How Safe is the Air You Breathe in Planes?

October 15th, 2014 by Roy W. Spencer, Ph. D.

sneeze_682_473022a-755805With increasing concerns that Ebola apparently spreads more readily than we were told, I thought it might be useful to mention a little experiment I performed a few months ago. I was on the way to Las Vegas to give climate talks, and I wanted to show how much greater the CO2 content of air is in the confined spaces we share than out in the ambient atmosphere.

Let me say up front I am not a germaphobe. I have flown hundreds of times over the years. I wash my hands a few times a day, but consider some limited exposure to germs to be healthy and necessary to keep our immune systems strong.

But I would wager no one — medical experts, doctors, nurses, or the CDC Director – is willing to expose themselves to tiny amounts of sputum from Ebola patients to prove that point.

I’ve always wanted to know just how much of the air in planes is recycled, versus fresh. It’s hard to find an answer to this question. This Wall Street Journal article from a few years ago summarizes several studies that did indeed document increased incidence of illness contracted by recent airline passengers.

I have a good handheld air quality meter that measures the carbon dioxide content of the atmosphere. Humans exhale large concentrations of CO2, so I used the meter on one recent trip to see just how high the CO2 concentration gets on airplanes. The higher the CO2 content, the more you are breathing air that other passengers have exhaled.

Yes, I know the official word is that, unless you are swapping spit with someone who has contracted Ebola, you don’t have anything to worry about. But in the very confined space of an aircraft, there is some inadvertent spit-swapping going on, anyway.

And think of all of the surfaces inside the plane that MANY people are touching with unclean hands: Seat headrests along the aisles, overhead luggage compartment latches, air flow nozzles, trays, passing cups and trash, etc.

Oh, and those miniscule rest rooms.

Anyway, to the answer. On two flights — one a large plane, the other small — I measured CO2 concentrations of 1,600 ppm or more (coming out of the nozzles), which is 4 times ambient (400 ppm). In my office building I might measure 700 ppm, late in the afternoon. In small offices with several people confined I’ve measured 1,000 ppm, the point at which some people consider the start of “reduced” air quality.

So, it is true, a greater proportion of air you breathe on an airplane has been exhaled by others than in most other environments you are likely to be exposed to. It’s still hard to say from my measurement of 1,600+ ppm just how much fresh air is mixed in with the air that is recycled by the aircraft ventilation system, but I think the bigger concern is this: that you are in such close proximity to other people in a confined space, you are breathing other peoples air — including tiny aerosols — even before all of the exhaled air gets sucked back into the ventilation system and filtered.

Now, this doesn’t mean I’m going to forgo flying…unless many more Ebola cases start showing up which might have occurred through casual contact. I suspect we should know much more in the coming weeks and months.

20 Responses to “How Safe is the Air You Breathe in Planes?”

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  1. DHR says:

    Submarines run around 4,000 ppm.

  2. RW says:

    Very interesting. I’ve never thought about it, but don’t fly much either.

  3. Alan says:

    Don’t you normally fly around on a private jet purchased with money from some of the huge grants you have received from the Koch brothers? 😉

  4. CC Reader says:

    I have spent four years under water on the first boomer class. Are you saying that the scrubbers and burners allowed this much CO2 on a normal basis?

    • DHR says:

      Yes. Abt 4,000 ppm is the typical value. The scrubbers cannot get CO2 much lower because of their physical limitations. Levels can be higher during events such as sea trials when many more people are aboard and, of course, if a scrubber fails.

  5. CC Reader says:

    Yes, we also generated O2.

  6. Gordon Robertson says:

    My doctor was discussing that with me today, about pathogens being passed through the air. He wants to inject me with Pneumovax 23 which is described here:

    Also, here…

    People working in close proximity to other workers, as in camps, are prone to such illnesses. I would imagine the same applies in planes.

    I caught a lung infection while working on a Tar Sands site. Not a nice infection as infections go. Took me months to stop coughing.

    This vaccine is for only one form of pneumonia that is prevalent at the moment.

    • dave says:


      Despite its name, the vaccine is not really aimed at lung disease.

