The atmosphere is one of Earth's most dynamic and least visible systems. Alongside gases that sustain life, it carries microscopic particles that affect air quality and transport pollutants, including micro- and nanoplastics.

In this episode of the ALLATRA Global Research Center Podcast, Anastasia Pashigreva, PhD, Chemist & Sustainable Technologies Researcher | Micro- & Nanoplastics, ALLATRA Global Research Center, speaks with Yue Zhang, PhD, Assistant Professor of Atmospheric Sciences, Texas A&M University and recipient of the NSF CAREER Award. Dr. Zhang's research focuses on atmospheric chemistry, aerosols, air quality, and the emerging science of airborne micro- and nanoplastics. Using advanced laboratory techniques and real-time atmospheric measurements, his team investigates how these microscopic particles are transported through the atmosphere and why understanding them has become an important scientific challenge.

Rather than focusing only on what we already know, this conversation explores the questions scientists are still working to answer — from identifying the major sources of airborne microplastics to understanding their distribution, transport, and potential impacts on climate and human health.

In this episode:

- The science behind atmospheric aerosols and why they matter

- How airborne micro- and nanoplastics are measured in real time

- The most likely sources of microplastics in the atmosphere

- Indoor vs. outdoor exposure — what current research suggests

- Mobile atmospheric laboratories and field measurements

Learn more about Dr. Yue Zhang's research:
https://artsci.tamu.edu/atmos-science/contact/profiles/yue-zhang.html

Report of the ALLATRA Global Research Center “Nanoplastics. A Systematic Risk Analysis for Human Health, Ecosystems, and the Environment”
https://allatra.org/global-research-center/publications/agrc.report.mnp.2026.04001

The podcast is hosted on the ALLATRA Global Research Center platform.

This material is for informational and discussion purposes only. The statements, assessments, interpretations, conclusions, and hypotheses contained herein represent personal views of their authors as of the date of publication and do not constitute an official stance of the ALLATRA international organization or any other public association, organization, project, partner, or affiliated entity or person, unless expressly stated otherwise.

Publication of this material provides an opportunity for open discussion and does not in itself imply institutional endorsement, confirmation, or scientific verification of the views expressed. The material does not constitute an official statement, expert opinion, or professional advice.

Full Podcast Transcript

Anastasia Pashigreva, PhD

Hello and welcome to this podcast from the ALLATRA Global Research Center. My name is Anastasia and I am your host today. And today's topic is truly fascinating for me because the atmosphere is so much more than the air we breathe. This dynamic system connects every region of our planet. The atmosphere makes flights possible, influences satellites, communication, and operation. It drives the weather and climate. The atmospheric chemistry of many of these processes shapes the air composition, influences both the environment and human health.

And I'm really excited to welcome Professor Zhang from Texas A&M University. He's a leading researcher in atmospheric chemistry with expertise in atmospheric aerosols and air quality, and he made substantial contribution to the understanding of how micro- and nanoplastics affects the atmospheric chemistry. His recent work on airborne micro- and nanoplastics, combined with innovative laboratory studies and atmospheric measurements, is helping us to understand this field better. Welcome, Professor Zhang, and it's a pleasure to have you with us today. Thank you very much for joining us.

Yue Zhang, PhD

Thank you very much, Anastasia, it's really nice to be here and sharing with you through this podcast of some of the research you have been doing and also sharing with the audience. So hi, everyone.

Anastasia Pashigreva, PhD

Welcome. And to begin, it's always exciting to hear about the scientific journey that scientists made. Could you share what inspired you to study atmospheric chemistry and what questions continue to motivate your research today?

Yue Zhang, PhD

Yeah, for me. So my interest in studying the environment and air started when I was in high school because I was very interested in chemistry, biology and physics. So in my college, I was trying to decide what would be a good way for me to combine all these different knowledge together. And in general, environmental sciences is such a nice, broad, interdisciplinary area that you can apply all this knowledge to solve the most pioneering, but also urgent issues in the world. And that's why I decided to choose this as my undergraduate major. So what I did is I had my undergraduate in Beijing University, and then afterwards I continued with my PhD at Harvard University working with Scott Martin, who was my PhD advisor at that time. So when I was at Harvard, we had to dive a little bit deeper into a subfield of the environmental sciences. And that's where I choose to study atmospheric chemistry. The reason is because for the air there are a lot of very fast reactions happening, and then because the air is continuously moving. So this part is really fascinating for me. The other part is that every day we breathe in and out the air continuously. So what's happening in the air also has lots of impacts on our health as well.

Yue Zhang, PhD

And at that time when I was studying, there was lots of air pollution issues all over the world, which now still do, but have changed a lot from the past 10-20 years. So that's also part of the research. I'm very excited because it's always changing and there's always a new emerging topic that is worth studying for us to understand what's in the air, what's happening, and how does that impact our health as well as climate.

After my PhD I actually received a NSF, US National Science Foundation, a postdoc fellowship. So this fellowship was really nice. It allows me to work at different universities within the US more freely and independently. So I was working at UNC Chapel Hill, University of North Carolina, and then also jointly working with Aerodyne Research at Boston College and MIT. And then to jointly explore the climate impacts as well as the chemical process of different species in the air. And then that made me really realize, “Okay, I actually want to go into this field even deeper and have my own research lab.” And so I applied for different universities, and I eventually decided to join Texas A&M as a faculty there to continue the research and building my research lab.

Anastasia Pashigreva, PhD

Yeah, that's a really interesting journey, I think for many people atmosphere is a pretty simple system. Just oxygen, nitrogen, and some CO2. But in fact, I understand how little we know and it is continuously changing. And if we take into account the entire air column, the upper layers of atmosphere, that becomes even more challenging. So this is one of the reasons why I'm super excited to have our conversation. And could you tell us about these atmospheric aerosols? So we know that they both influence climate and health, but people know very little about them. What makes aerosol such a fascinating and challenging field of research?

