You're Looking a Little Ozoned-out

May 2, 2004
Outside Magazine
Outside magazine, October 1995

You're Looking a Little Ozoned-out

When it comes to the air you breathe, what you can't see will hurt you
By Mark Jannot

I have a friend who's always complaining about the tribulations of running in his own New York City: the paroled sociopaths, the anxious taxi drivers, the street drones pressing handbills into palms. But he rarely mentions Gotham's--make that any city's--only surefire danger, the air.

"When the air conditions are particularly bad, you might just be better off staying indoors," says David Martin, a physiologist at Georgia State University and chair of the sports sciences committee of USA Track & Field. "If the only time you can run is 5:30 in the afternoon and you choose Fifth Avenue in Manhattan, you could certainly question whether the cardiovascular conditioning benefits would be outweighed by the large amount of pollution you'd be breathing in."

While the perils of sucking down dark brown diesel fumes may seem obvious, the harsher truth is that we often can't see or smell the nastiness we're inhaling. Pollutants such as nitrogen dioxide and sulfur dioxide, acid particles, and the two most notorious airborne kamikazes, ozone and carbon monoxide, can affect you on a blue-sky day. And certain pollutants will carry and metamorphose over hundreds of miles, which is why cyclists in Flagstaff, Arizona, have a right to complain about California smog.

Of course, it doesn't help that we athletes love our oxygen. An adult at rest consumes about eight liters of air per minute. During mild exercise that can jump to 25 liters; go all-out and you can pull in 100. To add insult to intake, once this "minute volume" exceeds 30 liters, it's difficult to funnel it all through the nose, where large particulates are easily trapped by mucus. Suddenly an air-conditioned mall seems inviting. "We tell our patients that they can go outdoors but that they shouldn't always exercise there," says Henry Gong Jr., chief of environmental health services at Rancho Los Amigos Medical Center, a research unit in Downey, California, that specializes in the health effects of air pollution. "But most athletes don't see that as a realistic choice."

Dodge the Ozone
You are going to go out there, so at least you should know what you're up against. The pollutant most likely to cause physical discomfort and impair performance is ozone--not to be confused with the naturally occurring ozone in the atmosphere-- and nobody knows its effects better than Gong: His office neighbors Los Angeles, smog capital of the nation, where conditions conspire to form a breeding ground for the stuff. Ozone, an off-kilter form of oxygen thanks to an extra O atom in every molecule, is formed by the collision of sunlight and hydrocarbon-rich auto or industry exhaust, two things L.A. gets in plenitude. In your respiratory tract, the reactive ozone molecule oxidizes cells, destroying membranes, causing inflammation, and ultimately affecting your breathing. And because ozone is a gas rather than a particulate, mucus provides little safeguard.

Unfortunately, though you can run from L.A., it's hard to hide from ozone. The U.S. Environmental Protection Agency has determined that air containing ozone at a level of 0.12 parts per million is unfit to breathe for more than an hour. Los Angeles regularly exceeds that figure, but the numbers also occasionally get that dismal in Milwaukee, El Paso, Texas, and Portsmouth, New Hampshire (see "Where the Air Is Unfair"). The great wide-open spaces don't go unscathed either, since ozone can be blown far from cities. Take a trip to the Grand Canyon in the fall--a season when conditions can be extremely bad--and you might feel L.A.'s bad air.

Or, perhaps thanks to your genetic makeup, you might not. Two recent tests by the EPA's National Health and Environmental Effects Research Laboratory showed that sensitivity to ozone varies greatly. One test group worked out steadily and moderately for 6.6 hours--about the length of a good day hike--and even at ozone levels as low as 0.08 parts per million a significant number of subjects developed symptoms such as dry coughs and chest pain. In the second test, volunteers exercised strenuously (breathing in 60 liters of air per minute) for an hour at 0.4 parts per million of ozone--a much higher concentration than most of us will ever encounter. The results were startling. "Some subjects experienced as much as 50 percent reduction in their lung function," says Donald Horstman, one of the researchers. "And other people weren't affected at all."

Horstman and his colleagues are still searching for the exact physiological reason for those results, but they have nailed down the fact that we have all learned to tolerate a little ozone. It's another way in which humankind, for better or worse, has adapted: Studies have shown that while reaction to ozone gets worse on the second day of exposure, it declines from there, and after five consecutive days of exposure virtually all symptoms disappear. Horstman warns, however, that adaptation isn't necessarily the same as immunity. "Smokers respond less to ozone, too, but that's probably because their irritant receptors have been blasted," he says. "Those receptors are in your airways for a reason--to keep you from breathing those toxins in deeper." While nobody's sure of the long-term effects of ozone, Horstman says scientists suspect that it could increase the risk of respiratory diseases such as emphysema.

How to beat ozone has been the recent subject of much magic-pill debate, what with the emergence of so-called antioxidant supplements rich in vitamins C and E. But tests of the effectiveness of such remedies have been inconclusive at best--so the most sound advice is still to practice ozone avoidance. On sunny days, exercise in the morning, before traffic spills heaps of exhaust into the sunlight, or in the late evening, when the ozone has dissipated. Cloudy days or rainstorms also provide clear-air opportunities. If your schedule allows you only a noontime workout on the city streets, consider a mask with a charcoal filter. Masks such as those from Respro (800-473-7776) may look something like Orwellian fashion statements, but they filter out ozone along with soot, smoke, and other particulates.

Keep Carbon Monoxide Out of Your Sink
In a month or so the days will get much shorter, the sun scarcer, the weather worse--and our attention should turn toward carbon monoxide. Just about the time that ozone levels start to fade for the winter, carbon monoxide, sulfur dioxide, and other industrial pollutants begin crowding the air as more fossil fuel is burned and colder engines work less efficiently.

Carbon monoxide is just as common a pollutant as ozone, but it's not as apparent a threat to athletic performance. Like ozone, it's a gas, yet it doesn't irritate the airways. It also doesn't disperse as widely as ozone. In fact, one study showed that bike messengers, who spend their days zipping in and out of traffic, had lower than average concentrations of carbon monoxide in their blood. "That's really not surprising," says Gong. "Messengers are usually moving at fast speeds, in and out of pockets of carbon monoxide. That'll give them less exposure than people get standing on the corner or sitting at a stoplight."

And, most likely, less exposure than the rest of us get just chugging down city sidewalks. It's then, when we get carbon monoxide in large doses, that our performance can be severely impaired. "Without wind to whisk it away, there's only one sink to suck in carbon monoxide," says Gong. "That's blood."

Each carbon monoxide molecule that enters our lungs attaches to a hemoglobin molecule in our blood, taking up the space usually reserved for oxygen. It does so tenaciously--carbon monoxide's affinity for hemoglobin is 200 times greater than that of oxygen--and in the process shoves oxygen molecules out of the way, reducing the amount that goes to feed the muscles. Normally, less than 1 percent of our hemoglobin molecules are connected to carbon monoxide molecules; when that concentration rises to 15 percent, you'll get headaches and fatigue more easily.

Fortunately, if you veer away from traffic and into a park, you should stay well below that figure. But even on a sequestered path you're not out of the pollutant woods. "Someone running around the reservoir in Central Park may think, 'Gee, it's nice to get away from that bad air,' " says physiologist David Martin. "Remember, that dust on the track can get into your lungs--it's pollution, too."

Mark Jannot wrote about 40-minute workouts in the July issue. He is a frequent contributor to Bodywork.

See also:

Conditions: Where the Air Is Unfair

Trends: How to Get Low-Level-Pollutant Clean

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