      Infection of the brain by these agents is a major cause of death in infants and older people. In Great Britain about 9,000 a year die from “pus on the brain” – which is not a pretty sight at autopsy. The vaccine is quite effective; it is one injection, never repeated; and it is routinely offered to people aged 65. A problem is that sometimes there is serious pain in the muscles near the injection site, as a side-effect. This seems to be caused by minute traces of aluminium in the injected material.

      I made the mistake of having a flu injection in one arm and the polyvalent in the other AT THE SAME TIME. I never had a reaction to a flu shot before, but that time I had problems in BOTH shoulders which lasted about a year.

      These bugs are everywhere, and so you do not really “catch them” – in aeroplanes or elsewhere; but rather succumb to them, eventually, for some reason.

      • Gordon Robertson says:

        @dave…”Infection of the brain by these agents is a major cause of death in infants and older people”.

        Could you expand on that or supply a link? I am concerned about vaccines, flu shots, etc. I had a buddy nearly die from a small pox vaccine.

  7. Back in the days when smoking was permitted on flights; very little of the air was recycled. That meant more fresh air; bled from the early compressor stages of one or more of the jet engines; then somewhat filtered before fed into the aircraft’s interior.

    The brown stains on the outside of the aircraft were from the smokers’ cigarettes. The location of the stains allowed service crews to locate some types of defects more quickly.

    In some ways; smoking made flying safer.

    BTW: ASHRAE comfort(?) limit for airconditioned space used to be 1000 ppm CO2. Lecture theatres and the like peak above that.

  8. dave says:

    Fresh air fiend or fug lover. You can’t win. James Herriot*,
    the vet who wrote those popular , whimsical, books about rural Yorkshire, volunteered in WW2 for aircrew training.
    The recruits were put up in, in winter, in Scarborough which
    is on the North Sea, in a hotel.

    The commandant made sure all the windows were nailed OPEN. The result was pneumonia for just about everyone, however fit they were when they arrived.

    * a nom-de-plume

  9. Aaron S says:

    “It got hot during my flight once, and now you say CO2 increases dramatically. That correlation clearly shows the warming was caused by the CO2.” IPCC

    • There are two different scientific evaluations i.e. some scientists say that warming from “CO2 Back radiation” is going to be catastrophic and some say any warming from the “doubling” of “CO2 Back radiation” will only amount to about 1degree C.
      Which one of those two opinions is correct? Well, so far data show that for the past decade and a half no “global warming” has taken place – at all, even thou atmospheric CO2 concentration has gone up by around 40%. – Therefore chances may be that they are both wrong.

      But that is a different discussion. As far as I can understand it, in this article, CO2 is used as a measure of how much of the passenger’s exhaled air (gases) is being recycled and how much is being filtered & oxygenized. Therefore, is the “also exhaled” water vapour dense enough to carry the Ebola (and other) viruses.

      – The percentage of Methane in the “Cabin air” would probably also have increased. Especially if a lot of the passengers are afraid of flying. (And fear of flying may increase if it comes to pass that passengers are exchanging spittle. – 1st class getting spittle from the “tourists” – Yuk, Yuk.)

      But that too, is for a different study.

    • In a confined space of an aircraft the body heat of the passengers would be far more significant. There is also the air conditioning to regulate temperature.

  10. jimc says:

    Don’t let that get around; it’ll be in the headlines tomorrow.
    An FAA study showed 1500ppm is average and reached 4900ppm during an extended gate time. No mention of passenger or crew fatalities.

  11. BBould says:

    I’d study the flight crew rather than the passengers, they take many flights a day.

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  13. Chris Walcek says:

    You should be able to calculate the “turnover rate” of air in the confined space, given the respiration rate of all the people in the plane. I thought the concentration of CO2 in exhaled air was about 40000 ppm (4%), and you can estimate breathing rates (liters/min) and the volume of air in the plane. Alternately, you can directly estimate the “food combustion rate” of people, each with a sitting “calorie burn rate” (really a kCal burn rate) of about 2000 calories/day, convert that to a CO2 emission rate assuming sugar being burned. Heat content of sugar is 4 kCal/gram. Sugar is so much percent carbon. So all you need is the number of people sharing the air volume, right?

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