Episode description: 

Take a deep breath, and you’re inhaling oxygen from Earth’s atmosphere. Take a walk outside, and the atmosphere is shielding you from harmful radiation. NASA research provides crucial data to understand air quality and the intricate processes happening in the sky above us. In this episode, hear the inside story of NASA’s research into the ozone layer. Left unchecked, our reliance on ozone-depleting chemicals threatened to expose the entire planet to dangerous UV radiation. We’ll also fly along with Laura Judd, a NASA scientist studying air quality in the U.S. and around the world. 

 

[Music: Curiosity by SYSTEM Sounds] 

PADI BOYD: This is NASA’s Curious Universe, a show full of wild and wonderful adventures from our home planet all the way across the universe. I’m your host, Padi Boyd. 

JACOB PINTER: I’m your host, Jacob Pinter, and you’re listening to our series celebrating Earth. It’s not only our home, it’s also the planet NASA studies more than any other. If this is the first episode you’re hearing in the series, we’re so glad you’re here. And you should know that there are more stories about our home planet just like this one. All you have to do is scroll back in your podcast feed.  

PADI: So far we’ve covered NASA’s view of Earth’s ocean, including tracking tiny plankton by the way they change the color of the ocean surface, and measuring sea level rise around the world. 

JACOB: We also explored NASA’s satellite data about Earth’s surface and learned how farmers can use them for better crop management.  

PADI: In this episode, we’re tackling the air.  

[Music: Evolving Horizons by Alto Clark and Rémi Blanc] 

Without an atmosphere, Earth would be a much different place. It provides the oxygen we breathe, it regulates temperature, and it shields us from some of the dangers of space. 

JACOB: Now, there’s not one, single way to figure out exactly where the atmosphere ends and where space begins, but according to one common measurement, the atmosphere extends about 60 miles above Earth’s surface.  

PADI: At a human scale, the atmosphere is huge. Sixty miles is about 10 times higher than commercial airplanes fly.  

JACOB: But from space, the atmosphere looks awfully thin. Here’s one way to picture it: If Earth were the size of a basketball, the atmosphere would be thinner than an American dime. We’re about to hear how scientists identified a major threat to our atmosphere, how NASA research prompted a landmark agreement involving almost 200 countries, and how we continue to find innovative ways to study the air.   

PADI: It’s important to study the atmosphere at ground level because that’s what we breathe. We also get a global view from satellites orbiting in space. Then we can connect the dots with data from airplanes flying through the atmosphere. 

JACOB: NASA, together with the National Oceanic and Atmospheric Administration, has a number of satellites collecting data about the atmosphere, and there are many scientists combing through it. Recently I met up with one of them.  

[to Paul Newman] I’ve got a million questions for you, but first and most importantly, can you introduce yourself for me? 

PAUL NEWMAN: OK. My name is Paul Newman. I was here in the Atmospheric Chemistry and Dynamics Lab at the Goddard Space Flight Center. Now I’m retired and doing the emeritus thing, where I come in and work a few hours a day. So my hobby is now doing science—not doing spreadsheets but doing science.  

JACOB: The fun part.  

PAUL: The fun part. 

[Music: Binary Fission by Tom Kane]

JACOB: Paul has been at NASA since 1984. He worked his way up to become the Chief Scientist for Earth Science at NASA’s Goddard Space Flight Center. And he’s also contributed to some extremely august and influential scientific reports, which we’ll get into later.  

PADI: If you think of the atmosphere as a layer cake, we live in a layer called the troposphere. It’s the bottom layer, and it’s about seven miles thick. Just above the troposphere, the next layer is Paul’s specialty.   

PAUL: What I do here is look at the—mainly the stratosphere, that layer of the atmosphere that is about 35,000 feet, all the way up over 100,000 feet.  

JACOB: Now, there’s a lot of action in the layer we live in, the troposphere. It’s where we find 99 percent of water vapor. It’s where most weather happens. And of course, it’s the air we breathe. But the stratosphere has something we don’t have: the ozone layer.  