Yue Zhang, PhD

So I think you made a really good and interesting point that, you know, people commonly think that the air composition is fixed and it has nitrogen and oxygen and carbon dioxide, CO2 and all these compounds. And that is true that for this majority of the species in the air, they don't change as much. And CO2 is slowly increasing, but over a shorter period of time, they remain roughly the same. But what's actually really interesting is that in air, there's this less than 1% of the compounds, including some of the organic gas, inorganic gas, as well as aerosols. They even consider such a small portion, but they have such a huge impact on many, many things. And then so that's speaking about aerosols, which are the main topic for today. So they actually have very, very little mass in their air. Sometimes people estimating to be less than 0.1% or even less. So it's such a tiny fraction, but they can have huge impacts. The first thing we know is that there's air quality issue, right? So these aerosols could be inhaled into our lungs, and then they can transport it through all these alveoli and vessels and be carried all around our body and affect our health. But they can also impact the climate as well. The reason is because for the clouds to form in the air in general, you need these aerosols to serve as a nucleus for water vapor to condense into water droplets or ice.

Yue Zhang, PhD

And without aerosols, it's going to be really difficult for these clouds to form. So if you have air that's purely free of any aerosols in the Earth's atmosphere, then the cloud will be very difficult to even make. So that's why they're very important.

So people have been studying aerosols for some time. And then initially, scientists over 100 years ago thought that there must be something in the air, right to potentially form clouds? And that's one of the first parts once people discovered aerosols. But as time goes on, so for the past 20-30 years, our understanding of aerosols have improved a lot. But there are still many unsolved questions that we're working on.

So these aerosols, we normally think they're essentially suspended liquid or solid particles in air and together with a little bit of air molecules around it. So that's the scientific definition of aerosol. And then in layman's words, essentially it's some small particles that's suspended in the air and then can stay there for some periods of time. And there are differences when we talk about aerosols compared with aerosol hair spray gels, right? These are different terms. And one is more scientific. The other is what we use every day.

Anastasia Pashigreva, PhD

Yeah. And, you know, just as we talk, you dedicated a lot of time in your research and studying the behavior and properties. And I'm really curious what led you into the micro- and nanoplastics, and why do you believe that they have become such an important area today?

Yue Zhang, PhD

This is also something I'm quite passionate about. So my lab's work — we have a few different areas. And then the micro- and nanoplastics is actually a natural extension of some of the work I have done in the past. So previously I was working a lot on organic aerosol, a specific type of organic aerosol we call secondary organic aerosol. So these are the aerosol components in the air that are made of organics, and then they come from the reactions of different kinds of organic vapor reacting with atmospheric oxidants such as ozone and other species to gradually make this organic aerosol suspended in air.
So I studied a lot of their composition and also how to detect them in real time, as well as their impacts on the climate. And organic aerosols in general are important because they comprise a large portion of the total aerosol mass in the atmosphere, and so understanding their pathway is very important for climate as well as human health.

And then after that, as recently as we heard a lot of micro- and nanoplastic pollution in the water, in the ocean — there's studies that have been done to show that for an average person, you may eat one card weight of microplastic every year, right? So this kind of question tries to understand there's a lot of exposure to the micro- and nanoplastic in our food. But how about in the air? How much are they in the air for their concentration, as well as how do we inhale them and what are their health effects through inhaling instead of digestion? So this was one of the research questions I was curious about, and that led me into this field.

Anastasia Pashigreva, PhD

It's really interesting — that was such a natural transition to the field of micro- and nanoplastics. And just during this recent decade, how has our understanding of airborne micro- and nanoplastics evolved, and what is our current understanding of that?

Yue Zhang, PhD

So I think initially, when people were trying to understand micro- and nanoplastics, it first came in the water — so in the fresh water and ocean water — and then people started to try to collect air samples. And then the first type of air samples people collected was essentially a large passive collector. The reason we call it passive is you're letting the aerosols essentially sediment onto the collector — there's no active drawing of air or anything like that. So you can think of putting a big metal plate outdoors in the air and letting it stay there for a while so all the dust and all the micro- and nanoplastic particles would also condense onto it. And then after staying there for a week or a month, you bring it back to the lab to analyze what are these large particles that deposit onto these passive samplers.
And people found out there were some fibers and some microplastics, and that was the first part, “Okay, they actually exist in the air.” And then they have different shapes and different composition. And then from that aspect, it motivated more people to use other, more advanced instruments to look at how they are in the air. So people started to characterize their size, and found out that some sizes are larger and some are even smaller — that's why nanoplastics started to be discovered and identified in the air. And there are also some other research labs — what they do is try to look at the composition. They found there's polyethylene, there's polystyrene, and all these different types of micro- and nanoplastic composition — it's just not one type. And some other labs try to look at their shape — they see this long chain of fibers, but they also see this smaller round shape or irregular shape of particles as well.

So there has been a tremendous amount of understanding from almost no understanding at all over the past decade. And then part of my lab's work — we're very interested in real-time detection of micro- and nanoplastics in the air. The main reason here is that these micro- and nanoplastics are very low in quantity in the air, so if you want to sample them, sometimes it will take days, weeks, or maybe even months to collect enough mass to bring to the lab. And we have some very advanced instruments to study organic aerosols, and one of them is called an aerosol mass spectrometer. This is an instrument that can draw in the air and start to analyze the composition of some of the aerosols in the air in real time, and provide the size and also the chemical species of these different compounds.

And then we essentially used this to sample the air outside our lab window — we put through a hole in the window and connected our instrument. And then, to our surprise — or maybe it's not surprising — we found out that there was some significant enough mass to be detected by our instrument for these micro- and nanoplastic particles, and that's how we did our first real-time measurement, which we published. And then after that, some of the research I'm trying to answer is to understand what are their normal concentrations in the air, what are their potential impacts on health and climate, and also what are their sources. That's why I recently received the U.S. National Science Foundation CAREER Award, which is an award for five years to look at all these research questions that I proposed.

