Aerosol formation in clouds


Research News


Researchers at the Paul Scherrer Institute PSI have studied for the first time how chemical reactions in clouds can influence the global climate. They found that isoprene, the dominant non-methane organic compound emitted into the atmosphere, can strongly contribute to the formation of organic aerosols in clouds. They published their results today in the journal Science Advances.

Aerosols, a mixture of solid or liquid particles suspended in the air, play an important role in Earth’s climate. Aerosols originate either from natural or human sources. They influence Earth’s radiation balance by interacting with sunlight and forming clouds. However, their effect remains the single most significant uncertainty in climate models.

One substance that is very common in the atmosphere is isoprene, an organic compound whose reactions in the gas phase are relatively well understood. Isoprene is given off by trees and can produce aerosols when it is oxidised. How isoprene and its reaction products react in cloud droplets is still largely unknown. That’s why researchers at the Paul Scherrer Institute PSI have used a type of flow reactor with wetted walls, together with the most advanced mass spectrometers, to investigate what could be happening chemically inside clouds for the first time under atmospherically relevant conditions.

“Our experimental setup allows us for the first time to precisely investigate the distribution of organic vapours at the air-water interface under near-environmental conditions,” says Houssni Lamkaddam, a researcher in the Laboratory of Atmospheric Chemistry at PSI. “With our apparatus, we can now simulate what happens in clouds.”

What exactly happens in clouds?

In the special apparatus, a so-called wetting reactor, a thin film of water is maintained on the inside of a quartz tube. A gas mixture containing, among other substances, isoprene, ozone, and so-called hydroxyl radicals is fed into the glass cylinder. UV lamps are installed around the glass cylinder to simulate daylight conditions for some of the experiments.

Using this setup, the researchers found that up to 70 percent of the isoprene oxidation products can be dissolved in the water film. The subsequent aqueous oxidation of the dissolved species produces substantial amounts of secondary organic aerosols. On the basis of these analyses, they calculated that the chemical reactions that take place in clouds are responsible for up to 20 percent of the secondary organic aerosols on a global scale.

“This is another important contribution to a better understanding of the processes in the atmosphere,” sums up Urs Baltensperger, scientific head of the Laboratory of Atmospheric Chemistry at PSI. Earth’s radiation balance is a very important factor in the entire climate process and thus also in climate change. “And aerosols play a crucial role in this,” says the atmospheric scientist. While aerosols form cloud droplets, this research shows that clouds can also form aerosols through the aqueous chemistry of organic vapours, a process that is well known with regard to sulfate aerosols but here is also shown for the organic fraction. This new experimental setup, developed at PSI, opens up the possibility of investigating aerosol formation in clouds under near-atmospheric conditions so that these processes can ultimately be included in climate models.


Text: Paul Scherrer Institute/Sebastian Jutzi

About PSI

The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The institute’s own key research priorities are in the fields of matter and materials, energy and environment and human health. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 2100 people, thus being the largest research institute in Switzerland. The annual budget amounts to approximately CHF 400 million. PSI is part of the ETH Domain, with the other members being the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (Swiss Federal Institute of Aquatic Science and Technology), Empa (Swiss Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research).

Original publication

Large contribution to secondary organic aerosol from isoprene cloud chemistry
H. Lamkaddam, J. Dommen, A. Ranjithkumar, H. Gordon, G. Wehrle, J. Krechmer, F. Majluf, D. Salionov, J. Schmale, S. Bjeli?, K. S. Carslaw, I. El Haddad, U. Baltensperger
Science Advances, 24.03.2021
DOI: 10.1126/sciadv.abe2952

From EurekAlert!

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Ron Long
March 26, 2021 2:46 am

OK, it looks like PSI might have identified one small part of the chaotic weather system, which is isoprene generation by trees, and its possible cloud interaction. This whole process of how weather is generated around the earth is complicated, the evidence of which is the accuracy (and timeliness) of weather forecasts. Here in central Argentina they are doing a fairly good job of predicting when cold rain systems will arrive (one is here now) by data from weather-observing satellites. These cold rain (sometimes snow) events originate near Antarctica, where there are no trees to produce isoprene.

Reply to  Ron Long
March 26, 2021 4:49 am

Yeah, it’s complicated.

There are also marine sources of isoprene and dimethyl sulfide from both marine and terrestrial sources behaves similarly with respect to formation of aerosols. In any case, like competition, research not focused on CO2 is a good thing.

