In 2020, Dr. Ruan and his team unveiled their creation: a type of white paint that can act as a reflector, bouncing 95 percent of the sun’s rays away from the Earth’s surface, up through the atmosphere and into deep space. A few months later, they announced an even more potent formulation that increased sunlight reflection to 98 percent.
...
The paint’s properties are almost superheroic. It can make surfaces as much as eight degrees Fahrenheit cooler than ambient air temperatures at midday, and up to 19 degrees cooler at night, reducing temperatures inside buildings and decreasing air-conditioning needs by as much as 40 percent. It is cool to the touch, even under a blazing sun, Dr. Ruan said. Unlike air-conditioners, the paint doesn’t need any energy to work, and it doesn’t warm the outside air.
...
He calculated that if materials such as Purdue’s ultra-white paint were to coat between 1 percent and 2 percent of the Earth’s surface, slightly more than half the size of the Sahara, the planet would no longer absorb more heat than it was emitting, and global temperatures would stop rising.
...
Still, there are concerns. The standard version of Purdue’s ultrawhite paint uses barium sulfate, which has to be mined, driving up its carbon footprint, though Dr. Ruan noted that titanium dioxide, which is used in the vast majority of commercial paints, also has to be mined.
I'm calling bullshit here. As far as I know, the basic laws of thermodynamics will not allow to sustain a state like this. The heat energy of the ambient air will inevitably migrate into the...
It can make surfaces as much as eight degrees Fahrenheit cooler than ambient air temperatures
I'm calling bullshit here. As far as I know, the basic laws of thermodynamics will not allow to sustain a state like this. The heat energy of the ambient air will inevitably migrate into the painted surface, heat it up, and even out the temperature difference into an equilibrium.
doesn’t warm the outside air
Again, I'm sceptical. If 98 % of the heat energy is reflected, what happens to the rest? It will be absorbed, in the process will heat up the surface, and then be emitted as IR waves, heating up the air above the surface.
It's good to be skeptical, but a major reason so many cities (E.g. Chicago) have been making huge strides lately in reducing their local urban heat island is due to simple changes in the...
It's good to be skeptical, but a major reason so many cities (E.g. Chicago) have been making huge strides lately in reducing their local urban heat island is due to simple changes in the reflective properties of the materials used in large surfaces (roads, pavement, roofing, etc). So a highly reflective paint like this is likely to help with that even more.
Are they sensational? AFAIK cooler than ambient air temp passive surfaces are possible to achieve with high enough albedo and infrared emissivity. And this isn't a new concept. See:...
Are they sensational? AFAIK cooler than ambient air temp passive surfaces are possible to achieve with high enough albedo and infrared emissivity. And this isn't a new concept. See: https://en.wikipedia.org/wiki/Radiative_cooling
Mechanism
Infrared radiation can pass through dry, clear air in the wavelength range of 8–13 µm. Materials that can absorb energy and radiate it in those wavelengths exhibit a strong cooling effect. Materials that can also reflect 95% or more of sunlight in the 200 nanometres to 2.5 µm range can exhibit cooling even in direct sunlight.
So I guess I'm just not seeing what the issue is. cc: @h6nry
You don't have to convince me, I'm not disagreeing with you. I'm not informed enough on the topic to make any statements, so I won't. Yes, as far as you know. And as far as h6nry knows, or knew at...
You don't have to convince me, I'm not disagreeing with you. I'm not informed enough on the topic to make any statements, so I won't.
AFAIK cooler than ambient air temp passive surfaces are possible
Yes, as far as you know. And as far as h6nry knows, or knew at the time of commenting, a paint that cools below ambient air temp as a result of direct sunlight is a wild claim on the level of perpetual motion.
Furthermore, this is a NY Times article; not exactly scientifically-exhaustive journalism. If I read claims that seem to violate the fundamentals of reality in The NY Times, I'm probably going to write it off as sensational bullshit too.
Fair enough. I guess they're one of the Ten Thouand today, and I shouldn't have assumed it was common knowledge. But as to your own question about linking to more in-depth articles, why does every...
