As the lead vehicles and motorcade drove by mile 10.3, escorting the elite athletes toward Boylston Street in Boston this past April, my husband and I started waving our hands to clear the air. The exhaust fumes were heavy. My husband, a sustainability consultant who specializes in greenhouse gas emissions, made a deadpan remark about how the world’s best runners position themselves directly behind vehicle emissions for more than two hours, exposing their precious, world-class lungs to noxious gases and particulate matter.
And that’s how I came to speak with scientists, physicians, the Environmental Protection Agency, runners, and race organizations about the concerns of athletes breathing in these emissions.
What’s in a Tailpipe?
It’s helpful to understand the types of pollution we’re looking at because there is plenty, and not all of it is created equal; some is much, much worse for our bodies. A regular car or truck emits various gases from combusting gasoline, including methane and nitrous oxide from its tailpipe.
Nitrogen and oxygen are released during combustion, forming NOx, which are known to cause respiratory problems. On top of that, NOx reacts with chemicals in the atmosphere to create secondary fine particulate matter (PM 2.5), explains Eric Balaban, M.D., a pulmonologist at Best Recovery Shoes in Philadelphia. We’ll get more into PM 2.5 in a minute.
But the “local pollution chain is very long,” says Maria Cecilia Pinto de Moura, a scientist who focuses on clean transportation with the Faith Kipyegon Just Misses 3K World Record. “We can look at ‘well to wheel,’” which covers tailpipe emissions as well as pollution from tires, brakes, and whatever is getting kicked up on the road.
The Health Effects of Particulate Matter
There are different types of particulate matter, 2.5 referring to its size of just one-thirtieth of a strand of human hair, Pinto de Moura tells Runner’s World. Its miniscule size makes it one of the most dangerous pollutants because it infiltrates all of our organs, Pinto de Moura says. These particles cross into our brains, cross into an unborn fetus, and the particles don’t leave our bodies, she says.
Not only is PM 2.5 found in vehicle emissions, it’s created when those NOx gases mix with the atmosphere, a one-two punch, Pinto de Moura says.
And then there are spikes of PM 2.5, or acute increases that we inhale—around cars or behind a race lead vehicle. These spikes, as opposed to chronic or long-term pollutant exposure (also not good), are very dangerous because they’re not included in year-round averages of exposure, Pinto de Moura says.
“These spikes are especially dangerous to people with preexisting conditions, or people who use their lungs more, like athletes, and children with smaller lungs,” she explains.
PM 2.5 and ultrafine particulate matter, which is even smaller and also found in emission and ambient pollution, causes a host of respiratory and other health conditions: inflammation to the respiratory tract, reduction in lung function, worsening asthma or symptoms of chronic obstruction pulmonary disease (COPD), and decrease in immune function.
Balaban, a 2:36 marathoner who has additional training in climate change and health policy science from the University of Colorado at Boulder, says we’re also seeing the effects of particulate matter on our cardiovascular health, including stroke and heart attack. It might even play a role in neurological dysfunction like Alzheimer’s disease and Parkinson’s disease, and diabetes.
“This goes far beyond the lungs,” Balaban tells Runner’s World.
Balaban also explains ground-level ozone—not the good, atmospheric kind that protects us from the sun. Ground-level ozone in the air around us comes from tailpipe emissions, nitric oxide, and volatile organic compounds (VOCs), which are found in emissions and lots of other things—paints, plastics, clothing, flooring, cleaning supplies; the list is never-ending.
In warmer temperatures, like during summer running, those particles create ground-level ozone. Those numbers increase even more during extreme heat, which is a symptom of global climate change, driven largely by emissions from cars.
Ground-level ozone is an irritant; it can cause eye and throat irritation, tightness of the chest, and coughing. When those effects are combined with the particulate matter, it changes the way people breathe, Balaban says. “It can be harder to breathe in deeply and empty the lungs when you're exposed to this type of pollution in the short term.”
Runners and Vehicle Pollution
The good news for runners, elite and otherwise, is that for healthy individuals, some of these acute health effects aren’t as bad in the short term, Balaban says. Living and training in areas where pollution is low (and air quality is good) can help further mitigate the effects.
But ozone and particulate matter can actually impede physical performance.
In 1984 researchers looked at the potential effects of pollution, specifically smog, and heat on athletes, thanks to Los Angeles hosting the 1984 Olympics, says David Diaz-Sanchez, the director of the Environmental Protection Agency’s public health and integrated toxicology division in the ldquo;The rate of breathing in, or ventilation, increases 10 to 20 fold,” Balaban says.
Since then the studies have typically looked at ground-level ozone, and some suggest that “particulate matter can reduce physical activity levels,” Diaz-Sanchez told Runner’s World by e-mail.
A study from December 2024 published in Sports Medicine looked specifically at the impact of particulate matter on marathon finishing times. It examined finishing times from nine large, popular marathons (Boston, New York City, Chicago, Philadelphia, Marine Corps, Los Angeles, Twin Cities, Grandma’s, and Houston) from 2003 to 2019, which included 1.5 million men’s and 1 million women’s results.
The researchers, led by Elvira Fleury who was at Brown University, found that, after adjusting for heat and humidity, race days with higher PM 2.5 (1 microgram per cubic meter above the location’s baseline) were associated with 32-second slower finishing times for men and 25-second slower finishing times for women. This was seen more with “faster-than-median finishers.” That could be, the authors speculate, because although they’re running for a shorter amount of time, their rate of ventilation is much higher.
