Most people living in New Jersey live in counties with unhealthy levels of smog, according to an annual report by the American Lung Association.

The group, which advocates for the extension of the federal Clean Air Act, gave failing grades to 12 of New Jersey's 21 counties based on measurements of ozone, a pollutant that comes from power plant and vehicle emissions.

The counties fared better on the measurement of days that saw high levels of particle pollution in the air.

Both forms of pollution increase the risk for asthma, lung cancer and other illnesses.

American Lung Association
American Lung Association
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The 2017 State of the Air report, measuring data from 2013 to 2015, finds that 4 in 10 Americans live in counties that have unhealthful levels of either ozone or particle pollution. That's a 25 percent improvement from last year's report, which measured 2012 to 2014 data.

Most of the cities with the worst air pollution were in California.

The data was obtained from the U.S. Environmental Protection Agency's Air Quality System, which does collect data for all of the state's counties.

The state Department of Environmental Protection this week told New Jersey 101.5 that New Jersey's air quality has been improving because of controls placed on power plants and vehicle emissions.

Grading NJ's air quality

Atlantic
Ozone - C
Particle pollution - A

Bergen
Ozone - F
Particle pollution - A

Burlington
Ozone - N/A
Particle pollution - N/A

Camden
Ozone - F
Particle pollution - B

Cape May
Ozone - N/A
Particle pollution - N/A

Cumberland
Ozone - F
Particle pollution - N/A

Essex
Ozone - F
Particle pollution - B

Gloucester
Ozone - F
Particle pollution - A

Hudson
Ozone - F
Particle pollution - B

Hunterdon
Ozone - F
Particle pollution - N/A

Mercer
Ozone - F
Particle pollution - A

Middlesex
Ozone - F
Particle pollution - A

Monmouth
Ozone - F
Particle pollution - N/A

Morris
Ozone - F
Particle pollution - A

Ocean
Ozone - F
Particle pollution - B

Passaic
Ozone - D
Particle pollution - A

Salem
Ozone - N/A
Particle pollution - N/A

Somerset
Ozone - N/A
Particle pollution - N/A

Sussex
Ozone - N/A
Particle pollution - N/A

Warren
Ozone - C
Particle pollution - A

American Lung Association
American Lung Association
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