiting a week for a package really that big of a deal? Is traveling less really that much to ask?

It’s totally ok to be skeptical of the claims. I can’t make a judgement on them as I know even less than you might. But that’s not a reason to doubt that human’s environment impact matters and that maybe part of the solution is for those of us with access to 2day delivery for everything and cheap flights live a teeny bit more like those who don’t.

[nephihaha]

There is a big anti-tourism movement being built up across the world which is also being pushed by mass media. In Barcelona and Venice this has turned physical in a few instances. Flying is going to be made more expensive in the near future, I've no doubt of it. The environmental lobby will call for it.

By the way, I have not flown for over a decade. I can't stand airports...

[zamalek]

> Is traveling less really that much to ask?

I'm currently on dating apps and the amount of people who define their personalities by their travel habits is staggering.

[chrneu]

lol thanks for saying this. "Travel" and "dogs" make up a crazy amount of dating profiles. Like 60% maybe? It's nuts. It's really weird.

then you look at most of their profiles and it's the same handful of tourist photos or them paying to take a photo, basically. travel is just another status symbol thing to a lot of people. they do the same things they see on social media. it's weird. it's just another way of showing how much money you can spend on frivolous* stuff. "30 countries by 30" and stuff like that.

the dog version of it is huskies. every one has a husky in their apartment. there are like 3-4 breeds that every woman in a city/urban area has. so weird.

*not saying travel is frivolous. I'm saying the modern stereotypical version of it is very conforming and repetitive.

the annoying thing is if someone were to ever say, in the real world, that maybe this version of travel isn't worth the damage to the environment, they would most likely get labeled an asshole or something. a "downer" or someone who is a "hater", or they are "ruining the vibe". more and more often "the vibe" is just an excuse to engage in crazy excess consumption that we label as "self care".

lol sorry to go off on this. it's just so weird how we've twisted these things around as a culture/society.

[harddrivereque]

It is easy to suggest to fly less but it is going to be impossible to convince society where core values include agressive "extra" consumption, which in turn is the backbone of the world's current economy. Flying is one of top "extra" consumption types out there. I know many people are trying to convince people of that, but the society is moving in the opposite direction - bigger cars (both us and eu), more travel. Maybe arguments used currently are not convincing enough? I mean, sure, keep trying and you will obviously reach a certain 0.00x% of the population, but that's not really going to make any difference

[JKCalhoun]

The general way to affect public habits (whether it works or not) is to apply a "sin tax" to that activity.

[mavhc]

Just tax everything the amount it costs to clean up the pollution it causes, then use that money to clean up the pollution, now everything will have the correct price including externalities

[counters]

The general point here is that your individual behavior as a consumer likely doesn't impact this mechanism. An aircraft doesn't skip a flight just because you waited a week to go on vacation. Aviation infrastructure is something of a fixed-cost which would likely only respond to systemic changes in travel demand, economic impacts on maintenance or fueling, or possibly some other form of regulation (e.g. a penalty for inducing contrails).

[somat]

but contrails are not made of soot, where I define soot as dark unburned carbon, contrails actual are made of water. There is also a highly likely chance I am being to literal and the word choice of soot was a bit of poetic license on the part of the author.

As a bonus consideration it might be better if they were made of soot, it would be ugly but water vapor is a tremendous greenhouse gas, several times as potent as CO2, soot blocking the sun might have more of a neutral effect, And related, we worked hard to get sulfur out of our fuels but sulfur dioxide turns out to be a negative greenhouse gas, it has a net cooling effect, I am not saying we should deliberately add sulfur back in, the downsides are too great, but it is an interesting bit of irony.

[bird0861]

The water is actually ice crystals and the ice crystals form around the soot.

[wolttam]

There is also an immense amount of water vapour being produced by the combustion of a hydrocarbon.

[counters]

Sure, but water vapor doesn't spontaneously transition to a liquid and accrete onto surfaces - there needs to be a super-saturation of water vapor, and given the temperatures of jet exhaust, that's not trivial to achieve. However, the super-saturation needed for water vapor to deposit onto surfaces as ice is much lower, hence the preference for ice crystal nucleation.

[ant6n]

Night trains

[baobun]

What would make you say such a thing?

[tzs]

> As for contrails, disturbing the atmosphere is going to cause some freezing (clouds) at that altitude, at that temperature. How do you suggest we mitigate that? Fly lower and burn more fuel? Fly less and tell people to take the train or that their package will arrive next week?

See this article: https://www.technologyreview.com/2024/03/12/1089620/how-rero...

Here are some highlights, in case the paywall is a problem for some.

First, how much do contrails matter?

> This cirrus-forming phenomenon could account for around 35% of aviation’s total contribution to climate change—or about 1% to 2% of overall global warming, according to some estimates

> A small fraction of overall flights, between 2% and 10%, create about 80% of the contrails. So the growing hope is that simply rerouting those flights could significantly reduce the effect, presenting a potentially high leverage, low cost and fast way of easing warming.

Breakthrough Energy, Google Research, and American Airlines conducted a test:

> They employed satellite imagery, weather data, software models, and AI prediction tools to steer pilots over or under areas where their planes would be likely to produce contrails. American Airlines used these tools in 70 test flights over six months, and subsequent satellite data indicated that they reduced the total length of contrails by 54%, relative to flights that weren’t rerouted

Avoiding the contrail prone regions would use more fuel, so the question is how much would it cost to avoid those regions?

> A new study published in Environmental Research: Infrastructure and Sustainability explored this issue by coupling commercial tools for optimizing flight trajectories with models that simulated nearly 85,000 American Airlines flights, both domestic and international, under various weather conditions last summer and this winter.

> In those simulations, the researchers found that reducing the warming effect of contrails by 73% increased fuel costs by just 0.11% and overall costs by 0.08%, when averaged across those tens of thousands of flights. (Only about 14% of the flights needed to be adjusted to avoid forming warming contrails in the simulations.)

There are also a couple of other factors to consider, such as:

> There are also some thorny complications that still need to be resolved, like the fact that cirrus clouds can also reduce warming by reflecting away short-wave radiation from the sun.

> The loss of this cooling effect would have to be tallied into any calculation of the net benefit—or, perhaps, avoided. For instance, Shapiro says the initial strategy might be to reroute flights only during the early evening and night, which would eliminate the sunlight-reflecting complication.

Another one is the the increased fuel will add to CO2 to the atmosphere. CO2 stays in the atmosphere a lot longer than water, so it is possible that reducing contrails would be a net positive in the short term but a net negative over the long term.