Can you make contrails with just ice nuclei, and what would that look like?

Hama Neggs

Senior Member.
Mick West said:
Well smoke is essentially a "fine powder", and it creates skywriting that looks initially like a contrail. But you can't make the mile wide and 50 mile long trails we see. And something that actually starts out as a powder (like in the powder contrail generator) would probably have a particle size too large to stay up very long. But then I've never seen a trail of powder as far as I know. Maybe there's some aerial application that uses powder?

A current CT claim is that it is "nano-particles" which are being "sprayed" an it is that which creates what WE call contrails, which THEY call "chemtrails". It got me wondering whether that has any merit. Can the mere introduction of condensation nuclei trigger a contrail?
 
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MikeC

Closed Account
A current CT claim is that it is "nano-particles" which are being "sprayed" an it is that which creates what WE call contrails, which THEY call "chemtrails". It got me wondering whether that has any merit. Can the mere introduction of condensation nuclei trigger a contrail?

That is exactly what contrails are AFAIK - the introduction of ice nucleation particles into a super-saturated atmosphere.

There is invariably miuch more water in such an atmosphere than the engine itself generates, so the large majority of any persistent contrail is water that has been precipitated due to those particles.
 

Hama Neggs

Senior Member.
That is exactly what contrails are AFAIK - the introduction of ice nucleation particles into a super-saturated atmosphere.

There is invariably miuch more water in such an atmosphere than the engine itself generates, so the large majority of any persistent contrail is water that has been precipitated due to those particles.
Yes, that's a given, but what about particles without added moisture from combustion?
 

MikeC

Closed Account
Yes they do - that was my point - the soot wil cause precipitation - and then those new ice crystals will continue the process. Moisture from the exhaust is just more precipitation nuclei.
 

Hama Neggs

Senior Member.
Yes they do - that was my point - the soot wil cause precipitation - and then those new ice crystals will continue the process. Moisture from the exhaust is just more precipitation nuclei.

Well, then... what they are saying could be somewhat correct. They are claiming that it is just "nano-particles" which are creating the trails. I don't know what they do with the moisture issue. Ignore it, I guess. That is not to say that commercial airliners have any way to disperse "nano-particles" of whatever-it-is.
 

Mick West

Administrator
Staff member
Exhaust particles alone will not create a contrail.

Contrails form when excess water on the exhaust condenses on cloud condensation nuclei. This liquid water then freezes and it is this frozen water that creates the ice-nuclei for the contrail to form from.

If you just had exhaust particles sprayed into ice-supersaturated air, you would not get much of a contrail (if any).

And if you has just high humidity hot air (say, from a hydrogen engine) sprayed into cold air, you WOULD get a contrail, as there's lots of natural cloud condensation nuclei.
 

MikeC

Closed Account
Not quite - if there WAS just "dry" paticles there would still be contrails - albeit probably they wold form more slowly.

But the moisture that does get generated adds to the process considerably - the vast majority of nucleation particles are probably ice crystals - so the moisture means contrails form much faster (IMO)

Contrails formed solely from "dry" nucleation sites would probably look quite different - there would be a larger gap, they would form slowly, etc.
 

Mick West

Administrator
Staff member
Not quite - if there WAS just "dry" paticles there would still be contrails - albeit probably they wold form more slowly.

But the moisture that does get generated adds to the process considerably - the vast majority of nucleation particles are probably ice crystals - so the moisture means contrails form much faster (IMO)

Contrails formed solely from "dry" nucleation sites would probably look quite different - there would be a larger gap, they would form slowly, etc.

Citation needed!

I think I've had this conversation a few times with @Ross Marsden, so should probably write up something more definitive.
 

Trailspotter

Senior Member.
A current CT claim is that it is "nano-particles" which are being "sprayed" an it is that which creates what WE call contrails, which THEY call "chemtrails". It got me wondering whether that has any merit. Can the mere introduction of condensation nuclei trigger a contrail?
Yes, it can, but only under ice-supersaturated conditions. And, as Mick and MikeC just said, "dry nuclei" contrail would probably look quite different from usual "wet" exhaust contrails.

