Just one more thing to worry about next time you're sitting on an airplane.

According to a University of California study, ozone levels inside the cabins of some commercial aircraft exceed federal limits, increasing the chance of health problems.

While ozone is a good thing when it's blocking the UV rays that cause skin cancer, it's not something you want to be inhaling during your seven hour flight to Dusseldorf.

Exposure to in-cabin ozone is linked to a variety of not-so-cool health symptoms including breathing discomfort, headache, and respiratory irritation. Chronic exposure and physical activity (think flight attendants) can magnify the impact.

The University of California study took place between 2006 and 2007, and involved 76 commercial jets flying both domestic and international routes.

William Nazaroff, one of study's authors, says his team used something called a UV photometric meter to test ozone levels in each plane. The photometric method involves shining a specific wavelength of light that is absorbed by ozone. Measure how much light attenuation occurs, and you can calculate ozone levels.

Nazaroff and company found that ozone levels exceeded the federal action level of 100 parts per billion on four of the planes tested.

Several factors influence in-flight ozone levels. They're usually lower on domestic flights, because those planes tend to fly at lower altitudes. Because ozone reacts with skin oils, it is thought that cabin levels change based on passenger count (though Nazaroff's research wasn't able to confirm this).

But the study did establish that flying in or around storms also bumps up ozone counts because rough weather churns things up and knocks ozone down to lower altitudes. "Seems obvious in hindsight, but we didn't anticipate that one," Nazaroff admits.

Nazaroff says that although plenty of airline types are aware of his findings, reaction from the industry has been minimal.

The solution to all of this is simple enough: outfit planes with ozone converters, which work the same way as catayltic converters. Most widebody planes are already equipped because they're more likely to fly polar routes, but many smaller jets are not.

Nazaroff thinks it could take years or even a decade before all planes have ozone converters installed, and while he thinks ozone exposure is a serious problem, he's also a realist.

"It doesn't rise to the highest level of concern," he said. "The central emphasis is keeping planes flying and landing safely."

by Dave Demerjian for Wired.com