Flying on an airplane used to be something special. Now it's just another means of mass transit, with all that implies. So our attention is more and more directed to the unpleasant parts of flying, which, for many is the lousy air quality. Modern pressurized airliners fly high -- very high indeed. Stratospherically, literally. When you are up 35,000 or 40,000 feet you are in the stratosphere, a layer of the atmosphere where there is little vertical movement of air (it is essentially a temperature inversion) and high ozone levels. Those ozone levels are a good thing for those of us at on the ground because ozone absorbs radiation in the ultraviolet, shielding us from a solar carcinogen. Ozone isn't very good to breathe, however, and high ozone levels (90% of photochemical smog is ozone) are an air pollutant. We aren't in the stratosphere very long in an airplane so the increased ozone levels when the craft passes through the stratosphere aren't that much of an issue for passengers, although for crew there is some increased risk, just as there would be for living in an area with chronic photochemical air pollution on the ground. The 8-hour standard for ozone at ground level is 80 ppb (parts per billion), with no one hour to exceed 120 ppb.
It turns out that cabin ozone might have be even more troublesome than previously suspected, however:
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A study in the current issue of ACS' Environmental Science & Technology suggests interactions between body oils and ozone found in airplane cabins could lead to the formation of chemical byproducts that might worsen nasal irritation, headaches, dry eyes and lips, and other common air traveler complaints.In simulated flights lasting four hours, American and Danish researchers placed two groups of 16 volunteers in a mockup of an airline cabin and then exposed them to varying levels of ozone and air flow, including levels typically experienced in real flights. Consistently, ozone in the cabin increased production of identifiable chemical byproducts including nonanal and decanal, a pair of aldehyde compounds associated with headaches, nasal irritation and with other symptoms of "sick building" syndrome.
More than half of the byproducts were the result of reactions with skin, hair and clothing, according to Charles Weschler, Ph.D., the study's lead author, who is with University of Medicine and Dentistry of New Jersey. These oxidative byproducts are produced when ozone reacts with squalene, oleic acid and other compounds in natural skin oils, he said. (ScienceDaily)
Outside an airplane at cruising altitude, ozone can be as high as 500 ppb, but most widebody planes have ozone destroying catalytic systems in their HVAC systems, keeping levels below the 250 ppb stipulated by FAA regulations for planes flying above 32,000 feet. But many smaller regional jets don't have these catalytic ozone systems. This study shows that both the smaller jets and the larger ones will generate new and novel chemicals, some of which may be irritating or have other biological effects. The same is true at ground level, where many of the most unpleasant effects of smog are due to the 10% of the air pollution that is not ozone.
I worked my way through school in a radiology department and when taking an x-ray we used to say, "Take a deep breath. Hold it. . . " Then after we took the shot, "You can breathe now."
Same advice for the airplane. When you get on: "Take a deep breath. Hold it . . ." When you get off: "You can breathe, now."
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Sorry to be the first commentor and to be OT, but one thing about flying has been bugging me for years. I understand that at high altitudes the air is much cooler. However, I have been on a number of flights lately where the air in the plane was too warm. Is the friction of the plane moving through the air what causes it to be warm in the cabin and thus the need for air conditioning, despite the high altitude?
Texas: No, my impression this is a result of climate control in the plane. It is pretty well thermally insulated from the outslde.
It's a cramped space filled with a lot of warm people and machinery. You need air conditioning just to keep the temperature down no matter what the outside temperature. I find airplanes too warm as well. One guess as to the cause is that people tend to want to sleep on the plane - and the staff certainly prefers if you do - and a cool cabin will make it more difficult to do so for many.
A possible side cause could be that you don't want to use more energy as necessary; a large airconditioning system is a pretty energy-hungry device and that gets taken from your fuel allotment. Off the top of my head it doesn't sound plausible, though.
There is a guy that lives in a B707-320 in Greenwood Ms. and I can tell you its hot having been in the thing. He uses solar cells to heat it in the winter and once its toasty. My crews and I are in them day in and out and they are exceptionally well insulated and not a breath of air in them unless the APU or engine bleed air is on. This guys "house" is better insulated than a house in fact.
