Sensor problems with ship based CO2 flux measurements – readings too high, affected by humidity

From a National Oceanography Centre, Southampton (NOCS) press release

Measuring carbon dioxide over the ocean

Reliable measurements of the air-sea flux of carbon dioxide – an important greenhouse gas – are needed for a better understanding of the impact of ocean-atmosphere interactions on climate. A new method developed by researchers at the National Oceanography Centre, Southampton (NOCS) working in collaboration with colleagues at the Bjerknes Center for Climate Research (Bergen, Norway) promises to make this task considerably easier.

The Norwegian weather ship Polarfront

Infrared gas sensors measure carbon dioxide based on its characteristic absorption spectra and are used to evaluate the air-sea flux of the gas¬¬. So-called closed-path sensors precondition air before measurements are made, while open-path sensors can be used to measure the air in situ.

One advantage of using open-path sensors at sea is that wind measurements can be taken contemporaneously in the same place. Moreover, because they are small and don’t use much power they can be used on buoys.

“Open-path sensors have the potential greatly to increase our understanding of the variability of air-sea carbon dioxide fluxes,” said John Prytherch of NOCS.

However, a long-standing concern has been that the values from open-path sensors do not tally with those from closed-path sensors, or with measurements made using other techniques.

“Other scientists have been sceptical about the reliability of carbon dioxide flux measurements taken at sea using open-path sensors,” says Prytherch: “However, we now believe that we understand the reason for the discrepancy and that we can correct for it.”

The problem turns out to be that the sensors are sensitive to humidity, meaning that fluctuations in the amount of water vapour in the sample air skew the carbon dioxide measurements. This is probably caused by salt particles on the sensor lens that absorb water.

Having identified the problem, Prytherch and his colleagues developed and rigorously tested a novel method for correcting the data for the cross-sensitivity to humidity.

Data were collected aboard the Norwegian weather ship Polarfront, equipped with a battery of instruments to measure wind speed, humidity and carbon dioxide. Even the motion of the ship was monitored.

The researchers noted that carbon dioxide fluxes calculated from open-path sensor data were clearly too high and affected by humidity. They were also very variable, suggesting that the effect is caused by salt on the optics, which accumulate before being washed off by rain. Indeed, the researchers were able to mimic this effect in the laboratory.

However, after correction using their newly developed method, the calculated carbon dioxide fluxes were in line with previous studies that used different sensors or techniques.

“This robust method opens the way for widespread use of open-path sensors for air-sea carbon dioxide flux estimation,” said Dr Margaret Yelland of NOCS: “This will greatly increase the information available on the transfer of carbon dioxide between the air and sea – information crucial for understanding how the interaction between the oceans and the atmosphere impacts climate.”

The work was supported by the United Kingdom’s Natural Environment Research Council and is part of the UK SOLAS project HiWASE (High Wind Air-Sea Exchanges).

The researchers are John Prytherch, Margaret Yelland, Robin Pascal and Bengamin Moat (NOCS), and Ingunn Skjelvan and Craig Neill (Bjerknes Center for Climate Research, Bergen, Norway).

Prytherch, J., et al. Direct Measurements of the CO2 flux over the ocean: development of a novel method. Geophys. Res. Lett. (published on-line, 2010) doi:10.1029/2009GL041482.

www.agu.org/journals/pip/gl/2009GL041482-pip.pdf

www.noc.soton.ac.uk/ooc/CRUISES/HiWASE/

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64 thoughts on “Sensor problems with ship based CO2 flux measurements – readings too high, affected by humidity

  1. “suggesting that the effect is caused by salt on the optics, which accumulate before being washed off by rain.”
    Could they not install a fresh water washing device? You know, as fitted to cars.
    LOL.

  2. However, after correction using their newly developed method, the calculated carbon dioxide fluxes were in line with previous studies that used different sensors or techniques.
    There are a great deal of corrections involved in climate science. Has anyone considered the possibility that observation has refuted the proposition of AGW, but the data was erroneously corrected?

  3. Ah, good. I feel better. All that’s needed is for the data to be adjusted a little. What could possibly go wrong with that?

