The invisible impacts of air pollution

Boy looking out window

Join Population Healthy as we explore the air we breathe and its implications on our well-being. Sara Adar, an environmental epidemiologist and associate professor at the University of Michigan School of Public Health, discusses inefficient school buses, far-reaching wildfires, and brain-damaging particles in this episode on air pollution. From the subtle effects of day-to-day air quality to the long-term consequences on health, Adar shares some of her own research to shed light on sources of air pollution beyond the usual suspects. 

Discover the surprising links between air pollution and common health conditions like asthma, heart disease, and even dementia. In this episode, Adar explores the effects of pollution on vulnerable populations like children and highlights the importance of rethinking pollution in the wake of climate change. 

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Listen to "Breathing Easy: Navigating the Invisible Impact of Air Pollution" on Spreaker.

Sara Adar: Air pollution is most certainly a universal concern. I went to a talk one time where somebody joked that we're all obligatory breathers. So we are breathing in air pollution throughout our daily lives, from the time we take our first breath to our last breath. We've found no safe level so everybody is being impacted to some extent. But we certainly know that there are some people who are more sensitive to air pollution. So children, the elderly and people with chronic diseases are often more sensitive to the exposures than others. One of the interesting things about the wildfire smoke events that we've seen here is it was really, many Americans' first experience with seeing what it looks like when the pollution levels are really high. We got to levels that were much more similar to what people say in India or China or other parts of the world might experience frequently.

Host: Hello and welcome to Population Healthy, a podcast from the University of Michigan School of Public Health. Join us as we dig into important health topics, stuff that affects the health of all of us at a population level. From the microscopic to the macroeconomic, the social to the environmental, from cities to neighborhoods, states to countries and around the world.

Host: Sara Adar is an environmental epidemiologist and an associate professor at the University of Michigan School of Public Health. Adar's research focuses on how characteristics of our physical environment impact our health. That includes exploring how air pollution from a variety of sources impacts us all.

SA: So we have many different sources of air pollution in our communities. Some common sources to communities across the United States would include transportation. So things like cars, airplanes, power generation. So also things like coal-fired power plants, industry and increasingly these days we have a lot of smoke coming into our communities from wildfires. Day-to-day fluctuations in our air pollution levels, even the ones that we don't notice, are impacting our bodies. We can see that in terms of inflammation, we can see that in our blood. It also can often cause things like irritation to our lungs. For the most susceptible people, especially on high pollution days, they can even wind up in the hospital for things like asthma attacks, heart disease, and unfortunately we see more deaths on high air pollution days. When we're thinking about long-term, this is where the day in and day out of air pollution exposures are accumulating on our health.

SA: I think one of the most interesting examples of this is from the children's health study out in California where they demonstrated that children who are living with higher levels of air pollution experienced smaller lung growth, so that their lungs were actually smaller by the time that they hit adulthood than children living in cleaner areas. We also, in my own work, have demonstrated that people living in areas with high pollution have more atherosclerosis or sort of a gunk in their arteries than people living in clean areas and are more likely to get heart disease and dementia. It might be surprising that air pollution leads to things like dementia. What we do know is that air pollution gets into our lungs, and our body really almost perceives it as a threat. It thinks, oh, this is something attacking me and so it launches an inflammation response that can sort of cause problems throughout the body.

SA: If you sort of think of collateral damage happening, our blood vessels can sort of change their size and elasticity and everything. When you have these pollution exposures being inhaled, it impacts your heart health, which then can really damage your brain. And to me, almost the most interesting/frightening one is that when you breathe these really small particles into your nose, there's actually a pathway by which those particles can go up through what's called your olfactory bulb and directly get into your brain where you can imagine if you've got these toxic particles in your brain, they can really cause local damage as well.

Host: Adar grew up in Los Angeles, a city notorious for poor air quality.

SA: My family was quite fortunate. We lived actually up in the hills in California and LA, but my school was down lower. And so every day when I got driven to school, I remember the moment when we would drive from clean air down into the smog for me to go to school and for us to go shopping and things like that. Yeah, you could see the layer as you drove down. So I do have that very vivid memory of what it looks like to have a polluted environment. And I'm sure that impacted my career trajectory to some extent. In thinking about how long-term exposures to air pollution impacts our health, I thought I would walk us through two examples. So if you take myself who grew up in Los Angeles, I shouldn't fess up to how old I am, but I was born in the 1970s when the Clean Air Act was really just coming into play and air pollution levels in Los Angeles were exceedingly high.

