Air pollution still remains one of the key environmental issues in the United States. Although it has seen incredible improvement since the 1970s, more than 4 in 10 Americans are still estimated to live in counties with poor air quality. Every year, air pollution kills more than 6 million people worldwide from heart attacks, stroke and diabetes. So just how clean is the air we breathe in the U.S.? More more than 135 million Americans live with polluted air, placing their health and lives at risk, according to an American Lung Association report published Wednesday. “It is impacting you, whether you know it or not,” said Becki Baker, an asthma patient. “People don’t realize that over time, this is cumulative.” Air pollution remains one of the key environmental issues in the United States. Although it has seen incredible improvement since the 1970s thanks to the Environmental Protection Agency and the Clean Air Act, the number of Americans exposed to poor air quality has consistently stayed over 125 million since 2013. “Generally, there are two local air pollutants that the U.S., EPA, and other researchers tend to focus on,” explained Nicholas Muller, associate professor of economics, engineering, and public policy at Carnegie Mellon University. “Those are fine particulate matter and tropospheric or ground-level ozone.” Particle matter pollution refers to tiny pieces of solids or liquids in the air that consist of contaminants like dust, dirt soot and smoke. Nearly 21 million people in the U.S. are estimated to live in counties with unhealthy levels of particle pollution year-round, Wednesday’s report said. “It comes very small, much smaller than a human hair,” American Lung Association national senior vice president of advocacy Paul Billings said. “You can often see them when you look at a sunset and you see all of that haze in the evening.” Ground-level ozone pollutants, meanwhile, are often better known by another name: smog. This is created when pollutants from cars, power plants, and other known sources chemically react in the air under sunlight. More than 123 million people in the U.S. are thought to live in counties with bad ozone pollution, with just over 28 million of them being children and 18.2 million aged 65 or older, the report said. “It’s likened to a sunburn of the lung because it irritates the respiratory tract,” Billings said. The report also found that communities and people of color are disproportionately affected by poor air quality. People of color are 3 times as likely to live in the most polluted places. “And that’s actually not surprising,” Yale University environmental justice professor Gerald Torres said. “The data has indicated that before Covid-19 but what Covid-19 did was highlight that.” Poor air quality is also costing the U.S. roughly $617 billion in damages every year, according to the World Economic Forum. Additionally, the EPA estimates the U.S. spends about $65 billion every year to clean the air. » Subscribe to CNBC: https://cnb.cx/SubscribeCNBC » Subscribe to CNBC TV: https://cnb.cx/SubscribeCNBCtelevision » Subscribe to CNBC Classic: https://cnb.cx/SubscribeCNBCclassic About CNBC: From 'Wall Street' to 'Main Street' to award winning original documentaries and Reality TV series, CNBC has you covered. Experience special sneak peeks of your favorite shows, exclusive video and more. Connect with CNBC News Online Get the latest news: https://www.cnbc.com/ Follow CNBC on LinkedIn: https://cnb.cx/LinkedInCNBC Follow CNBC News on Facebook: https://cnb.cx/LikeCNBC Follow CNBC News on Twitter: https://cnb.cx/FollowCNBC Follow CNBC News on Instagram: https://cnb.cx/InstagramCNBC Subscribe to CNBC PRO: https://cnb.cx/2NLi9AN #CNBC Why Clean Air Is So Expensive In The U.S.