News release: "Average air pollution levels from secondhand smoke directly outside designated smoking areas in airports are five times higher than levels in smoke-free airports, according to a study by the Centers for Disease Control and Prevention. The study conducted in five large hub U.S. airports also showed that air pollution levels inside designated smoking areas were 23 times higher than levels in smoke-free airports. In the study, designated smoking areas in airports included restaurants, bars, and ventilated smoking rooms. Five of the 29 largest airports in the United States allow smoking in designated areas that are accessible to the public. The airports that allow smoking include Hartsfield-Jackson Atlanta International Airport, Washington Dulles International Airport, McCarran International Airport in Las Vegas, Denver International Airport, and Salt Lake City International Airport. More than 110 million passenger boardings—about 15 percent of all U.S. air travel—occurred at these five airports last year."