Nearly 148 Americans live in regions where air pollution levels are a threat to their health, according to the American Lung Association’s 2014 State of the Air report.

The report examined particle pollution from vehicle exhaust, coal-fired plants, and ozone (smog) levels. Air pollution is reported to increase the risk of heart disease, asthma, and lung cancer.

Here are the report’s highlights:

  • Nearly half of the people in the United States (147.6 million) live in counties with unhealthy levels of either ozone or particle pollution
  • More than 27.8 million people (8.9%) in the United States live in 17 counties with unhealthful levels of all pollutants measured in the report
  • Twenty-two of the 25 most ozone-polluted cities in the 2014 report – including Los Angeles, New York City, and Chicago – had more high ozone days on average when compared to the 2013 report
  • Thirteen of the 25 cities with the worst year-round particle pollution reached their lowest levels yet, including Los Angeles, Atlanta, Pittsburgh and Bakersfield

Although the United States has made progress in providing healthier air, the ALA issued a warning for several at-risk groups:

  • Infant, child, teenage and senior patients
  • Patients with lung diseases like asthma or COPD
  • Patients with heart disease or diabetes
  • Low-income patients
  • Patients who work or exercise outdoors

“Ozone was much worse in 2010-2012 compared to 2009-2011, likely due to warmer temperatures, especially in 2012,” wrote the ALA. “Fortunately, even these higher levels represent much better air quality compared to ten or 15 years ago.”