Fleury, a runner, who’s currently a Ph.D. student at Harvard University studying environmental health, told Runner’s World that her work didn’t factor in ground-level ozone, and that if it did, it could show times have slowed even more.
“Particulate matter 2.5 is something you should take stock of when you think about how your race went, in the same way you think about how the heat impacted your race,” she says.
When we run, whether we’re beginners or the elites positioned directly behind lead vehicles and alongside motorcades, we breathe more frequently because our bodies need more oxygen.
“The rate of breathing in, or ventilation, increases 10 to 20 fold,” Balaban says.
This exposure can be exacerbated while moving quickly, Diaz-Sanchez says. And even exposure to one spike can be “really bad,” Pinto de Moura says. Research is still being done to better understand this, but we know that symptoms of acute exposure can occur up to four days after, she explains.
When it comes to exposure to lead vehicle emissions throughout the year—elites tend to race one to two marathons a year and several half marathons—it really depends on the frequency, Diaz-Sanchez says. And the concentration of that exposure fluctuates on a variety of factors: wind speed and direction, temperature, humidity, street canyons—a city street flanked by tall buildings—and tunnels, for example.
“Most gases dissipate or react with the airways very quickly so there is no cumulative exposure,” he says. “Particles, however, can be retained for weeks or longer in the lower airways, depending on their composition, the dose, and how well the individual’s process of mucociliary clearance is in the upper airways.” He says that a healthy person, presumably like an elite runner, with good clearance should not see buildup between races spaced months apart.
But perhaps equally, if not more concerning is the chronic and long-term exposure to particulate matter and pollution.
“Inhaling this air [from lead vehicle emissions] at 10 to 20 times the normal rate is relatively minor when compared to the ambient air quality during the other [20-plus] hours a day,” Balaban says.
Pinto de Moura reminds us of every industry that has pollution and how that negatively affects the air we breathe every day. And Balaban says even that short-term exposure behind a race vehicle “pales in comparison to the air quality you’re breathing outside of the times you’re racing.”
Races are Taking Action
Remember when Eliud Kipchoge first attempted to break two hours in the marathon in 2017? He was running behind electric pace cars. He was onto something. (One of the engineers said, “There will be no emissions out of the back to upset any of the runners.”)
Aaron Gruen, 26, the Austrian record holder in the marathon (2:09:53), has had his fair share of time behind lead race vehicles over the past several years.
“Every race I wonder if they’re finally going to have an EV,” Gruen, who lives in Boston, tells Runner’s World. “You can smell the fumes, and while I don’t know what impact it’ll have on me, I know it can’t be that good to be that close to a car.”
Gruen, who will represent Austria at the World Athletics Championships marathon in Japan in September, says that eventually he becomes desensitized to the smell and just focuses on his race.
New York Road Runners (NYRR), one of the largest race and running organizations in the world and host of the New York City marathon, started converting its lead race vehicles and support cars to a cleaner option. In 2019, its six pace cars for the New York City marathon were plug-in hybrid cars from Volvo, its corporate sponsor, with its 14 support cars hybrid and mild hybrid (a smaller electric motor).
In 2021, two pace cars were fully electric and four were plug-in hybrids. In 2024 all six pace cars were fully electric and 14 pace cars were plug-in hybrids. Participants in this year’s marathon will see the same setup.
The shift to electric vehicles for the organization’s marquee events is part of NYRR’s commitment to becoming a more sustainable entity, says Aly Criscuolo, director of sustainability and corporate social responsibility.
Criscuolo told Runner’s World that the move to electric vehicles helps NYRR toward its goal of net zero emissions by 2040. (In 2019 NYRR signed the sports for climate action framework, which is part of the United Nations Framework Convention on Climate Change.)
“This was a no-brainer,” Criscuolo says. “The science backs [the use of EVs] and it made sense with our mission. We want to make sure the air is clean for generations to come to enjoy the sport we love.”
NYRR also uses solar and electric generators for the marathon, which means cleaner air for athletes lingering around race hot spots. The organization also uses electric vehicles for the Brooklyn Half Marathon and the New York City Half Marathon. Its vendor, MediaMotos provides electric motorcycles for broadcasts across other big-name events, including the New York Mini 10K, the Fifth Ave Mile, and the Dash to the Finish 5K.
In a city known for its smog, the Los Angeles Marathon uses electric lead vehicles as well, with its sponsor, Kia. The Boulderthon race series in Boulder, Colorado, uses a Rivian electric vehicle, and the OC Marathon in California uses a Kia electric vehicle. Although the Boston Marathon uses gas-powered motorcycles and scooters for the broadcast, in 2025 its lead vehicle, trail vehicle, and hydration vehicles were electric, according to a spokesperson from the Boston Athletic Association.
These are just a handful of examples of race organizers trending toward cleaner race vehicles and motorcades.
That’s good news for the environment and for runners who are keenly aware of inhaling gases and emissions, like Gruen.
“We don’t really have that decision [to choose races based on electric vehicle use],” he says. “We go where there is prize money.”
ldquo;This goes far beyond the lungs,” Balaban tells Runner’s World, But ozone and particulate matter can actually impede physical performance The Runner’s World Vegetarian Cookbook, and a nine-time marathoner with a best of 3:23. She’s also proud of her 19:40 5K and 5:33 mile. Heather is an RRCA certified run coach.