  4. At last, something I know about!
    Measurement of CO2 in gases by infra-red absorption is a very old technique. As a retired anaesthetist (anesthesiologist for N American readers) we used these all the time. The technique has always been very sensitive to temperature, water vapour, vapour condensation so no surprises here. Several other gases interfere with the measurement as they have some absorption at the relevant wavelengths, including oxygen. I wonder how they check the calibration; premixed standardised gases, mass spectrometer? At the concentrations they are measuring small errors in calibration could result in big errors in measurement.

  5. I don’t have access to the paper. Can anyone summerize the method used to correct the data. Is it a numerical adjustment? Is it calebrated against some standard reference? Is it a mechanical “cleaning” of the lens?
    Tim

  6. Instrumental based correction where they sense the amount of humidity would be a fine. If they calibrate correctly during the manufacturing process, it should be correct. Perhaps there would need to recalibration of these instruments at time, but then it should be reliable. If they do the adjustments back at the data center, then it would be more prone to manipulation.

  7. Funny how, every time there is some sort of a mistake or an error in calculation, etc, it always produces more warming, and in this case more CO2.
    It must be a coincidence.

  8. This sounds great if there are people where the sensor is to determine when an adjustment is needed based on weather conditions.
    But at an automated station how do they know how much salt is on the lens? How do they know when rain has rinsed the lens? Just because it rains other factors such as wind direction may prevent the lens from being cleaned or a short rain may only partially clean the lens.
    I am sure there are many other issues that an automated station can’t audequately take account of, which means I don’t believe that an automated stations output can’t be accurately adjusted. Only a manned station, which would allow for fudging of data.

  9. ” The researchers noted that carbon dioxide fluxes calculated from open-path sensor data were clearly too high and affected by humidity. They were also very variable, ”
    Humidity.
    Mauna loa, who’d of believed that. !
    also,
    After the fact corrections to get the “right” answer.
    Mauna Loa, who’d of believed that. !

  10. Can’t they ever use traceable methods to measure things? This is insane to have used methods that were not fully tested in laboratories with simulated environments and so on. The instruments and methods should have been certified before being put in place. They patch up the data from a questionable instrumentation and method and expect people to take their words that all is good… with such convincing phrases as “However, after correction using their newly developed method, the calculated carbon dioxide fluxes WERE IN LINE with previous studies that used different sensors or techniques.”
    WERE IN LINE!!!!???? That translates to what in term of error and deviation? Apparently they were not convinced to use the term “exactly comparable” or “right on the button”… no they used “were in line”… yeah, sure… I will take your words for it and give you my tax money for you guys to travel around and publish papers…
    From the start the data are questionable and no amount of “correction” will give them credibility. Bandaid data won’t give healthy results.

  11. Quoting from above
    So-called closed-path sensors precondition air before measurements are made, while open-path sensors can be used to measure the air in situ.
    I think the closed path capture the air and then freeze the humidity out.
    In the Greek constitution there is an ending paragraph:
    “Faithful adherence to these statements rests on the conscience of the Greeks”.
    The scientific system is an honor system. Of course there will be calibrations and corrections to any real measurements.
    Unfortunately the honor system has been badly broken in any climate “science” that has to do with AGW, and CO2 is a red flag :(. Is there a link to the article to see what the “other methods” are and how the corrections are made?

  12. There is another problem here they don’t mention.
    Humidity sensors are notoriously difficult to calibrate and keep in calibration. Typically errors are several percent.
    Unless they have some super-special set-up rather than your run-of-the-mill temperature and humidity sensors, the correction based on humidity is itself suspect.

  13. Anna, the physiological “closed-path” sensors keep the chamber heated so that all water is present as vapour and can’t condense on the lens. The only problem is that you have to control the chamber temperature to very tight limits, not easy if the incoming gas is very cold and very humid as it will be over the sea

  14. Like I’m going to trust any data that has been – ahem – “corrected.”
    And like I’m going to trust anyone who tells me I should, because the method is “robust.” Those words have me reaching for my tinnitus medicine, such is the noise from those internal alarm bells.

