Sea Spray’s Tie To The Sky
For years, researchers have known that the oceans create aerosols—sprays of tiny particles suspended in the air. Depending on their size and composition, those aerosolized particles can mix high up into the atmosphere and travel for thousands of miles.
Writing this week in the journal Chem, researchers have used a laboratory model of ocean waves to tease apart some of the contributions that phytoplankton and ocean-dwelling bacteria make to ocean aerosols. “Sea spray is not just sea salt,” says Vicki Grassian, who co-directs the Center for Aerosol Impacts on Climate and the Environment. Organic compounds contained within a microlayer “skin” on the ocean surface can enter the atmosphere when sea foam bubbles pop.
Grassian and colleagues are working to understand how different materials wend their way into the atmosphere, and how they can interact in ways that affect the climate.
Vicki Grassian is co-director of the Center for Aerosol Impacts on Climate and the Environment and a Distinguished Professor at the University of California, San Diego.
IRA FLATOW: And now, we’re going to move on to something totally different. We’re going to talk about the ocean. With each splash of a wave in the ocean, the ocean makes a froth of bubbles. But what happens next is complicated. With each of these bubbles, when they pop, stuff from the ocean’s surface can be released as particles into the air. And some of these particles can even get swept up into the upper atmosphere. Yeah, where they can interact with other chemicals and potentially, they can travel for thousands of miles.
My next guest studies the chemistry of these aerosols and how they form and interact with the environment. She’s written about plankton and bacteria and the aerosol process and she’s published her work this week in the Journal Chem. Vicki Grassian is Co-Director of the Center for Aerosol Impact on Climate and the Environment. Professor also at University of San Diego, UC San Diego. She joins me from the campus there. Welcome to Science Friday.
VICKI GRASSIAN: Thank you, I– thank you for having me.
IRA FLATOW: You’re quite welcome. So let’s talk about the particles. What kinds of particles are we talking about that get thrown up into the air?
VICKI GRASSIAN: So mainly, we’re talking about sea spray aerosol. So these are aerosols produced from wave action, from these bursting bubbles, as you just mentioned a moment ago. And they actually consist of a wide range of different compositions and different sizes.
So one of the things that we wanted to do in this paper that just came out this week in the Journal Chem was look at the detail– in detail at the molecules coming out of the water within these particles. And tried to say something about how that changed during the course of a phytoplankton bloom.
And so, in general, I just want to add that what gets out of the ocean are things like salts. Typically, that’s what people think about. But also organic compounds and biological components, even whole bacteria.
IRA FLATOW: Tell us what happens when the bubble– are we talking about the waves crashing on the shore? Or are we talking about foam out in the ocean? What kind of bubbles are we talking about here?
VICKI GRASSIAN: In this study, we basically looked at when we had waves and we have bubble bursting during that wave process. And we captured the aerosols and looked at them individually to see what they were made up as. And what was unique about this experiment is that we did this in an ocean atmosphere facility, where we can cut off and close off all other influences and just look at that sea spray forming from– mainly from that wave action.
IRA FLATOW: So you brought them inside, into a big tank, and created the waves and watched the bubbles– created the foam and watched the bubbles burst. And how does a bubble burst? I mean, in slow motion, if you watch a bubble in your wave action, what do you see happening?
VICKI GRASSIAN: So the bubble-bursting process is something that I’ve learned quite a lot about from my physical oceanography friends here at the University of California San Diego. And basically what you have is you have the bubble bursts so that the film bursts. And then, that forms film drops. And then subsequent to that, you get the jet drops from underneath.
And so, whether you get the film rupture that forms very small particles– which have a lot of organic compounds associated with them– versus the jet drops, which tend to form the larger particles. Although we’re questioning that understanding right now within our center as well. But that’s what we’re interested in looking at is the different mechanisms and what molecules come out of the water because of these different mechanisms.
IRA FLATOW: You got to tell me what a jet drop is. It’s not a 747 hitting anything, right?
VICKI GRASSIAN: No, it’s basically– that’s a good point. So basically, when you have the film rupture, there’s some energy left over. And so, what you end up getting is from the bottom of that drop some additional– if you were to look at that with a microscope– you’d see another small droplet of water coming out of the ocean from the middle after that bubble-bursting process, from the top.