And as far as h6nry knows, or knew at the time of commenting, a paint that cools below ambient air temp as a result of direct sunlight is a wild claim on the level of perpetual motion.
Fair enough. I guess they're one of the Ten Thouand today, and I shouldn't have assumed it was common knowledge.
But as to your own question about linking to more in-depth articles, why does every source need to be scientifically exhaustive? Not everyone wants to read (or is capable of understanding) scientifically exhaustive articles, or research papers, which is why popular science/general audience articles exist. And worth noting is that the Purdue anouncement, as well several other related resources, are directly linked to in the NYT article... so if someone wanted to look into the topic further after reading it, they quite easily can by following those links.
I feel that "unscientific" sources in a science discussion are a waste of everyone's time. We're all going to translate the journalistic flair into digestible, actionable logic anyway, so why not...
I feel that "unscientific" sources in a science discussion are a waste of everyone's time. We're all going to translate the journalistic flair into digestible, actionable logic anyway, so why not skip that step and go directly to the research?
I can speak only for myself, and I would much rather get a link to a science journal than a diluted magazine article. I'm interested in the facts, I want to understand the concept; it would be pretty inefficient to read anything other than the research.
And I can only speak for myself (based on my experience posting on social media), and I think that linking to scientific journals is often a waste of time, since so few people are actually...
And I can only speak for myself (based on my experience posting on social media), and I think that linking to scientific journals is often a waste of time, since so few people are actually interested in reading studies, often can't actually access them in the first place since many are hard paywalled, and/or are incapable of understanding them (myself included in many cases). :P
So for spreading awareness about issues, and helping inform the general public about new scientific developments, they're far less effective. Popsci articles and videos aren't perfect, but they're a better entry point for the vast majority of people. And the whole reason science communication exists as a career and field is because of that.
What are we talking about here, exactly? You're speaking in very broad terms. I'm referring to science discussions in science forums like this one. Presumably, people read posts here because they...
What are we talking about here, exactly? You're speaking in very broad terms. I'm referring to science discussions in science forums like this one. Presumably, people read posts here because they are interested in science. Presumably, those people are more likely to glean understanding from the research than from something watered-down for accessibility. In places like ~science and on posts like these, much of the discussion revolves around extracting facts from the jazzy article (case in point, this very thread).
I think non-scientific publications often do a disservice to the actual science. That doesn't mean I'm discounting science communication or insisting that everyone become an expert on any topic that interests them. There is a balance to be struck between the raw research and presenting that research in a manner that laypeople can grasp, I recognize that. I just feel that media sources, more often than not, butcher the science in their presentation of it.
This isn't a science forum... it's a group on a general interest aggregation site meant to house all science related topics; A group that everyone who joins Tildes is automatically subscribed to....
This isn't a science forum... it's a group on a general interest aggregation site meant to house all science related topics; A group that everyone who joins Tildes is automatically subscribed to. And sure, some people will probably prefer reading studies here, and are capable of accessing and understanding them. However, I guarantee you that the vast majority of people subscribed here would generally prefer more laymen digestible articles. Studies do still get posted here occasionally too, and there are no rules against that. But there is no rule about them being the only sources allowed here either. ~science isn't /r/science.
I think non-scientific publications often do a disservice to the actual science... I just feel that media sources, more often than not, butcher the science in their presentation of it.
For the record, I agree. But at the same time, without them, most people wouldn't ever hear about most new scientific advancements. And if only studies were allowed to be posted here the majority of users would probably just unsubscribe from this group. But thankfully they don't need to, and we can have the best of both worlds, since both types of content can be posted. And people also often link to the actual studies in the comments of more general audience intended articles (which the top comment in this topic has done). And if people don't understand or misunderstand either then they can simply ask, and others who do understand them can try to clear things up in the comments for everyone.
Did you read the section on Nocturnal surface cooling from that Wikipedia page on radiative cooling? Admittedly, I’m no expert but to me the principles for that phenomenon explains how cooling...
Did you read the section on Nocturnal surface cooling from that Wikipedia page on radiative cooling?
Admittedly, I’m no expert but to me the principles for that phenomenon explains how cooling from this highly reflective paint work.