  15. The wording seems somewhat curious. Part of it reads as if they just recently thought of water vapor, yelled “eureka”, and a long-standing puzzle was solved.
    Obviously it didn’t happen that way. Apparently they have constructed an adjustment protocol. The words “robust” and “novel” make me uneasy.
    IMO this approach to solving a measurement error seems backward. Perhaps I don’t understand the matter.
    I would have first approached companies – chemical equipment makers, medical equipment firms, etc. – that make sensors and asked them how to improve the devices.
    Until we learn more ….. At the moment the PDF seems to be behind some wall I won’t bother to scale.

  16. Surely they don’t propose (in the case of buoys) regular washing with fresh water. Further, is there not a question of how consistently such washing can be done?
    I would suggest something other than washing, like a filtration process that eliminates salt.
    Presuming that salt is not present as free ions in the air, place the sensors along a passage designed to settle out all but the finest particles, simply by gravity. Around the sensor place several meshes to filter out first, macro particulate matter, then liquid-spray born particulate matter, then micorfilters to filter out all but purely molecular gaseous particles. The passage could be open on two ends and wind would suffice to refresh the air around the sensor.
    The design I have in mind, unfortunately, doesn’t fit into a text box very well, but it would also avoid the problem of physical wash-over, even short-interval submersion of such a buoy.
    However, as others have pointed out here, there remains a question of humidity. It appears these guys are dealing with the effects of spray-borne salt, which is not the same thing as humidity, which would not be eliminated out by the procedure I have in mind. If there is a humidity-dependence that is not well-understood, perhaps it could be determined empirically to calibrate the readings.
    I would think one should also determine temperature-dependence as well (I can’t think of other factors, but perhaps mechanical, electrical and magnetic influences could be problematic, say during inclement weather). If this thing is coupled with a good array of instruments to measure these things, proper calibration should give reliable readings, and I think it is possible to design a robust buoy system based on it.

  17. First, I thought, oh no, not another robust method. Then after rereading this: ” However, after correction using their newly developed method, the calculated carbon dioxide fluxes were in line with previous studies that used different sensors or techniques.
    This robust method opens the way for widespread use of open-path sensors for air-sea carbon dioxide flux estimation,” said Dr Margaret Yelland of NOCS: “This will greatly increase the information available on the transfer of carbon dioxide between the air and sea – information crucial for understanding how the interaction between the oceans and the atmosphere impacts climate.” my reaction changed to: Whut?(copied from a former president). Are their procedures valid?

  18. How much do these open path sensors cost, and, can a public network be set up on the same buoys to allow analysis of raw data controlled by a second source of info?

  19. This is probably caused by salt particles on the sensor lens that absorb water.

    Doesn’t inspire confidence.
    DaveE.

  20. Why bother? I thought the tipping point has already passed or soon to be passed (depending on which loony you listen to) and we are all doomed. Or are the “climate scientists” having second thoughts?