Anastasia Pashigreva, PhD

Yeah, as you describe, I really want to go deeper and deeper. First, congratulations on your Award. I would really love to learn more about your studies and your progress for them, because I'm pretty sure there will be a lot of surprising findings.

So maybe let's first talk a bit about your work — I saw that you have a very cool trailer with a lot of equipment, and I think any student would probably love to walk in and jump into the trailer and do measurements. So what brought you to this idea? How did you come up with that?

Yue Zhang, PhD

So, for this trailer — I'm actually really surprised you found out the information about it. So thank you for doing the research on that, and I'm actually very excited about this kind of measurement we do. So, in traditional atmospheric sciences there are… we call them three main legs that support atmospheric chemistry.

The first part is called Experiment, where we do different reactions to simulate what's happening in the air in a more well-controlled environment. So this type of reaction is normally done in a flow reactor or environmental chamber, where we have artificial lights, UV lights, and we inject all these species and oxidants and observe them. A lot of these are repeatable, and we want to create these repeatable conditions to make sure we can study the reactions in a controlled environment, to understand the reaction mechanism and its impact. So that's very important.

Another part is Atmospheric Modeling, where people try to take in all the different parameters in the atmosphere and simulate how the chemical reaction happens in the air while the air is also moving as well. We call these chemical transport models, because it has chemical reactions inside, but there's also atmospheric movement and transport included as well, along with other physics. So this is also an important way of predicting, let's say, what the air quality is going to be like for the next day in New York, in Houston, or in Washington, D.C. — we need to rely on these computer models to tell us these different answers. And then the third part of the leg is Field Measurement, where we bring our instruments into the actual outdoor air environment to look at what's inside, and as the sun rises and goes down, what are the changes in the composition of these different species we study, and when there's pollution happening and when there's no pollution happening, what are the differences. So these three different fields, or sub-fields, connect very well with each other for us to jointly understand atmospheric chemistry and air pollution issues.

So part of my lab would do a lot of things on the experimental side — we work a lot with modelers — but my lab also does this field measurement part, which involves a research mobile lab. So for field measurement, you can essentially put instruments into one site, and this site potentially often has air conditioning. Then you put a tube from outside to draw the air in where all the research equipments are housed.. The advantage of this is that you can stay at one location and just look at how different environmental parameters change and how that's going to affect the air chemistry.

But on the other hand, if you want to cover a relatively wide area, you need some kind of mobile measurement. People have been putting these instruments into an airplane and flying it around at different regions and different heights to look at how the air composition and chemistry change.

For instance, recently NOAA — the National Oceanic and Atmospheric Administration they have done a large aircraft field study where they put their instrument into a large aircraft and flew all over Houston, Dallas, Austin, San Antonio, and the western part of Texas, as well as New Mexico, to look at all the atmospheric pollution and air quality issues.

But on the other hand, if you want to go into different neighborhoods — let's say you want to look at how this community between different streets and different communities or neighborhoods, how their air quality is impacted compared with a different community or neighborhood within the same city — then you need something in between: not a really large aircraft, because it covers a really wide area, but also not a station size that just stays at one location. And that's where mobile measurement came up, which my lab has been working a lot on. So we put a lot of our instruments into either an electrical van or an electrical trailer, which has very little emissions from engines, and then this has a line also sampling the outside air to draw all the air inside the van or the research trailer and distribute it among all instruments to analyze. So when we drive the mobile lab at each street and through each neighborhood, it can provide air quality information from each of these locations, and overall it can provide a comprehensive map of the air quality within a city or district.

Anastasia Pashigreva, PhD

Wow, this is very interesting, and I think every resident who knows about your trailer would love for you to drive to their neighborhood and measure air quality. So are you able to measure micro- and nanoplastics with your trailer?

Yue Zhang, PhD

Yes, we have been doing that too. So we measure a lot of things — there are EPA criteria pollutants, which are the main regulated pollutants that we measure, but we also measure all these emerging pollutants, including micro- and nanoplastics, PFAS, and other compounds as well.

Anastasia Pashigreva, PhD

Can you share what your preliminary conclusions are on these micro- and nanoplastics, I don’t know, "forever chemicals" — what are your findings?

Yue Zhang, PhD

So we have performed some mobile measurements within Houston, and we went to a more industrial area of Houston to try to look at the micro- and nanoplastic concentration inside these communities. The results are still relatively preliminary since we're still analyzing the data and finalizing our analysis, but I would say the preliminary result is that we see very high variation in micro- and nanoplastic concentrations across the neighborhoods.

At certain locations we saw the concentration increase a lot, while at other locations the concentration stayed relatively average or low. So we're trying to understand why some areas have such high concentrations while others have less. It could be due to nearby sources — it could be a regular plastic manufacturing plant, which can create some additional pollution — but it can also depend on the wind and everything. So that's one thing we found out.

The second thing we found out is that when there was heavy burning activity, we found all these aerosols associated with burning start to get enhanced, and that's very understandable. But on the other hand, we also found out that the micro- and nanoplastic concentration increased as well with this burning activity. So we think that combustion processes, especially burning trash or other kinds of household compounds, are actually one of the important ways to produce micro- and nanoplastics in the air, because it emits lots of these compounds through this uncontrolled flame combustion process.

Anastasia Pashigreva, PhD

Yeah, absolutely. And thanks for doing those measurements and bringing this topic up, because that is extremely important, and as you describe I really want to ask more and more questions. So I wanted to go deeper into incineration processes — they are advertised as one of the ways to mitigate micro- and nanoplastics or plastic pollution, and this is definitely a big field, like burning plastic. We know that even burning trash causes micro- and nanoplastic formation. So based on your studies and what we know in the literature, what would you say are the major sources of micro- and nanoplastics in the atmosphere, and do we have spots with higher concentrations of microplastic, I don’t know, like seashore areas, rural areas, cities? What does the current data show us?

Yue Zhang, PhD

So for now, some known sources of these micro- and nanoplastics include tire and road wear, because a lot of these tires, when actually they rub on the surface of the road, generate these little small tire particles, and tire particles are considered one type of micro- and nanoplastics. So they can be generated and distributed around the roads and highway areas — that's one way.