Unintuitive, sure. But not a wild claim on the level of perpetual motion.
I'm pretty sure cooler than air temperatures have already been achieved by DIY people. So long as you are putting more energy out into the environment than the air is adding back in you can...
I'm pretty sure cooler than air temperatures have already been achieved by DIY people. So long as you are putting more energy out into the environment than the air is adding back in you can maintain a temperature lower than air.
It seems to violate thermodynamics, but at the end of the day it's just putting its energy out in a form that doesn't interact with the air around it so it goes out into space.
and then be emitted as IR waves, heating up the air above the surface.
That's the thing, these panels are designed to emit infrared radiation that doesn't interact with the air. It's a wavelength that just passes through the atmosphere.
Seems like every year there's some new invention that's gonna undo anthropogenic climate change, or make it better in some way, and every year it goes nowhere. Still waiting on all that bacteria...
Seems like every year there's some new invention that's gonna undo anthropogenic climate change, or make it better in some way, and every year it goes nowhere. Still waiting on all that bacteria that's gonna eat the microplastics in the ocean
How much of that ambient heat is only there because it radiated from surfaces that had absorbed it from the sun? Quite a bit (pdf). How much of it came from condenser units that displaced the heat...
As far as I know, the basic laws of thermodynamics will not allow to sustain a state like this. The heat energy of the ambient air will inevitably migrate into the painted surface, heat it up, and even out the temperature difference into an equilibrium.
How much of that ambient heat is only there because it radiated from surfaces that had absorbed it from the sun? Quite a bit (pdf).
How much of it came from condenser units that displaced the heat inside of the building (heat that wouldn't be there in the first place if the albedo of the surfaces was higher)?
Ok, so just going through this thread, the paper, the article and all, it took a while for everything to click into place for me. I'm very much with you as far as calling BS goes; the phenomena...
Ok, so just going through this thread, the paper, the article and all, it took a while for everything to click into place for me. I'm very much with you as far as calling BS goes; the phenomena involved here are a bit subtle and deviate from the first-order approximations that help a lot in explaining the world.
Firstly: Every material that emits a wavelength must also absorb that wavelength. If you want to build the optimal night time radiator, charcoal black is a good color to start with because it absorbs almost everything and can thus emit in a broad band of wavelengths. Unfortunately, it'll get wicked hot at daytime.
Now... we're all probably used to thinking of absorption primarily in shades of grey, and not in terms of color or spectra. This is where we run into trouble, because if the absorption/emission isn't wavelength-specific, there is no way a surface could actually turn cooler-than-ambient. This is where my bullshit meter peaked. Assuming wavelength independence, this isn't possible because either you absorb a ton of energy, but can radiate it, or you reflect the energy, but also can't radiate it. Either way you won't be cooler-than-ambient. But you can engineer a surface to be highly absorbent and radiative in the IR, while being highly reflective in the visible. The result is a surface that outright rejects almost all energy coming in, but it has a window in the spectrum in which to emit excess energy. It's probably almost black in this spectrum, to aid emission, and it's probably a spectrum chosen for a relatively low intensity of ambient radiation, which means the absorption doesn't matter too much. Additionally, this spectrum is definitely chosen such that the air doesn't absorb this IR light, which means it can leave all the way to space, not heating up the ambient air much.
On conservation of energy, it does raise alarms as well, as you could theoretically drive a perpetually moving heat engine using this paint. But, that's so far been predicated upon either outer space or the sun being there to absorb or emit heat. If we remove that and put this paint into a ambient-temperature room (i.e. a closed system), I expect all spooky effects to stop and everything in the room to equalize at one temperature.
Regarding science journalism, I'd like to see less fluff in these articles and more critical thinking from authors. Not saying this didn't happen, but it isn't evident. I'd like articles that, when presented with the claims made here, drill deep enough to dispel the magic. It's perhaps unnecessary to read all the relevant papers, but enough to address common questions like "how does this not break X principle" or "are these numbers even plausible?". I've experienced it too many times now that there's very common questions that scientifically literate members of the general public will have about such a piece that are both (a) entirely reasonable questions for an outsider and (b) probably common knowledge among experts. This kind of expert-layman communication is what we pay journalists for, and I've often found that to be lacking in mainstream science journalism. Independent creators seem to get this right more frequently, perhaps because they can elaborate more because of matters of format.