  21. Well here we go again. I see that term; “CO2 fluxes”, and off go a dozen sirens playing all kinds of tunes. Well I see in the first line of the small print, that it says; “air-sea flux” …”of carbon dioxide – an important (read inconsequential) Greenhouse gas”. Now lookie here “the readings are too high and are affected by humidity”. NO ! the Readings are wrong, and are not measurments of CO2 air-sea flux. They might be even better measures of “humidity” which evidences the presence of a real Greenhouse gas H2O !
    So what means “air-sea flux” ? Well put that way, and sans translation for those not indoctrinated into the “climatology theology”, ordinary street lingo; jargon, interprets that to mean the rate of flow of CO2 from air into sea; air > sea; how simple is that ! Of course that is the party line version. To others, the logical assumption might be that the flux is from sea-air as in sea > Air. Well a simple negative sign convention could settle that.
    Well a totally dumb 8th grade science idea might be to set up a stable (small diameter) column of air, in contact with the water of not too great a height (I’d vote for 1 metre the SI unit of length; well maybe 2 metres, and then I would have sampling tubes at say 1 metre height (hence the need for two total), and as close to zero height as water surface disturbances would allow. Hey make the tube smaller in diameter to reduce those surface disturbances. Then I would siphon off those zero and one metre air samples, and feed them to a mass spec; to actually count the molecules of any species I might find there that I could ionize. From the difference in the one metere and near zero metre samples, one over time could infer the loss of CO2 at one end or tother and decide the amount and polarity of the CO2 flux.
    For good measure, a similar contraption could be maintained below the water line, and samples of the water at two heights be made and MS’d to determine the changes, and prove continuity of the flux across the air-sea interfaced.
    Well that’s a hand waving description; you can fill in the finesse points; I did say it was a dumb 8th grade approach.
    Process control engineers know too well to measure THAT WHICH THEY WANT TO CONTROL and then control that (via feedback); rather than deriving a supposed relation between THAT WHICH THEY WANT TO CONTROL and their sister’s dandruff itchiness, and then measuring their sister’s dandruff itchiness, to control THAT WHICH THEY WANT TO CONTROL. NOW that is a truly dumb idea.
    Hey I said a MASS spectrometer; not a MASSIVE spectrometer. In this day and age, I would think you could build a mass spec about the size of a sugar cube. Well if I can build a complete 3,000 frames per second digital videocamera, along with the illumination sytem to see in total darkness, and the computer and digital image processor, needed to process all those images in real time, and compute some desired output function; and don’t forget all the highly aspheric tilted and decentered custom Optics for that videocamera; and get the whole shebang into the size of one ordinary sugar cube; somebody ought ot be amble to build a mass spec that size. Oh and it helps if you can make them for under a buck ($1) like I can.
    Well I do cheat a little, I do feed the necessary power to run the thing in from the outside on a couple of fine wires; not counting the wire that spits out the results. So yes I do have to use up a couple of AA cells to run the thing for six months; but I can’t work real miracles.
    Well I do hope this new ship based (sounds humungous) CO2 air-sea fluxometer works and keeps a whole lot of otherwise unemployed “scientists” gainfully occupied. Don’t forget to make the (raw) data available to us tax paying chumps who anted up for your grants.

  22. Why not just put the laser in a small plane or unmanned drone and fly over the water every week or so? That might actually be less costly than doing what they are trying to do. The windows will stay clean at least.

  23. How long has the erroneous data been collected with the type of instrument in question? What is the date it was first commissioned?

  24. OT,slightly. Phys-Org.com has noted Schwartz/Charlson paper on the mysterious failure of the earth to warm as predicted.
    http://www.physorg.com/news183142998.html
    Probably not worth going there, it ends like all the rest of them; we still need to do something even if we don’t know what’s wrong.
    REPLY: Thanks for the tip – Anthony

  25. Ray, that’s like suggesting that drones could do a better job than the Caitlin Arctic Ice survey did of measuring Arctic ice thickness! I mean, LOL! LITERALLY!!!
    Or not.

  26. Murray Duffin (13:25:25) :
    “There’s that word “robust” again. Why does that give me doubt?”
    Everytime I hear robust I think “thou protesteth too much.”

  27. Murray Duffin (13:25:25) :
    “There’s that word “robust” again. Why does that give me doubt?”
    Everytime I read “robust” I think “thou protesteth too much.”

  28. Jimbo (15:39:47) :
    Murray Duffin (13:25:25) :
    “There’s that word “robust” again. Why does that give me doubt?”
    “Everytime I read “robust” I think “thou protesteth too much.” ”
    Every time I read “robust” I think that what they are really trying to say is “rob us”.

  29. Derek (13:16:28) :
    ” The researchers noted that carbon dioxide fluxes calculated from open-path sensor data were clearly too high and affected by humidity. They were also very variable, ”
    Humidity.
    Mauna loa, who’d of believed that. !
    also,
    After the fact corrections to get the “right” answer.
    Mauna Loa, who’d of believed that.

    Derek, the Mauna Loa data don’t need to be corrected, as (near) all water is freezed out at -70 C before CO2 measurements are done… That is a little more difficult on a buoy with limited power supply.

  30. K (13:52:46) :
    The wording seems somewhat curious. Part of it reads as if they just recently thought of water vapor, yelled “eureka”, and a long-standing puzzle was solved.

    Sometimes the difference in thinking between scientists and engineers (and other people with common knowledge) is glaring.
    My favorite example comes from a nature show just a few years back. They were wondering if dinosaurs in the past could have crossed the land bridge at the Bering Straits and migrated to the Americas. After all, dinosaurs were cold blooded and needed external heat (like from the Sun) to keep moving. Thus at sunset they would chill off and fall over, and possibly die.
    Then after studying large sea tortoises, they realized dinosaurs were basically largely water, and water retains heat, so after nightfall the dinosaurs could keep moving. Given their size and all the retained heat, they could keep going all through the night.
    These scientists discovered, within about a decade ago, that water retains heat, creatures are largely water, therefore creatures retain heat. Isn’t science amazing?

