The American Lung Association says more than 160 million people in the United States live in areas with unhealthy levels of air pollution.
In a new report released Wednesday, the health group cited overall progress in reducing pollution through increased use of cleaner power plants and automobiles, but said short-term spikes in pollution -- many linked to drought and wildfires -- have gotten worse. It warned that global warming is likely to make those triggers happen more often.
The group said the bad air puts people at risk of premature death, lung cancer, asthma attacks, cardiovascular damage and reproductive problems.
The report focuses on ozone pollution and high levels of both short-term and long-term particle pollutants in the air.
Los Angeles ranked as one of the worst cities when it comes to air quality. It topped the list of those with the most ozone pollution and was in the top 10 for particle pollution. Still, the association said the air quality in Los Angeles was the best the city has had in at least 15 years.
Like Los Angeles, many of the poorest performing cities are located in California. The western state has been hit by major drought in the past few years, as well as its usual wildfires that burn large areas of forests and send smoke into the air.
On the opposite end of the spectrum from Los Angeles, the report listed only four cities that rank at the top of the list of cleanest cities in terms of ozone and particle pollution. Those include the northern California city of Salinas; Honolulu, Hawaii; Burlington, Vermont; and Elmira, New York.
Because of data issues, the report does not include any cities in Illinois, Florida or Tennessee, which the association said leaves out historically polluted Chicago and St. Louis.
It calls for a number of actions to improve air quality in the United States, such as further cutting carbon pollution from power plants and retro-fitting older diesel vehicles.
"The Lung Association calls on every state to adopt strong Clean Power Plans to reduce emissions from power plants that worsen climate change and immediately harm health," said the group's president and CEO Harold Wimmer. "The Supreme Court has put a temporary hold on EPA's enforcement of the federal Clean Power Plan, but states should not wait to clean up carbon pollution from their power plants."
U.S. President Barack Obama announced plans in August to reduce the amount of carbon emission from the nation's power plants. The Environmental Protection Agency set up guidelines that left it up to states to design their own roadmaps for achieving the cuts, and said that by 2030 overall emissions would be down by 32 percent from 2005 levels.
A group of 27 states balked at the plan and filed a lawsuit, saying it amounted to an overstep by the EPA and would unnecessarily hurt businesses and cost jobs. The Supreme Court suspended implementation of the plan for now while the case moves forward.
Even before the president issued the new regulations, power companies across the United States had already begun converting their energy generation away from coal to rely more on natural gas, solar and wind.
As a result, carbon emissions from coal-burning power plants fell by 13 percent nationwide between 2011 and 2013, according to government data.