How are the amounts of greenhouse gases measured?
Non-isotopic measurements of greenhouse gases are generally made with two techniques: Non-Dispersive Infrared (NDIR) analysis, or by gas chromatography. The amount of CO2 in the atmosphere is large enough that the NDIR method of measurement works well. An NDIR analyzer relies on the same principle of IR absorption that makes greenhouse gases important in the first place. An infrared analyzer consists of an infrared source at one end, and an infrared detector separated by a gas cell. The gas of interest is passed through this cell, and absorbs some of the infrared radiation coming from the source. The detector converts the amount of IR reaching it to a usable signal, such as a voltage. So as the concentration of CO2 changes in the sample, the signal from the detector changes. By flowing a gas with a known amount of CO2 through the cell, we can calibrate the analyzer so that the voltage output from the detector can be converted into amounts of CO2. Gas Chromatography is a separation meth