PAUL: Now, ozone is a really important gas in our atmosphere. If you didn’t have an ozone layer, life on the Earth’s surface would not be possible. 

PADI: Ozone is a gas made of oxygen atoms, but it’s not something we can breathe. The oxygen we need is called O 2. It’s two oxygen atoms smushed together. Ozone is O3. And that third oxygen atom makes a big difference. It makes ozone toxic for us, but it also turns oxygen into a kind of shield.  

Jacob: As Earth receives light and energy from the Sun, some of that comes in the form of ultraviolet radiation, which causes sunburn and skin cancer. And too much UV radiation can also disrupt the ocean food web and can even kill plants, if there’s enough of it. Ozone protects us from the worst effects.  

PAUL: It absorbs ultraviolet radiation very effectively. In fact, it’ll absorb a UV photon and then regenerate itself and absorb another, regenerate itself and absorb another. And so it’s constantly cycling, absorbing UV radiation and converting that UV radiation into heat. So you need an ozone layer. It’s important. 

JACOB: By this point, you may know where the story is going.  

[Music: Sporangium by Tom Kane] 

In the 1970s, scientists first proposed that the ozone layer could be depleted, and in 1985, they discovered ozone was rapidly decreasing over Antarctica. 

PADI: This turned into one of the biggest environmental stories in the world. I can still remember when it was all over the news. Now it’s in textbooks, for people who grew up afterwards. 

JACOB: And Paul was not only around at the beginning of that story, he and other NASA scientists were major players in helping the world understand exactly what was happening and what we could do about it. I wanted to hear how this played out from his perspective, so I asked Paul to take me back to the beginning. 

[To Paul] Do you remember, like, the very first time that you heard the words “ozone hole”? 

PAUL: Yeah, it’s kind of funny. I got here in ‘84—1984—and people began to talk about some odd measurements. Now, at the time, nobody called it an ozone hole. That was a term that was coined later. 

PADI: Before it became a global crisis, the ozone hole was just an unexpected data point. By the mid-80s, a few groups of scientists—including NASA researchers using satellites—noticed that the ozone was getting noticeably thinner during Antarctica’s springtime. It’s not what Paul and his colleagues were expecting.  

PAUL: Your first inclination is, Oh, geez. What did we do wrong? How did we foul this up? How did we break the instrument? But just like, you know, Sherlock Holmes, when you’ve excluded all these possible things, the thing that remains—the impossible thing—is probably what’s true. 

[Music: Inside Science by Carl David Harms] 

PADI: In 1987, NASA launched a campaign to get more answers. It was called the Antarctic Airborne Ozone Expedition, and it went straight to the source.  

JACOB: A couple of NASA airplanes were stationed at the very southern tip of South America. They flew into the sky above Antarctica, collecting data on the way. First, NASA scientists wanted clearer information about the ozone layer. Was there really a hole? If so, they wanted to figure out what was causing it.  

PADI: There were a couple of competing theories. One was based on chemistry. There were some hints that the gases chlorine and bromine were affecting the ozone. If that was true, the atmosphere was reacting to something humans had released. We were effectively poking a hole in our own shield. But other scientists thought the cause was some kind of change in weather patterns.  

JACOB: At the time, Paul was on Team Weather. As the NASA planes soared through southern skies, Paul was helping from the U.S.  

PAUL: This was pretty crude back in the day, compared to what we have nowadays, where you can pull up, you know, any number of pictures of the ozone hole instantly. Back then we were still using pencils and computer paper to draw pictures and then fax them down, where the people down there would look at them and then make plans. 

JACOB: And do you remember just how you were feeling in the middle of all that? Like, was it, I don’t know. Was it exciting? 

PAUL: It was pretty exciting, and you knew that you were doing something that was really important. It was a very exciting time. It’s very concerning time too, because if it was chemistry, where did it end?  

[Music: Life Support by Carl David Harms] 

Chlorine and bromine were still going up. People were using them like mad all over the world. And so there were some sleepless nights there where you thought, you know, where does it end? 

