According to a newly released report from the Centers for Disease Control and Prevention, at many of the world’s busiest airports travelers continue to be explosed to second-hand cigarette smoke, which the Surgeon General has declared a health risk at any level of exposure.

The report, published this week, found that as of August 2017 more than half (27) of the world’s 50 busiest airport still allow smoking in certain areas, while 23 (46 percent) were smoke-free.

Among the 10 busiest airports in the world, the report found that half still allow smoking in certain indoor areas: Atlanta Hartsfield Jackson International, Dubai International, Hong Kong International, Paris’s Charles de Gaulle, and Tokyo International.

Beijing Capital International, Chicago O’Hare, London Heathrow, Los Angeles International and Shanghai Pudong International, also among the top 10 busiest airports, are smoke-free.

Among North American airports on the list of the 50 busiest, the CDC report found that 14 of 18 had a smoke-free policy, but that Atlanta, Denver, McCarran International in Las Vegas and Mexico City International airports still permit smoking in some areas. (Washington-Dulles, a busy hub, but not among the 50 world’s busiest airports, also has smoking areas.)

Denver International, the report notes, closed three of its four smoking indoor smoking rooms in the past few years and is scheduled to snuff out the final one in 2018 when its lease expires. And while it is not among the 50 world’s busiest airports, the report mentions that Salt Lake City International, a large-hub U.S. airport, also recently implemented a smoke-free policy.

But while Beijing Capital International Airport, the world’s second busiest airport, is smoke-free, “Sadly, Las Vegas, Dulles and Atlanta have not budged on going smoke-free,” said Cynthia Hallett, president and CEO of Americans for Nonsmokers’ Rights.

Officials at Atlanta International, the world’s busiest airport, say they are well aware of the calls to create a smoke-free environment at the airport, but have no plans to close their smoking areas.

“Creating a smoke-free policy would force smokers to find locations throughout the airport to light up and expose other guests to secondhand smoke,” said ATL spokesperson Andrew Gobeil, “And smokers might move outside the terminal and create an additional burden on security lines as those passengers re-enter screening areas.”

Inconvenience aside, “Millions of people who travel through and work in airports that allow smoking are unnecessarily exposed to secondhand smoke,” said U.S. Surgeon General Jerome Adams, “Smoke-free airports can protect people from this preventable health risk.”

My story about smoking at airports first appeared in a slightly different form on USATODAY’s Today in the Sky.