They could be right Revere. I know a number of flight attendants who use a certain type of makeup to prevent acne. Quite a few are reporting that they have developled eczema from/while flying. It is a sulfur based makeup and it wouldnt surprise me at all to find that its reacting with all sorts of stuff. Keep us posted. I will forward on the posting.... very interesting.
Since you fly often revere do you ever use nose spray or any other preventative measures to ensure your overall health and well-being?
I fly occasionally, and fairly long stretches at a time (Japan-Europe). A few good tips:
* Don't drink alcohol on board, and if you must, just have that one glass of wine or beer with your food and nothing more. It dries you out and the secondary effects makes all jetlag symptoms worse.
* Drink water. Constantly, and more than you think you need. I find that half of my jeptlag is actually due to being dehydrated for hours at an end on the plane. The stewards are usually happy to supply you with all the water you want. The Lufthansa flight between Osaka and Frankfurt has a water and juice bar next to the downstairs bathrooms in economy class; I wish more airlines could have that.
* Earplugs. Most of the other half of jetlag for me turns out to be mental fatigue from many hours of loud whining and roaring from the engines, air circulation system and whatnot. Use earplugs and you'll feel a lot less mushy in the head when you arrive.
* Move around. Walk about a bit, or at least stretch your legs. Perhaps go over to the emergency exit area to look out the window for a while. When you want more water, walk over to the pentry area instead of pinging the overhead lamp thingy. Your body isn't going to feel particularly fresh if you've been sitting stock still throughout the flight.
At 10 KM the atmospheric pressure is less than 30 KPa or less than 30% of the 100 KPa pressure at sea level. When air is compressed it is heated, probably polytropically, with n~1.3 in the equation P ^ ((n-1)/n) / T = const. which solves for those assumptions to give a temperature ratio of around 1.4.
If the outside air was at 220K, (about -65 F) and was compressed to 100 KPa, then the air would be heated by about 90C (to about 100F).
So after compression the outside air probably has to be cooled, which should be possible with some sort of heat exchanger with the outside air. Heating from skin friction would be trivial below Mach 1, (from memory thats about 700MPH at NTP)
Lea: No, I don't do anything special, although all of Janne's advice is good (and commonly given).
bar: Adiabatic heating from compression on descent makes sense but it goes the other way around on ascent to altitude, so I don't see that as the reason, unless you are saying that pressurizing the cabin without any thermal exchange with the environment is causing it. Could be, but I think the other explanations are probably more likely. don't really know, however.
Kerosene (or jet fuel - I might not be using the correct or usual US terms) is not taxed, contrary to (in many countries) petrol (for cars), heating fuel, diesel, natural gas, etc., which is one of the reasons that cheap flights can compete successfully with rail in Europe.
(Rail = about 1/10 noxious emissions *at least* per passenger as compared to plane, off my scruffy cuff.)
The CO2 and *other* emissions of planes are spectacular, google will provide, I don t have a "best" article at hand; and the issue is fraught with the usual controversies and even outright lies, as a non-expert not on top of this question I can t summarize. In any case afaik no grand summary or good meta-study exists, but who am I.
So flying may be bad for ppl but it sure as hell contributes to global warming in a consequent way; this in turn will kill many others...
The link to science daily at the end of your blockquote is munged. Try:
http://www.sciencedaily.com/releases/2007/09/070905140105.htm
MoM
MoM: Thanks. Had a semicolon instead of an endquote in the anchor tag.
Good advice Janne, thanks.
The only thing I can't do is wear ear plugs because of inner ear issues. Would buy the Bose headset noise reducer's if we could afford them but not sure that would work either.
"When you are up 35,000 or 40,000 feet, you are in the stratosphere, a layer of the atmosphere where there is little vertical movement of air (it is essentially a temperature inversion)..."
