The air in the U.S. has been getting cleaner since the 1963 passage of the Clean Air Act. But the pace of improvements has been declining significantly in recent years, according to a new study published today.

And this could damage your health. It's long been known that for people with asthma, pollutants in the air can trigger wheezing, coughing, and chest discomfort. 

Fine particulate from dust, soot, smoke, and more appear to have negative effects on others, too. Air pollution is considered a potential cause of lung cancer by the World Health Organization and a possible risk factor for heart disease and stroke, according to the American Heart Association.

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Despite Clean Air Act improvements, we’re still exposed to dirty air, according to Robert Brook, M.D., a professor of medicine at the University of Michigan who studies air pollution and health.

And the study published today in Proceedings of the National Academy of Sciences suggests that the regulations designed to make our air cleaner are reaching the limits of their potential, and that emissions of two common pollutants—nitrogen oxides and carbon monoxide—fell much more slowly between 2011 and 2015 than they did between 2005 and 2009.

“The U.S. is experiencing a slowdown in its efforts to clean up the unhealthy air after decades of progress,” says Helen Worden, Ph.D., a scientist at the National Center for Atmospheric Research and one of the study’s authors.

One possible reason is that most power plants and passenger cars on the road are now equipped with pollution-control technology, but equivalent progress has not yet been made for other sources of pollution, such as heavy-duty diesel trucks, construction equipment, and industrial boilers.

For Air Quality Awareness Week, here's what you need to know about the health effects of air pollution and how to protect yourself.

How Dirty Air Can Harm Your Health

In addition to the potential role of air pollution in heart and lung disease, recent studies have unearthed a wide variety of other possible health consequences. 

“When I started to study air pollution 10 years ago, all we knew was that it affected the lungs and the cardiovascular system. Now we are realizing there is much more to it,” says Andrea Baccarelli, M.D., Ph.D., chair of the environmental health sciences department at the Columbia University Mailman School of Public Health.  

Late last year Baccarelli and researchers from Harvard and other universities published a study in the journal Lancet Planetary Health that found that regularly inhaling tiny particles of pollutants might be linked to poor bone health and fractures.

They found that the more polluted the air was in a particular ZIP code, the greater the number of hospital admissions for broken bones, and that living in more polluted areas was associated with losing more bone density over time.

Other studies in the past year have connected long-term air pollution exposure to psychological distress and poorer sperm quality in men. A study published in December 2017 in the Journal of Pediatrics found that even short-term exposure to fine particles of pollution early in pregnancy—or even a month before conception—was linked a small increased risk of birth defects.

Cut Your Exposure to Air Pollution

On a positive note, for a healthy individual in the U.S., the risks of pollution are typically low, notes Brook. Still, he says, “we don't see much of a threshold where any level is deemed safe.”

And reducing exposure to air pollution may be important for those who seem to be more vulnerable to its effects: children; older adults; and people who have asthma, heart or lung disease and those at high risk for those conditions. Where you live could increase your risk of negative health consequences as well. Air pollution levels are higher in urban areas and near highly trafficked roads.

The following steps will help reduce your exposure to dirty air:

Filter your air at home. Evidence for the effectiveness of air purifiers in reducing the health effects of air pollution is mixed. But they may be helpful for people with allergies. And a small study published last year in the journal Circulation found that a small group of college students in Shanghai who ran an air purifier in their dorm had lower levels of stress hormones, blood pressure, and insulin resistance after nine days than those who used a sham purifier. Consumer Reports tests how well portable air purifiers remove dust, pollen, and smoke from the air. Check our air purifier ratings.

Ban smoking and reduce fireplace use. The smoking of tobacco is a key source of air pollution indoors, and that cozy fire in your fireplace also releases plenty of fine particles. Get the Environmental Protection Agency's advice on burning wood at home.

And be aware of other sources of indoor pollution, such as gas cook stoves. Read more about how to reduce your exposure to indoor air pollution.

Avoid particle pollution. Combustion from car and truck engines as well as from power plants is the most common source of harmful particles in the air in the U.S. More than half of all air pollution comes from mobile sources, primarily automobiles, according to the EPA.

So if you exercise outside—and especially if you have a heart or lung problem—try to avoid heavily trafficked roads where automobile-generated pollution could be significant. You can also check this EPA website for air-quality alerts and, depending on your personal health, consider limiting outdoor activity when the air quality index is 101 or higher.

If you live near a busy road, you may want to keep your windows closed during the day or times of more traffic, such as rush hour. Instead, open them at night, when traffic may be lighter.

Make yourself less vulnerable. Because the health effects of air pollution may weigh more heavily on those already at risk for heart disease, take smart lifestyle steps. Talk with your doctor about getting your blood pressure and cholesterol under control if you need to. Improve your diet by including more fruit, vegetables, whole grains, and lean proteins. And try to exercise every day.

Reduce your pollution footprint. Because so much of air pollution is created by traffic, Baccarelli suggests considering alternate ways of getting around. “Walk, bike, take public transportation,” he says. “If you drive and need a new car, consider an electric or hybrid car.” (Check our electric and hybrid vehicle ratings.)

Shannon Baker-Branstetter, senior policy counsel for energy and environment at Consumers Union, the policy and mobilization division of Consumer Reports, says that improving your home’s efficiency or adding rooftop solar can also help.

She says that there’s a role for policymakers to play as well. “Improving emission standards for power plants and cars and trucks, especially heavy-duty trucks, will help continue the progress made under the Clean Air Act.”