  31. George E. Smith (14:38:10) :
    So what means “air-sea flux” ? Well put that way, and sans translation for those not indoctrinated into the “climatology theology”, ordinary street lingo; jargon, interprets that to mean the rate of flow of CO2 from air into sea; air > sea; how simple is that ! Of course that is the party line version. To others, the logical assumption might be that the flux is from sea-air as in sea > Air. Well a simple negative sign convention could settle that.
    I don’t think that the researchers are interested in one way CO2 transfer between air and oceans. Both are of interest, as the equatorial oceans acts as permanent sources and polar waters as permanent sinks, while the mid-latitude oceans work in both directions, depending of the seasons.
    See Feely e.a.: http://www.pmel.noaa.gov/pubs/outstand/feel2331/maps.shtm
    And as the detailed description gives, both seawater pCO2 and CO2 in the atmosphere are measured, thus the flux in both directions is measured, depending which is the highest:
    http://www.noc.soton.ac.uk/ooc/CRUISES/HiWASE/DOCS/Fluxes-English-web.pdf
    And I fear that your proposed system will not work when waves are 1 or more meters high… The “Pacific” is not always that peaceful…

  32. R. Craigen (14:06:06) :
    However, as others have pointed out here, there remains a question of humidity. It appears these guys are dealing with the effects of spray-borne salt, which is not the same thing as humidity, which would not be eliminated out by the procedure I have in mind. If there is a humidity-dependence that is not well-understood, perhaps it could be determined empirically to calibrate the readings
    As far as I have read, they measure both humidity and CO2, at different spectral lines. The pure water line then is used to substract the water part of the mixed CO2/water spectral line via a fixed algorithm. And some calculation is done to compensate for the influence of temperature. That is what is done in many hand-held CO2 measurement devices. In this case there seems to be an additional problem not directly caused by water vapor, but by water adhered to salt particles on the lens.

  33. Well not surprisingly, the article is about as uninformative as it could be. Not a mention of the operating wavelength range of the CO2 detector..
    No real point in using the 15 micron CO2 band, since water vapor overlaps pretty much all of that to some extent, and other issues.
    But CO2 also has a strong absorption line at around 3.5-4.0 microns, whcih is right in a water hole.
    So a source, possibly laser based at around 3.75 microns could be grabbed by CO2 with not much water effect at all; but it would be not such a big deal to remo=ve any water vapor, through prefreezing or dessication etc, to remove H2O from the sample.
    Given a sizeable government Grant, i am sure I could develop an even more definitive method to measure actual CO2 and not H2O.

  34. “”” Ferdinand Engelbeen (16:14:23) :
    George E. Smith (14:38:10) :
    So what means “air-sea flux” ? Well put that way, and sans translation for those not indoctrinated into the “climatology theology”, ordinary street lingo; jargon, interprets that to mean the rate of flow of CO2 from air into sea; air > sea; how simple is that ! Of course that is the party line version. To others, the logical assumption might be that the flux is from sea-air as in sea > Air. Well a simple negative sign convention could settle that.
    And I fear that your proposed system will not work when waves are 1 or more meters high… The “Pacific” is not always that peaceful… “””
    Well I did not write the story above, which only mentioned air-sea flux; but I don’t mind. I’ll double the computer power to handle all those measurements, and maybe make it the size of two sugar cubes instead (not counting the standpipe and floating buoy.)
    As to your last comment, I understand that the Pacific Ocean depth also varies from a few inches to over 36,000 feet. So ok my gizmo won’t likely work for water shallower than maybe two metres. Well I could scale it down to say 20 cm instead of +/- 2 metres. The 36,000 foot depth won’t bother it a bit; after all if that ship can ride up and down on that water depth and those waves you mentioned, so can my gizmo; and mine is just an 8th grade gizmo remember; not a NASA or NOAA unlimited budget gizmo