Here's the published paper on their advancements: https://www.cell.com/cell-reports-physical-science/fulltext/S2666-3864(22)00352-6 Seems like a massive improvement. Being able to mix it with an...
Seems like a massive improvement. Being able to mix it with an acrylic base and apply like normal paint is much better than the thick and brittle coatings that were needed in previous papers (and in DIY formulations)
The only frustrating bit is that the secret sauce, the Boron Nitride nanoplatelets are only available from a 3rd party: "PCTP2 hBN nanoplatelets were acquired from Saint Gobain Advanced Ceramics, LLC"
When I stayed in Mykonos all the construction is smooth white plaster. The buildings we stayed in were organic shapes rather than squares and right angles, and every was white and cool....
I wish the article had more details on what potential applications there are from using this kind of paint, specifically. They say that regular paint reflects 80-90% of sunlight. Seems like......
I wish the article had more details on what potential applications there are from using this kind of paint, specifically. They say that regular paint reflects 80-90% of sunlight. Seems like... pretty much most of way there? Given the hypothetical that we would need to cover 1-2% of the earth with this super reflective paint to equalize warming, that's basically the same as 1.1-2.2% of coverage with regular paint, pretty much a rounding error given that the estimate is probably quite rough to begin with.
I can imagine this kind of thing should be useful for certain applications where you're trying to minimize heating of an object, but it seems like regular white paint ought to be fine if the idea is to paint large numbers of roofs and other exposed surfaces. Kind of interesting that this topic is still hanging around. I remember when Obama's energy secretary suggested we paint roofs white to combat global warming over 10 years ago, then nothing happened.
I’m not an expert on this subject by any means. Wasn’t a big problem about climate change related to the pollution we put in the atmosphere creating a greenhouse effect which keeps the heat inside...
I’m not an expert on this subject by any means.
Wasn’t a big problem about climate change related to the pollution we put in the atmosphere creating a greenhouse effect which keeps the heat inside our atmosphere?
So with that being said, even if we could deflect the heat, wouldn’t it still be trapped on earth and thus not change anything?
Again, I’m not even slightly an expert, I just down understand how this helps rather than push the problem elsewhere in the world.
I'm not an expert either, but here's my understanding. Although some of the reflected light would be absorbed by particles in the atmosphere, some of the energy should also escape the earth. Like...
I'm not an expert either, but here's my understanding. Although some of the reflected light would be absorbed by particles in the atmosphere, some of the energy should also escape the earth. Like when you see a photograph of the earth from space, all the light that goes into the camera sensor is energy that has escaped the earth. So if you painted every roof in a city white, that city should look brighter when viewed from space because more energy is going into space. I have no idea if the economics would make this a net benefit since it would take a lot of energy and resources to paint everything, but that's the idea.
Also there's the point about air conditioning that was already mentioned.
The greenhouse effect's strength is granular, not binary. It's not that heat cannot escape at all, but simply that more of it is retained than usual. Without any greenhouse effect at all, we'd be...
The greenhouse effect's strength is granular, not binary. It's not that heat cannot escape at all, but simply that more of it is retained than usual. Without any greenhouse effect at all, we'd be quite chilly. If it kept it in with 100% effectiveness, we'd fry in no time. The Earth is between those extremes, and industrialization has added more insulation than we're "supposed" to have, causing climate change.
There's more to it when you get into what wavelengths interact with what that I sure don't remember from my childhood Earth Science classes, but I think that's the core of your misunderstanding...any additional bouncing lets more escape.
cc @Benson I just found a nice little graphic of the processes involved on wikipedia: https://en.wikipedia.org/wiki/Atmospheric_window In this figure, the thin blue curve up top is what earth is...
In this figure, the thin blue curve up top is what earth is supposed to radiate theoretically. The solid blue area right below it is what of that actually makes it through the atmosphere. The difference is explained by the gray "absorption" curve. Where the absorption curve is imperfect, IR radiation can leave.