So the film drops versus the jet drops. And one is bigger than the other. And so, that’s what we’re looking at is the differences in the composition of each of these. Because how they get out there is very, very different.
IRA FLATOW: And so, once the stuff– once you have your film drop and your jet drop, now we have droplets all through the air. Where do they go?
VICKI GRASSIAN: So these aerosols get into the air. And then, they– from their formation, they undergo long range transport. And so, then they start interacting with gases and other particles in the atmosphere. And so, as they move out from the ocean, they can really change in terms of their composition, in terms of what they’re associated with. Whether they’re associated with other particles that were in the atmosphere from other sources as well.
IRA FLATOW: So when all these particles are traveling and you’ve now got the particles in the air and you– if you capture them in your lab and you look at them under the microscope, what do you see there?
VICKI GRASSIAN: So that’s what this study focuses on, is basically us capturing and then we capture them onto a substrate. So we just put them on a piece of glass, a glass slide, if you will. And then, we look at them in great detail, in terms of their composition, using a variety of different state of the art techniques in order to get that information about their composition.
So we use a lot of what we call spectroscopy in our lab– or mass spectrometry– in order to see what the composition of each of these individual particles are, what they’re made up of.
IRA FLATOW: And what are they– what do you see?
VICKI GRASSIAN: So very interestingly, we see things like fatty acids. We see sugars. We see simple sugars like glucose. We see more complex sugars like what we call polysaccharides. So we see a wide range of different types of compounds coming out of the ocean.
They also– these particles can contain both salt– so sodium chloride– plus these organic compounds. And so, what we were able to really do in our paper was look at individual particles and say something about their individual compositions.
IRA FLATOW: Wow. It’s fascinating by– first, you’ve described two ways of the bubble, when the bubble bursts. I had no idea there’s a compound action going off in the membrane and then the jet at the bottom. And then, once you get these particles in the air. Now, I understand from reading stuff that for storms, for example, for it to rain, you need to have nuclei, little bits of stuff. Could the stuff coming out of the ocean form the nuclei that creates some of the showers, thunderstorms, or something like that?
VICKI GRASSIAN: So, that’s right. And so, these particles can nucleate clouds, they can nucleate ice crystals in the atmosphere. And so, yes, very much so. They can be part of how we think about precipitation and cloud formation. And so, that’s a big component of what our center studies. And so, what we provide is information on what these particles are made of. And then others provide information on, how can they nucleate a cloud? How can they nucleate ice crystals?
IRA FLATOW: So you study a lot of particles. Do you study dust? Just plain dust, too, in the air?
VICKI GRASSIAN: You know, I’m the dust queen. And what I mean by–
IRA FLATOW: I’m glad you said that and not me, because I’d get in trouble if I said it. Is that what they call you around the office, the lab? The dust queen?
VICKI GRASSIAN: I’ve been called the dust queen. And the reason why is that a lot of my work has also focused on mineral dust and trying to understand mineral dust in the atmosphere. And mineral dust comes from a different source, doesn’t come– it comes from desert regions. And they, too, can undergo long range transport, these dust particles.
And very similar to sea spray, each individual particle is a bit different. And so, what we do is we study the composition of these particles. We study how they react in the atmosphere. And we study how they can nucleate clouds.
IRA FLATOW: Can dust– thinking about the water, can there be dust in the water, too? You said that they’re from dry places. But could you have dust being spread by the waves and the bubbles bursting?
VICKI GRASSIAN: Oh, so now you’re asking sort of another interesting question. Because what we know is that mineral dust from desert regions undergo long range transport. And some of it deposits into the oceans. And that’s actually an important process, because sometimes the iron in the dust particles is a nutrient for ocean life under certain circumstances. That’s often– that nutrient is limited.
And so, we know that dust goes into the ocean. And then you’re asking the next question, does it come back out of the ocean? And so, that’s something that we’re actually looking at in our center.
IRA FLATOW: Tell me about the particles themselves. How large are they, ranging in size?