M Courtney
Reply to  Ron Long
March 26, 2021 3:41 pm

And how does that vary when there are ice crystal surfaces to adhere to as well as water films?
It’s complicated.
But real observations are real science. It’s the way to go.

Peta of Newark
March 26, 2021 4:29 am

They’re like children playing on a beach, so deeply concentrating on their own little sandcastles/pies and quite perfectly unaware of the how, why, the wherefore..

OK, let’s call on Gaia for this one.
Why do trees especially produce this stuff?
It’s got to be a fantastic building block for ‘tree-making’ yet seemingly let vast amounts, 500 million tonnes per year, blow away in the wind.

We hear that it interacts with solar originated UV. No surprises there.

But, UV is horrible horrible stuff. It destroys not only oxygen molecules to create Ozone, but also anything and everything containing carbon-carbon bonds
Trees for example
Oddly enough, Ozone does the same.

So, Gaia, is it beyond the bounds that the trees are responding to what UV they see hitting them and release Isoprene, a very reactive substance containing carbon-carbon bonds, to intercept the UV before it hits them.
Also being very reactive by containing double bonded carbon atoms, ## it will very readily react with any Ozone it comes upon
Thus the trees will not be damaged by either UV or by Ozone.
The Isoprene will have taken both of them out.

And this is why I pointed out the 500 Million tonnes pa
Has that amount changed during the last however. Has any stuff we’ve put into the air done what the Isoprene does?
You know many of them, methane plus petrol & kerosene fumes not very least.

Because the trees would have responded by not releasing as much Isoprene or other VOCs

Has that happened?
That is what these folks should have been looking for
i.e. What makes the waves on the beach do what they do or why is the beach and the water even there in the 1st place.
Not on the mechanics of how sandcastles hold together or whether my dad makes bigger & better ones than your dad does.

## Isoprene. A double bonded ‘monomer’, precursor to rubber and all variations on what we call plastic. i.e. Polymers

What if the likes of me or you ingested some double bonded ‘stuff’.
Is it beyond the bounds that it might polymerise?

Would unsaturated fat i.e. vegetable oil, count as a double bonded monomer?
If any of us own or have used a deep-fat fryer, we know that that stuff polymerises.
Its the rubbery gunk all around the edges of the fryer where its not too hot

Wouldn’t be the stuff that blocks up your blood vessels would it?

PS. When Covid first kicked off, a talking head somewhere on t’interweb asserted that on every square metre of Earth and on every 24 hour day, some 3 Billion fragments of stuff landed down.
(Seems rather a lot to me but, hey ho, over to you)
Stuff with the chemical analysis of RNA i.e fragments of virus
Apart from the Covid aspect, what about all that for cloud seeding?

Last edited 1 month ago by Peta of Newark
Reply to  Peta of Newark
March 27, 2021 3:38 am

“It destroys not only oxygen molecules to create Ozone,…”
C’mon Loydo, man, you gonna let a phrase like that walk free?
Do your job, bro’!

March 26, 2021 4:40 am

I’ve looked at clouds from both sides now
From up and down and still somehow
It’s cloud’s illusions I recall
I really don’t know clouds at all. – Joni Mitchell

I think these science guys should listen to her. They can write up all sorts of stuff, all they want to, but really, they really don’t know clouds at all.

Happy Friday!

Reply to  Sara
March 26, 2021 4:53 am

Yep. For the time being, that’s a good thing. The alarmists don’t actually know what results from these experiments would support their chosen dialectic. That means the researchers are free to do real science.

M Courtney
Reply to  Sara
March 26, 2021 3:42 pm

Glad I read the comments before commenting as I was going to post exactly what you did.
Actually I’m quite peeved.

Rod Evans
March 26, 2021 4:54 am

Whenever the term aerosol is mentioned particularly heading for the clouds aerosols. I am immediately visualising Michael Mann for some unexplainable reason…,😊

March 26, 2021 5:43 am

Wow! Some actual real experimental science done on the climate issue. No computer? There is hope still.

Bruce Cobb
March 26, 2021 5:48 am

Aerosols are useful as fudge factors for climate schmodels.
What’s a “climate schmodel”, you ask?
I’m glad you asked.
Climate schmodels use a smorgasbord of factors with the goal being to “show” a manmade signal to either warming, or to “climate change”. The oceans are another great fudge factor, useful when “global heating” stops for a decade or two, for a “breather”. Of course, they call this period a “slowdown”, and heating is “in the pipeline”, by which they usually mean it’s “hiding in the oceans”. Handy, that.

