Study: Bad In-Flight Air Exacerbated by Passengers A new study has found that oils on passengers' hair, skin and clothing are partly to blame for stale in-flight air. Researchers show that ozone, which enters the cabin during flight, combines with oils and other materials to create potentially irritating airborne chemicals.
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Study: Bad In-Flight Air Exacerbated by Passengers

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Study: Bad In-Flight Air Exacerbated by Passengers

Study: Bad In-Flight Air Exacerbated by Passengers

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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You're listening to TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow.

Up next, I'm willing to bet that most of you step off an airplane sometimes feeling a bit worse than when you got on. You know, maybe it's a nagging headache or a stuffy nose or a dry throat. And I bet you blame the bad air on the plane. It must be that re-circulated air that's not as fresh as it should be.

Well, if so, there is a new study that will provide some answers why and has a really a couple of surprising findings, surprising at least to those of us flying in coach.

And one surprise is that the air in many planes has ozone concentrations comparable to a bad day in Los Angeles. This is not a health-inducing situation. Surprise number two, you, the passenger, are part of the problem. By just being in the cabin, you make the situation worse. You turn that ozone air into noxious chemicals like acetone. And you really don't have any choice in the matter.

We're joined now by one of the study's authors who's here to explain how airplane air and passengers combine to form a chemical brew that can make us feel sick. Their paper is out this month in the journal Environmental Science and Technology.

Our number, 1-800-989-8255, 1-800-989-TALK. Also you can surf over to our Web site at or find us on "Second Life."

Let me introduce my guest. Charles Weschler is a visiting professor with the International Center for Indoor Environment and Energy at the Technical University of Denmark in Copenhagen, or Copenhagen, if you prefer. He joins us today by phone from that city. Welcome to the program, Dr. Weschler.

Dr. CHARLES WESCHLER (Professor, International Center for Indoor Environment and Energy, Technical University of Denmark): Well, thank you very much. I appreciate your interest.

FLATOW: Dr. Weschler, I imagine a lot of people look out airplane quality, air quality, how is your study different? What did you - how did you find something different, Dr. Weschler?

Dr. WESCHLER: Well, I should back up a moment. Several years ago, I was a member of a national academy panel that was interested in this subject - air quality on airplanes. That was its charge. And as we conducted our study, ozone rose to the top as one of the issues of concern. And that led to these studies that were funded by the FAA and the Center of Excellence that they've actually established to look at this issue of air quality on airplanes.

FLATOW: I was astounded to read your study this week and see how much ozone there is in a cabin of an airplane.

Dr. WESCHLER: Well, it depends on the plane. If it's a wide body plane - a plane with two aisles like a 747 or 8340 - they normally have catalysts that take ozone out of the ventilation air. On the other hand, most of the narrow body planes, most of the single aisle planes, do not use those kinds of catalysts.

So you were right in your lead-in. Indeed, it's not unusual to have ozone levels on a plane that are higher than they are in Los Angeles or D.C. on a smoggy summer day.

FLATOW: And that can't be good for us.

Dr. WESCHLER: No. It can't be good for us. And the first thing you'd think about is the direct effects of ozone. We appreciate that ozone is not good for our health and study after study has shown that. But what we've also come to learn is that ozone reacts with other pollutants in the air and often make some of those pollutants worst than they were in the first place.

FLATOW: Such as?

Dr. WESCHLER: Such as limonene, it has a pleasant smell. It smells like a lemon or pinene, a pleasant smell. It sounds - it smells like a pine tree. And they're relatively innocuous chemicals. But when they react with ozone, they make compounds like formaldehyde or carcinogen - they can make particles. So that's an example of taking something good and making it not so good.

FLATOW: And where would we find those on the plane?

Dr. WESCHLER: Well, those are common odorants. So perhaps the towelette you opened before your meal is scented with limonene. But also on the plane it turns out that the single most important source of chemicals to react with limonene are the passengers themselves. We were able to evaluate how much of the ozone was being consumed by different substances in the plane, how much ozone get chewed up by the seats, how much is chewed up by the carpets and we found that over 50 percent of the ozone was being chewed up by the passengers themselves. And that chemistry - that reaction of ozone with the passengers, specifically their skin oils, that was leading to products in the air that wouldn't have been there otherwise.

FLATOW: Such as?

Dr. WESCHLER: You mentioned acetone.

FLATOW: Like nail polish remover?

Dr. WESCHLER: Right. And actually, we shouldn't be too concerned about acetone. It's a relatively benign chemical as chemicals go. But other products include nonenal and decanal. Those are higher molecular weight aldehydes with nine and ten carbons, respectively. And at higher concentrations, they're irritants. They irritate our mucous membranes. They can make our eyes itch or our throat scratchy. One of the compounds we identified was nonenal, an unsaturated aldehyde that has a very low odor threshold. It's odor threshold is two parts per trillion. And we well exceeded the odor threshold when we had the ozone reacting with the passengers in the plane and it's an unpleasant smell. The Japanese have described the smell of nonenal as the smell of an old man.