Revere--
Minor bone #1 to pick: You seem to be suggesting that relatively calm vertical winds and the associated temperature inversions are common. My decidedly amateur knowledge of meterology (and abbreviated flight training) tell me otherwise. They happen, but they're not the norm.
#2: An altitude of 35-40K feet is borderline stratosphere, going back, again, to pilot reference materials. 20-30K over the poles and 50-60K over the equator is what my references describe as the upper limit of the troposphere. Don't ask me why, but you never hear anyone casually mentioning the troposphere when they're waxing poetic about the wild blue yonder.
Janne is absolutely right about staying hydrated and wearing earplugs. For me, the latter seem to have no effect on staying comfortable at pressurized altitude, but they boost my mood considerably by drowning out the conversations around me.
Lea, The Bose headsets work. My husband is an airline pilot and he uses his Bose noise reduction head set when he has to fly for company business (dead head to a flight in another city to fly that plane where ever it is going to go.) If you have to fly a lot, they are a worthwhile investment and can double as head phone for your music devices (CD players and iPods). You can find other types that are less expensive, my husband's were a 20th anniversary present or else he would have the cheap ones!
Janne's advice is right on target. I would also advise drinking water, a lot of it, before you get on the plane too. And no coffee or caffeine drinks. Eat something as well for it can make it easier to fall asleep.
As for the temperature, as a pilot my husband gets complaints about the temperatures but MOST of the time is because it is too cold. The flight attendants want it cooler as it is more comfortable for them to hand out drinks and food (remember they are moving a lot and at a slightly higher altitude than you, breathing in your hot breathe.)
That said, in my humble household, warm air makes it much more difficult to sleep. We prefer colder temps at night but lots of weight in the blankets. Body warm, breath coming in cool.
B: Troposphere and stratosphere are layers of the atmosphere defined by temperature profiles, and you are right, they vary with latitude. You are also right that 35,000 to 40,000 feet is borderline, more like what's called the tropopause, but for purposes of the post it doesn't matter that much. With true inversions (rather than, say, just stable air) any vertical motions are immediately damped out. With a strong force you can make the air move vertically, but it tends to come back to its starting point fairly quickly. The reason for this has to do with the fact that when a packet of air rises it expands and cools (adiabatically) and if the temperature is getting warmer with altitude (as in a true inversion) that makes it sink. The same thing happens (in reverse) for a sinking packet of air which heats on compression and, finding itself in cooler climes (remember this is an inversion) will rise again: stability. You can have stable air even without an inversion. All you need is for the environmental lapse rate (the decrease in temperature with height) to be less than the (thermodynamically given) adiabatic lapse rate of about 1 degree C. per 100 meters.
Bar is right, the air coming into the cabin has been compressed -- that's outside air you're breathing, and it has been compressed (and so become hot) both for you to breathe and for the engines to breathe.
The inside air is a bit less dense than air at sea level (that's "cabin pressure of X thousand feet") --trivial.
Hank: So the air in the cabin is warm because of adiabatic compression of outside air? Didn't know that. Thanks.
Giddy, forgot about caffeine - probably because I'm addicted to it and wouldn't consider skipping my coffee no matter how lousy it makes me feel :)
Lea, noise-canceling headphones are expensive, yes - too expensive for me too. So why not get a normal, cheap pair of collapsible noise earcovers, like the ones used by construction workers and anybody else working in noisy conditions? Not the most fashion forward items, true, but you're sitting among a bunch of strangers so why worry about it?
An adiabatic process is an ideal gas, isentropic process, and obeys the law PV^(gamma) = const, where gamma = Cp/Cv.
Real life processes are polytropic, which is somewhere between isothermal and isentropic, and obey the law PV^n = const where n has a value between 1 and gamma.
Bar's answer is too precise for me to understand (grin)
"Pressurized air for the cabin comes from the compressor stages in the aircraft's jet engines. Moving through the compressor, the outside air gets very hot ..."
www.boeing.com/commercial/cabinair/index.html
Hank: Thanks for the link. Interesting, although not too forthcoming about problems we know exist. Still, very informative. To summarize, compression of outside air is what produces heated air in the cabin.