Another way is the textile fiber shedding process, so this is more happening indoors. What happens is, a lot of times, one good example is when you use the washer and dryer — when you dry all these different clothes, you can see the lint on the filter, and the lint itself, besides containing fibers, also contains different types of micro- and nanoplastics inside. And if the ventilation is not good during the drying process, these micro- and nanoplastics could also come out of the dryer and be distributed into the indoor environment.

And then there's also degraded plastic waste and packaging materials — a lot of times when people throw plastic waste away, under natural environmental conditions it will gradually start to degrade into smaller and smaller pieces, and eventually they become micro- and nanoplastics and either stay in the water or in the soil, or get into the air.

And then agricultural film is also another way these micro- and nanoplastics get into the soil and also the air. And then one other source people have found a lot is sea spray aerosols — there are lots of micro- and nanoplastic materials or particles in the ocean water, and as the wind brings the ocean waves, it starts to bring some of the micro- and nanoplastics from the ocean into the air, and that's another source of micro- and nanoplastics. And then, besides this, some recent studies also show that combustion processes can also generate micro- and nanoplastics — let's say trash incineration or open outdoor fire — these things will make micro- and nanoplastics in the air as well.

Anastasia Pashigreva, PhD

And if we talk about all these sources that you listed, what would have the bigger impact — sea spray aerosol or tires? Do we have data on that?

Yue Zhang, PhD

So I would say that for now, to understand which one contributes more to atmospheric micro- and nanoplastics is still an ongoing research question which I should answer. My personal thinking is that it's going to depend on different locations and areas. So for urban areas, I would say tire wear and potentially different kinds of opendoor burning activity, as well as degraded plastic waste are potentially higher contributors to the urban air. But if people are actually living in coastal areas or these high mountain, remote areas, then it's potentially coming from different sources, including ocean sea spray aerosols, which can transport it long-range. So understanding where they're coming from is still a very exciting, ongoing question that we're trying to understand, and we have some tools to look at the sources of these different compounds and try to piece up a map to understand where they potentially come from, because once we know that, we'll have ways to reduce their concentration in the air.

Anastasia Pashigreva, PhD

So it sounds like right now we cannot tell — is it above the seashore where there's a high concentration, or is it in the city, or in a forest — can we kind of guess, or do we have some estimate?

Yue Zhang, PhD

I think for now we don't have a unified, completed picture yet, but we can have some hints. For instance, in the indoor environment, I would say textile lint and textile fiber shedding — these are potentially important contributors to the indoor environment due to our human activities. But for the outdoor environment, I think, for instance, we have seen that the micro- and nanoplastic concentration starts to increase when there's open, outdoor fire, when fire events or smoke start to show up. So we can see that, but it's hard to generalize that the whole urban area is mostly contributed to by outdoor or trash-burning events — we still need a bit more data points to find out where they are. So I think that because there are so many different sources for micro- and nanoplastics in the air, that's why, I think, depending on whether you're near certain sources, their contribution can also start to vary across time and space.

Anastasia Pashigreva, PhD

Yeah, I understand. You mentioned indoors — we spend indoors 90% of our time, and if we talk concentration-wise, is indoor safer than outdoor, if we don't take into account extreme events like nearby fires?

Yue Zhang, PhD

I would say that there's a lot of research groups that have been looking at indoor air compared to outdoor air, since they have very different air quality issues and different sources of pollution. And then, regarding the topic of micro- and nanoplastics, I would share that some research has shown that the indoor concentration can actually potentially be higher than outdoor for certain periods of time — if we don't consider these outdoor different pollutions.

The reason is because for indoor, this microplastic comes from synthetic textiles — a lot of the clothes we wear have some fibers and plastics in them — and furniture also contributes a lot of plastic to the indoor air, and there's also lots of dust resuspension for indoor air to bring this microplastics that are already on the floor or on surfaces back into the air. So these have been some studies people have shown, but these were mostly confined to microplastics, which are the larger compounds — these larger plastic particles. For smaller plastic particles, I would say that for nanoplastics there hasn't been too much study yet to look at where they are, or whether indoor is higher than outdoor yet — so that's still an ongoing question that’s worth examining.

Anastasia Pashigreva, PhD

Yeah, that's kind of surprising for me — not surprising, but it's really interesting to see whether it is higher or not, but I was really hoping that to be inside is safer. I think most people think this way, but we do have so many sources of microplastics in our homes. And if we look at the numbers — if we talk about the measurements of micro- and nanoplastics — could you give us a feel for how significant micro- and nanoplastics are versus normal dust, if we make a general comparison, and why we should care, why it's so important?

Yue Zhang, PhD

So that's also another really excellent question to ask about micro- and nanoplastics. So for micro- and nanoplastics, their number and their mass concentration in the air is actually quite small compared with existing aerosols — for micro- and nanoplastics, their total mass is probably just 1%, or even less than 1%, of the total aerosols in the air, right? But just because their mass is small does not mean they're actually not important, and there are different reasons for that.

The first part is that the usage and production of plastic for us, for humans, is actually increasing — some people say exponentially. So with this exponential increase, production has been increasing a lot — let's provide an example of COVID, which this contagious COVID during that time was also exponentially increasing. So over a very short period of time you can have a large number of people infected. The same as well goes for micro- and nanoplastics, because plastic production has been increasing exponentially, so for now we're looking at them, but in the next ten or twenty years their mass loading could increase by a lot due to this exponential increase. So we want to look at them before they become a major part of the air pollution — that's one motivation why people actually want to know about them.

The second part is that even though they're relatively low in their mass now, plastic is very persistent — it doesn't decompose very easily. So when we inhale or eat different kinds of compounds or species, our lungs can take in a lot of kinds of air pollutants, but a lot of them are organics, and organics can dissolve in water and be transported — eventually they can come out of your body or be metabolized.