March 26, 2021 5:51 am

“With our apparatus, we can now simulate what happens in clouds.”

Have they spoken with someone who has actually done a bit of research in this area? Maybe Svensmark or even CERN?

But then those ‘experiments’ weren’t about computer models.

Last edited 1 month ago by fretslider
March 26, 2021 7:09 am

Well, I read the paper and it seems they describe their methods and findings pretty well. Beyond my ability to judge the validity of it all, so I will leave that to those with the necessary background.

I do wonder, though, if the global climate model UKESM1 is a standard model normally used.

The paper:

Large contribution to secondary organic aerosol from isoprene cloud chemistry

To assess the atmospheric implication of aqSOA formation from isoprene on a global scale, we implement the parameterizations of experimental data in the global climate model UKESM1. The uptake fraction of isoprene oxidation products in cloud droplets was parameterized as a function of liquid water content using our measured solubility distribution; it ranges between 50 and 70% under typical atmospheric conditions (see the Supplementary Materials and fig. S6).

March 26, 2021 7:09 am

Oh, it is almost like trees have evolved to extract available moisture from the air, using aerosols.

Last edited 1 month ago by RLu
John Chism
March 26, 2021 7:31 am

So…flora that is reliant on water and ultraviolet radiation gives off carbon dioxide and these isoprene that seed cloud formation and cause a heating of the atmosphere that creates a more favorable climate for themselves to grow, is somehow seen as a problem?

Chris Hall
March 26, 2021 8:51 am

One thing that worries me after just reading this posting and not the article is that the experiment deals with reactions on basically a 2-dimensional flat water surface. In the real world, cloud droplets are nearly spherical, with sometimes enormous internal pressures caused by surface tension, and anomalous water vapor pressure nearby. It would be difficult to do this sort of experiment on droplets, but it would be interesting to see if their results hold up.

Robert of Texas
March 26, 2021 9:55 am

“With our apparatus, we can now simulate what happens in clouds.”

No, no, and no. Bad scientist. (/Slap_the_wrist) The correct statement is “With our apparatus, we can now simulate what WE THINK IS happenING in clouds.”

Until they go demonstrate this IS happening in clouds using the same mixture and producing the same results, it is just a simulation of their hypothesis.

Reply to  Robert of Texas
March 27, 2021 3:17 am

Ah, some common sense…but
“With our apparatus, we can make various chemicals do various (mildly) interseting things which we will use to ‘prove’ various bullshit theories”
There, fixed it for you.

Julian Flood
March 26, 2021 2:00 pm

Do synthetic surfactants get into clouds. I can imagine a polluted droplet merging more readily with others and raining out. Fewer droplets, less cloud, warming.

What is the cloud cover trend?


March 26, 2021 2:20 pm

On the subject of clouds, the picture of the clouds with the accompanying rock formation is beautiful. The clouds with a backdrop of the rock is what does it!

March 27, 2021 3:34 am

Ho hum. We can make chemicals react in ways we find interesting, should we be interested in how these chemicals react in a glass tube.
I do not deny that particulates are involved in cloud formation, and it may even extend to these single-molecule aerosols, but I don’t think it is the only mechanism, there are also purely electrical, mechanical and electro-mechanic processes involved, like simple cohesion between water molecules. There is, however, one mechanism nobody seems to discuss:
How many of you have seen a wind-break in action? That’s where a farmer plants a row of trees on the edge of a plowing field. The common misconception is that this “breaks the wind” so the crop does not get blown around, but actually, it is about harvesting atmospheric water.
On a moist daybreak, one can actually observe little ground-level clouds (fog) forming beyond the wind break, too early in the day for the VOCs to form, as reported on this site just this week. So what is happening?
Close your eyes (while you keep reading, of course!) and imagine the wind as it blows past a leaf. Observe the eddy currents forming around the leaf edge. Look closely at the eddies, inject some of that smoke they use in wind tunnels to test aerodynamics. Where you see smoke particles, imagine higher pressure than where you see no smoke. Look very closely, because at the miniscule interface between two strands of air, where a high pressure area suddenly dissipates and loses pressure, the air cools down, and the water condenses into droplets.
And that is how many, if not most clouds form!
Now you see how ocean currents blowing over a mountain edge can form clouds, while showing clear sky before the turbulence was inserted. Think of the famous phenomenon of the weird cloud hanging on the leeward side of the Toblerone peak. What’s it called again? Somewhere in the Alps? Matterhorn!

Last edited 1 month ago by paranoid goy
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