Smog alert - protecting oneself from the harmful effects of exercising in the outdoors

Men's Fitness, August, 1998 by Eric Olsen

Exercising in polluted air can do you as much harm as good. Here's how to protect yourself.

What's that gasping, wheezing and choking you hear? Why, it s just millions of people getting their outdoor workouts.

Unless you spend your time miles from any city or close enough to the ocean to smell the salt, chances are you live, work and train in air that's fouled by auto and factory emissions. That's too bad if you like to breathe, particularly if you breathe deeply when you exercise. Air pollution can cause a host of problems, the least of which are chest pain, coughing, wheezing and watery eyes. If you're working out in that dirty air, things can get a lot worse.

When you exercise vigorously, you breathe through your mouth, bypassing the filtering action of your nose. You also breathe harder than normal, pulling dirty air deeper into your lungs. This results in further irritation of your delicate lung tissues and makes it more difficult for you to get enough air in them, which means you won't be able to train your hardest. If you're competing or going for a personal best, pollution can seriously hamper your performance.

What's more, bad air doesn't just affect your training now there's evidence that exposure to polluted air over a number of years prematurely ages lung tissues. This speeds up the normally slow decline in lung function that occurs naturally as you get older.

If it's any consolation, the air is generally cleaner now than it was before 1970, when Congress passed the Clean Air Act. Since then, pollution has dropped by 20 to 30 percent nationwide, though it has yet to fall to mandated levels. On the other hand, according to the American Lung Association, that initial progress has ground to a halt in recent years, and levels of some pollutants have begun to creep back up.

The gook is out there

Urban air includes lots of nasty stuff, including sulfur dioxide, nitrogen dioxide and particulates (smoke and dust). But the two nastiest pollutants - the ones you really want to avoid - are ozone and carbon monoxide.

Ozone, the major urban pollutant, is produced when sunlight interacts with the nitrogen dioxide in auto and factory emissions. Ozone levels begin to climb as soon as the sun comes up and usually reach their peak in the afternoon; the more sun and traffic there is, the more ozone. The Los Angeles basin has the dubious honor of bearing the highest average ozone levels in the U.S. (Mexico City has some of the world's highest.) But don't assume you're safe from ozone in the suburbs, either. It can spread for miles, and depending on prevailing winds, the areas around a big city can end up with fouler air than the urban center that produced it.

Ozone is an airway irritant - when you breathe air containing lots of it, you'll likely find yourself coughing and feeling chest pain when you breathe deeply. Your airways will also constrict as they try to protect themselves from the stuff, making it more difficult for you to pull air into your lungs and push it out. Your breathing will become shallower and more rapid.

Your performance will begin to suffer when ozone levels reach concentrations of about 0.18 parts per million, which has become less common over the years but still happens occasionally in the Los Angeles basin. Workouts lasting longer than an hour can be compromised by even lower ozone concentrations.

Studies have shown that athletes can build up a tolerance to ozone - after a few repeated exposures, their bodies become used to the stuff. That doesn't mean it can't irritate your lungs; it just means you won't notice it while it does its damage.

Carbon monoxide (CO), meanwhile, is an odorless, colorless toxic gas that's created by burning organic substances - wood, coal, tobacco, charcoal briquets, diesel fuel and, of course, gasoline. Automobiles are the primary source of the CO in city air.

In one of nature's cruel jokes on the human species, CO binds about 200 times more tightly to the hemoglobin in our blood than oxygen does. That means that whenever a CO molecule sticks to a hemoglobin molecule, that's one less oxygen molecule the hemoglobin can carry to your muscles and your brain. The result is that too much CO makes you sluggish and thick-headed. At high enough concentrations - say, about 60 percent - it can kill you.

A little carbon monoxide is a normal byproduct of metabolism; even without pollution, about 1 percent of your hemoglobin would be carrying it instead of oxygen. If you smoke, you'll have CO concentrations ranging from 4 to 7 percent, depending on how much of the demon tobacco you suck in. Sadly, that's about the same concentration you'll have if you jog or ride your bike along a street packed with CO-belching cars.

If you're not exerting yourself, you might not notice anything is wrong. But if you're pushing against the limits of your aerobic capacity, then any CO concentrations above that normal 1 percent will impact your athletic performance, which will steadily decline as CO levels climb.