JACOB: The results from that campaign changed Paul’s mind. He became convinced that chemistry was causing ozone depletion, and he wasn’t alone. The data were so persuasive that they became known as the smoking gun plot.  

There was a chain reaction that went like this: Manufacturers in the 1980s relied on chemicals called CFCs, which stands for chlorofluorocarbons. These chemicals showed up in refrigerants and solvents. So you’d find them in all kinds of cans, like cleaning solution or inside air conditioners— even hairspray.   

PADI: When we spray CFCs into the air, those chemicals rise miles up into the stratosphere. UV radiation breaks the CFC molecules apart and chlorine atoms begin to wreak havoc. Just one chlorine atom can destroy thousands of ozone molecules.  

JACOB: In his office, Paul keeps a small collection of old spray cans holding some of these chemicals. As long as they stay in their cans and out of the air, they won’t do any harm. He pulls one spray can off the shelf. To my untrained eye, it looks a little retro but pretty innocuous. It’s the kind of thing you could find in anybody’s garage. 

PAUL: Yeah, this is CFC 12. It actually—it’s a can. 

JACOB: Can I hold it?  

PAUL: Yeah, yeah, yeah.   

JACOB: Yeah, it’s just like a full—”DuPont Freon 12. Dichlorodifluoromethane, CCI2F2 for automotive air conditioning systems”. 

PAUL: Yeah, it’s CFC 12, is what it is. it’s a liquid in the can, but if you dump it out, it’ll evaporate, just like, you know, if you dumped out, you know, water, it will evaporate. And it’ll evaporate pretty quickly. 

JACOB: Did you go out and buy this specifically? Or, like, how did you end up with this? 

PAUL: This is what I was going to use in my old car air conditioner. And I just saved it.  

JACOB: You just saved it?   

PAUL: I just kept it. 

[Music: Science Network by Carl David Harms] 

JACOB: Now that scientists had confirmed the cause, it was time to figure out what to do about ozone depletion.  

PADI: The problem was that in the ’80s, CFCs were everywhere. Around the world, we produced millions of metric tons of CFCs every year. And even worse, the damage from CFCs didn’t heal quickly.  

JACOB: CFC 12, which is that can Paul showed me, stays in the atmosphere for a hundred years. Even as scientists were looking for answers, it became clear that if we had any chance of solving this problem, the world had to work together.  

PAUL: OK, we don’t know what’s going on, but let’s sign the agreement now that will limit production and consumption. Not stop it, but limit it, because we can always back off of that. But you know, we’re going 100 miles per hour. Why don’t we hit the brakes and get it down to 60, OK, rather than just keep rolling along at 100 miles per hour when we don’t know if there’s a concrete wall in front of us. 

PADI: In 1987, the United States and a few dozen other countries signed an international treaty. Its full name was the Montreal Protocol on Substances that Deplete the Ozone Layer. The countries that signed the treaty pledged to phase out CFCs over time. And as the years went on more and more countries signed on. As of today, 198 countries have ratified the Montreal Protocol.

Jacob: The Montreal Protocol also created a group called the Scientific Assessment Panel. To track the effects of the agreement, researchers study the ozone layer and write reports. Paul was one of the scientists on the panel. 

PAUL: A couple of hundred scientists are involved in writing these, and they’re pretty thick. These are big, thick books. You can see a couple of them on my wall here. And so my initial involvement was in one of these early reports documenting what was going on with the ozone layer. 

PADI: Whenever there are meetings to discuss the Montreal Protocol, diplomats run the show. The scientists don’t make the decisions. But Paul and other researchers are there, ready to lend a hand.  

[Music: Intense Concentration by Carl David Harms] 

PAUL: We scientists sit in the back. It’s like in a classroom where the bad boys sit in the back with their mohawks and everything. And so we only speak when we’re asked to speak. Somebody will say, “And the Scientific Assessment Panel can address that,” and all of a sudden, it’s a little bit fire drill-like. You know, even if you’re paying close attention, you’ll hear the question, and you think to yourself, Oh my gosh. What do I have to say about triethylene chloride? And so now you start rushing around because you don’t remember these hundreds of gases. So it can be boring and exciting at the same thing.  