  35. The sensors that are affected by humidity are being deployed at sea? Is the humidity stable at sea?

  36. Humidity has always been a problem in CO² readings. See Pettenkofer’s apparatus, which has a sulfuric acid drying tube to remove water from the inlet gas sample.
    Now, if I read this correctly, they want to use cheap-ass CO² sensors on buoys all over the oceans. Said cheap-ass sensors are affected by humidity and/or (somehow) sea salt crystals on the lenses. They’ve come up with a novel method to get around this. But they don’t tell us in the abstract what the novel method is…do they? Just that it’s “robust!
    My hackles are up.
    The intent seems to be good, but I guess we’re all cynical after reading the UEA emails. I’d really like to see more about the design, the methodology, and some of the standardization results before commenting further. My suspicion is that the ‘novel’ correction method may not be valid after about 4 months.

  37. Pardon me, I’m only a humble engineer, but I would have thought one would have tested for humidity effects in an ocean deployed sensor. Is this stupidity or naivety?
    Before I woulsd have launched such a project dependant on these sensors, I would have characterized them versus humidity, atmospheric pressure, temperature. The buoys would be strapped up to measure these other parameters, and the “CO2 content” and then we would have vaguely reliable data.

  38. er………………..why is it nessesary to measure CO2 on the oceans surface??
    was this dreampt up by some with more money then brains? Oh yeh government grants. Just seems to me that the Mauna Loa data and satellite pictures already provide the data needed although George E. Smith’s toy sounds real cool and way to well thought out.

  39. “Robert of Ottawa (19:04:56) :
    Pardon me, I’m only a humble engineer, but I would have thought one would have tested for humidity effects in an ocean deployed sensor. Is this stupidity or naivety?”
    What good is data if it can’t be adjusted to match the climate models?

  40. George E. Smith (16:30:44) :
    Well not surprisingly, the article is about as uninformative as it could be. Not a mention of the operating wavelength range of the CO2 detector..
    No real point in using the 15 micron CO2 band, since water vapor overlaps pretty much all of that to some extent, and other issues.
    But CO2 also has a strong absorption line at around 3.5-4.0 microns, whcih is right in a water hole.

    Not much overlap in the 15μm band really, there are plenty of lines to work with. Check out the spectra below: H2O top, CO2 below.
    http://i302.photobucket.com/albums/nn107/Sprintstar400/H2OCO2.gif

  41. More CO2 than we thought? Disaster is nearer.
    Less CO2 than we thought? The model sensitivity to CO2 must be increased.
    And no mater what climate science is improved.

  42. Computers on floating buoys use floating point numbers.
    Ocean bottom sensors use sinking point numbers. And on ocean bottoms where the instruments are held in place fixed point numbers are appropriate.
    Conversion algorithms for inter conversion will be necessary. If the conversions are round up ready a few conversions back and forth will show a steadily increasing temperature in no more time than it takes to run the algorithm.
    And you know the result. The unprecedented warming is much worse than we thought.

  43. There is some confusion here:
    The measurements are about the sea-air CO2 flux, not about absolute CO2 levels. The CO2 levels in the atmosphere must be measured and the absolute humidity, as that gives the real pCO2 in the atmosphere. Also the pCO2 of the surface water must be measured, to see how high the driving force (pCO2 air vs. pCO2 water) is and in what direction the flow is. With wind speed and wave forms one can calculate the CO2 flux between air and oceans (whatever the direction), with still some large margin of errors.
    Thus “sea-air” flux is not meant to be one-way, but simply that all CO2 movements are measured between sea and air or reverse. This is of direct interest for the carbon cycle models, to know where the main natural sources and sinks of CO2 are situated. Not of direct interest for AGW. Only indirect, if the oceans should decline in sink capacity, of which there is no sign until now.
    The problem they have now is not directly with water vapor (which is measured), but with liquid water around salt crystals which interfere with the CO2/water vapor measurements. I have no idea what they use as compensation, but some extra measurement of an absorption line in the liquid water spectrum may be of help?

  44. It’s funny that these “adjustments” to the data could be avoided if they could just come down off their high horse and ask NASCAR for some of their nifty rotating/self-cleaning camera protectors.
    Git’er Done!