VICKI GRASSIAN: Yes, so that’s a great question. So for the sea spray, I’ll focus on that, because that’s what we started talking about. The particles are anywhere from– and I’ll use my speak for a moment and then I’ll put it into perspective.
IRA FLATOW: Please.
VICKI GRASSIAN: They go from 30 nanometers– and a nanometer is 1 times 10 to the minus 9 meters– to about 10 microns or 10 micrometers, where a micrometer is 1 times 10 to the minus 6 meters. And so, let’s put it in a different perspective. So if I think about a single hair, OK? So these particles can be anywhere from 10 to 1,000 times smaller than a single width of a hair.
IRA FLATOW: Wow. Well, you’ve set off my break meter. I have to remind everybody that I’m Ira Flatow, and this is Science Friday from PRI, Public Radio International, Talking with Dr. Vicki Grassian, Co-Director of the Center for Aerosol Impacts on Climate and the Environment. And no wonder you have a long name, you study a lot of things like that.
So how much of these particles– I’m thinking now about pollution. How much of the particles that get spread around the world are natural and how much are they man-made, person-made, people-made?
VICKI GRASSIAN: So that’s a great question, because– and that’s a lot about what we think about as well. Because we really want to understand natural sources of aerosols, what their input into the atmosphere is. And then we can better understand what the influence of pollution particles may be. Particles from anthropogenic sources.
So from a mass perspective, if we were to weigh all the particles, many of the particles in the atmosphere are from sea spray and from mineral dust. So from dust storms and from wave action. But when we look at the number of particles– so if we look at it a little bit differently instead of just weighing it, we look at the number– a lot of the smaller particles are actually anthropogenic particles, pollution particles. As you just mentioned a moment ago.
And so, it depends on the size. It depends on whether we’re looking at number of particles or mass of particles. But both are very important in the atmosphere. Both play a role in the atmosphere, I should say.
IRA FLATOW: Are you seeing nanoparticles? Because they’re ubiquitous, these man-made nanoparticles. Are you seeing them being spread around in the air by the waves or the dust?
VICKI GRASSIAN: So I just told you a moment ago that some of the particles coming out of the ocean are nanoparticles. So we actually– so they’re naturally occurring nanoparticles.
IRA FLATOW: Natural. Natural ones.
VICKI GRASSIAN: That’s right.
IRA FLATOW: Not that we engineer those particles, those kinds I’m speaking of.
VICKI GRASSIAN: Yes. And so, then there’s a whole other set of particles, engineered nanoparticles. And so, yeah, you can see some of them. Some of the engineered nanoparticles can make it in the air. There’s been some studies to try to quantify that. But I think that’s something we’re still interested in understanding and interested in knowing. And so, these things would be like titanium dioxide nanoparticles or zinc oxide nanoparticles.
IRA FLATOW: Stuff from makeup and things like that.
VICKI GRASSIAN: Makeup, sunscreen. So just think about sunscreen for a minute.
IRA FLATOW: Yeah.
VICKI GRASSIAN: OK? You put it on. And then you go into the water. It comes off. Then you come back and put it on again. So where did it go?
IRA FLATOW: Oh, what a question. That’s a very good question. It’s still with us, obviously, right? It’s getting washed off in the ocean and then maybe the waves are going to throw back up in the air.
VICKI GRASSIAN: Maybe.
IRA FLATOW: Do people think enough about this, do you think? Pay enough attention to this stuff?
VICKI GRASSIAN: You know, I think we could think more about it, because there are consequences to everything we do. And so, I really do feel like sometimes we don’t think about the next step. So I put this on, I go in the water, it comes off. OK, the ocean is large. Do you think it just goes away, far away? Or does it stay– what is it made of? Is it at the surface of the ocean? Can it come back out into the air? I think that those are questions that are really important to think about and to ask.
IRA FLATOW: I’m very glad that you brought that up, because it’s always something good to think about. Leave everybody with something good to think about. Thank you, Dr. Grassian.
VICKI GRASSIAN: Thank you.
IRA FLATOW: And have a Happy Mother’s Day, if you are. Vicki Grassian, Co-Director of the Center for Aerosol Impacts on Climate and the Environment in San Diego.