Below you can find the absorption curves of all the individual relevant gases. Most of it is water vapor, while carbon dioxide and methane contribute much less. Most of the greenhouse effect is good for us, and the amount of water in the atmosphere is hard to influence anyway. But we see here why more CO2 would be worse: CO2 mostly absorbs wavelengths that are left untouched by other gases.
Any we also see why what Purdue is doing to passively cool things works: Their paint emits mostly 10 micrometer wavelength light. Which is right in that big blue band of transparency. It won't get scattered back down, because the atmosphere is transparent to it. Naturally occuring IR radiation will at least in part be absorbed; that's the difference between the two blue curves from the beginning.
Thanks, that actually makes lots of sense to me now. I was too fixated on the bounce happening one way for light. Didn’t consider to would also bounce back out again haha
Thanks, that actually makes lots of sense to me now.
I was too fixated on the bounce happening one way for light. Didn’t consider to would also bounce back out again haha
If the emitted light passes through the atmosphere, it would also pass through the CO2. Absorption and emission works upon very specific wavelengths for any given atom/structure. CO2 contributes...
If the emitted light passes through the atmosphere, it would also pass through the CO2. Absorption and emission works upon very specific wavelengths for any given atom/structure. CO2 contributes to global warming my absorbing more of a spectrum than the atmosphere without CO2 does.
But if you're emitting light at a frequency that co2 does not interact with, it'll just go right out.
Part of what happens is that heat in buildings and roads keeps the area around them warm so if they're absorbing less heat even if that heat does go somewhere else we then emit less by not needing...
Part of what happens is that heat in buildings and roads keeps the area around them warm so if they're absorbing less heat even if that heat does go somewhere else we then emit less by not needing to run the AC as hard or as long.
Essentially yeah you're right the heat stays around but if it's not around us we don't need as much as and fans.
What's the lifespan of the reflectivity? And how well does it hold up to exposure to the elements? I'm assuming that rain, dust, and pollution are all going to lower the efficacy of this paint, so...
What's the lifespan of the reflectivity? And how well does it hold up to exposure to the elements? I'm assuming that rain, dust, and pollution are all going to lower the efficacy of this paint, so how often will it need to be re-applied?
...
...
...
I'm calling bullshit here. As far as I know, the basic laws of thermodynamics will not allow to sustain a state like this. The heat energy of the ambient air will inevitably migrate into the painted surface, heat it up, and even out the temperature difference into an equilibrium.
Again, I'm sceptical. If 98 % of the heat energy is reflected, what happens to the rest? It will be absorbed, in the process will heat up the surface, and then be emitted as IR waves, heating up the air above the surface.
It's good to be skeptical, but a major reason so many cities (E.g. Chicago) have been making huge strides lately in reducing their local urban heat island is due to simple changes in the reflective properties of the materials used in large surfaces (roads, pavement, roofing, etc). So a highly reflective paint like this is likely to help with that even more.
See also:
https://en.wikipedia.org/wiki/Reflective_surfaces_(climate_engineering)
I don't think they were arguing any of that, just calling out sensational claims.
Are they sensational? AFAIK cooler than ambient air temp passive surfaces are possible to achieve with high enough albedo and infrared emissivity. And this isn't a new concept. See: https://en.wikipedia.org/wiki/Radiative_cooling
So I guess I'm just not seeing what the issue is. cc: @h6nry
You don't have to convince me, I'm not disagreeing with you. I'm not informed enough on the topic to make any statements, so I won't.
Yes, as far as you know. And as far as h6nry knows, or knew at the time of commenting, a paint that cools below ambient air temp as a result of direct sunlight is a wild claim on the level of perpetual motion.
Furthermore, this is a NY Times article; not exactly scientifically-exhaustive journalism. If I read claims that seem to violate the fundamentals of reality in The NY Times, I'm probably going to write it off as sensational bullshit too.
If I'm sharing science news, I link to the most reputable source I can find. In this case, why not Purdue's own article? Or perhaps this one, from 2021.
