Tiny particles have outsize impact on storm clouds, precipitation

January 25, 2018, Pacific Northwest National Laboratory
A heavily instrumented ground site downwind of Manaus captured measurements of aerosols, clouds, and solar and thermal energy during GoAmazon. Credit: US Department of Energy ARM Climate Research Facility

Tiny particles fuel powerful storms and influence weather much more than has been appreciated, according to a study in the Jan. 26 issue of the journal Science.

The research focuses on the power of minute airborne known as aerosols, which can come from urban and , wildfires and other sources. While scientists have known that aerosols may play an important role in shaping weather and climate, the new study shows that the smallest of particles have an outsize effect: Particles smaller than one-thousandth the width of a human hair can cause storms to intensify, to grow and more rain to fall.

The tiny pollutants - long considered too small to have much impact on droplet formation - are, in effect, diminutive downpour-makers.

"We showed that the presence of these particles is one reason why some storms become so strong and produce so much rain. In a warm and humid area where atmospheric conditions are otherwise very clean, the intrusion of very small particles can make quite an impact," said Jiwen Fan of the Department of Energy's Pacific Northwest National Laboratory, who is lead author of the paper in Science. Fan led 21 authors from 15 institutions around the world to do the study.

Tiny particles have a lot of clout when it comes to powering large storms in the Amazon. Credit: Nathan Johnson/PNNL

The findings are based largely on unique data made possible by the GoAmazon research campaign, where scientists made ground-based and airborne measurements related to climate during 2014-2015. The campaign was run by the Atmospheric Radiation Measurement (ARM) Climate Research Facility, a U.S. Department of Energy Office of Science user facility.

The study capitalized on data from an area of the Amazon that is pristine except for the region around Manaus, the largest city in the Amazon, with a population of more than 2 million people. The setting gave scientists the rare opportunity to look at the impact of pollution on atmospheric processes in a largely pre-industrial environment and pinpoint the effects of the particles apart from other factors such as temperature and humidity.

In this study, scientists studied the role of less than 50 nanometers wide in the development of thunderstorms. Similar but larger particles are known to play a role in feeding powerful, fast-moving updrafts of air from the land surface to the atmosphere, creating the clouds that play a central role in the formation of water droplets that fall as rain.

But scientists had not observed - until now - that smaller particles below 50 nanometers, such as particles produced by vehicles and industrial processes, could do the same. Not only that. The new study revealed that these particles, whose effects on clouds have been mostly neglected until now, can invigorate clouds in a much more powerful way than their larger counterparts.

Research aircraft outfitted with aerosol probes and sensors obtained data from the sky above Manaus during the GoAmazon research campaign. Credit: US Department of Energy ARM Climate Research Facility

Through detailed computer simulations, the scientists showed how the smaller particles have a powerful impact on clouds.

It turns out that when larger particles aren't present high in a warm and humid environment, it spells opportunity for the smaller particles to act and form cloud droplets. The low concentration of large particles contributes to high levels of excessive water vapor, with relative humidity that can go well beyond 100 percent. That's a key condition spurring ultrafine particles to transform into .

While the particles are small in size, they are large in number, and they can form many small droplets on which the excess water vapor condenses. That enhanced condensation releases more heat, and that heat makes the updrafts much more powerful: More warm air is pulled into the clouds, pulling more droplets aloft and producing more ice and snow pellets, lightning, and rain.

The result: "Invigorated convection," as Fan says - and stronger storms.

"We've shown that under clean and humid conditions, like those that exist over the ocean and some land in the tropics, tiny aerosols have a big impact on weather and climate and can intensify storms a great deal," said Fan, an expert on the effects of pollution on storms and weather. "More broadly, the results suggest that from pre-industrial to the present day, human activity possibly may have changed storms in these regions in powerful ways."

Explore further: Image: Signs of ships in the clouds

More information: J. Fan el al., "Substantial convection and precipitation enhancements by ultrafine aerosol particles," Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aan8461

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9 comments

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cantdrive85
1.8 / 5 (5) Jan 25, 2018
Who'da thunk charged particles would affect storms and precipitation?
RealScience
4.2 / 5 (5) Jan 25, 2018
Who'da thunk charged particles would affect storms and precipitation?


I am curious - is there something in the article leads you to conclude that the particles it discusses are charged?
cantdrive85
1 / 5 (5) Jan 26, 2018
Who'da thunk charged particles would affect storms and precipitation?


I am curious - is there something in the article leads you to conclude that the particles it discusses are charged?

From article;
"urban and industrial air pollution, wildfires and other sources."
Bart_A
1 / 5 (4) Jan 26, 2018
Real, this has to do with cosmic rays. Scientists have shown that cosmic rays may also have a large impact on cloud cover. And when they hit the atmosphere they create charged particles.
RealScience
5 / 5 (4) Jan 26, 2018
Real, this has to do with cosmic rays. Scientists have shown that cosmic rays may also have a large impact on cloud cover. And when they hit the atmosphere they create charged particles.

BartA -
If I had asked what the link was between charged particles and clouds, your answer would be an excellent answer – concise, accurate and to the point.
However that is NOT what I asked CD.

This article is specifically about particles less 50 nm across that were NOT known to influence cloud formation. CD referred to charged particles as if the article had focused on them, so I politely and specifically asked CD where CD got the idea that the particles discussed in the article were charged.

"urban and industrial air pollution, wildfires and other sources."

CD –
Are you claiming that all particles from these sources are charged?
cantdrive85
2.3 / 5 (3) Jan 27, 2018
CD –
Are you claiming that all particles from these sources are charged?

'Introduction to Air Pollution Science'
https://books.goo...oECA0QAQ
Chapter 3- Electrical Charges on Particles;
"Under ordinary conditions a significant portion of any aerosol will be electrically charged."

As questioned, "Who'da thunk charged particles would affect storms and precipitation?"
cantdrive85
1 / 5 (3) Jan 28, 2018
Creating rain and thunderstorms in the desert by introducing electric charges to atmosphere;
http://newsfeed.t...-desert/

But alas, who cares about facts when one has preconceived notions.
RealScience
5 / 5 (3) Jan 28, 2018
Charged particles are known to influence clouds, but smaller aerosols are also known to have lower average charge, so I was curious.

The 'Introduction to Air Pollution Science' reference is a excellent reference - thank you for providing it.

The reference has enough detail to calculate the average particle charge.

Eq. 3.11 says the average charge (relative to the charge of an electron) will be 2.37 sqrt(D), where D is the diameter in microns. For the largest <50 nm particles D= 0.05 um so the average charge is +/- 0.53 electrons, so roughly half of the largest particles have a tiny charge.

Your reference also says (bottom left of p. 54) that "Unless the particles are highly charged, or the external field is strong" the effect of charged particles are minor.

- continued -
RealScience
5 / 5 (3) Jan 28, 2018
I checked the article and it never mentions charge. I checked the supplementary figures and they show increasing particle count with small size but it is not strong - 10 nm particles (20% with a +/-1 charge) out number 50 nm particles by only 2x, so very roughly 1/3 of the particles studied would have a +/-1 charge. A thunderstorm does have areas of strong fields, but 1 electron is a pretty small charge.

The article on creating rain is interesting, and certainly supports the general understanding that charged particles influence clouds and rain, but without studying the size of the dust particles it could be just the well-known effect of larger highly-charged particles.

I am open minded toward the possibility that the 1/3 of the <50 nm particles that are have a +/- one electron charge cause or dominate the intensity enhancement that the 'tiny particle' article is about, but I don't think that one should jump to it as a conclusion based on the references.

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