Provided by: Jonas Ardö on 07/28/2010
I got 6-7 responses where all but one said it was OK to use N gas with 400 ppm CO2 for calibration of a LI-7500. The person answering that N-gas was not suitable refereed to Agricultural and Forest Meteorology 118 (2003) 1–19, (see especially Bischof and Griffith refs). I also asked LICOR and they answered: You can certainly use nitrogen gas for calibration. CO2 in air is slightly more accurate because it includes the balance of oxygen present in normal air (which can have a slight effect on the infrared response), but nitrogen gas is entirely usable and quite a few customers do use it. (The main issue was about the N-gas and not regarding the 400 ppm, it was maybe badly formulated)