Why These Tiny Particles Are A Big Deal : Short Wave For much of the pandemic, some scientists had been pushing the Centers for Disease Control and Prevention to recognize that the coronavirus is spread through aerosols--very small particles that can linger in the air. The CDC did that this month, so we brought Senior Science Correspondent Maria Godoy onto the show to explain the distinction, and the implications for staying safe during the pandemic.

Is the constant refining of the science behind the coronavirus leaving you confused? Send us your questions at shortwave@npr.org and we might answer them on a future episode.
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Why These Tiny Particles Are A Big Deal

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Why These Tiny Particles Are A Big Deal

Why These Tiny Particles Are A Big Deal

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You're listening to SHORT WAVE from NPR.


SOFIA: Hey there. Maddie Sofia here today with NPR science desk correspondent Maria Godoy. Hi, Maria.


SOFIA: Maria, we're talking today because you have spent a good chunk of this pandemic reporting on ways people can try to stay safe from the coronavirus.

GODOY: Yeah. I'm basically the pandemic news-you-can-use reporter.

SOFIA: (Laughter).

GODOY: You know, since the earliest days, I've been researching things like mask-wearing - do it, by the way...


GODOY: ...How to interact safely outside your house or what to do if you live with somebody who gets ill, you know, all kinds of fun topics.

SOFIA: And that's not easy - right? - because we are learning so much every day. You know, like, I feel like if I take a week off reporting on coronavirus, I've missed so much.

GODOY: Oh, yeah, absolutely, 100%. We went from not knowing this virus even existed to having hundreds and hundreds of scientific studies on it in, like, months.

SOFIA: Yeah, which means that a lot of what experts are saying is being refined as they learn more about the virus, including how it's spread.

GODOY: Oh, absolutely. And, you know, one real sticking point is how much transmission occurs from very, very small particles that can linger in the air. They're called aerosols.


LANA ZAK: Scientists have been debating how the coronavirus spreads since the pandemic began last spring. Those conversations have been heating up recently as some experts argue that aerosols may, in fact, be playing a bigger role in its transmission than previously thought.

GODOY: And, you know, just in the last few weeks, the CDC has finally updated its guidance to note that, indeed, some transmission happens this way.


UNIDENTIFIED REPORTER: They say there have been cases where people were infected at distances greater than six feet apart through airborne particles.


SOFIA: And this new guidance can be kind of confusing. But, Maria, we are here to sort this out. So today, we look at the science of aerosols, what they are and what role they play in the spread of coronavirus.


SOFIA: So Maria, before we get into the nitty gritty of aerosol transmission, let's start off by walking through the ways this virus can spread - close contact, contaminated surfaces and aerosols.

GODOY: So what we've known for a long time is that the coronavirus can spread when you come into close contact with an infected person. So that can be physically touching them or just be, you know, right in their close vicinity. And that's often through what we call respiratory droplets. So if you're sick, you could generate these droplets by coughing or sneezing or just breathing. And this is what public health bodies like the CDC and the WHO say is how most people catch the coronavirus.

SOFIA: Right. And that's what a lot of the guidance has been focused on so far, those droplets that fly out of your mouth when you cough, sneeze and, to a lesser amount, talk and breathe.

GODOY: Right. And those droplets can also land on a surface and then contaminate it. And then if someone else touches that surface, like, say, a doorknob, they could potentially become infected. Now, as we've learned more about the virus, you know, it's become clearer that's actually not the main way people are getting sick. It's still possible, but it's not really common.

SOFIA: Right. And, Maria, this is why I get sassed right up when I see gyms or restaurants only focusing on disinfecting surfaces. Like, great, dudes. It's not going to hurt. But, like, let's crack a window. Let's get another round of masks in here. You know, let's talk about how many people can be in here and how long because time's a factor. You know what I'm saying?

GODOY: Yeah. It's basically hygiene theater. And I feel you. It's...

SOFIA: Oh, I just...

GODOY: ...Kind of not where we should be focusing all our efforts. Yeah.

SOFIA: With hygiene theater, there's no intermission. There's only transmission. Am I right? Am I right?

GODOY: (Laughter).

SOFIA: Honestly, NPR makes me worse about these puns.

GODOY: Anyway (laughter).

SOFIA: OK. Yeah. So that's droplets, which brings us to our third form of transmission, what we wanted to talk about today.