SA: So you take me and then you take my children who grew up much more recently here in Ann Arbor where the levels are low. Now, we have the same genes give or take a little bit. We have similar accesses to resources, we had really similar home environments growing up. But in my day-to-day life, I was breathing in so much more pollution into my lungs as I drove to school, as I exercised outside, I played with my friends. And those pollutants that I was breathing into my lungs may have contributed to the asthma that I had as a child. So I have really vivid memories of being on the bathroom floor, having an asthma attack, my parents putting on the steam from the shower and trying to feel better. Whereas luckily my kids didn't experience that because they're now living in a cleaner environment, the air is much better when they're outside playing. They will commute to school, they actually got to walk to school, whereas I was riding really old buses that were highly polluting. So ultimately, those probably had different impacts on our long-term health trajectories.

SA: So in contrast to my experience where my play and exercise and everything else was impacted by high levels of pollution, when my son, for example, is out going running for his 5K with his cross country team, the air that he's experiencing is generally much cleaner than what I had. One thing that's interesting to note is that the wildfire smoke, however, is much worse now than it was when I was a kid. On those really high pollution days, the amount of smoke he would be breathing in if he was out there running for the cross country team really could impact his health.

Host: The health impacts of air pollution on children is an issue Adar is deeply familiar with. She spent years studying the impact of air pollution from school buses on children, and actually found that replacing older, highly polluting buses with newer, more efficient vehicles can lead to fewer sick days for kids.

SA: Here in the United States, we have 25 million kids who ride buses to and from school every day. And we know from past work that I've done and other people have done that the old buses that many children ride to school are pretty highly polluting. Many of our buses, actually probably most of our old buses were run by diesel and in the earliest years, they didn't have very many control technologies on them. So the tailpipe, as well as even the engine block are creating particles and other gases that can get inside of the bus and impact the health of those kids. Just like in ambient air, breathing in the particles and gases from the bus can irritate kids' lungs. It can cause inflammation in their bodies. And especially for asthmatic children, this damage or sort of irritation of their bodies can lead to them missing school. And so that's something that was quite interesting to us and we've seen in the past, is that when children's buses were being cleaned up, they were actually more likely to be present in class because likely their health was better and therefore they were able to go to school. And so, because the EPA knows that this is a problem, they invested a bunch of money in helping school districts to purchase new buses because the new buses are much cleaner, they make much less pollution, they have a lot of cleaner air control technologies on them.

SA: But even though this program was ongoing and the EPA is investing millions of dollars into it, no one had actually previously gone through and conducted a study to ask the question of whether or not this is working. Are we seeing improvements into children's health with the purchasing of new buses? And so that was what we set out to do really, was to see whether or not this large government program to help school districts replace their highly polluting buses with cleaner buses, had any measurable improvements on children's experiences. Some ways in which the newer buses create less pollution than the older buses is they often leverage technologies like diesel oxidative catalysts, which makes sure that when you're burning the fuel, it goes all the way to complete combustion. Other technologies, there's ways in which they put a filter on the bus so that it traps any particles that do escape from incomplete combustion. And another one that we often don't think about is trying to catch the smoke from burning oil in the crank case or the engine block of the bus. And there they even put a closed container effectively around that crank case system and any emissions that come off of that, they go back and re-burn in the engine. And that really makes sure that you have cleaner air coming off of the bus.

SA: In this new study that we did, looking at the impacts of the clean school bus funding by the EPA, we saw that those districts that were randomly picked to replace their buses had improvements in children's attendance at school and in their educational performance on standardized testing as compared to those districts that did not win that lottery. And this was especially true for when the oldest buses were replaced. So buses like from the 1990s, for example, when they really were much more polluting. If we just look at attendance, what we saw was for an average district of about 10,000 children. We expected to see about 45 more kids in their seats at school every day after their buses were replaced as compared to if their buses were not replaced. Now, it may not seem like such a big deal that kids are in attendance at school, but when you think about it from a personal perspective as a parent, you know that you have to miss work, right? So there's economic costs that come in because somebody needs to stay home from work to take care of children who stay at home. And there's also longer-term risks of the children not learning as much if they're not in school every day. And so the government has put a number in terms of the economic value of being in attendance at school.

SA: And I think what's quite exciting about our finding is if you balance the cost of the program, which was about $27 million by the EPA for these lotteries that happened between 2012 and 2017, and our predicted number of additional kids in school each day, the benefits that you would attribute to that $27 million were about $350 million in benefits and that's per year.

Host: The EPA's investment in cleaning up school buses is the kind of policy that is improving the quality of our air. Adar hopes we can continue to evaluate and push policies to reduce pollution levels on a large scale.

SA: We've seen that the National Ambient Air Quality Standards have been very effective as a policy in reducing our pollution levels throughout the country. It was actually this amazing paper several years ago, by a leader in our field, Arden Pope, who demonstrated that the reductions that we saw in air pollution levels in the country because of the National Ambient Air Quality Standards were associated with about half a year of additional life expectancy for everyone in the country. So I would say that the National Ambient Air Quality Standards are effective, and that is something that we should keep on. We need to keep evaluating if they're set at the right level. But that is one great way that we can reduce air pollution levels at the population levels. I would say it's also very important for us to continue with our efforts to clean up our electrical grid and reduce our consumption of electricity. I think that has important implications for air pollution, but also for climate. So the health impacts of air pollution, but also the longer term impacts on our climate and the resulting changes that can come about because of that.