Here's the research in full: https://docs.lib.purdue.edu/coolingpubs/376
Fair enough. I guess they're one of the Ten Thouand today, and I shouldn't have assumed it was common knowledge.
But as to your own question about linking to more in-depth articles, why does every source need to be scientifically exhaustive? Not everyone wants to read (or is capable of understanding) scientifically exhaustive articles, or research papers, which is why popular science/general audience articles exist. And worth noting is that the Purdue anouncement, as well several other related resources, are directly linked to in the NYT article... so if someone wanted to look into the topic further after reading it, they quite easily can by following those links.
I feel that "unscientific" sources in a science discussion are a waste of everyone's time. We're all going to translate the journalistic flair into digestible, actionable logic anyway, so why not skip that step and go directly to the research?
I can speak only for myself, and I would much rather get a link to a science journal than a diluted magazine article. I'm interested in the facts, I want to understand the concept; it would be pretty inefficient to read anything other than the research.
And I can only speak for myself (based on my experience posting on social media), and I think that linking to scientific journals is often a waste of time, since so few people are actually interested in reading studies, often can't actually access them in the first place since many are hard paywalled, and/or are incapable of understanding them (myself included in many cases). :P
So for spreading awareness about issues, and helping inform the general public about new scientific developments, they're far less effective. Popsci articles and videos aren't perfect, but they're a better entry point for the vast majority of people. And the whole reason science communication exists as a career and field is because of that.
What are we talking about here, exactly? You're speaking in very broad terms. I'm referring to science discussions in science forums like this one. Presumably, people read posts here because they are interested in science. Presumably, those people are more likely to glean understanding from the research than from something watered-down for accessibility. In places like ~science and on posts like these, much of the discussion revolves around extracting facts from the jazzy article (case in point, this very thread).
I think non-scientific publications often do a disservice to the actual science. That doesn't mean I'm discounting science communication or insisting that everyone become an expert on any topic that interests them. There is a balance to be struck between the raw research and presenting that research in a manner that laypeople can grasp, I recognize that. I just feel that media sources, more often than not, butcher the science in their presentation of it.
This isn't a science forum... it's a group on a general interest aggregation site meant to house all science related topics; A group that everyone who joins Tildes is automatically subscribed to. And sure, some people will probably prefer reading studies here, and are capable of accessing and understanding them. However, I guarantee you that the vast majority of people subscribed here would generally prefer more laymen digestible articles. Studies do still get posted here occasionally too, and there are no rules against that. But there is no rule about them being the only sources allowed here either. ~science isn't /r/science.
For the record, I agree. But at the same time, without them, most people wouldn't ever hear about most new scientific advancements. And if only studies were allowed to be posted here the majority of users would probably just unsubscribe from this group. But thankfully they don't need to, and we can have the best of both worlds, since both types of content can be posted. And people also often link to the actual studies in the comments of more general audience intended articles (which the top comment in this topic has done). And if people don't understand or misunderstand either then they can simply ask, and others who do understand them can try to clear things up in the comments for everyone.
You have an interesting knack for talking around a point.
How about we agree to disagree, eh? Have a good weekend.
Did you read the section on Nocturnal surface cooling from that Wikipedia page on radiative cooling?
Admittedly, I’m no expert but to me the principles for that phenomenon explains how cooling from this highly reflective paint work.
Unintuitive, sure. But not a wild claim on the level of perpetual motion.
I was making a point, nothing more.
I'm pretty sure cooler than air temperatures have already been achieved by DIY people. So long as you are putting more energy out into the environment than the air is adding back in you can maintain a temperature lower than air.
It seems to violate thermodynamics, but at the end of the day it's just putting its energy out in a form that doesn't interact with the air around it so it goes out into space.
That's the thing, these panels are designed to emit infrared radiation that doesn't interact with the air. It's a wavelength that just passes through the atmosphere.
https://www.youtube.com/watch?v=dNs_kNilSjk&t=2836
And this guy has a way to do it with common ingredients
https://www.youtube.com/watch?v=KDRnEm-B3AI&t=26
Seems like every year there's some new invention that's gonna undo anthropogenic climate change, or make it better in some way, and every year it goes nowhere. Still waiting on all that bacteria that's gonna eat the microplastics in the ocean
How much of that ambient heat is only there because it radiated from surfaces that had absorbed it from the sun? Quite a bit (pdf).