"Pressurized air for the cabin comes from the compressor stages in the aircraft's jet engines. Moving through the compressor, the outside air gets very hot ..."
Yes, and this is an efficient, elegant engineering arrangement, except for one small thing. It is often possible for tiny amounts of vaporized lubricant from the engine to permeate the bleed air which is headed for the cabin.
At best, the passengers might be subjected to an annoying but not clinically harmful oil odor. At worst, they could get substantial inhaled doses of things like tricresyl phosphate, an anti-wear additive from the engine lubricant, which does not play well with others. Being shut up in a sealed metal tube for hours with an airborne neurotoxin can ruin your day. Or the rest of your life. Take your pick.
The flight deck crew are not insulated from this. They get higher flow rates and fresher air than do the cabin crew and the passengers, but the ultimate source is the same: the engine bleed air packs. There are several disability lawsuits now pending in which former pilots contend that occupational exposure to organophosphate vapors have caused physiological damage sufficient to end their professional flying careers.
--
Revere-
Thanks for the explanation. I'll be keeping that one on file.
The Ozone is a concern. I guess the main question is why FAA is not enforcing it's own regulations.
Like many others, temperature has become my biggest nemesis, especially on long haul flights. I fly a lot between Asia and the US, which are typically 10-12 hr flights (one lasted 35 hrs but thats another story). What I have noticed is that the air temperatures are usually fine (about 72-73 deg F) the first 2-3 hrs as they prepare and serve the meals. After this there is a gradual increase as they want to induce passengers to sleep, as well as save on fuel. I bring a digital thermometer on every flight. Within a fairly short period of time the temperature is up to 78. On a good flight this is where it stays. But the last couple of years it has went as high as 84. The last year or so I have anticpated this and as soon as it gets to 80 I complain and show them the evidence, and then it goes down to maybe 78 deg F, but usually only for a short time, and then it creeps back up again until about 90 minutes before arrival when the temperature is lowered to get people to wake up and serve breakfast.
The pilot controls the minimum temperature, but I believe the flight crew can increase this, so depending on the crew I find the problem is better or worse. The older and skinnier the flight crew chief is the worse it is.
I used to fly twice a week, back and forth for 90 minutes each way for several years. I always felt lousy for the rest of the day even if the cabin temperature is fine and everything else went smoothly (International travel in Asia is an order of magnitude superior to the US domestic "cattle" air travel experience). The main culprit IMO is the cabin pressure. I believe it is maintained at the equivelant of 8000 ft and some people are more sensitive to this than others.
Since 8000 ft is when altitude sickness starts, and 25% less Oxygen than at sea level, then why is the 8000 ft the standard. Maybe 6000 ft might be better. I have been on several flights where someone has died near the end of the flight, maybe it was a clot from inactivity, but it may be there is a relationship between clot formation and low oxygen levels. The one study I am aware of that says there is no relationship curiously limited the study to 8 hrs.
http://www.sciencedaily.com/releases/2006/05/060517084330.htm
Also, since many people on long haul flight are also flying again on another flight several hrs later, you would think any study would follow a sequence of 12 hrs low pressure, 3 hr sea level, 5 hrs low pressure. Better simulates the stress of flying. Also, limiting the study to only healthy volunteers does not help validate the conclusions.
The PlaneQuiet noise cancelling headphones are very good and much cheaper than the Bose. They do make an amazing difference to your well-being. Be good to yourself and buy a pair.
I agree that we should keep an eye on the levels of ozone that can be present during a flight. Even if the levels of ozone in a plain are not as bad as we think we are there still should be some precautions taken just for the simple fact that ozone is a toxic gas. I found an article about a type of catalitic convertor that can remove some of the ozone that can be present in a plain. More research should be done to ensure that the safety of employees and customers is protected.
http://www.google.com/patents?hl=en&lr=&vid=USPAT4348360&id=rfI2AAAAEBA…