It's a story of good news and bad news in the new State of the Air report released by the American Lung Association.
The study found close to half of all Americans live in areas, including 14 Indiana counties, where the air is unhealthy at times.
While the nation's overall air quality has worsened over the past few years, Lung Association spokeswoman Janice Nolen says the picture is still better than 10 years ago.
"And we have good evidence, just looking at the 15 years of this report, that those steps of cleaning up power plants, cleaning up diesel, cleaning up cars, cleaning up SUVs - things like that - have made a huge difference in reducing pollution across the nation," she says.
According to the report, despite a trend of lower particle pollution levels across the nation, Indianapolis has seen an increase compared with 2013, ranking as the 20th most polluted city year round for particle pollution.
Ozone and particulate matter are measured at monitoring sites, and Nolen says both are very serious health threats - especially affecting the very young, the very old and people of all ages with lung and heart conditions, as well as disproportionately affecting people living in poverty.
"They can cause asthma attacks," she points out. "They can cause difficulty breathing, send people to the hospital.
"But most importantly, they can shorten life - they can shorten life, as we've learned, by months to years."
Climate change is complicating the nation's progress in ensuring cleaner air, adds Nolen, who explains how rising temperatures boost pollution levels.
"You've got more heat, and that's what we're seeing with climate change," she says. "You're going to have more ozone. You're going to have a likelihood that you're going to have higher levels than you would otherwise."
The report recommends improving the air quality monitoring network, reducing carbon pollution from power plants, lowering tailpipe emissions, cutting wood smoke, adopting ozone standards proposed by the Environmental Protection Agency and educating people about what they can do to reduce pollution, as well as how to protect themselves when air quality is poor.