How much of it came from condenser units that displaced the heat inside of the building (heat that wouldn't be there in the first place if the albedo of the surfaces was higher)?
Ok, so just going through this thread, the paper, the article and all, it took a while for everything to click into place for me. I'm very much with you as far as calling BS goes; the phenomena involved here are a bit subtle and deviate from the first-order approximations that help a lot in explaining the world.
Firstly: Every material that emits a wavelength must also absorb that wavelength. If you want to build the optimal night time radiator, charcoal black is a good color to start with because it absorbs almost everything and can thus emit in a broad band of wavelengths. Unfortunately, it'll get wicked hot at daytime.
Now... we're all probably used to thinking of absorption primarily in shades of grey, and not in terms of color or spectra. This is where we run into trouble, because if the absorption/emission isn't wavelength-specific, there is no way a surface could actually turn cooler-than-ambient. This is where my bullshit meter peaked. Assuming wavelength independence, this isn't possible because either you absorb a ton of energy, but can radiate it, or you reflect the energy, but also can't radiate it. Either way you won't be cooler-than-ambient. But you can engineer a surface to be highly absorbent and radiative in the IR, while being highly reflective in the visible. The result is a surface that outright rejects almost all energy coming in, but it has a window in the spectrum in which to emit excess energy. It's probably almost black in this spectrum, to aid emission, and it's probably a spectrum chosen for a relatively low intensity of ambient radiation, which means the absorption doesn't matter too much. Additionally, this spectrum is definitely chosen such that the air doesn't absorb this IR light, which means it can leave all the way to space, not heating up the ambient air much.
On conservation of energy, it does raise alarms as well, as you could theoretically drive a perpetually moving heat engine using this paint. But, that's so far been predicated upon either outer space or the sun being there to absorb or emit heat. If we remove that and put this paint into a ambient-temperature room (i.e. a closed system), I expect all spooky effects to stop and everything in the room to equalize at one temperature.
Regarding science journalism, I'd like to see less fluff in these articles and more critical thinking from authors. Not saying this didn't happen, but it isn't evident. I'd like articles that, when presented with the claims made here, drill deep enough to dispel the magic. It's perhaps unnecessary to read all the relevant papers, but enough to address common questions like "how does this not break X principle" or "are these numbers even plausible?". I've experienced it too many times now that there's very common questions that scientifically literate members of the general public will have about such a piece that are both (a) entirely reasonable questions for an outsider and (b) probably common knowledge among experts. This kind of expert-layman communication is what we pay journalists for, and I've often found that to be lacking in mainstream science journalism. Independent creators seem to get this right more frequently, perhaps because they can elaborate more because of matters of format.
Here's the published paper on their advancements: https://www.cell.com/cell-reports-physical-science/fulltext/S2666-3864(22)00352-6
Seems like a massive improvement. Being able to mix it with an acrylic base and apply like normal paint is much better than the thick and brittle coatings that were needed in previous papers (and in DIY formulations)
The only frustrating bit is that the secret sauce, the Boron Nitride nanoplatelets are only available from a 3rd party: "PCTP2 hBN nanoplatelets were acquired from Saint Gobain Advanced Ceramics, LLC"
any idea on what happens to that stuff after its life span? Will it be another "forever" chemical?
When I stayed in Mykonos all the construction is smooth white plaster. The buildings we stayed in were organic shapes rather than squares and right angles, and every was white and cool. http://3.bp.blogspot.com/-VEUDT1Ts_lM/UZNJCLqTHCI/AAAAAAAAD6M/nucNpV5k_fc/s1600/Mykonos-Greece.jpg
My point being we know white painted things can keep places cool, I’m not sure we need special paint to do this.
I wish the article had more details on what potential applications there are from using this kind of paint, specifically. They say that regular paint reflects 80-90% of sunlight. Seems like... pretty much most of way there? Given the hypothetical that we would need to cover 1-2% of the earth with this super reflective paint to equalize warming, that's basically the same as 1.1-2.2% of coverage with regular paint, pretty much a rounding error given that the estimate is probably quite rough to begin with.