Jacob: Starting in 2007, Paul was actually one of the co-chairs of the Scientific Assessment Panel, so he was one of the people responsible for wrangling all of the relevant research and compiling it into those thick reports that are on his bookshelf every few years.  

Padi: So far, nearly 40 years after it took effect, the science is clear: the Montreal Protocol works. CFCs are banned all over the world. And over the years, a few amendments were added to limit other chemicals too.  

Jacob: In 2009, Paul led a study that modeled a hypothetical Earth in the year 2065. If we never slowed down CFC production and if the ozone layer kept getting worse, there would be devastating ripple effects that reached basically every living thing on the planet. Paul’s study showed that levels of DNA-damaging UV radiation would rise 500 percent.  If you stepped outside somewhere in the mid-latitudes—which is a lot of the United States—you’d get a sunburn in just five minutes.   

PADI: But thankfully that’s not the world we live in.  

[Music: Justified by Chris McCormack] 

The ozone hole is healing, although it will take more time until it’s fully repaired. CFCs can linger in the air for decades, or even a century.  

PAUL: Use my analogy of a pond: you’re dumping garbage or oil into a pond. You can dump it in really fast, and now it’s polluted, and it’ll take decades to—or many, many years—to recover. Same thing with the ozone layer. Easy to—it was easy to put chlorofluorocarbons in the atmosphere. It’s going to take a long time for them to come out. But we’re on the improvement slope, which is good. So things are getting better. Slowly, things are getting better. 

PADI: The Montreal Protocol shows what’s possible when governments work together. Some problems are so big that they can’t be contained by international borders.   

JACOB: Talking to Paul made me wonder what else we might be able to address. For instance, Earth is getting warmer, and humans are still producing greenhouse gases. Paul reminded me that at one point, society felt like it needed CFCs. They were so ubiquitous. But we did find other ways to make car air conditioners work.  

PADI: And hairspray! 

JACOB: And hairspray. And Paul told me that although the climate is a more complex issue than ozone depletion, he thinks we can find some answers to that too.   

PAUL: So we’ve gotten really good, I think, at improving efficiency of energy. And so I’m a bit of an optimist. But the road is never straight. There’s going to be some doubling back. But I think in the end, I’m optimistic that we’ll come to some solutions. The question is, how far do we go down the road without acknowledging—getting the major acknowledgements that this is a problem that needs to be dealt with.  

Jacob Pinter: I think there are a fair number of young people and even teenagers who are pretty pessimistic about the world and our ability to work together to make it better, I guess. Do you have any advice for them, or anything that might make them more optimistic like you are? 

Paul Newman: Actually, I think—I grew up as a young man or young boy climbing under desks because of the worry about an atomic exchange between the Soviet Union and the U.S. Things do change. And I’ve sat through a huge number of Montreal Protocol meetings, and I’ve seen the commitment of people to solve these problems. So I would say that I went from being a pessimist to being optimistic.  

[Music: Organic Elements by Lincoln Jaeger]  

We live in an amazing technological society that is just as capable of creating problems as solving problems. That’s where I become an optimist, because I see so much skill in solving these things. 

JACOB: Paul Newman is an emeritus scientist at NASA. You can find a lot more information, and you can even see current measurements of the ozone layer by searching for NASA OzoneWatch.

Now, ozone depletion is just one aspect of the atmosphere that NASA studies. There’s a lot going on in the sky, and it really affects how we live our lives. Air pollution is the biggest cause of premature mortality in the world. It kills about eight million people each year. To understand the causes, you have to untangle a complex mix of chemistry and weather and how they interact with chemicals emitted into the air.  

PADI: Laura Judd is a scientist at NASA’s Langley Research Center, specializing in pollution and air quality. She also focuses on ozone. This is going to add a wrinkle, but bear with me.  

[Music: Driving by Paul Hartnoll]

Sometimes ozone shows up close to the ground, where we might breathe it in. And since ozone is toxic for humans, that’s bad news. Laura says that kind of ozone comes from a reaction involving a few types of polluting gases, including nitrogen oxides and a group called volatile organic compounds, or VOCs.  