AFAIK, there is no other chemical but water that can emulate contrails in the Earth conditions, as well as there is no chemical that would induce premature condensation of unsaturated water vapour.
 

Mick West

Administrator
Staff member
AFAIK, there is no other chemical but water that can emulate contrails in the Earth conditions, as well as there is no chemical that would induce premature condensation of unsaturated water vapour.

I've often wondered what would happen if you sprayed silver iodide into ice-supersaturated air. Silver iodide initiates freezing in liquid water, but does it act as an ice nuclei for deposition?
 

MikeC

Closed Account
Citation needed!

I think I've had this conversation a few times with @Ross Marsden, so should probably write up something more definitive.

There's plenty of "scholar" articles on the topic of soot as ice nucleation sites available - Here's a couple

or

-source
 

MikeC

Closed Account
I've often wondered what would happen if you sprayed silver iodide into ice-supersaturated air. Silver iodide initiates freezing in liquid water, but does it act as an ice nuclei for deposition?
Others have also thought about this, and been in a position to study it - there's a bunch of scholar articles (since I'm there already :))

Here's the abstract of one from 1947:

 

Hama Neggs

Senior Member.
Yes, it can, but only under ice-supersaturated conditions.

Yes, but isn't that the same conditions as for conventional contrails? No difference in the conditions needed? Maybe that isn't a known thing. I do see where you said more about how the trail would look different.
 

skephu

Senior Member.
I've often wondered what would happen if you sprayed silver iodide into ice-supersaturated air. Silver iodide initiates freezing in liquid water, but does it act as an ice nuclei for deposition?
I think you must know this paper because it is often cited by chemtrail believers:

Modification of cirrus clouds to reduce global warming
David L Mitchell and William Finnegan 2009 Environ. Res. Lett. 4 045102

It recommends modifying cirrus clouds and seeding new cirrus clouds by releasing ice nucleating materials. It notes that silver iodide is the best ice nucleating agent known, but recommends other options because of price and other considerations.

The reason it is often cited by chemtrail activists is this part:
 

Mick West

Administrator
Staff member
It recommends modifying cirrus clouds and seeding new cirrus clouds by releasing ice nucleating materials. It notes that silver iodide is the best ice nucleating agent known, but recommends other options because of price and other considerations.

Right, but what I'm wondering here is if a spray of silver iodide into ice-superstaurated air would look like a contrail.
 

Trailspotter

Senior Member.
Yes, but isn't that the same conditions as for conventional contrails? No difference in the conditions needed? Maybe that isn't a known thing. I do see where you said more about how the trail would look different.
Yes, this is the point: contrails would form only in the "contrail" (ice-supersaturated) conditions. The "dry" trail, that is, the trail formed by injecting only ice nuclei without added vapour from the engine exhaust, would probably look like aerodynamic contrails, in terms of optical density that depends on the absolute humidity. The latter in turn depends on the ambient temperature.
I'm wondering here is if a spray of silver iodide into ice-superstaurated air would look like a contrail
There must be some temperature threshold for the visibility of such a trail, analogous to that for aerodynamic contrails.
 
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Mick West

Administrator
Staff member
Of course a major problem with this thought experiment is how you get the ice nuclei into the right position to form a contrail without a big old jet engine spewing out water and aerosols and messing with your experiment.

[Edit] although I guess you could briefly shut off the engines :)
 

Trailspotter

Senior Member.
Of course a major problem with this thought experiment is how you get the ice nuclei into the right position to form a contrail without a big old jet engine spewing out water and aerosols and messing with your experiment.

[Edit] although I guess you could briefly shut off the engines :)
I guess that a solid-fuel air-to-air missile could do the job ;)
 

Trailspotter

Senior Member.
Still produces water and aerosols though.
http://en.wikipedia.org/wiki/Ammonium_perchlorate_composite_propellant
Well, water and carbon dioxide come from organic binder (rubber?) and can be eliminated by using a different propellant, e.g., old-fashioned black powder. As for aerosol, isn't it what we want - well dispersed condensation nuclei?
 