I can imagine this kind of thing should be useful for certain applications where you're trying to minimize heating of an object, but it seems like regular white paint ought to be fine if the idea is to paint large numbers of roofs and other exposed surfaces. Kind of interesting that this topic is still hanging around. I remember when Obama's energy secretary suggested we paint roofs white to combat global warming over 10 years ago, then nothing happened.
I’m not an expert on this subject by any means.
Wasn’t a big problem about climate change related to the pollution we put in the atmosphere creating a greenhouse effect which keeps the heat inside our atmosphere?
So with that being said, even if we could deflect the heat, wouldn’t it still be trapped on earth and thus not change anything?
Again, I’m not even slightly an expert, I just down understand how this helps rather than push the problem elsewhere in the world.
I'm not an expert either, but here's my understanding. Although some of the reflected light would be absorbed by particles in the atmosphere, some of the energy should also escape the earth. Like when you see a photograph of the earth from space, all the light that goes into the camera sensor is energy that has escaped the earth. So if you painted every roof in a city white, that city should look brighter when viewed from space because more energy is going into space. I have no idea if the economics would make this a net benefit since it would take a lot of energy and resources to paint everything, but that's the idea.
Also there's the point about air conditioning that was already mentioned.
The heat isn't deflected, it's emitted in a wavelength that passes through the atmosphere and leaves the planet, which would help global warming
But don’t greenhouse gases reflect it back down to earth again?
The greenhouse effect's strength is granular, not binary. It's not that heat cannot escape at all, but simply that more of it is retained than usual. Without any greenhouse effect at all, we'd be quite chilly. If it kept it in with 100% effectiveness, we'd fry in no time. The Earth is between those extremes, and industrialization has added more insulation than we're "supposed" to have, causing climate change.
There's more to it when you get into what wavelengths interact with what that I sure don't remember from my childhood Earth Science classes, but I think that's the core of your misunderstanding...any additional bouncing lets more escape.
cc @Benson
I just found a nice little graphic of the processes involved on wikipedia:
https://en.wikipedia.org/wiki/Atmospheric_window
In this figure, the thin blue curve up top is what earth is supposed to radiate theoretically. The solid blue area right below it is what of that actually makes it through the atmosphere. The difference is explained by the gray "absorption" curve. Where the absorption curve is imperfect, IR radiation can leave.
Below you can find the absorption curves of all the individual relevant gases. Most of it is water vapor, while carbon dioxide and methane contribute much less. Most of the greenhouse effect is good for us, and the amount of water in the atmosphere is hard to influence anyway. But we see here why more CO2 would be worse: CO2 mostly absorbs wavelengths that are left untouched by other gases.
Any we also see why what Purdue is doing to passively cool things works: Their paint emits mostly 10 micrometer wavelength light. Which is right in that big blue band of transparency. It won't get scattered back down, because the atmosphere is transparent to it. Naturally occuring IR radiation will at least in part be absorbed; that's the difference between the two blue curves from the beginning.
Thanks, that actually makes lots of sense to me now.
I was too fixated on the bounce happening one way for light. Didn’t consider to would also bounce back out again haha
If the emitted light passes through the atmosphere, it would also pass through the CO2. Absorption and emission works upon very specific wavelengths for any given atom/structure. CO2 contributes to global warming my absorbing more of a spectrum than the atmosphere without CO2 does.
But if you're emitting light at a frequency that co2 does not interact with, it'll just go right out.
Part of what happens is that heat in buildings and roads keeps the area around them warm so if they're absorbing less heat even if that heat does go somewhere else we then emit less by not needing to run the AC as hard or as long.
Essentially yeah you're right the heat stays around but if it's not around us we don't need as much as and fans.
Oh right, I hadn’t considered the power consumption from things like air conditioning. So this is still a positive thing to do it sounds like.
What's the lifespan of the reflectivity? And how well does it hold up to exposure to the elements? I'm assuming that rain, dust, and pollution are all going to lower the efficacy of this paint, so how often will it need to be re-applied?