LAURA JUDD: It is produced through chemistry in the atmosphere of other pollutants that are emitted. Those two combined with sunlight, can create excess amounts of ozone that can be harmful to human health. 

PADI: One of the ways NASA studies these gases is with a satellite instrument called TEMPO. Like many NASA missions, that’s an acronym. It stands for Tropospheric Emissions: Monitoring of Pollution. TEMPO is in a geostationary orbit. It’s always over the same part of Earth, so TEMPO gives us consistent updates of the atmosphere over North America. A couple of complementary satellites watch over Europe and Asia.  

JACOB: Laura also leads airborne campaigns, which involve several airplanes working together. You’re going to hear her mention a couple of different types of planes. One is a Gulfstream jet. And then there’s the DC-8, a converted passenger plane that was retired in 2024 after 37 years of airborne science. In a mission called ASIA-AQ, Laura helped measure air quality in four different Asian countries. And in a project called STAQS, which we’ll hear about shortly, she took a close look at several American cities.   

[to Laura] Now that you’re so deep in this, when you go to a new city, like, even if you’re on vacation, are you paying attention to the air quality? Are you like, Well, there’s a power plant over there, and the wind is blowing this way? 

LAURA: There’s a couple things that I notice when I go to a city that I’ve measured before or even a new city. In the morning, you might see this brown cloud near the surface, and it’s the pollution being kind of capped near the surface early in the morning because we don’t have an actively growing—what they call a mixed layer, or a boundary layer. And on days that have worse air quality, probably have a darker brown cloud that’s closer to the surface. Another thing that I notice, which is kind of a joke, but when we’re out in the field and we’re trying to measure air pollution, one of the things that gets in the way is clouds. So if there’s a cloud between me and, you know, the pollution source, we’re not going to see that air pollution. So when we’re out in the field, I actually become really obsessed with cloud forecasts and looking at clouds on satellites. And there’s a lot of times now where I’ll go outside in the summer when I’m not in the field, and I would be like, This would be a really good day to fly. 

JACOB: Those cloudy days always find you when you don’t want ‘em.  

LAURA: Yes they do. And, I mean, it’s one of the other reasons why we need to measure air pollution from more than just satellites and aircraft, because we can only see when clouds aren’t in the way. And an important component to that is the ground network, and then also models that help tell us that even when there’s clouds there, we still have air quality forecasts and one of our goals is to make sure that those forecasts are as accurate as possible.  

JACOB: I’d love to talk about a couple of specific NASA missions you’ve been a part of. The first one on my list is STAQS, which I’m sure is another acronym. What does that one stand for? 

LAURA: I actually like this acronym! I came up with it. It stands for the Synergistic Tempo Air Quality Science mission.  

[Music: Robotica by Carl David Harms] 

I liked the name STAQS at first hand, because when I think of pollution, I think of smokestacks.  

JACOB: Yeah. 

LAURA: But actually, in reality, the better description as to why it’s fitting is because it was truly a stacking of our observing system vertically by thinking about how satellites connect with ground-based measurements and filling in those gaps with aircraft in between. So we were stacking our points of view. So that happened in summer of 2023.  

UNIDENTIFIED VOICE 1: Very exciting day. Historic day. We’ve been waiting over a decade for the TEMPO instrument to start collecting data.  

LAURA: We took two Gulfstreams out that had remote sensing instruments on them. 

UNIDENTIFIED VOICE 2: We have actually a flight plan that takes that wind pattern into account … (fades out) 

LAURA: And we went to New York City, Chicago, Toronto, and Los Angeles, with the goal of mapping these areas multiple times per day underneath the satellite.  

JACOB: I know that these field campaigns are— they’re big, and there’s a lot of moving parts. I’m really trying to imagine, like, what you were doing. You know, if I was sitting next to you, where were you physically sitting? What were you looking at? And, like, what was stressing you out in the moment? 