But for plastic — they're man-made and they’re synthetic, they don't dissolve in water, and they're also very difficult to be metabolized by us, so they just gradually accumulate there. So even though they're low in mass now, over time the exposure can be quite high, because they don't go away, compared with many other organic species, which can gradually be oxidized and removed within a matter of days to weeks — that's not going to be the case for micro- and nanoplastics. So their health effects could potentially be more significant due to their persistence.

And then the third part is that a lot of atmospheric processes are actually depending not just on their mass or number, but also on properties — so some people think that these micro- and nanoplastics can be very effective in making certain types of clouds, which may change or alter the climate. So that's another reason that despite they're low in mass, but we're curious about them.

Anastasia Pashigreva, PhD

Wow, it's a big challenge. I think, when you talk about this exponential growth, as we progress and make more advanced measurements, more precise instruments, we can see smaller and smaller particles, and based on ocean research, what we observe is that as we go to smaller and smaller particles, the number of particles is growing exponentially, and we also know from ocean studies that microplastics are getting chopped down continuously into nanoplastics. So nanoplastic is continuously, naturally rising — extra addition to what already exists naturally forms the nanoplastics, and based on the research we know that nanoplastic is much more toxic than microplastic, so it might be a big concern too, right?

Yue Zhang, PhD

Yeah, these are very good points as well.

Anastasia Pashigreva, PhD

When we talk about these plastics and their properties, can you tell us more about what is going on when these micro- and nanoplastics get into the atmosphere, and how are they changing?

Yue Zhang, PhD

So a lot of times, the process of them going into the atmosphere is through the degradation of large plastic waste — a lot of times, as they become smaller and smaller, as the size starts to decrease, they can have more resistance in the air against gravitational falling, so eventually their size is so small that they can just stay afloat in the air for a significantly enough of time. That's why they actually get into the air.

And the other part is that when we burn this kind of trash and things, a lot of times there's advection of the air going up with the heat process to make a lot of the organic or inorganic compounds start to gradually become a little bit more volatile under this really high-temperature environment. But as the temperature cools down, those volatile species start to gradually recondense to make these organic aerosols — that's another way this plastic and other species get into the air.

The sea spray part is also from wind process— it just keeps pushing the ocean water, makes these waves, and these waves break down into smaller droplets that stay in the air, and as the water evaporates, what's left in the water, including some of the salts and some of the plastics and other materials, starts to stay afloat in the air.

Anastasia Pashigreva, PhD

Thank you. Yeah, all your answers are giving me so much food for thought, and thanks a lot for sharing your knowledge — that's a really amazing opportunity to learn more. So, if the particles are getting smaller — what we know from physics is that when the particles are about 100 nanometers, they’re not behaving like solids anymore, and that changes their transport properties. That changes the way they act, and that of course affects filtering, because if we have bigger particles, we can just use filter technology — we can have a small-pore filter that removes everything — but with smaller particles that doesn't work, right? So what does it mean when we go to the smaller particles?

Yue Zhang, PhD

So that's a really good point to mention about how aerosol sizes change and their properties will also change. So you're right that when particles are a bit larger, they behave more like what we know as a solid ball or liquid droplet. But as these aerosols start shrinking in size, the boundaries between a particle and air molecules starts to gradually smear or get blurry a little bit, due to their smaller size — they can interact much more frequently with gas molecules.

So there are processes — there are lots of studies people have done, which we call aerosol physics — they’re trying to look at these smaller aerosols, and as they become smaller, as you mentioned, less than 100 nanometers, or even smaller, less than three nanometers or five nanometers, their behavior gets closer and closer into gas molecules. They can suspend in air for sometimes weeks to even months, and they can actually travel in this curved way instead of the linear way an aerosol would, if they hit a wall or resistance. So there are lots of different changes.
And also, their mass becomes increasingly small because the volume is actually quadruply decreasing as the size starts to decrease. So once they get to a certain size their mass becomes so little that you have to collect for a certain very, very long time to be able detect enough mass for the instrument to see.

So these are all different challenges that we've encountered, especially when studying nanoplastics. So nanoplastics are defined as having sizes less than a thousand nanometers, or one micrometer, and at this size, we actually truly go to the field where these nanoplastics can stay in the air for days, if not weeks, which will allow them to have this long-range transportation. If you emit this nanoplastics from one location, they can travel to a different continent or all over the world to other locations within a few weeks, because they can stay afloat in the air. But their mass is also becoming small — especially since a lot of instruments have difficulty detecting particles less than 50 nanometers in real time. There are some instruments that can still do it, but this is becoming increasingly difficult. So these are challenges we're actually facing now, to look at these really small nanoplastic particles, and even smaller size within the nanoplastic range.

Anastasia Pashigreva, PhD

Yeah. And if we talk about small particles, how high can they travel — when we say they're small, they can behave like a gas, and we know there's gas exchange up to the very upper layers of the atmosphere — what do we know about these upper layers, beyond the troposphere, and what is happening there? Is it also that nanoplastics also accumulate in the upper layers of the atmosphere, and what can be the potential effect of them?

Yue Zhang, PhD

So when we look at these small nanoplastic particles, or aerosols in general, initially people were looking at their distribution and concentration within the lowest part of the troposphere, which we call the boundary layer — that's where most of our activities are. We have lots of emissions from different industrial sources and everything within the boundary layer, and we consider it to be relatively mixed, because the air is constantly going up and down to mix everything.

But then, once you have a longer enough time, a lot of aerosols can penetrate through this boundary layer and to go through this long-range transport which we call, which involves large air mass movements — let's say from the western part of the U.S. to the eastern part, within the continent, or go across continents, from North America to Europe to Asia. So that's the horizontal scale of this transportation part, but vertically there's also transportation.

The troposphere is the lowest part of the atmosphere, it covers from about 8 to 12 kilometers, and then the unique part here is that as height increases, the temperature of the air starts to drop. But once you pass through the top of the troposphere, you go into a layer called the stratosphere, which was a little understudied in the past but has now gained a lot of interest.

