The Story Of Aerosols: From Spray Can To Ocean Spray

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

[SPRAYING]

You know that sound, right? The aerosol spray can. If you were around during the 1970s, you remember when consumer aerosol products like hairspray contained chlorofluorocarbons that depleted the ozone layer. And even though these products have not used CFC since the late 1970s, the connection between a can of hairspray and a warming planet has erroneously stuck around for decades.

In fact, aerosols– which is just a fancy word for air particles– do have a role to play in climate change, but not the one that you might think. Here to tell us more are my guests. Rajan Chakrabarty, assistant professor of aerosol science and engineering at Washington University in St. Louis. Welcome to Science Friday.

RAJAN CHAKRABARTY: Thank you, Ira. Thank you for having me on your show.

IRA FLATOW: You’re welcome. Vicki Grassian, professor of chemistry and biochemistry at the Scripps Institute of Oceanography at UC San Diego. Welcome back to Science Friday, Dr. Grassian.

VICKI GRASSIAN: Thank you, Ira. Thank you for having me back.

IRA FLATOW: You’re welcome. Dr. Chakrabarty, we get aerosols confused with the stuff that comes out of a spray can. But it’s a general term for particles, isn’t it? What’s the characteristics of an aerosol?

RAJAN CHAKRABARTY: So aerosol is essentially– it is made up of two words, which is asol, which is a phase, which could be a liquid phase or a particle phase. And it is suspended in air. So hence the term, we call it aerosol. And it also constitutes bought liquid and solid particles, but suspended in air.

IRA FLATOW: There you go. And Dr. Grassian, do aerosols actually cool the atmosphere?

VICKI GRASSIAN: So aerosols are some of the more interesting aspects of our Earth’s atmosphere. They have the ability to scatter and absorb solar radiation. They have the ability to nucleate clouds. And because of this, they can actually cause cooling of our atmosphere.

IRA FLATOW: You’ve been on the program before talking about sea spray, I remember. It was very interesting. Are these aerosols themselves?

VICKI GRASSIAN: Yeah, so sea spray aerosol is one of my favorite aerosol out there in the Earth’s system. These aerosol particles come from a bubble bursting at the ocean’s surface, from wave breaking. So many of us are used to seeing this when we go to the seashore.

And these aerosol particles get into the air. And they can travel miles and miles away from the source region. And so I’ll give you an example of that. There was sea spray aerosols detected in Alabama during a campaign where people were measuring the aerosols in Alabama. And they actually detected some sea spray.

IRA FLATOW: And how far away from the ocean was that?

VICKI GRASSIAN: So it’s pretty far from the ocean. Just think about the map of the US, where you have Alabama. So you have the Atlantic Ocean, you have the Gulf of Mexico, but inland into Alabama, there was actually sea spray particles. And we know that here in California, where I am in San Diego, we have wave breaking.

And these aerosol particles get into the air, entrained into the air. And then they go eastward. They can make its way all the way to the middle of the US. So somewhere in the Midwest there might be sea spray aerosol that originated from San Diego a day or two ago.

IRA FLATOW: No kidding. That far?

VICKI GRASSIAN: I’m not kidding. Oh yeah. I can tell you many more stories about how far aerosols go. I’ll give you another example. There can be a dust storm in China. So these particles get lofted into the air and then start making its way from desert regions over to more urban areas, like Tokyo and other parts of Asia, and then makes its way across the Pacific Ocean. And then actually makes its way to the Western United States.

IRA FLATOW: Wow. Dr. Chakrabarty, the other thing I know about aerosols is that they’re an important part of cloud formation. Isn’t that right?

RAJAN CHAKRABARTY: Yes. So aerosols, they act as sort of cloud droplets, what you see. The seed which constitute each water droplet is essentially an aerosol. So you need to have these particles to form clouds. And this whole connection between aerosol and cloud formation is one of the challenging topics of research, currently. As we are dealing with more pollution episodes, how does it affect the cloud formation?

And also, how does it affect precipitation patterns and drought? And so these are some of these events which different parts of the planet are encountering. They have been connected to different pollution events. So specifically, my area of research is carbonaceous aerosols. So these are carbon-containing particles which are emitted from combustion sources.

