With every deep draught of oxygen, I also gulp down alarming quantities of ozone, carbon monoxide, microscopic particulate matter, sulfur dioxide, nitrogen dioxide, lead, and a witch's brew of other pollutants. By conducting part of my workout at midday along a congested street, I am reducing my lung function, constricting my air passages, courting chest pain, increasing my chances of developing asthma, unleashing free radicals to catalyze carcinogens in my bloodstream, and activating cellular processes that might lead to a heart attack.
A sedentary person inhales approximately 15,000 liters of air per day, or 6 to 10 liters per minute. During heavy aerobic exercise, however, you draw in 60 to 150 liters per minute, delivering oxygen throughout 600 to 900 square feet of surface area in the lungs.
"That means the exerciser breathes in 10 to 15 times more pollution than the sedentary person, and he's sucking it deeper into his lungs," says Rob McConnell, M.D., a researcher in the department of preventive medicine at the University of Southern California medical school. "In fact, just by stepping out the door, you could be exposed to five times the ozone you'd inhale if you stayed inside. So if you're outdoors and exercising . . . well, do the math."