Forty-seven percent of Americans live in counties with potentially dangerous levels of air pollution, according to the American Lung Association's 15th annual State of the Air report, a worrisome finding as climate change threatens to make air quality worse.

The two main pollutants measured were ozone, also known as smog, and particle pollution, the kind that comes out of exhaust pipes. Ozone can cause breathing problems and premature death. Particle pollution can increase the risk of heart disease, lung cancer, and asthma.

Ozone can cause breathing problems and an early death

The pollution data compiled in the report was taken from the Environmental Protection Agency (EPA). The report used the EPA's Air Quality Index, which ranks pollution levels into five tiers from "good" to "hazardous." You can use the State of the Air website to look up air pollution levels in your zip code and compare metropolitan areas.

Ozone pollution levels were "much worse" than last year, the Association says, and are expected to worsen due to global warming. Particle pollution was down, however, due to environmental regulations. Ozone and particle pollution are especially dangerous for sensitive populations, like children and the elderly.

The finding follows a Supreme Court decision that reinforced environmental protection laws by upholding the Cross-State Air Pollution Rule. The ruling authorized the EPA to impose extra limits on power plants that produce pollution that floats over state lines, and is likely to have a positive effect on overall air pollution levels.