LAURA: Ooh, the stress question’s easy. Clouds.  

JACOB: Right. Should have known! 

LAURA: I was on the ground. We were stationed in Dayton, Ohio, when we were focusing on New York and Chicago. We could kind of decide between the two cities depending on the day. And we have a forecasting team that put together daily forecasts for us to look at, What are the air quality models telling us, what are the cloud models telling us? And then on a flight day, it’s me getting up at four or five in the morning and looking at the satellite and different observations that I could find, and be like, did our forecast hold? Did something happen? Like, one of the things that can happen is, Oh, a severe storm blew up in Iowa overnight, and so now we have this huge cirrus shield over Chicago, and we’re not going to get the measurements that we want. And so there’s times where I’ll be like, Okay, I’m going to call off a flight, and I have to call everyone at five in the morning and be like, “Don’t get up.” Otherwise, you know, most of the time we’re like, OK, let’s go. We would fly typically about nine hours. That was about an average flight. So it was a long day. We just lived in that airplane. We had a LIDAR on board. And so with that, we could actually see in the LIDAR— estimate what the boundary layer height, or the mixed layer height is, of the pollutant. So that’s largely the layer closest to the surface where most pollution resides. So we’re communicating in real time, or if we just see something interesting, like, Oh man, ozone is really high over Long Island Sound right now. This is something we need to take note of. And as we’re analyzing the data down the line like this is an event that we could look at. It’s activities like that.  

[Music: Event Horizon by Brandon Seliga] 

JACOB: So there’s, you know, there are the planes flying around full of scientists and science equipment, and then obviously there are a lot more people supporting those on the ground. And what I hear you saying, I believe, is that for STAQS, you were on the ground doing that kind of work. Have you been inside those planes, actually like at the science stations as well?  

LAURA: Oh yeah. So I got to fly on the NASA DC-8 and do similar types of measurements of flying low to the ground and measuring air pollution. One of the goals was to go into airports and do low approaches, because that’s the lowest that we can get to the ground to get a full profile. So if you think about it that way, it’s doing that for eight hours out of a day. The DC-8 would do that for six to eight hours. I’ve also been on the remote sensing aircraft, and those are a little bit easier on the body. We’re—think about it as lawn mower-ing a city. So I’d have these flight lines spaced, you know, like three and a half miles apart, and it would be from an altitude of 28,000 feet to 40,000 feet, depending on the plane that we were on. It’s a lot of fun to be up there. I think—I’m not a fan of flying, but when I do it for science, I enjoy it thoroughly.

JACOB: I’m no airplane expert, but from the pictures I’ve seen, the DC-8 looks about the size of a passenger plane, like maybe a one-aisle passenger plane?  

LAURA: Yeah. But what’s different is, instead of just being full of seats, it would be full of these metal racks that hold the instruments, and behind those racks there would be a couple of first-class seats. That’s where the instrument operators would sit. You would just walk down the plane, and you’d see a rack here with a couple scientists, and so it’s a little different than when you fly commercial. There’s a lot more going on. There’s a lot more obstacles to be careful of. We do get a lot of, you know, training on what you can and can’t touch, how you need to be careful. There’s a lot of risk assessment that goes on and is briefed to people before they fly on those planes.

JACOB: And as you’re flying around, I mean, what’s the the mood, like? Like, what’s the vibe? Is it? Is it tense? Are you talking to the person sitting next to you? Did they give you, like, little NASA-branded bags of peanuts? 

LAURA: It is bring your own snacks. [laughter] Most of the time it’s not tense. It might be a little tense if it’s—largely the beginning of the flight is, people are turning on their instruments and getting their first looks and being like, OK, is everything fine? So it’s pretty quiet toward the front end, and then we might get first look at the data and say, Oh, like, aerosols are really high right now. Or I see a peak in NO2 over this area, and it’s at this level. When it’s a nine hour flight, there’s a lot of quiet time too or a lot of time where we, you know, talk about our hobbies or eat lunch, make coffee. 

JACOB: Important stuff.  