  45. From what I gather, none of the “heavily used” CO2 measurement techniques actually measure CO2. Rather, they measure a “proxy signal” that, in every case, must be “corrected”. Corrected to what? Why corrected to “what we know the answer must be”.
    Personally, I think the “official” CO2 measurements used to support AGW arguments are not to be trusted. They “may” be reasonable. However, how would we know — besides taking it on “faith”?

  46. Allen63 (06:41:51) :
    From what I gather, none of the “heavily used” CO2 measurement techniques actually measure CO2. Rather, they measure a “proxy signal” that, in every case, must be “corrected”. Corrected to what? Why corrected to “what we know the answer must be”.
    Allen, it is not because the measurement is indirect, that it must be wrong. We don’t measure temperature directly, we measure it with a proxy: either the expansion of a liquid or the millivoltage of a thermocouple or the current through a resistor,… In all cases we need calibration of the instrument to known values. In the case of CO2 the absorption of a beam of IR at a certain frequency is calibrated with different calibration gases of known composition.
    Once the calibration is done, one can calculate the composition of the atmosphere. No corrections are necessary. See e.g. the calibration procedures at Mauna Loa: http://www.esrl.noaa.gov/gmd/ccgg/about/co2_measurements.html
    On buoys, similar procedures are practically impossible, therefore one need a different technique to compensate for water vapor and temperature changes. The results are less accurate than these at MLO, but that is less important for their purpose, which needs the differential partial pressure (pCO2) between the air and the ocean’s surface. In polar waters, that is around +240 microatm difference, while near the equator it is around -360 microatm. Thus a lot of CO2 is coming out the oceans near the equator, and a lot (more) sinks with the THC in the deep oceans near the North Pole.

  47. Yesterday I was sitting on my local beach (not freezing here in Natal), contemplating the waves and wondering how much Co2 was hovering above the surface and what the sea was doing about sequestering it. I noticed that the sea doe not reach up its arms and grab the stuff, but that countless little organisms along the waterline were busy growing their shells, presumably sequestering CO2 to make calcium carbonate. I was quite unable to determine the level of CO2 available at that time, or to measure satisfactorily the metabolic rate of these diverse organisms. However, if some kind group would be willing to fund me (modest need for apparatus and rehydrating beverage) I would be happy enough to spend three or four afternoons a week down there, water vapour permitting, to take measurements, which, I am sure, would be very useful to NOCS. My hand may not be too steady, and my eyes are a little dim, but I am still a whiz bang expert at mathematical extrapolation. Any offers?

  48. Ferdinand,
    I agree with your comment that the “proxy” method does not mean the answer is wrong. And, the “official” CO2 measurement may, in fact, be accurate.
    My concern is that “proxy” measurement of CO2 seems to be “confounded” by several factors (i.e. not as straight forward as the rise of mercury in a thermometer due to temperature — which is a simple physical situation that is easy to understand and feel confident about).
    Its not clear to me that the confounding factors have been adequately addressed — to guarantee accuracy that adequately supports spending trillions of dollars/euros. The magnitude of the topic and the cost of solving AGW enters into my judgment regarding the adequacy of the measurement techniques.
    And, as usual, in Science, its the person making the claim (in this case that they’ve got CO2 measurement figured out) that has to provide a clear explanation and logically sound proof.
    So, while we can probably agree on the generalities of this topic, I am concerned that “official” historical CO2 measurements may not be that accurate once one digs into the details. However, I do not know.
    Thanks for the response.

  49. For a few hundred euro’s you may obtain a hand held CO2 measurement device with sufficient accuracy, but don’t drink before or while at work: one burp of CO2 from the beverage may give a “peak” of several tenthousands ppmv… And hold your breath for the same reason…

  50. “”” Phil. (20:48:41) :
    George E. Smith (16:30:44) :
    Well not surprisingly, the article is about as uninformative as it could be. Not a mention of the operating wavelength range of the CO2 detector..
    No real point in using the 15 micron CO2 band, since water vapor overlaps pretty much all of that to some extent, and other issues.
    But CO2 also has a strong absorption line at around 3.5-4.0 microns, whcih is right in a water hole.
    Not much overlap in the 15μm band really, there are plenty of lines to work with. Check out the spectra below: H2O top, CO2 below.
    http://i302.photobucket.com/albums/nn107/Sprintstar400/H2OCO2.gif “””
    Phil, thanks for the reference. Looks like a useful site to know. Of course it begs more questions than it answers; such as under exactly what physical conditions are these spectra calculated; and how would they be modified in a real atmosphere situation. But very cool place to know of.
    Thanks again.
    George

