Sciencemadness Discussion Board

How to Measure CO2 Concentration in Air?

hodges - 24-2-2006 at 15:15

Does anyone have any ideas how I could measure, to within a few percent accuracy, the amount of CO2 in the atmosphere? I would like to do my own measurements of changes in CO2 concentration in the atmosphere with seasons and with time.

One "brute force" way I can think of might be to bubble a known amount of air through a basic solution such as NaOH and measure the amount of mass increase. However, since some of the solution would evaporate, it would be necessary to dry the resulting product to determine an accurate mass. Big unknowns would be the percentage of CO2 from the air that actually reacts, and what the final compound is (bicarbonate vs carbonate vs compounds based on other chemicals in the air).

Any ideas for this or other methods?

Thanks,
Hodges

12AX7 - 24-2-2006 at 19:19

Use concentrated Ca(OH)2 solution and weigh the precipitate. :)

Tim

BromicAcid - 24-2-2006 at 19:35

In my quant class the method of measuring CO<sub>2</sub> in the air was covered. The exact method escapes me but there was something about drawing air over asbestos plates coated in NaOH and doing something with them, sorry that I don't recall any details, my quant book was one of the few chemistry books in my life that I felt the need to sell.

IrC - 25-2-2006 at 00:55

I would look into Figaro gas sensor IC's, add an op amp or two and make you a nice little circuit with real time readout. The CO sensor is only around 11 buckaroos, I once build a CO warning meter with alarm and it worked so well. The circuit is typical for their products and you can find it online around, or in app notes right at Figaro. Don't know if they have a CO2 sensor but I imagine they do, they make them for about every gas.

One caution, burned and especially unburned hydrocarbons will saturate the sensor even with no detected gas around, too much in the way of raw fuel gasses and your sensor will be DOA. Not much power to run, little heating element to clean the sensor which is handy. Check into it, by far the easy way to do what you want.

S.C. Wack - 25-2-2006 at 03:13

Fairly accurate chemical method article on hand:

Attachment: jacs_25_150_1903.pdf (531kB)
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hodges - 25-2-2006 at 09:06

Quote:
Originally posted by S.C. Wack
Fairly accurate chemical method article on hand:


Thanks! This seems like the way to go. I wonder if calcium hydroxide could be used in place of barium hydroxide.

What I get from the article is to use a weak solution of a base which forms an insuluable carbonate, and expose this to a known amount of air. The precipitated carbonate is then filtered out, and the remaining solution titrated to determine how much of the base is left. This allows calculation of how much carbonate was formed, and thus how much CO2 was in the sample.

This procedure sounds easy enough; the hard part being to ensure purity of the water used (from dissolved CO2) and avoiding contamination from the container.

unionised - 26-2-2006 at 02:40

"Use concentrated Ca(OH)2 solution and weigh the precipitate.

Tim "
In what solvent?
Water only disolves 1 or 2 g/litre.
Ba(OH)2 is much more soluble; but also more toxic. The method we use at work is based on BaCO3 ppt.

gsd - 26-2-2006 at 10:14

I believe "Orsat Apparatus" is a fairly standard way to go about it.

Following link may be useful:

http://www.dpi.vic.gov.au/dpi/nreninf.nsf/9e58661e880ba9e44a...

[Edited on 26-2-2006 by gsd]

12AX7 - 26-2-2006 at 10:45

Quote:
Originally posted by unionised
"Use concentrated Ca(OH)2 solution and weigh the precipitate.

Tim "
In what solvent?
Water only disolves 1 or 2 g/litre.
Ba(OH)2 is much more soluble; but also more toxic. The method we use at work is based on BaCO3 ppt.


Yeah, but BaCO3 and CaCO3 are both much less soluble than the hydroxides, so it'll work either way. Besides, there isn't much CO2 in a generic "sample" of air, so it won't take much hydroxide.

Ba(OH)2 is certainly more soluble, so you can use less solution.

Tim

JohnWW - 27-2-2006 at 00:24

Quote:
Originally posted by gsd
I believe "Orsat Apparatus" is a fairly standard way to go about it.
Following link may be useful:
http://www.dpi.vic.gov.au/dpi/nreninf.nsf/9e58661e880ba9e44a...
[Edited on 26-2-2006 by gsd]

Yes, I was hoping someone would mention the Orsat Apparatus. I once used it to analyse flue gas coming from the distillation furnace of an oil refinery. I think the apparatus and method is also described in Vogel's Quantitave Inorganic Chemical Analysis.