And it could be anthropogenic, which is essentially human-caused, or it could be natural sources– wildfires and [INAUDIBLE] burning. And so these particles, they have their action happening in the visible solar spectrum, meaning they absorb most of the incoming solar radiation, or they scatter. So if you think about it, if you think about an existing cloud, and surrounded by a bunch of these carbonaceous aerosols which are trapping the incoming sunlight– so what is it going to do? It is going to warm up the vicinity of the cloud, which causes the cloud to actually sort of burn away and shrink.

So that affects the precipitation pattern. The other thing is if you have a fixed amount of water vapor available, and you have a pollution event, so there are more predators. There are more particles which could act as a seed. So what would happen is although they would form cloud particles, they would not grow to sizes large enough to precipitate. So that is sort of hindering the precipitation, which would have occurred in a more pristine type of environment.

IRA FLATOW: I get it. And we had some very intense wildfires out in California just a few months ago. So what happened to the aerosols from all that black smoke? I mean, was there an impact from that?

RAJAN CHAKRABARTY: Yes, so Ira, it’s very interesting. So fire has been studied for thousands of years by humanity. And still it is one of the least understood of natural phenomena. Why? Because first of all, there are different phases of fires.

What you’re talking about, the black smoke, these are the particles and emissions coming from the flaming, or the hot temperature. But what follows the hot temperature phase is what we call the smoldering, or this whitish-looking smoke. Which, you know–

IRA FLATOW: Yeah, well, anybody who’s put out a campfire, we see if you leave a little bit of ash, white smoke comes out.

RAJAN CHAKRABARTY: Yes. So both of these types of– so these two different phases, they emit two very different types of carbonaceous aerosols. And what these particles do is– the black smoke, of course it looks black, or we call it soot, so it absorbs most of the incoming visible solar radiation. And the white color smoke, we conventionally think it is going to scatter most of the sunlight, because of its white color.

But what we are finding is that these white color particles actually have a strong absorption, most of it, near the ultraviolet or near the blue spectrum. So they are not completely white, what has been conventionally taught. So now we are ending up in a situation where not only we have the black soot particles absorbing, but the other species of particles which we thought to offset this warming effect could be also adding to the heating effect of the atmosphere. Yeah.

IRA FLATOW: Wow. Yeah, because we thought it might be reflecting itself. Dr. Grassian, do we know if these particles from the– let’s talk about your sea foam again. Do we know if these particles bump into one another or into other particles in the atmosphere? Do you know anything about what happens to them?

VICKI GRASSIAN: So these particles, yes, they can bump into one another. They can interact with gases in the atmosphere. And those gases can actually change the properties of the particle as they react in the atmosphere. These particles come out of the atmosphere through different mechanisms, what’s called wet deposition or dry deposition. So a rainfall can cause all the particles to come out of the atmosphere.

So yeah, they do interact with each other. And they also interact with gasses out in the atmosphere. But I want to go back to that last point for a moment that was just made. You asked about the wildfires and whether there was a cause for concern of the aerosols getting out into the air and people breathing these aerosols. So there’s definitely a lot of interest in the health effects of aerosols. And you also talked about how these aerosol particles can affect clouds and climate.

So it just points to, I mean, these are some of the most interesting aspects our air. Which we don’t understand well, because they can affect everything from our lungs and our health to the Earth’s climate. And so that’s what makes them so fascinating. And the reason why they can do so many different things is that each individual aerosol particle out there is slightly different from one another.

Some are very, very small, thousands and thousands and thousands of times smaller than a width of a hair. Some are close to the size of a width of a hair. They have different compositions. They have different shapes. And so for all these reasons, they have very interesting properties. And each one of them can be slightly different than the other one.

IRA FLATOW: Do the climate models we have now– talking about creating global warming or climate change– do they adequately model the cloud formation and the aerosols that are up there, Dr. Grassian?

VICKI GRASSIAN: I think that what we just heard a moment ago is that it’s very complicated. And perhaps the climate models right now are not taking into account everything that they need to take into account. And so what we just heard was that there’s a lot– these are some of the research questions that people are asking. How do we describe these in a global climate model?

