WASHINGTON (WUSA) -- The Centers for Disease Control and Prevention conducted a study on secondhand smoke exposure at major U.S. airports and the results are in.

The study shows that "average air pollution levels from secondhand smoke directly outside designated smoking areas in airports are five times high than levels in smoke-free airports." The study also showed that levels inside designated area were 23 times higher than levels in smoke-free airports.

Washington Dulles International Airport is one of the five airports that allow smoking in designated indoor areas. The other four are: Denver International, Hartsfield-Jackson Atlanta International, McCarran International in Las Vegas, and Salt Lake City International.

The CDC study concludes that the only way to eliminate involuntary is to completely ban smoking in all indoor areas. Federal laws banned smoking on all U.S. commercial airline flights, but there is no federal law on smoking for airports.

See the detailed results of the study at the links.

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