GODOY: Yeah. And the third way coronavirus spreads is via very tiny, tiny particles that travel farther and hang around longer in the air than those droplets. And these are called aerosols.

SOFIA: Yeah. And let's put the sizes in perspective because close up, both bigger droplets and tiny aerosols can get you sick. But at a distance - and I'm talking way farther than six feet - is where you generally only see aerosols playing a role. And that's because of their size.

GODOY: Exactly. So with droplet spread - droplets are what you might think of when you sneeze or cough. They vary a bit in size. But think, maybe, like, the size of a speck of dust or the width of a human hair. And even though that's pretty small, they are generally heavy enough to fall to the ground fairly quickly. That's why we've heard all the guidance about staying six feet away from people. The larger droplets really don't travel all that far. Although, they can travel farther from a sneeze or cough.

SOFIA: Right. Right. And the aerosols are even smaller than the smallest of these droplets. They hang out in the hair longer, like you said. They travel farther than the bigger droplets, certainly way more than six feet. And, you know, as we talked about, recently, the CDC has acknowledged that, yeah, these super tiny particles can get you sick.

GODOY: Right. And, you know, these tiny, infectious aerosols can linger in the air for minutes or even a couple of hours in some situations. And they can travel farther than six feet. And, actually, some scientists are arguing that those tiny particles are the primary way that the disease is spread, partially because those big droplets we were just talking about, they're more common when people are coughing and hacking. And with this coronavirus, a lot of people don't have any symptoms. But they still can get other people sick.

SOFIA: Right.

GODOY: But how much of a role these tiny infectious particles are playing in transmission, that is pretty controversial. At this point, the CDC is saying that they think this is a far less common way that this virus spreads than those bigger droplets. And it's only been observed in certain situations. For example, there was this infamous choir practice that resulted in a big outbreak back in March.

SOFIA: Oh, yeah. I remember this. I remember this. The one near Seattle, right?

GODOY: Yeah. So 53 out of the 61 attendees came down with COVID-19 after spending 2 1/2 hours together at a singing rehearsal.

SOFIA: Wild. Wild.

GODOY: And they were all indoors. Yeah, I know. Wow. They were all indoors. They were obviously singing. And so they were projecting their voices.

JOSE-LUIS JIMENEZ: And basically, there is no way to explain it if it's not through aerosols.

GODOY: That's Jose-Luis Jimenez. He's an atmospheric chemistry professor at the University of Colorado Boulder. And he was on the team that investigated that outbreak. And he said...

JIMENEZ: People who were 50 feet from the index case got infected.

GODOY: And that is just one clear example of aerosol transmission.

SOFIA: OK. So we know these tiny, little particles can get people sick. And how much of coronavirus transmission is happening via that route is being hotly debated. But, you know, the real question, Maria, is, what does this all mean? Like, does this matter?

GODOY: Yeah. It matters because it means that we need to be extra careful, like even more careful than maybe you've already been. And, hopefully, you have been careful already...

SOFIA: Yeah.

GODOY: ...But especially careful in indoor spaces because these are places where those tiny, infectious particles can hang out for longer because maybe there's not a lot of fresh air moving around. And so that means they build up in the air over time. And, you know, some scientists have said we really need to rethink that six-foot rule, especially in indoor spaces. You might want to be farther away.

SOFIA: Right.

GODOY: You know, you definitely want to be wearing a mask if you are indoors with someone outside of your household bubble.

SOFIA: But more to the point, you want to be outside when you meet people whenever you can.

GODOY: Right. Absolutely. You know, the researchers I've spoken with say airflow is just so much better outside. So your risk of contracting coronavirus is lower if you're in the great outdoors because the air is constantly moving. So it's dispersing infectious particles just a lot faster than if you were inside. But even then, if you're going to be spending a lot of time with someone outdoors - so more than just a brief hi-bye, you know, brief chat - one of the experts I talked to said that's a good idea to wear masks outdoors, too.

SOFIA: Yeah. And, I mean, this is the thing, Maria. Like, it's really complicated when you're trying to estimate risk - right? - because you have to think about so many factors. Like, when I'm deciding whether or not I'm going to go somewhere, I asked myself, all right, indoors or outdoors? How much fresh air is going to be circulating? How many people are going to be there? The fewer the better, obviously. How long will we be there? The shorter the better. Is everybody wearing masks? You know, the truth is there's no situation where you are with people that's zero-risk.