FLATOW: And so this would explain why if you're sitting four, five, six hours on a big flight, you're in one of these single-aisled planes and you come off with a headache and your nasal passages are irritated, there's a good reason for it. You're not just - you're just not making it up.

Dr. WESCHLER: It certainly might be contributing.

FLATOW: Mm-hmm. But there are not, as you say, there are not really any acutely dangerous products being made that we know of?

Dr. WESCHLER: No. Some of the oxidization products formed when ozone reacts with various substances on the plane, some of them are known carcinogens. But the - formaldehyde is an example. But the concentrations in the plane are not really any higher than you encounter in your day-to-day activities.

FLATOW: On the other hand, you know, they tell people, on a smoggy day, who have heart conditions to stay indoors in some bad cities. If you have a heart condition, you're indoors and trapped in this plane with a high ozone level.

Dr. WESCHLER: Well, that's correct.

FLATOW: Wow. What - why can't we get rid of the ozone in the single-aisled planes like they do in the wide bodies?

Dr. WESCHLER: Well, it's technically feasible and some of the planes do it. And most of the planes are constructed so you can insert an ozone catalyst to take ozone out of the ventilation air if the airline chooses to do that. But it's a very competitive environment, the airline industry, and it costs money to put in the ozone converter, and they have to be serviced and they have to be replaced. So for now, the ozone converters are primarily on the wide body planes.

FLATOW: And how do they work? Do they work something like the catalytic converter in our car?

Dr. WESCHLER: Very much so.

FLATOW: Cleans the air that way.

Dr. WESCHLER: They tend to be precious metal catalysts.


Dr. WESCHLER: Or they consist of compounds like platinum or palladium. And the air coming off the engine, the bleed air that's used for ventilation is at a high temperature, and that high temperature air passing over the platinum or palladium catalyst results in any ozone in that air being destroyed.

FLATOW: Let's go to the phones. Faith(ph) in Portland, Oregon. Hi, Faith.

FAITH (Caller): Hi, there.

FLATOW: All right, good.

FAITH: I'm a - yeah, I'm a flight attendant, and my company has fought tooth and nail over the past 10 years - I'm not going to name my company, of course, because I'd want to keep my job - but, against this kind of information becoming public. And my union has done, gone through even, like, sort of espionage techniques to uncover some of this and some of the cover-up.

And I just want to let you know that the flight attendants tend to, you know, we spend 10 hours on the plane and at a straight shot and have chronic sinus infections and all - and we've even had people dizzy and, you know, nauseous and everything else. And I just wondered what the chronic exposure for a plane employee like myself, who is on a plane for so long. Is there extra oxidative stress and things like this that might lead to cancer or other kinds of health risks that might be immediately evident?

FLATOW: Dr. Weschler?

DR. WESCHLER: It's too early to really know what the chronic effects from exposure to these oxidation products on the plane are. Faith makes an excellent point that the crew is - the primary concern here is it's the crew who is exposed to these oxidized chemicals day in and day out. They just log so many more hours in the air than you or I do. We recognize the acute effects of some of these chemicals, but it's difficult to tease out the long-term effects.

FLATOW: Do you think your study is going to help Faith bring out some facts, ma'am, just the facts, you know, when…

Dr. WESCHLER: I think what…

FAITH: Well, I know - for example, the pilots have fresh - more fresh air than the people in the cabin do. And I don't know if that's well known and - so it's the flight attendants that are most at risk and have probably not as much toll being a group of women of sorts.

(Soundbite of laughter)

FLATOW: Well, you have another research paper to site, Faith. Good luck to you.

FAITH: Thank you.

FLATOW: Thank you. 1-800-989-8255 is our number. Talking about the cabin air in planes.

Well, where do you go from here? Anything - any forward-looking that you can do on this study to take you to a next step?

Dr. WESCHLER: Well, the next step is to measure these planes on actual aircraft. This work was done in a simulated aircraft that - here at the Technical University of Denmark. And we have studies planned next year and the year after to actually make these similar measurements on airplanes and, at the same time, monitor the ozone levels and just see what type of levels we measure for these oxidization products. And then, going back to Faith's question, obviously, further studies on the health effects, potential health effects of exposure to these chemicals.

FLATOW: What do the ozone actually interact with on your skin and in your body? How does that work?

Dr. WESCHLER: Well, primary compound is squalene. Squalene is a long carbon molecule of 30 carbon atoms and it has six unsaturated carbon bonds. And it's a tremendous antioxidant. It just does a great job of chewing up ozone. But when ozone reacts with the squalene molecules, you get these oxidation products such as acetone and something called 6-MHO and something else called for 4-OPA.

