The air outside keeps you aloft, but the air inside keeps you alive in a jet airliner. And passengers give the quality of that air mixed reviews.
"On the flights I do fly a lot - this was probably the worst I've had in months, but it was acceptable I guess," said an airline passenger.
"It was actually very pleasant. Warm when we started off, but once the cabin cooled off it seemed to be fine," said an airline passenger.
Actually, an ozone monitor recently showed the air on some flights wasn't so fine.
"On a plane, of course, if you encounter ozone there's no place to go and there's generally a lack of knowledge that we're even being exposed to the ozone," said William Nazaroff Ph.D., UC Berkeley.
Ozone is one component of the polluted air on "Spare the Air", and other smoggy days. It's an irritant that could trigger asthma attacks and other respiratory problems. It can also be a problem at the cruising altitudes of modern jets. With the support of the FAA, a research team from UC Berkeley tested the ozone levels on 76 international and domestic flights. Four domestic flights showed very high levels of ozone.
"The most extreme cases we observed were like being outdoors on a quite smoggy day," said Nazaroff.
Air quality was best on overseas flights, which are required to have devices to filter the ozone out of the air - U.S. domestic flights are not. And even on flights with moderate ozone levels, researchers found that the pollutant actually reacts with the natural oils in your skin to make chemicals that themselves may be harmful.
"We can inhale those and in the aircraft cabin where the density of people is so high, this raises some interesting questions about the potential health consequences of breathing those reaction byproducts," said Nazaroff.
"If you're an elderly person, if you're carrying an infant onboard, or if you have asthma it is something you might think about," said Seema Bhanger, UC Berkeley researcher.
That part of their findings needs more study. It's worth noting that the overwhelming majority of flights - even without special filters - had acceptable levels of ozone in their cabins. For those that don't, Nazaroff says the ultimate solution may be ozone converters on every flight. Of course airlines would pass that along to consumers - probably not a popular idea in the age of sky high fuel prices.
The airline industry said that cabin air is replaced every seven to 10 minutes. Nazaroff says a rough estimate is that it would cost an extra buck or two per ticket to pay for ozone converters on every jetliner. But, with several airlines flirting with bankruptcy, most are looking for ways to cut costs not add them.