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I have the following question:

Which of the following would not be used to measure changes in atmospheric gases?

i) Satellites

ii) Mass Spectrometer

iii) Digital Thermometer

iv) Fractional Distillation

I assumed it would be fractional distillation since you cannot really measure anything with it? You only separate the fractions of different materials such as crude oil.

However the answer was Digital Thermometer. I guess I can understand how this object would be useless at measuring atmospheric changes relating to gases however how would you detect atmospheric gases changes using fractional distillation?

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    $\begingroup$ Before answering such question, you must define properly what you means by 'change' and 'atmospheric gases'. Are talking about atmosphere composition or state variables? Could you please clarify your question. $\endgroup$ – jlandercy May 4 '14 at 13:31
  • $\begingroup$ The question is put at the back of a book with hundreds others. It does not gives me any more information. $\endgroup$ – Bula May 4 '14 at 14:05
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    $\begingroup$ Terrible answers. Not a "satellite" but remote sensors in orbit. MS is only as good as its sample. Fractional distillation does not quantitate parts-per-billion species: 1000 metric tonnes of air - with zero loses - to recover one gram of a ppb contaminant. Dry air has an average MW - 29. How many liters of atmosphere, 22.4 l/mole, are necessary to dry (no selective losses!) and cryogenically liquefy, then cryogenically spinning band distill (good luck with that, too)? $\endgroup$ – Uncle Al May 4 '14 at 14:56
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Assuming 'change' means modification of composition, the answer is Digital Thermometer because even if temperature is linked to atmosphere composition it does not provide you any information about it.

  • Satelite can embed LIDAR system which will provide you crude qualitative (spectrum) and quantitative (intensities) informations on atmosphere composition, but it requires complex mathematical processing and relies on weak hypothesis;
  • Mass spectrography is probably the most accurate way because it is highly qualitative (retention time) and quantitative (ionization current);
  • Distillation will allow you to qualitatively 'separate' (boiling point) and 'quantify' (mass flow rate) distinct components.

Obviously temperature measurement is not able to provide any informations of this kind. Further more, temperature gradient in atmosphere is not only dominated by its composition, there is a lot of other phenomena involved in it.

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