LAURA: Yeah, it’s—I get to fly with some of my closest friends and spend a lot of hours together. 

JACOB: Yeah. You know, NASA studies the earth in a lot of different ways, including with satellites, and when it comes to pollution and air quality specifically, what can NASA satellites see that other research tools can’t see?  

[Music: Robot Reborn by Nick Herbertsen, Tord Jungsten, and Danny Cullen] 

LAURA: Yeah. So the standard when you’re thinking about air pollution is, we have a ground monitor, and when you’re standing next to the ground monitor, you can see, This is the quality of the air that I’m breathing if you have knowledge as to what those numbers mean. But you’re only measuring at that monitoring site. There’s a lot of variability in changes between monitoring sites, and we can’t measure everywhere. The satellites that we’re using get continuous spatial coverage, so it can kind of fill in gaps between monitoring areas. What’s really neat with new instruments and improved technology is we’re getting higher spatial resolution, and so now we can fill in some gaps on our interpretation of what’s happening with the satellite data. 

JACOB: What are you still curious about? 

LAURA: I think what I’m curious about is where we’re going to be throughout my career. I see how much I’ve learned and my community has learned in the last eight years of just me being here, and I feel like we’re just at—in a very new realm of the science that we’re at. So I’m so excited about us just seeing the atmosphere that we live in at such finer detail all the time. So I’m really curious how far we’re going to push it over hopefully many decades.  

JACOB: Do you have any notions of what that kind of research might look like in, I don’t know, 20 years? 

LAURA: I think a lot of it depends on two things. It depends on where technology takes us and whether we can push the limits on the measurements that we’re taking right now. One of the neat things about nitrogen dioxide, which is a trace gas I’m a little obsessed with because it’s my expertise, but it’s also such a beautiful product. If you’ve ever looked at a map of NO2—and anybody can reach out, and I’m happy to share with them—no matter how fine the resolution that we push it, we always see a new spatial pattern that’s within there. There’s so much variance within that gas. And I’m wondering, what is the limit before we stop learning something new? But then also, I’ve seen how, over the last two decades—it’s really a success story in clean air—is we can see that nitrogen dioxide has been cut in half around many areas of the globe. It’s really fascinating to see, on the decisions we make, and how does that come about into a change in the trends that we’re seeing over time.  

JACOB: Anytime I hear someone say something like, “I’m obsessed with nitrogen dioxide,” I know I’m in good hands. 

LAURA: [laughs] It’s probably a rarity out there. But maybe—with the pictures, I might be able to convince some new folks to have an obsession.  

[Music: Four Floors Up by Andy Hopkins, Jacob Nicholas Stonewall Jackson, and Ella Ryan] 

Jacob: Laura Judd is a research scientist based at NASA’s Langley Research Center. And if you too want to become obsessed with nitrogen dioxide, we’ll put a photo in the transcript page for this episode. You can find this episode and all of our wild and wonderful adventures at nasa.gov/curiousuniverse. 

Check out these links to see nitrogen dioxide for yourself:

• Nitrogen Dioxide Over the United States, 2005-2022
• Nitrogen Dioxide over the Continental US and Los Angeles

Jacob: We’ve got a little bit of extra curiosity for you.  

[Music: Marimba Mayhem by Harry T. Croxford] 

When we talk to NASA experts and even astronauts, we always ask, What are you still curious about? I mean, I want to know what everyone’s curious about. So please welcome in Rachel Feltman. She’s the host of the podcast Science Quickly from Scientific American. Hey Rachel, glad you’re here.  

RACHEL FELTMAN: Hey, thanks so much for having me.  

JACOB: So for people who haven’t heard your show, what is Science Quickly? 

RACHEL: Yeah, well Science Quickly is—in some ways, it’s exactly what it says on the tin. We have pretty efficient science podcast stories for folks. You know, we recently did one from MIT’s nanotechnology clean room. Lots of fun stuff like that.  

JACOB: And on a personal level, how do you feel about space? Are you into it? Are you, I don’t know, scared of it? 