GODOY: Yeah. Absolutely. And, you know, for me, I am only indoors with my family bubble. And even then - so my mom only recently started coming over inside my house. And I wear a mask around her because she's high risk.

SOFIA: Yeah.

GODOY: And for people who are not in my family bubble, I only see them outdoors, you know? And that's, unfortunately, about to get a lot more difficult.

SOFIA: Yes. Winter is coming, as they say.

GODOY: (Laughter) You know nothing, Jon Snow.

SOFIA: (Laughter).

GODOY: No, actually, you know a lot, Maddie.

SOFIA: (Laughter).

GODOY: And you're right. And when winter comes, we are going to be spending a lot more time indoors. And that means we really need to think about ventilation. I talked to this one researcher, Kimberly Prather. And she's an atmospheric chemist at Scripps Institution of Oceanography. She says ventilation is key.

KIMBERLY PRATHER: You know, ventilation, really, is just so important. And sometimes, in some places, that's just a matter, you know, opening the door and opening the windows. You know, just having clean air is really the best thing you can do. Where I live in San Diego, you know, we're in a good position. We can also move activities outdoors. That's another thing that we also encourage. If you don't have good ventilation, you can put stand-alone air filters in your space.

SOFIA: Air filters. OK. Let's talk about this for a second, Maria. Are they actually useful during this pandemic to cut down on the risk?

GODOY: Yeah. So Kimberly says that a lot of those respiratory droplets can be caught by masks and some stand-alone air filters. So we don't have data specific to this coronavirus. But some medical isolation units from the 2003 SARS outbreak used them. And the EPA website says that air cleaners and HVAC filters can help reduce airborne contaminants, including viruses, in a building or small space.

SOFIA: Right. And there's this beautiful resource you sent me as we were reporting this episode. It's a document all about how to protect yourself from aerosol transmission. We'll link to it in the show notes. It was made by scientists and engineers with a bunch of years of collective research experience.

GODOY: Right. These are people actively investigating aerosol transmission of COVID-19. Some were part of a COVID-19 expert group for the World Health Organization. And they have an entire section of guidance on filtering and cleaning, which I recommend you check out to see what filter could possibly work for you. But an important note here is that you absolutely should not rely on air filters solely to keep you safe.

SOFIA: Right.

GODOY: Instead, filtration can be part of a plan to protect people indoors. In most situations, there's really no replacement for fresh air. And that means air from outside. So have a fan blowing out a window while air is coming in through another window.

SOFIA: Yeah. And, I mean, real talk here, Maria - these next few months are going to be really tough. You know, as a country, we're currently seeing a surge of cases again. And that's not what you want to see heading into the winter. So, you know, if at all possible, think about establishing that small social bubble that you can be a part of that'll help you stay sane and also safe.

GODOY: You know, I'm with you. It's going to be really tough. It has been tough. It's going to be tougher in the cold. And the more time we spend indoors, we really have to think through our social pods and keeping indoor gatherings to a very small group. Keep those windows open. Run the air filters, et cetera. But, obviously, always wear masks when you have to be indoors with people outside your bubble. But try to keep those visits as short as possible.

SOFIA: Right.

GODOY: And, you know, trust me. I know the entire, entire world has some serious pandemic fatigue by now. I do. My kids do. My husband does. I have two small kids with a whole lot of energy to burn. And they need to socialize not just because they're bored, but because it's part of their development. And, you know, we are going to try and keep that group of kids that they play with very small, basically just a few whose families we know well. We know what they're doing to stay safe. And we're going to keep those interactions outdoors as much as possible, for as long as possible, which means that firepit we got last year is going to be on all the time this winter.

SOFIA: (Laughter) Absolutely. All right, Maria Godoy. We always appreciate you. Thanks for coming on the show.

GODOY: Always. For you, anything, Maddie.


SOFIA: For more information on how to create your own social bubble, make sure to check out our episode notes. We've got a link for you there. We'll also link to that aerosol transmission FAQ we mentioned earlier.


SOFIA: Today's episode was produced by Rebecca Ramirez and edited by Gisele Grayson. Berly McCoy and I checked the facts. I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.


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