And so the models are becoming more and more sophisticated. But because of what I just noted a moment ago, how these aerosols are very different from one another, there’s still work that needs to be done to get all that detail into the model the best that they can get it into the model.

IRA FLATOW: Let me see if I can go to the phones, get a quick call in here before we go. To Rob in Overland Park, Kansas. Hi, Rob.

SPEAKER 1: Hi, happy day. My question concerns a paper that was put out in the National Academy of Sciences in 2012 regarding your urinal peroxide enhanced nuclear fuel corrosion in seawater from Fukushima Daiichi power plant, and how these aerosols can contain radioactive elements that can be carried and deposited inland. And some of these have a very long half-life and are cumulative.

IRA FLATOW: All right, let me see. Any reaction from Vicki? Dr. Grassian?

VICKI GRASSIAN: Yeah, I’d like to take that one.

IRA FLATOW: Yeah, go ahead.

VICKI GRASSIAN: Thank you. So the question really goes to, when we talk about sea spray, we often think about the clean ocean seawater. But now we’re talking about some radioactive material getting into the water. Or there’s a sewage spill that gets into the ocean. And then, can that get into the air through this mechanism of bubble bursting and wave breaking?

And the answer is yes, it can get into the air. I don’t know– there are not that many reports. He points to a report in 2012. But we do need to think about that exchange between the ocean and the air through mechanisms like sea spray aerosol. Because what is in the water can get into the air.

IRA FLATOW: This is Science Friday from PRI, Public Radio International, talking about aerosols and sea spray. Dr. Chakrabarty, what would you like to know about aerosols that you don’t? I’m going to give you my blank check question, which is, if you had a blank check– I have it right here in my back pocket. Unfortunately, you’re not here to get it. And you could spend as much money as you want on research. What would you like to know? Where would you spend it?

RAJAN CHAKRABARTY: So one of my personal research interests is– and this is what Dr. Vicki Grassian briefly spoke about– what are the health impacts of these aerosols? Specifically if you look at most of the Asian countries, you have pollution episodes. Which, you know, people are choking because of these events. So we are still scratching the tip of the iceberg when it comes to the health effect side of it.

And most of these carbonaceous aerosols, what I just spoke about, is organic aerosols, or aerosols which are emitted from smoldering events. You have people in India and Africa– you have cookstove emissions. And they’re cooking. So what we have recently discovered is that most of these emissions, they contain what you call polycyclic aromatic hydrocarbons, we are cancer causing.

And most of the compounds which we found are typically labeled as carcinogenic by the EPA. And this is what people have been exposed to from the health side. And we also have found similar types of evidences from wildfire smoke. And wildfire, we have to really be ready for the impacts, especially in the coming 20 years or so. It’s going to be more frequent.

And we have to just deal with both the climate side of things, as well as the health side of things. And climatic side, one has to take into account the dynamic process involved in how this aerosol changes their properties, as well as how our atmosphere, once they’re emitted, what type of feedback it is providing.

IRA FLATOW: In the minute I have, I want to ask– people have discussed geoengineering as a possibility of controlling the right balances of aerosols in the atmosphere. Is this a little dangerous? I mean–

VICKI GRASSIAN: This is something that I do worry about. And the reason why I worry about it is that we don’t understand all the feedbacks. OK? So people talk about getting a bazooka gun and shooting sulfate aerosols into the atmosphere. And these aerosols will then reflect the light back into space.

But what are all the feedbacks? So the sulfate aerosol, when it comes back down to the Earth’s surface, is it going to get into the oceans, cover the forest? And so I think we need to think really carefully before doing those kinds of experiments on our Earth’s system.

Good place to end it. We’re going to take a break and continue our talk about aerosols right after the break. But I want to thank my guests– Rajan Chakrabarty, assistant professor of aerosol science and engineering at Washington University in St. Louis. Dr. Vicki Grassian, professor of chemistry and biochemistry and Scripps at UC San Diego. Thank you both for taking time to be with us today.

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