RACHEL: I love space. I guess I’m—I feel like I have a healthy fear of space. I respect it. You know, I don’t know that I would—if I had the opportunity to go to space—like, really, not just, you know, a quick little trip, technically going to space—if I had the opportunity to really be on the ISS, or, you know, go to the Moon, I think I would probably have a real crisis about it, because I’d be like, That is scary. Space is hard. But I do really love space, and I love covering space stories. We talk about space a lot on Science Quickly.  

JACOB: Well I can tell you’re a curious person, and I can tell you’re a person who also gets a lot of answers on a pretty regular basis. So what are you still curious about? 

RACHEL: So something I’ve been wondering about is, you know, of course, space is very big. What’s the smallest stuff on Earth that NASA can study from space? 

JACOB: Yeah, so I have a couple of answers for you here. I have a literal answer, and then I have a more trippy answer. So let’s start with the literal one. So NASA has been studying Earth for more than 50 years. Obviously, technology has just gotten better and better. In 2025 an upcoming satellite called NISAR will track changes on Earth’s landscape that are as small as one centimeter. So that means from space, we’ll be able to see things like a forest getting cut down or a building moving because of an earthquake as small as one centimeter, which is pretty crazy. 

RACHEL: Yeah. 

JACOB: But we can go even smaller. There’s a satellite currently orbiting called PACE, which can see plankton that are microscopic. So if you pick up a drop of water, there might be thousands of these phytoplankton in that one drop. And it can also see aerosols, which are particles in the atmosphere that can be as small as an individual virus. And the reason that we can see these from space is because even though plankton and aerosols are really small, they have a huge impact.  

[Music: String Switch by Rainman] 

So that’s my literal answer, but let me give you the trippy answer that is maybe more fun. So using satellites and these observing stations on the ground, we can detect the precise center of the Earth down to within a few millimeters. And so when you think of Earth—like a lot of times, we just picture a ball,like a perfect sphere, you know. And you see those cutouts of the different layers of the earth, and the Earth’s core kind of looks like a bullseye right in the middle, you know?

RACHEL: Sure, yeah.  

JACOB: It’s not like that. Earth’s not a perfect spirit, and the exact geocenter or center of mass, it’s constantly changing. So even if there are earthquakes on the surface, if there is volcanic activity or even changes in atmospheric pressure, that can change where that center is. And that’s a really big deal, because the satellites that we have in space—and that’s not just NASA satellites, but you know, think about the GPS satellites that give you maps on your phone, any kind of satellite—they’re orbiting that geocenter, and so they need to know how far away from that point they are, not just the surface of the earth. We have these observing stations on the ground. They send laser pulses up to satellites, and using that information, we can determine the exact location of that geocenter to a few millimeters at any given time. There’s actually this whole field called geodesy, which is studying the shape of the Earth, which is a super important scientific discipline in its own right.   

RACHEL: Wow, that is such a cool word. I can’t believe I’ve never heard it before. Wow, that is so cool. I loved both the literal answer and the trippy answer. 

JACOB: I have a question for you as well. If you could point a satellite anywhere you wanted—like, if you could just see something on Earth from space—what would you want to see? 

[Music: Marimba Mayhem by Harry T. Croxford] 

RACHEL: That is such a good question. I mean, I guess the answer is that I would probably ask someone from NASA what would be cool and important to look at, because I think I it’s overwhelming. There’s a whole Earth, so hard to know where to start. 

JACOB: Yeah, that’s fair. Well, Rachel Feltman is the host of Science Quickly, a podcast from Scientific American. Rachel, thank you so much. Thanks for being curious.  

RACHEL: Yeah, thank you. 

[Credits]  

Padi: This is NASA’s Curious Universe. Our Earth series was written and produced by Jacob Pinter and Christian Elliott.   

Our executive producer is Katie Konans. Krystofer Kim is our show artist. Our theme song was composed by Matt Russo and Andrew Santaguida of SYSTEM Sounds.     

Special thanks to NASA’s Earth Science team, including Mike Carlowicz and Charlie Hatfield, and to Robert Lorkiewicz at NASA Langley. 

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