The stratosphere was very important for the ozone layer to essentially form and protect all of us — that's why there was a lot of focus on the ozone issue in the '80s, when people put a lot of effort into the stratosphere. But recently, a lot of research labs have also found that within the stratosphere there are lots of aerosols, especially during large-scale wildfire events or, let's say, volcanic eruptions, which can inject a tremendous amount of aerosols into the stratosphere. Because the stratosphere's air moves more horizontally — it doesn't move vertically as much — once aerosol goes into the stratosphere, it can stay there for years before it sediments back to the earth's surface, which also has a very important implication on climate aspect. So people have been trying to understand, if plastics are going to these high parts of the atmosphere, what could potentially cause them to affect the climate.

Anastasia Pashigreva, PhD

Yeah. This is fascinating — plastic can go up — but I'm really wondering about the properties of micro- and nanoplastics, because they're unique, they're not the same as normal pollen or dust. Could you please share more about the properties and how they affect atmospheric behavior — maybe how important the size, shape, density, composition, or electrical charge are — that’s a lot of factors.

Yue Zhang, PhD

Yes. So there are so many different aspects of micro- and nanoplastics that are interesting compared with traditional aerosols. They really do have a very unique shape, for a lot of them. For traditional aerosols, because we think they're mostly coming from a liquid or semi-solid state, they mostly retain a nearly round shape. They can still have some rough edges, especially for different kinds of solid particles or dusts — they can have rough edges or be like pollen, not exactly a spherical shape — but they normally fit into what we think of as a rounded or elliptical shape. But for plastics, especially those fibers coming from textiles, they really have a long shape, and sometimes they have this long string and are getting twisted — there’s a very unique type of shape for a lot of them. So I would say that's one thing that's very different.

The other thing is that, for the micro- and nanoplastic itself, besides those polymers that make up the backbone of the microplastic, there are also different chemicals you put into the plastic to make it more elastic, and it's mixed with different colors — these plasticizers and coloring ingredients are also embedded into the plastic, which makes them very different from other types of aerosols.

And then for the majority of organic aerosols in the atmosphere, we normally consider them to be having some kind of fluid properties — either liquid, or acting as semi-solid, more like pitch or ketchup or peanut butter, which has a mushy kind of base state to it. But micro- and nanoplastics are mostly just pure solid — they're not in this liquid or semi-solid phase state, they maintain very hard, rigid, solid properties. So a lot of these unique properties make them different from traditional aerosols, but also make them challenging for the health and climate aspect, because they're unique and different.

Anastasia Pashigreva, PhD

I wanted to get your perspective on the charge of micro- and nanoplastics, because we know that they have a tremendous ability to accumulate and retain charge, and that seems to affect a lot of properties — how they behave in the environment and within living organisms. So what is your vision of the charge of micro- and nanoplastics, and what can be their effect on the atmosphere?

Yue Zhang, PhD

This is a relatively unexplored angle, but very interesting, but for now, there hasn't been too much study looking at the electricity part of micro- and nanoplastics in air. Plastics in general can retain lots of charge on them, so it's actually very possible that they can have this electrostatic charge, which makes them either repel each other or aggregate together. It can also affect how fast they deposit into the air, and even their interaction with cloud droplets. I think a lot of these are actually very interesting, and honestly, very promising open questions that we need to look at more to understand how they can impact all these different processes, given their unique properties compared with other organic materials in the air.

Anastasia Pashigreva, PhD

And when I looked at the atmosphere and studied that, one of the surprising properties for me was that the atmosphere is a truly electrical system, and it was really amazing for me to learn what is the difference in potential between the lower and upper layers. We understand that it's a working electrical system — clouds also work on electricity — and there are a lot of processes related to electricity. And I'm really wondering what the effect of these charged particles would be if they were present — small, charged particles — throughout the atmosphere. So can you share your understanding and thoughts on that?

Yue Zhang, PhD

I think that a lot of times if they do have these large numbers in the atmosphere, one thing is that it's going to affect a lot of the behaviors of other aerosols, because some aerosols also carry charges too, so they can start to have these interactions: either repel or attract. The other thing is that I'm actually curious to find out how this may affect lightning or other atmospheric charging processes. The main reason is that for lightning to happen — one of my colleagues, Tim Logan, has done a lot of work on this — you have to have separation layers of charges within the clouds where lightning can happen. So if there are lots of micro- and nanoplastics aerosols keeping there, and if they’re in a significant number concentrations, then maybe this could potentially alter the charging process to make lightning maybe even easier or harder. But these are open questions, and hypothetical — I think it shows how interesting micro- and nanoplastics can be if there are a lot of them, if our usage and production continue still were to increase exponentially.

Anastasia Pashigreva, PhD

Yeah, you know, ALLATRA Global Research Center collects data on natural disasters, including lightning, and it was showing a recent increase in the number of lightnings, especially in some locations — the numbers are growing, and that's significant. That's a really interesting connection you made, and I would be really curious to see what your findings would be in this field. When we talked, you mentioned several times about nanoplastic detection, and I wanted to ask you, as a person who’s deeply involved in the experimental side — what is the most challenging part in determining the concentration of micro- and nanoplastics? Is it sampling, identification, quantification, or distinguishing them from other particles? What are the biggest challenges?

Yue Zhang, PhD

I would say one of the challenges I consider quite significant is their low concentration in the air. Because they have a relatively low concentration, detecting them normally requires more sampling time, and a lot of times, when we do real-time measurements, if the concentration is too low, it gets very close to the detection limit, which makes it harder to separate it out from the noise. So that's one thing I'd consider. The other part is we currently don't have a 100% mature tool yet to look at them and separate them out from other organic aerosols.

Organic aerosols, in general, they are very complicated — there are known thousands of them — so people have developed different ways to characterize them into different categories. And micro- and nanoplastics themselves also have many different kinds of materials it can be comprised of, so to identify each type of them and then aggregate them together as one group of micro- and nanoplastics as a whole itself is also challenging. And we need more tools and understanding to first separate them out and then understand in total what they are. So these are different ways that I think can be challenging for now, but we're also working on resolving this using more advanced instruments, lower detection limits, and continuous methods I've developed to look at each type of micro- and nanoplastics in the air as well.