And, interestingly, in the case of that last compound 4-OPA, no talk studies have been done to date on 4-OPA. So we have really no idea what its toxicity is, whether it's benign or whether it's something we should be concerned about.

FLATOW: Can a passenger do anything to protect his or herself from any of these?

Dr. WESCHLER: It probably makes sense to, if you know you're going to be flying a single-aisle plane, and the odds are that it's not taking ozone out of the air, it make sense to go light on the perfume or cologne or scented soaps. But in terms of your body oils, I wouldn't recommend trying to reduce the body oils. You know, they serve an important function. And we all have that - we've all experienced, I think, that dried out feeling on a long, plane flight. The relative humidity in an aircraft cabin is very low, about 10 percent RH. So we want those body oils.

FLATOW: Let's go to Arthur(ph) in Kalkaska, Michigan. Hi, Arthur.

ARTHUR (Caller): Yeah. That's Kalkaska.

ARTHUR: I'm sorry.

ARTHUR: Yeah. That's okay. Hi, Ira. And question for your guest. I've always wondered about, you've answered the perfume and shaving lotion question because both compounds found in perfume and shaving lotion are quite complex and would also react with ozone to form some strange reaction products like you said.

I'm also wondering about the presence of carbon monoxide in the air and also from electrical wiring, and the usage of many electronic components could also emit vinyl chlorides into the atmosphere. Did you find any such compounds?

Dr. WESCHLER: We didn't find such compounds in our study. But recall, this is a simulated aircraft cabin we're in. Carbon monoxide - ozone does not react with carbon monoxide. But I - nor is carbon monoxide a major product of ozone-initiated reactions. But I assume what you mean, (unintelligible) is that other sources inside the aircraft could potentially contribute carbon monoxide. That was your point?

FLATOW: Well, he's gone. But I think he - that was his point, yeah.


FLATOW: All right. Thank you. We're talking about ozone in the aircraft, another compounds in the air on TALK OF THE NATION: SCIENCE FRIDAY from NPR NEWS.

FLATOW: What about just the outgassing from the furniture? Have people measured those things and, you know, the plastic parts of the plane, stuff like that?

Dr. WESCHLER: Yes, absolutely. And they all contribute chemicals to the air in an aircraft. When we're talking about the ozone, the chemistry involving ozone, it's important to realize that ozone reacts with only a subset of the pollutants typically found in the air. It reacts with compounds that have unsaturated carbon-carbon bonds.

If you think of cooking oils and you think of saturated cooking oils and unsaturated cooking oils, ozone reacts with the unsaturated cooking oil not the saturated cooking oil. So about 10 percent of the organic pollutants that you find in an aircraft have unsaturated bonds and will react with ozone to make something else.

FLATOW: Mm-hmm.

Dr. WESCHLER: Now, going back to your question about emissions from seat materials and carpeting. Certainly, those emissions are in the air and some of those emissions are plasticizers, some of them are flame-retardants. And there's concerns regarding both of those compounds, but not as regards to chemistry with ozone.

FLATOW: I've got one final question from the "Second Life" from Fifi(ph) there, saying, I'm a frequent flyer. Is there something I can carry with me to counteract the effects of bad airplane air?

Dr. WESCHLER: Short of taking a charcoal mask with you on the plane, I'm afraid not. And I don't know how effective that charcoal mask would be.

FLATOW: But, you would suggest then that if you have a choice of airplane models to fly, choose the one with the multi-aisles in it?

Dr. WESCHLER: That's correct. If your concern is ozone, you're going to have lower ozone levels more likely on a wide body plane than on a narrow body plane.

FLATOW: Now, when you do your next study with real airplanes, monitoring them, do you expect to find any surprises? Maybe things you hadn't even thought of might show off.

Dr. WESCHLER: Well, it's hard to expect surprises. We were certainly surprised in this study to find out that the passengers were so very important to the chemistry. We had done studies in the aircraft without passengers before we got ethical approval to have human subjects sit in the plane, in the simulated plane. And we thought we understood fairly well what was going on and what the major products of the ozone chemistry was. And it wasn't until we had passengers in the plane that we realized how very important they were to the whole story and how they were reacting with ozone more than anything else. So who knows what surprises we'll have when we actually start measurements on airplanes in the skies.

FLATOW: Well, that's where we're all flying these days. So we'll be watching your research, Dr. Weschler. Thank you very much for taking time to be with us.

Dr. WESCHLER: Again, thank you for your interest.

FLATOW: Charles Weschler is visiting professor with the International Center for Indoor Environment and Energy at the Technical University of Denmark in Copenhagen. And he's also adjunct professor of environmental and occupational medicine at the University of Medicine and Dentistry of New Jersey and Rutgers University in Piscataway, New Jersey.

That's about all the time we have today.

(Soundbite of credits)

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