Mick West

Administrator
Staff member
Well, water and carbon dioxide come from organic binder (rubber?) and can be eliminated by using a different propellant, e.g., old-fashioned black powder. As for aerosol, isn't it what we want - well dispersed condensation nuclei?

Black powder contains charcoal (roughly C7H4O), so makes water when burnt.

But what I was thinking about was a delivery vehicle specifically for ice nuclei, not just any old aerosol (which frequently don't work as ice nuclei). Like how would you make a trail of just silver iodide through an ice-supersaturated region.
 

cloudspotter

Senior Member.
Black powder contains charcoal (roughly C7H4O), so makes water when burnt.

But what I was thinking about was a delivery vehicle specifically for ice nuclei, not just any old aerosol (which frequently don't work as ice nuclei). Like how would you make a trail of just silver iodide through an ice-supersaturated region.


Tethered balloon? Obviously wouldn't make a long trail travelling across the sky but the silver iodide could stream out from it in the wind.
 

skephu

Senior Member.
Right, but what I'm wondering here is if a spray of silver iodide into ice-superstaurated air would look like a contrail.
Almost certainly it would look very similar. The reason silver iodide is a very good ice nucleant is that its crystal structure is very similar to that of ice. But the resulting ice crystal size distribution may be different, so the silver iodide seeded trail may fall faster.
 

Ross Marsden

Senior Member.
I think it would look more like an aerodynamic contrail. They do look different from exhaust contrails. There are no pendules, for instance. At least, I don't think there are.
 

deirdre

Senior Member.
Almost certainly it would look very similar
if you could make a cloud cloud (like a contrail) with silver iodide then why are geoengineers talking about sulpher and not silver iodide. or are they, and I'm getting mixed up?
 

Trailspotter

Senior Member.
if you could make a cloud cloud (like a contrail) with silver iodide then why are geoengineers talking about sulpher and not silver iodide. or are they, and I'm getting mixed up?
Sulfur oxides are considered because of their known effect on solar radiation from volcanic eruptions. They do not make good ice nuclei to induce cloud formation at contrail altitudes, but they do combine with small amount of water to make droplets of sulfuric acid that do not evaporate. Aerosol of these droplets remains in stratosphere for a long time, increasing haze (whitening sky).
 

Hama Neggs

Senior Member.
I had a couple of thoughts/question about the idea of dust-triggered contrails. Why couldn't you, on a humid day, just throw a handful of dust in the air and create a cloud? And... I forgot the second question... :oops:

Oh... it was that somebody was claiming that since contrails have "pendules", like skywriting, that contrails have to be made of "particles". I tried to point out, several times, that contrails DO have "particles" in the form of ice crystals. My point was repeatedly ignored. :rolleyes:
 

Mick West

Administrator
Staff member
Am I way off, or wouldn't pure hydrogen combustion be just ice nuclei?

Cued to the contrail.

https://www.metabunk.org/threads/pre-1995-persistent-contrail-archive.487/page-8#post-141174

The ice nuclei there is ice, which has to nucleate, generally on something.

Water vapor can nucleate into ice in several ways, AFAIK
  1. At RHw>100% the water condenses as a liquid on water nucleation sites, and then freezes, becoming ice (and hence ice nuclei
  2. At RHw>150% (or so???) water homogeneously nucleate out of thin air as liquid.
  3. At RHi >100% (RHw >60-70%) water is deposited on ice nuclei as ice.
And I think for #2 there's also the case where Temp < -40ish (the homogenous freezing temp of water) when it will essentially homogeneously nucleate as ice.

So with a hydrogen jet it's either nucleating on existing cloud condensation nuclei (like clouds do), or if the air was super clean it could conceivably still make a contrail if it pumped out enough water to raise the RHw above 150%(?)
 

Critical Thinker

Senior Member.
Wasn't sure where this would best be posted, but found it worthy of posting:

Science Alert Link

Birth-of-a-Cloud.gif

 
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