Anastasia Pashigreva, PhD

Thanks a lot for working in that area because I think we really need to make progress in order to get complete understanding in the field. So I have another question. You mentioned the impact on health and you cited that it's a lot of influence of micro- and nanoplastics on atmospheric chemistry and human exposure. You mentioned that since microplastics behave differently, they will be taken by the body differently. So what do you think in terms of exposure through breathing versus eating? How do we consume more particles: through inhalation or through digestion?

Yue Zhang, PhD

So I would say that for the total mass part of the micro- and nanoplastics, digestion probably counts for more mass. The reason is that in the food or the water we drink, there are more of these larger sized microplastics. And then as we start to put them into our digestion system, some would actually pass through.

But on the other hand, I was going to say that often the toxicity or the health impact between digestion and inhalation are actually quite different. So, potentially micro- nanoplastics could cause more health issues through inhalation than through digestion. Even though, you know, we're still trying to understand this part. The reason is that when you eat certain things, eventually a lot of them will come right back out. So if you eat micro- and nanoplastics mixed with the food, there's likely a chance that a lot of the micro- and nanoplastics you digest will still be removed out of your body eventually. But when you inhale micro- and nanoplastics, even though they are relatively low concentration in the air, they can stay inside your lungs for a long time. So the health impact on your lungs can be significant.

The other part is when the plastics become, entering the nanoplastics regime or some of the smaller microplastics sizes, they can deposit very deep into the lungs, and they can penetrate, circulate and move all around the body

So in toxicology and public health, people have shown that for particle sizes similar to nanoplastics, they can actually circulate to different parts of your organs and within your body, and they will stay there for a long time. And for the really small ones, they can actually penetrate a layer we call the blood-brain barrier, which is a kind of a shield between the human brain and the rest of the body to prevent some unfriendly species from entering. But once the sizes shrink down to a certain level, they can easily penetrate that area and enter the human brain. So sometimes people suspect that this plastic accumulation can lead to long-term health impact, such as dementia as well. And these are ongoing research work that people have been trying to do. So that's why I think that even though the total mass is probably higher through the digestion process, the health impacts from inhalation can be significant.

Anastasia Pashigreva, PhD

Yeah, that is an important concern. And we know that the concentration of micro- and nanoplastics in the brain is higher than in other organs. And our brains are kind of protected from other body systems, like the head is separated, right? But inhaling air with micro- and nanoplastics means they can go through the nose and the olfactory nerve, and that is really concerning, especially for these tiny particles.

So I wanted to talk to you about recycling because we hear a lot that this is one of the ways to mitigate, especially the plastics, micro- and nanoplastics as well. And we need to recycle. Scientists who studied this micro- and nanoplastics were surprised to find that in the areas close to recycling facilities the soil contained higher levels of micro- and nanoplastics. And you mentioned that you also measured the air quality around those recycling facilities. So could you share what were your findings? And how the incineration facilities, recycling facilities, and other waste management processes are affecting micro- and nanoplastics? And maybe they generate new particles with a different chemical composition? Do we have enough research to know?

Yue Zhang, PhD

The incineration and recycling absolutely generate new particles through different physical and chemical processes. And then for micro- and nanoplastics, what we have found in one of our research studies which is actually published in Environmental Science and Technology, is that when the air masses come from this incineration plant, we do see an increase in micro- and nanoplastics in the air as well. So we think that this correlation potentially reveals a causation, that the incineration process actually releases these micro- and nanoplastic.

And that also agrees with some of the recent observations from mobile measurements we were doing in Houston, looking at how when there are more burning aerosols in the air, that micro- and nanoplastic concentration also increases. And then outside that, there are a few other research labs that have provided this kind of research, such as the University of Toronto. People [researchers] have burnt different kinds of plastic materials to see what they emit. And they confirmed that once these plastic materials are burned, micro- and nanoplastics can also be emitted. And their properties are actually very different from the original material because the heat process has chemically altered some composition for this micro- and nanoplastics.

So I think that's one area to be potentially considered, especially for nanoplastics, which are much smaller and can stay in the air for longer. The emission process could be important. And recycling and waste management are also important because often they have two distinct effects. One is that if the process is done in the open air, a lot of this plastic waste may be grinded or just weathered into smaller pieces and released into the air. The other thing is through the underground water and leaking process, this plastic can mix with soil and water, eventually going to the ocean or lakes, and then being aerosolised back into the air. So these are different ways that we need to understand.

I would also say that tire wear is now becoming a very important issue for micro- and nanoplastics in the air, and for other sources of air pollution as well, especially when those tailpipe emissions coming from engines have been reduced significantly, making the tire wear more important.

Anastasia Pashigreva, PhD

Yeah. Well, and, you know, it's interesting that we talk about alternatives for recycling facilities. If they are generating micro- and nanoplastics, should we look for alternatives? Are there ways to make this technology safer?

Yue Zhang, PhD

Yes, there are different ways to handle this process. There are alternatives people can use to make those technologies safer. That's absolutely for sure. The other way is during this combustion process or trash incineration, there can be different filters put on and air purifying process added so that while combustion the process, we are trying to reduce emissions into the air.

Anastasia Pashigreva, PhD

You know, I'm an industry person and we're always thinking about the whole cycle. Basically, if you install a filter, at some point there will be an end of life of that filter and you still need to find a way to process the filter, containing microplastics. There are also other challenges that we discussed with you when we get down to the tiny particles, filtration needs to become more and more sophisticated. So I think it creates really a lot of challenges.

So, I think the biggest question that we hear a lot is: can we reduce exposure, especially when we talk about airborne micro- and nanoplastics?

