(NBCNC) - The quality of the air we breathe has improved over the past 15 years, yet there are still over 100-million Americans breathing smog or pollution every day.
Overall, the state of our air is much cleaner than it was a decade ago according to the American Lung Association's annual report, even in cities like busy Los Angeles.
"Even though they're at the top of the list for most pollution for ozone, they've still reduced about two months worth of unhealthy days every year over the past 15 years. And that's a great accomplishment," says the American Lung Association's Janice Nolen.
The Lung Association's analysis of air quality reports shows the most polluted cities are in California, Utah, Texas and Pennsylvania.
But Americans across the country are affected. The report shows four out of ten people live in counties with unhealthy levels of smog and soot.
"These particles and these ozone molecules go into our lungs and our lungs spread them throughout the body," Nolen explains.
Infants, the elderly and people with breathing disorders like asthma are most at risk for complications. People who work or exercise outdoors can also be affected.
The risks of exposure to too much pollution can range from difficulty breathing to heart disease.
A proposed EPA standard may reduce the amount of sulfur in gasoline used by cars and some trucks, effectively removing the pollution from 33 million vehicles on the road.