  51. Allen63 (11:25:22) :
    My concern is that “proxy” measurement of CO2 seems to be “confounded” by several factors (i.e. not as straight forward as the rise of mercury in a thermometer due to temperature — which is a simple physical situation that is easy to understand and feel confident about).
    Indeed one need to be aware of confounding factors: While there is a nice logarithmic relationship between level of CO2 and IR absorption at certain wavelengths, other gases/vapors may interfere at the same wavelength. That is the case for N2O and some CFC’s, but these are present in such low quantities that the influence is negligible. The main problem is water vapor. In the case of fixed stations like Mauna Loa, water vapor is almost all freezed out at -70 C. And the pressure in the measurement chamber must be kept constant, as pressure/density differences influence the measurement too.
    If these circumstances are kept within strict limits, the measurements have an accuracy of +/-0.2 ppmv. That is independently verified by inline and outside flask sampling which are measured in different laboratories (NOAA and Scripts) with different methods (again NDIR but also manometric).
    The NDIR method nowadays is used worldwide for near all CO2 measurements. For special purposes GC and/or mass spectrometers are used, the latter if one also wants to know the isotopic composition.

  52. Hmmm, I’m suspicious. Perhaps they are correct. But, they found the CO2 flux between ocean and atmosphere was “too high”?
    Wouldn’t a higher than expected flux mean a much shorter residence time in the atmosphere for a CO2 molecule, which is contrary to AGW theory, which re

  53. Hmmm, I’m suspicious. Perhaps they are correct. But, they found the CO2 flux between ocean and atmosphere was “too high”?
    Wouldn’t a higher than expected flux mean a much shorter residence time in the atmosphere for a CO2 molecule, which is contrary to AGW theory, which requires that all man-made CO2 molecules hang around doing theoir evil work for hundreds of years.
    So, going against “established theory” they must adjust the data; rather like the Argo sea temperatures.

  54. Robert of Ottawa (17:08:27) :
    Hmmm, I’m suspicious. Perhaps they are correct. But, they found the CO2 flux between ocean and atmosphere was “too high”?
    It is about the local CO2 measurements in air, where the open path devices give higher CO2 values than the closed path devices. That should mean less influx to the atmosphere from where the oceans have a higher pCO2 (equator) and more outflux to the oceans at the poles (lower pCO2 in the oceans). But as this is a clear error, the figures don’t add up with what is measured in the atmosphere as global CO2 levels and sink rates: about halve of the 8 GtC emitted by humans is absorbed by oceans and vegetation.
    The measurements are only important to know the partitioning in sink rate between oceans and vegetation and where most of the degassing and absorption in the oceans is situated. These are not important for the overall sink rate of extra CO2 in the atmosphere, which has an about 40 years half life time.

  55. George E. Smith (13:54:44) :
    “”” Phil. (20:48:41) :
    George E. Smith (16:30:44) :
    Well not surprisingly, the article is about as uninformative as it could be. Not a mention of the operating wavelength range of the CO2 detector..
    No real point in using the 15 micron CO2 band, since water vapor overlaps pretty much all of that to some extent, and other issues.
    But CO2 also has a strong absorption line at around 3.5-4.0 microns, whcih is right in a water hole.
    Not much overlap in the 15μm band really, there are plenty of lines to work with. Check out the spectra below: H2O top, CO2 below.
    http://i302.photobucket.com/albums/nn107/Sprintstar400/H2OCO2.gif “””
    Phil, thanks for the reference. Looks like a useful site to know. Of course it begs more questions than it answers; such as under exactly what physical conditions are these spectra calculated; and how would they be modified in a real atmosphere situation. But very cool place to know of.
    Thanks again.

    You’re welcome George, using Spectracalc you can calculate spectra for any conditions you want. I don’t recall the conditions used in that case but it’s main purpose was to show the relative scarcity of H2O lines in that region os the spectrum. If you use MODTRAN (free) you can get an ‘real atmosphere’ view but without sufficient resolution to see the individual lines.

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