If you think air quality in the U.S. has improved since the government has cracked down on industrial emissions and Priuses now zip down every highway, you're not totally off base. Many Americans are in fact breathing cleaner air. However, while North Dakotans may not be choking on smog, 132 million of us – or 42 percent of the population – live in areas with unhealthy levels of ozone and soot, according to a recent American Lung Association report. That's you, New York, L.A., Dallas, and D.C.

"No question, the stuff that spewed out of factories was dirtier back in the day," says Dr. Russell Luepker, an epidemiology professor at the University of Minnesota School of Public Health. "But you have to consider the aggregate of all the air pollution sources. Wherever large groups of people congregate, drive, and heat houses, you'll have lots of pollution."

What's more, Luepker says since we're living longer today compared to our great-grandparents' generation, we spend many more years exposed to pollution, which can ransack health. Breathing in fumes from factories and heavy traffic does a number on your lungs, and more and more research shows it also poses serious problems for the heart. A new study published in the journal 'PLoS Medicine' in April found that long-term exposure to polluted air can speed up hardening of the arteries, increasing chances of heart attack and stroke.

Short of pulling up stakes and moving to Bismarck, there are a few things you can do to protect yourself. According to the American Lung Association, you should always keep an eye on the local air quality index, and on days when it's poor, keep windows shut and hit the gym instead of running outside. Avoid walking along high-traffic roads whenever possible, even if the alternative route takes you a bit longer. Don't use gas-powered lawnmowers or leaf blowers, which can pollute the air more than cars. If you can, convert wood stoves in your home to cleaner-burning natural gas. And never let anyone smoke cigarettes in your pad, since the carbon lingers long after the butt goes out.