An article in today's NY Times doesn't help me feel any better:
[Cardiology professor] Dr. [David] Newby has seen, in action, the effects of [fine particulates] on active people. In 2005, he and his colleagues had 30 healthy volunteers ride exercise bikes inside a laboratory for 30 minutes, while breathing piped-in diesel exhaust at levels approximately those along a city highway at rush hour.Those fine particulates also happen to collect heavy metals and other toxics from engines and fuel and deliver them into the bloodstream when we inhale them. Athletes are particularly susceptible because they can take in 10 to 20 times as much air pollutants as sedentary people, although anyone who walks or bikes regularly near automotive traffic is at risk.
Afterward, the researchers did a “kind of stress test of the blood vessels” in the participants’ forearms, Dr. Newby said, and found that the vessels were abnormally dilated, meaning blood and oxygen could not flow easily to the muscles. At the same time, levels of tissue plasminogen activator, or tPA, a naturally-occurring protein that dissolves blood clots, had fallen.
“Those are ideal conditions for a heart attack,” Dr. Newby said.
Nevertheless, even the doctors who are experts on how unhealthy our air can be warn that exercising still beats the alternative. "The bottom line is that running and cycling are healthy and, over all, good for the heart," says Dr. Newby. "I ride my bike back and forth to work every day," he said. "If everyone else did that, too, we wouldn’t be having this problem at all, would we?"