Yue Zhang, PhD

To reduce exposure, there’s a really good way. It's like the ways to reduce exposure to aerosols in general. So I would recommend for indoor environments, a lot of the time putting on an air purifier would help a lot to reduce these different pollutants in air. So that's certainly one of the most effective ways. And there are different types of air purifiers. It actually doesn't have to be very expensive. But as long as the air purifiers can remove smaller aerosols, that would be good.

We call them HEPA filters. These types of filters are very effective in removing smaller aerosols, including micro- and nanoplastics in the air. So that's been, you know, highly recommended. Sometimes people can just make it using a fan and purchase a filter online. There are different DIY ways to make it for probably $20 or $30. So, it's going to be quite inexpensive, and helps a lot if people don't want to buy these commercial ones.

And then the other thing I was thinking of would be helpful is to reduce the exposure to these nearby plastic sources. For instance, if people are going to do this washing and drying process, maybe make sure that the filters for the dryers are always checked and cleaned so they can retain as many of these fibers as possible. And also pay attention to the air quality: when air quality is poor outside, it's good to normally stay indoors and avoid being exposed too much to the air from the outdoors as well.

Anastasia Pashigreva, PhD

And if we talk about the outdoors, is there a way to reduce exposure of micro- and nanoplastics?

Yue Zhang, PhD

So for outdoor areas, I would say that a lot of times when people are walking on the street… there have been studies to show that the distance of people living close to the highway can affect their health a lot. So, for people living closer to the highway – which has lots of pollutants coming from the cars and tires, including micro- and nanoplastics, but also other types of pollutants – the cardiovascular disease rate also increases. So, to stay away from these sources of combustion and highway and car engines – these are good ways to help protect everyone from the pollutants in the outdoor air.

Anastasia Pashigreva, PhD

Mr Zhang, coming closer to the end of our conversation, I wanted to ask you, what are the three most important research priorities that you see for the next decade? Or what kind of questions do we need to answer before we fully understand this micro- and nanoplastics impact on the environment, climate, and our health. So what would it be?

Yue Zhang, PhD

These are very important questions. To my mind, the first is from a chemical side, I think it's good to standardize the sampling and identification processes to look at these micro- and nanoplastics and look at their chemical reactions and their aging pathways in air. There are so many different technologies nowadays to look at micro- and nanoplastics in the air. You can visually observe them, you can use different instruments to look at their different properties and estimate their mass or number. But it would be good to cross-compare all these different methodologies to standardize them so everyone understands what are the pros and cons, the advantages and limitations of each technology. So I think standardizing all these is very important.

And then the other part that, I think, will be important, is to understand their atmospheric processes, including how fast they chemically age in the atmosphere. And what these aging reaction rates and chemical kinetics are. And also how does this atmospheric part affect the part in the ocean and in the soil for this micro- and nanoplastics? What other contribution of atmospheric nanoplastics and microplastics to the total environmental micro- and nanoplastics. So this is the second part.

The third part is to understand the impacts: the impacts on health, the impacts on climate. And then how would that actually affect the toxicology? How would that affect the lungs, cells, and long exposure? And would that impact long-term health, including dementia? As well as whether the plastics may cause the cloud formation processes to be either enhanced or changed?

So these are the three major questions I would be very interested in learning more about. Some of which, you know, are also included in my current NSF career proposal as well.

Anastasia Pashigreva, PhD

Yeah, that's really great. And I really hope that we will progress fast in all of these directions. We do see a lot of positive feedback from EPA. There is a STOMP program launched in the United States. But it definitely needs more and more resources and more scientists like you. And it's really cool to see how these things are going.

Just to be positive, what gives you optimism in the field? What really makes you think that we are going in the right direction?

Yue Zhang, PhD

We talk a lot about the issues and solutions coming from, you know, aerosols or micro- and nanoplastics. So I think that these are things, you know, we try to understand and they are urgent. That's why we want to know about it. But also, on the other hand, I want to share with all the audience here that most of the time throughout the past few decades, the air quality worldwide, especially in many countries, are actually going towards improving. Because we are raising awareness of the air quality issue, and we try to actively improve it.

In the US, the air quality has improved a lot over the past few decades. The emission from these car exhausts and tailpipe has been reduced dramatically due to all the development of the catalyst, also due to the Environmental Protection Agency. So they have been trying to monitor and work with state and city and local governments to make sure the air we breathe in is attainable within the criteria and also health.

And then this also happens not just within the US or maybe Europe, but also within many other developing countries as well. In China or many parts of Asia, the air quality has also improved a lot for the past decade as well because of the awareness we have. So I do believe that even though there are different kinds of issues still coming up, and there are always new emerging issues due to, you know, where inadvertently just releases into the atmosphere. But I do believe that together we can find a solution to resolve this and make it healthier and better for us, and also for the next generation.

Anastasia Pashigreva, PhD

Yeah. Thank you so much for sharing. And it's amazing. And if we are finalizing our talk today, what would be one message that you would like our listeners to take from our today's conversation?

Yue Zhang, PhD

So, you know, I think one thing I really like about and I want to share — it is something I read in the past — is to say that the atmosphere is barely a very thin layer around the Earth. If you compare the Earth to the egg, the atmosphere is like an eggshell or even thinner than that. But yet within this layer, every living creature, including us, draws breath in it. And that's why understanding air is such an important part for us, and also for everyone else, and every living creature on Earth.

Anastasia Pashigreva, PhD

Thank you very much for sharing. So it was a real pleasure for me to talk to you. And I learned so much. Thank you for all your insights and especially in understanding micro- and nanoplastics — what they do to the atmosphere and the environment. Thanks a lot for your contribution. I really wish you to progress and grow your team bigger so we can answer more questions.

Yue Zhang, PhD

Thank you so much for having me.

Anastasia Pashigreva, PhD

And to our listeners. Thank you for being with us today. This field is moving quickly and staying informed matters. Links to Doctor Zhang's research and to the ALLATRA report “Nanoplastic. A systematic risk analysis for human health, ecosystems, and environment” are in the description. We will see you next time.