Host: According to Adar, the National Ambient Air Quality Standards have been instrumental in curbing emissions from the usual suspects, buses, trucks, coal-fired power plants. But what about the less conventional contributors to pollution? To continue making progress for better air quality, we may need to start challenging our preconceived notions about the sources and impacts of air pollution.

SA: With the National Ambient Air Quality Standards. We have seen reductions in our pollution levels across the board in the United States. A lot of that has come into play because the EPA has helped to target emissions from some of those key sources that we often think about when we're thinking about dirty sources. So the dirty buses on the road, the dirty trucks and coal fire power plants. I think what's interesting is that some less traditional sources, or at least what you might not think of first when you're thinking of air pollution, we're learning have their own important effects. So we did a recent study looking at which sources of particles in our air may be contributing most to dementia risk among older adults in the United States. And we found that agriculture and wildfires, two sources of pollution that you might not be thinking about right away when I say, "Hey, air pollution is important for health," were really important for the brain. In hindsight, I think agriculture makes good sense because they're using neurotoxins as pesticides. And so that's quite logical. Wildfires sometimes surprises people because they're thinking just of trees burning or a campfire. And the reality is, is that these wildfires are consuming so much more than just our forests.

SA: They're also consuming things like gas stations and homes and cars, and they're burning without any controls on them at all. So the amount of pollution coming off of those, and especially as we're getting more and more of these events with climate change, I think is something that we're gonna have to pay really close attention to in the future. What I'm worrying a lot about right now when I'm thinking about climate change, when I'm thinking about air pollution, is the wildfire smoke events for the public health perspective. I think people think of these as being quite rare, but in parts of our country right now, especially in the west, some folks are experiencing half of their entire exposures to air pollution from these wildfire events. So it's no longer like, "Oh, we just had such a wild year this year with that smoke event," it's actually becoming full smoke seasons that people are seeing year in and year out.

SA: Many people think about wildfires as really impacting smaller locations. So maybe it's like if you're in California and there's a burn up in the Sierras, then it's gonna hit those local communities. But the reality is, is that these wildfire events produce smoke that goes vast differences across the country. And I think that folks in New York City, for example, experienced that recently where we had smoke plumes coming all the way from Canada and people going outside in New York City, which were thousands of miles away and seeing the orange skies surrounding the bridges and the Empire State Building. I'm sure many of us have seen those photographs.

Host: As Adar says, air pollution is a concern for anyone who breathes. We should all be taking part to protect ourselves from exposures, whether through policy or in our daily lives.

SA: Right now, the public is generally informed about air pollution exposures using this air quality index that's shared by the EPA can be very helpful. Although I would argue that most people are generally inattentive to that number. The one way in which I think that changed was during the wildfire smoke events, and yet still sometimes people weren't responding to the importance of how much smoke was outside. I really liked a statement I heard somebody else say, which is that if you got a warning that there was a tornado nearby, you wouldn't still send your kids outside. And yet in the middle of wildfire smoke events we were still sending our kids out to play soccer, which was probably not the best decision for their health. I suppose that what I really would love to see is that as a society, we value clean air, and we approach this as a nonpartisan issue because we're all breathing in air pollution no matter where you live or what side of the political divide you land on, and we're all experiencing the health impacts of that. In my dream world there would be value placed on clean air as a society.

Host: Thanks for listening to this episode of Population Healthy from the University of Michigan School of Public Health. We're glad you decided to join us and hope you learned something that'll help you improve your own health or make the world a healthier place. If you enjoyed the show, please subscribe or follow this podcast on iTunes, Apple Podcast, Google Play, Stitcher, Spotify, or wherever you listen to podcasts. Be sure to follow us @umichsph on Twitter, Instagram, and Facebook so you can share your perspectives on the issues we discuss, learn more from Michigan public health experts and share episodes of the podcast with your friends on social media. You're invited to subscribe to our weekly newsletter to get the latest research news and analysis from the University of Michigan School of Public Health. Visit to sign up. You can also check out the show notes on our website, for more resources on the topics discussed in this episode. We hope you can join us for our next edition, where we'll dig in further to public health topics that affect all of us at a population level.

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In This Episode

StrecherSara adar

Associate Professor of Epidemiology, University of Michigan School of Public Health 

Adar uses modern principles of epidemiology, environmental health, exposure science, and biostatistics to characterize the impacts of environmental hazards on human health. Her research primarily focuses on the effects of air pollution and noise on healthy aging, with additional interests in global health, extreme weather events, and intervention strategies to improve health. She currently leads several large cohort studies on the impacts of exposures on cognitive aging and dementia.